Timothy D Swindle

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• Bauer, J., Milam, S., Bjoraker, G., Carey, S., Daou, D., Fletcher, L., Harris, W., Hartogh, P., Hartzell, C., Hendrix, A., Nugent, C., Rivkin, A., Swindle, T., Thomas, C., Tiscareno, M., Villanueva, G., & Wolk, S. (2020). Planetary Science with Astrophysical Assets: Defining the Core Capabilities of Platforms. arXiv e-prints, arXiv:2002.05838.
• Devillepoix, H., Cup{\'ak}, M., Bland, P., Sansom, E., Towner, M., Howie, R., Hartig, B., Jansen-Sturgeon, T. .., Shober, P., Anderson, S., Benedix, G., Busan, D., Sayers, R., Jenniskens, P., Albers, J., Herd, C., Hill, P., Brown, P., Krzeminski, Z., , Osinski, G., et al. (2020). A Global Fireball Observatory. \planss, 191, 105036.
• Bauer, J., Milam, S., Bjoraker, G., Carey, S., Daou, D., Fletcher, L., Harris, W., Hartogh, P., Hartzell, C., Hendrix, A., Nugent, C., Rivkin, A., Swindle, T., Thomas, C., Tiscareno, M. S., Villanueva, G., & Wolk, S. (2019). Planetary Science with Astrophysical Assets: Defining the Core Capabilities of Platforms. \baas, 51(3), 477.
• Beaty, D., Grady, M., McSween, H., Sefton-Nash, E. .., Carrier, B., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Benning, L., Bishop, J., Borg, L., Boucher, D., Brucato, J., Busemann, H., Campbell, K., Czaja, A., Debaille, V., Des, M. D., , Dixon, M., et al. (2019). The potential science and engineering value of samples delivered to Earth by Mars sample return. Meteoritics and Planetary Science, 54(S1), S3-S152.
• Niihara, T., Beard, S. P., Swindle, T. D., Schaffer, L. A., Miyamoto, H., & Kring, D. A. (2019). Evidence for multiple 4.0-3.7 Ga impact events within the Apollo 16 collection. Meteoritics and Planetary Science, 54(4), 675-698.
• Objectives, I. M., (iMOST), S. T., Beaty, D., Grady, M., McSween, H., Sefton-Nash, E. .., Carrier, B., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Benning, L., Bishop, J., Borg, L., Boucher, D., Brucato, J., Busemann, H., Campbell, K., Czaja, A., , Debaille, V., et al. (2019). The potential science and engineering value of samples delivered to Earth by Mars sample return. Meteoritics and Planetary Science, 54(3), 667-671.
• Pickersgill}, A., Christou, E., Mark, D., Lee, M., Tremblay, M., Rasmussen, C., Morgan, J., Gulick, S., Schmieder, M., Bach, W., Osinski, G., Simpson, S., Kring, D., Cockell, C., Collins, G., Christeson, G., Tikoo, S., Stockli, D., Ross, C., , Wittmann, A., et al. (2019). Six Million Years of Hydrothermal Activity at Chicxulub?. LPI Contributions, 2136, 5082.
• Taylor, P. A., Rivera-Valent{\'\in}, E. G., Bonsall, A., Becker, T. M., Benner, A., Bhiravarasu, S. S., Brozovic, M., Busch, M. W., Campbell, B. A., Ghigo, F. D., Harris, A. W., Magri, C., Mainzer, A. K., Margot, J., Marshall, S. E., Masiero, J. R., Naidu, S. P., Nolan, M. C., Patterson, G. W., , Prockter, L. M., et al. (2019). Planetary Radar Astronomy with Ground-Based Astrophysical Assets. \baas, 51(3), 539.
• Beard, S., Weimer, D., Busemann, H., Maden, C., & Swindle, T. (2018). 21Ne Cosmic-Ray Exposure Ages of Brachinites and Brachinite-Like Achondrites. LPI Contributions, 2067, 6170.
• Swindle, T., & Kring, D. (2018). Asteroidal Constraints on the Early Bombardment History of the Inner Solar System. LPI Contributions, 2107, 2026.
• Schwenzer, S., Bart, G., Bridges, J., Crowther, S., Filiberto, J., Gilmour, J., Herrmann, S., Hicks, L., Kelley, S., Miller, M., Ott, U., Steer, E., Swindle, T., & Treiman, A. (2017). Fractionated Noble Gases in Martian Meteorite ALH 84001 \mdash An Indicator for Water-Rock Interaction, or a Sample of Ancient Atmosphere?. LPI Contributions, 2014, 3018.
• {Beard}, S., {Swindle}, T., , C. (2016). Ar-Ar Ages of Brachinite and Brachinite-Like Achondrites. LPI Contributions, 1921, 6411.
• {Schmieder}, M., {Kring}, D., {Swindle}, T., {Bond}, J., , C. (2016). The Gao-Guenie impact melt breccia{\mdash}Sampling a rapidly cooled impact melt dike on an H chondrite asteroid?. Meteoritics and Planetary Science, 51, 1022-1045.
• {Schwenzer}, S., {Barnes}, G., {Bridges}, J., {Bullock}, M., {Chavez}, C., {Filiberto}, J., {Herrmann}, S., {Hicks}, L., {Kelley}, S., {Miller}, M., {Moore}, J., {Ott}, U., {Smith}, H., {Steer}, E., {Swindle}, T., , A. (2016). Fractionated (Martian) Noble Gases {\mdash} EFA, Experiments and Meteorites. LPI Contributions, 1921, 6099.
• Bottke, W., Vokrouhlicky, D., Marchi, S., Swindle, T., Scott, E., Weirich, J., & Levison, H. (2015). Dating the Moon-forming impact event with asteroidal meteorites. Science, 348, 321-323.
• {Gombosi}, D., {Baldwin}, S., {Watson}, E., {Swindle}, T., {Delano}, J., , W. (2015). Argon diffusion in Apollo 16 impact glass spherules: Implications for $^{40}$Ar/$^{39}$Ar dating of lunar impact events. \gca, 148, 251-268.
• Swindle, T., Kring, D., & Weirich JR, . (2014). 40Ar/39Ar ages of impacts involving ordinary chondrite meteorites. Geological Society of London Special Publications, 378, 333-347.
• {Friedrich}, J., {Rubin}, A., {Beard}, S., {Swindle}, T., {Isachsen}, C., {Rivers}, M., , R. (2014). Ancient porosity preserved in ordinary chondrites: Examining shock and compaction on young asteroids. Meteoritics and Planetary Science, 49, 1214-1231.
• {Swindle}, T. (2014). "{Comparing Meteorite and Spacecraft Noble Gas Measurements to Trace Processes in the Martian Crust and Atmosphere}". AGU Fall Meeting Abstracts.
• Mousis, O., Chassefière, E., Lasue, J., Chevrier, V., E., M., Lakhlifi, A., Lunine, J. I., Montmessin, F., Picaud, S., Schmidt, F., & Swindle, T. D. (2013). Volatile trapping in martian clathrates. Space Science Reviews, 174(1-4), 213-250.
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  Abstract: Thermodynamic conditions suggest that clathrates might exist on Mars. Despite observations which show that the dominant condensed phases on the surface of Mars are solid carbon dioxide and water ice, clathrates have been repeatedly proposed to play an important role in the distribution and total inventory of the planet's volatiles. Here we review the potential consequences of the presence of clathrates on Mars. We investigate how clathrates could be a potential source for the claimed existence of atmospheric methane. In this context, plausible clathrate formation processes, either in the close subsurface or at the base of the cryosphere, are reviewed. Mechanisms that would allow for methane release into the atmosphere from an existing clathrate layer are addressed as well. We also discuss the proposed relationship between clathrate formation/dissociation cycles and how potential seasonal variations influence the atmospheric abundances of argon, krypton and xenon. Moreover, we examine several Martian geomorphologic features that could have been generated by the dissociation of extended subsurface clathrate layers. Finally we investigate the future in situ measurements, as well as the theoretical and experimental improvements that will be needed to better understand the influence of clathrates on the evolution of Mars and its atmosphere. © 2012 Springer Science+Business Media Dordrecht.
• Glavin, D. P., Malespin, C., L., I., Getty, S. A., Holmes, V. E., Mumm, E., Franz, H. B., Noreiga, M., Dobson, N., Southard, A. E., Feng, S. H., Kotecki, C. A., Dworkin, J. P., Swindle, T. D., Bleacher, J. E., Rice, J. W., & Mahaffy, P. R. (2012). Volatile analysis by pyrolysis of regolith for planetary resource exploration. IEEE Aerospace Conference Proceedings.
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  Abstract: The extraction and identification of volatile resources that could be utilized by humans including water, oxygen, noble gases, and hydrocarbons on the Moon, Mars, and small planetary bodies will be critical for future long-term human exploration of these objects. Vacuum pyrolysis at elevated temperatures has been shown to be an efficient way to release volatiles trapped inside solid samples. In order to maximize the extraction of volatiles, including oxygen and noble gases from the breakdown of minerals, a pyrolysis temperature of 1400°C or higher is required, which greatly exceeds the maximum temperatures of current state-of-the-art flight pyrolysis instruments. Here we report on the recent optimization and field testing results of a high temperature pyrolysis oven and sample manipulation system coupled to a mass spectrometer instrument called Volatile Analysis by Pyrolysis of Regolith (VAPoR). VAPoR is capable of heating solid samples under vacuum to temperatures above 1300°C and determining the composition of volatiles released as a function of temperature. © 2012 IEEE.
• Weirich, J. R., Isachsen, C. E., Johnson, J. R., & Swindle, T. D. (2012). Variability of diffusion of argon in albite, pyroxene, and olivine in shocked and unshocked samples. Geochimica et Cosmochimica Acta, 77, 546-560.
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  Abstract: We analyzed the argon diffusion parameters of albite and pyroxene as a function of shock, as well as an olivine of unknown shock pressure. In albite, shock pressures of ~30-60GPa all have an equal effect on the diffusion parameters, lowering the activation energy (E) from ~45 to ~25kcal/mol, and the logD 0/a 2 from ~4 to ~1s -1. In a mixture of low-Ca and high-Ca pyroxene, similar shock pressures also have an equal effect, lowering the E from ~130 to ~80kcal/mol, and the logD 0/a 2 from ~14 to ~7s -1. However, given that some shocked and unshocked pyroxene splits have similar release patterns, making a clear distinction between the two is difficult. Additionally, splits of pure unshocked high-Ca pyroxene have an E of ~100kcal/mol and a logD 0/a 2 of ~10s -1, intermediate to the values of mixed pyroxene when shocked and unshocked. The olivine (Fa 18) has an E of ~45kcal/mol and a logD 0/a 2 of ~1s -1, somewhat similar to that of feldspar. These results will be useful in interpreting complex argon release patterns from shocked multi-mineral samples too fine-grained for easy mineral separation (such as chondrites). © 2011 Elsevier Ltd.
• Weirich, J. R., Swindle, T. D., & Isachsen, C. E. (2012). 40Ar-39Ar age of Northwest Africa 091: More evidence for a link between L chondrites and fossil meteorites. Meteoritics and Planetary Science, 47(8), 1324-1335.
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  Abstract: Most 40Ar- 39Ar ages of L chondrites record an event at approximately 500Ma, indicating a large collisional impact at that time. However, there is a spread in ages from 400 to 600Ma in these meteorites that is greater than the analytical uncertainty. Identification of, and correction for, trapped Ar in a few L chondrites has given an age of 470±6Ma. This age coincides with Ordivician fossil meteorites that fell to Earth at 467±2Ma. As these fossil meteorites were originally L chondrites, the apparent conclusion is that a large impact sent a flood of L chondrite material to Earth, while material that remained on the L chondrite parent body was strongly heated and reset. We have reduced 40Ar- 39Ar data for Northwest Africa 091 using various techniques that appear in the literature, including identification and subtraction of trapped Ar. These techniques give a range of ages from 455 to 520Ma, and show the importance of making accurate corrections. By using the most straightforward technique to identify and remove a trapped Ar component (which is neither terrestrial nor primordial), an 40Ar- 39Ar age of 475±6Ma is found for Northwest Africa 091, showing a temporal link to fossil meteorites. In addition, high temperature releases of Northwest Africa 091 contain evidence for a second trapped component, and subtraction of this component indicates a possible second collisional impact at approximately 800Ma. This earlier age coincides with 40Ar- 39Ar ages of some H and L chondrites, and lunar samples. © The Meteoritical Society, 2012.
• Weirich, J. R., Swindle, T. D., Isachsen, C. E., Sharp, T. G., Li, C., & Downs, R. T. (2012). Source of potassium in shocked ordinary chondrites. Geochimica et Cosmochimica Acta, 98, 125-139.
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  Abstract: Argon-argon dating (a variation of potassium-argon dating) of ordinary chondrites is being used to reconstruct the collisional impact history of their parent bodies. However, due to the fine-grained, multi-mineral, highly shocked nature of chondrites, the sources of potassium (K) in these meteorites have not been fully identified. By locating and isolating the different sources prior to analysis, better ages can be obtained. To distinguish between possible sources, we have analyzed Chico and Northwest Africa 091 (both L6 chondrites) via K mass balance, Raman spectroscopy, and argon (Ar) diffusion studies.In accordance with previous studies on other ordinary chondrites, the Ar in these two chondrites is nearly equally split between two releases, and the lower temperature release is identified as sodium-rich feldspar. Various scenarios for the higher temperature release are investigated, but no scenario meets all the required criteria. The Ar activation energy of the higher temperature release is the same as pyroxene, but the pyroxene has no detectable K. The K mass balance shows feldspar can account for all the K in the chondrite; hence feldspar must be the ultimate source of the higher temperature release. Raman spectroscopy rules out a high-pressure phase of feldspar. Neither melt veins, nor feldspar inclusions in pyroxene, are abundant enough to account for the higher temperature release in these meteorites. © 2012 Elsevier Ltd.
• Rubin, A. E., & Swindle, T. D. (2011). Flattened chondrules in the LAP 04581 LL5 chondrite: Evidence for an oblique impact into LL3 material and subsequent collisional heating. Meteoritics and Planetary Science, 46(4), 587-600.
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  Abstract: LaPaz Icefield (LAP) 04581 is a shock-stage S2 LL5 chondrite that initially consisted of unrecrystallized LL3 material with a moderately abundant fine-grained porous matrix (on the order of 15vol%). A rare oblique impact created shearing stresses that produced a petrofabric in the rock, induced frictional melting of troilite (thereby forming a large troilite vein), and caused chondrule flattening. The latter process was facilitated by impact-induced collapse of matrix pores. Chondrule flattening could not have occurred if the rock had been impacted after it had been metamorphosed to type 5 levels because the fine-grained matrix would have previously recrystallized and developed low porosity. Ar-Ar dating of LAP 04581 yields an age of 4175Ma. This date is long after 26Al had decayed away and most likely reflects the timing of a second impact event that shocked the rock to S4-S5 levels. The troilite vein became polycrystalline at this time and the whole rock was annealed to petrologic type 5, perhaps by being buried beneath hot ejecta of low thermal diffusivity. After annealing, the rock was weakly shocked to S2 levels. LAP 04581 serves as an example of impact-induced heating being a viable mechanism for chondrite metamorphism. © The Meteoritical Society, 2011.
• Wittmann, A., Friedrich, J. M., Troiano, J., Macke, R. J., Britt, D. T., Swindle, T. D., Weirich, J. R., Rumble, D., Lasue, J., & Kring, D. A. (2011). H/L chondrite LaPaz Icefield 031047 - A feather of Icarus?. Geochimica et Cosmochimica Acta, 75(20), 6140-6159.
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  Abstract: Antarctic meteorite LAP 031047 is an ordinary chondrite composed of loosely consolidated chondritic fragments. Its petrography, oxygen isotopic composition and geochemical inventory are ambiguous and indicate an intermediate character between H and L chondrites. Petrographic indicators suggest LAP 031047 suffered a shock metamorphic overprint below ∼10 GPa, which did not destroy its unusually high porosity of ∼27 vol%. Metallographic textures in LAP 031047 indicate heating above ∼700. °C and subsequent cooling, which caused massive transformation of taenite to kamacite. The depletion of thermally labile trace elements, the crystallization of chondritic glass to microcrystalline plagioclase of unusual composition, and the occurrence of coarsely crystallized chondrule fragments is further evidence for post-metamorphic heating to ∼700-750. °C. However, this heating event had a transient character because olivine and low-Ca pyroxene did not equilibrate. Nearly complete degassing up to very high temperatures is indicated by the thorough resetting of LAP 031047's Ar-Ar reservoir ∼100 ± 55 Ma ago. A noble gas cosmic-ray exposure age indicates it was reduced to a meter-size fragment at
• Kate, I. t., Cardiff, E. H., Dworkin, J. P., Feng, S. H., Holmes, V., Malespin, C., Stern, J. G., Swindle, T. D., & Glavin, D. P. (2010). VAPoR - Volatile Analysis by Pyrolysis of Regolith - an instrument for in situ detection of water, noble gases, and organics on the Moon. Planetary and Space Science, 58(7-8), 1007-1017.
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  Abstract: We present the Volatile Analysis by Pyrolysis of Regolith (VAPoR) instrument design and demonstrate the validity of an in situ pyrolysis mass spectrometer for evolved gas analyses of lunar and planetary regolith samples. In situ evolved gas analyses of the lunar regolith have not yet been carried out and no atmospheric or evolved gas measurements have been made at the lunar poles. VAPoR is designed to do both kinds of measurements, is currently under development at NASA's Goddard Space Flight Center, and will be able to heat powdered regolith samples or rock drill fines up to 1400 °C in vacuo. To validate the instrument concept, evolved gas species released from different planetary analogs were determined as a function of temperature using a laboratory breadboard. Evolved gas measurements of an Apollo 16 regolith sample and a fragment of the carbonaceous meteorite Murchison were made by VAPoR and our results compared with existing data. The results imply that in situ evolved gas measurements of the lunar regolith at the polar regions by VAPoR will be a very powerful tool for identifying water and other volatile signatures of lunar or exogenous origin as potential resources for future human exploration. © 2010 Elsevier Ltd.
• Weirich, J. R., Wittmann, A., Isachsen, C. E., Rumble, D., Swindle, T. D., & Kring, D. A. (2010). The Ar-Ar age and petrology of Miller Range 05029: Evidence for a large impact in the very early solar system. Meteoritics and Planetary Science, 45(12), 1868-1888.
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  Abstract: Miller Range (MIL) 05029 is a slowly cooled melt rock with metal/sulfide depletion and an Ar-Ar age of 4517 ± 11 Ma. Oxygen isotopes and mineral composition indicate that it is an L chondrite impact melt, and a well-equilibrated igneous rock texture with a lack of clasts favors a melt pool over a melt dike as its probable depositional setting. A metallographic cooling rate of approximately 14 °C Ma-1 indicates that the impact occurred at least approximately 20 Ma before the Ar-Ar closure age of 4517 Ma, possibly even shortly after accretion of its parent body. A metal grain with a Widmanstätten-like pattern further substantiates slow cooling. The formation age of MIL 05029 is at least as old as the Ar-Ar age of unshocked L and H chondrites, indicating that endogenous metamorphism on the parent asteroid was still ongoing at the time of impact. Its metallographic cooling rate of approximately 14 °C Ma-1 is similar to that typical for L6 chondrites, suggesting a collisional event on the L chondrite asteroid that produced impact melt at a minimum depth of 5-12 km. The inferred minimum crater diameter of 25-60 km may have shattered the 100-200 km diameter L chondrite asteroid. Therefore, MIL 05029 could record the timing and petrogenetic setting for the observed lack of correlation of cooling rates with metamorphic grades in many L chondrites. © The Meteoritical Society, 2010.
• Wittmann, A., Swindle, T. D., Cheek, L. C., Frank, E. A., & Kring, D. A. (2010). Impact cratering on the H chondrite parent asteroid. Journal of Geophysical Research E: Planets, 115(7).
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  Abstract: This paper reports petrological data for LaPaz Icefield 02240, 03922, 031125, 031173, 031308, 04462, and 04751, which are meteoritic samples of clast-rich impact melt rocks from the H chondrite parent asteroid. The size distribution and metallographic characteristics of Fe-Ni metal in the melts indicate very rapid 1 to 40C/s cooling in the temperature range between >1500 and ∼950C when the clast-melt mixtures were thermally equilibrating. Cooling slowed to values between 10-3 and 10-2C/s in the temperature range between 700 and 400C when the melt rocks were cooling to their surroundings. These data suggest that the rocks cooled near the surface of the H chondrite asteroid within suevitic impact deposits. Integrating these data with the petrologic characteristics of other H chondrite melt rocks and their radioisotopic ages indicates that the H chondrite asteroid suffered at least one large impact event while still cooling from endogenous metamorphism at ∼4500 Ma; this impact must have degraded the asteroid's integrity but did not cause shattering. Impact events in the era between ∼4100 and ∼3600 Ma produced melt volumes large enough to allow segregation of metal and troilite from silicate melts, possibly within continuous impact melt sheets contained in craters. The impact record after 3600 Ma does not display such assemblages, which suggests a decrease in the rate of large impact events or a catastrophic size reduction of the H chondrite parent asteroid at around this time.Copyright 2010 by the American Geophysical Union.
• Swindle, T. D., Isachsen, C. E., Weirich, J. R., & Kring, D. A. (2009). ⁴⁰Ar-³⁹Ar ages of H-chondrite impact melt breccias. Meteoritics and Planetary Science, 44(5), 747-762.
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  Abstract: 40Ar-39Ar analyses of a total of 26 samples from eight shock-darkened impact melt breccias of H-chondrite affinity (Gao-Guenie, LAP 02240, LAP 03922, LAP 031125, LAP 031173, LAP 031308, NWA 2058, and Ourique) are reported. These appear to record impacts ranging in time from 303 ± 56 Ma (Gao-Guenie) to 4360 ± 120 Ma (Ourique) ago. Three record impacts 300-400 Ma ago, while two others record impacts 3900-4000 Ma ago. Combining these with other impact ages from H chondrites in the literature, it appears that H chondrites record impacts in the first 100 Ma of solar system history, during the era of the "lunar cataclysm" and shortly thereafter (3500-4000 Ma ago), one or more impacts ∼300 Ma ago, and perhaps an impact ∼500 Ma ago (near the time of the L chondrite parent body disruption). Records of impacts on the H chondrite parent body are rare or absent between the era of planetary accretion and the "lunar cataclysm" (4400-4050 Ma), during the long stretch between heavy bombardment and recent breakup events (3500-1000 Ma), or at the time of final breakup into meteorite-sized bodies (
• Swindle, T. D., Thomas, C., Mousis, O., Lunine, J. I., & Picaud, S. (2009). Incorporation of argon, krypton and xenon into clathrates on Mars. Icarus, 203(1), 66-70.
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  Abstract: Calculations of the trapping of heavy noble gases within multiple guest clathrates under Mars-like conditions show that a substantial fraction of the martian Xe, perhaps even the vast majority, could be in clathrates. In addition, the Xe/Kr ratio in the clathrates would probably be much higher than in the atmosphere, so the formation or dissociation of a relatively small amount of clathrate could measurably change the atmospheric ratio. Relatively crude (factor of 2) measurements of the seasonal variability in that ratio by in situ spacecraft would be sensitive to ∼10% of the seasonal atmospheric CO2 variability being a result of clathrates, rather than pure CO2 frost. In addition, sequestration of Xe in clathrates remains a viable mechanism for explaining the variable Xe/Kr ratios seen in different suites of martian meteorites. © 2009 Elsevier Inc. All rights reserved.
• Zellner, N. E., Delano, J. W., Swindle, T. D., Barra, F., Olsen, E., & Whittet, D. C. (2009). Apollo 17 regolith, 71501,262: A record of impact events and mare volcanism in lunar glasses. Meteoritics and Planetary Science, 44(6), 839-851.
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  Abstract: Thirteen glasses from Apollo 17 regolith 71501,262 have been chemically analyzed by electron microprobe and isotopically dated with the 40Ar/59Ar dating method. We report here the first isotopic age obtained for the Apollo 17 very low titanium (VLT) volcanic glasses, 3630 ± 40 Ma. Twelve impact glasses that span a wide compositional range have been found to record ages ranging from 102 ± 20 Ma to 3740 ± 50 Ma. The compositions of these impact glasses show that some have been produced by impact events within the Apollo 17 region, whereas others appear to be exotic to the landing site. As the data sets that include compositions and ages of lunar impact glasses increase, the impact history in the Earth-Moon system will become better constrained. © The Meteoritical Society, 2009.
• Zellner, N. E., Delano, J. W., Swindle, T. D., Barra, F., Olsen, E., & Whittet, D. C. (2009). Evidence from ⁴⁰Ar/³⁹Ar ages of lunar impact glasses for an increase in the impact rate ∼800 Ma ago. Geochimica et Cosmochimica Acta, 73(15), 4590-4597.
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  Abstract: Geochemical and 40Ar/39Ar data on nine impact glasses from the Apollo 14, 16, and 17 landing sites indicate at least seven distinct impact events with ages ∼800 Ma. Rock fragments analyzed by Barra et al. [Barra F., Swindle T. D., Korotev R. L., Jolliff B. L., Zeigler R. A., and Olsen E. (2006) 40Ar-39Ar dating of Apollo 12 regolith: implications for the age of Copernicus and the source of nonmare materials, Geochim. Cosmochim. Acta, 70, 6016-6031] from the Apollo 12 landing site and some Apollo 12 spherules reported by Levine et al. [Levine J., Becker T. A., Muller R. A., Renne P. R. (2005) 40Ar/39Ar dating of Apollo 12 impact spherules, Geophys. Res. Let., 32, L15201, doi: 10.1029/2005GL022874.] show ∼800 Ma ages, close to the accepted age of the Copernicus event, 800 ± 15 Ma [Bogard D. D., Garrison D. H., Shih C. Y., and Nyquist L. E. (1994) 39Ar-40Ar dating of two lunar granites: The age of Copernicus, Geochim. Cosmochim. Acta, 58, 3093-3100]. These Apollo 12 samples are thought to have been affected by material from the Copernicus event since there is a Copernicus ray going through the Apollo 12 landing site. When all of these data are viewed collectively, including an Apollo 16 glass bomb [Borchardt R., Stöffler D., Spettel B., Palme H. and Wänke H. (1986) Composition, structure, and age of the Apollo 16 subregolith basement as deduced from the chemistry of post-Imbrium melt bombs. In Proceedings, 17th Lunar and Planetary Science Conference, pp. E43-E54], and in the context of diverse compositional range and sample location, there is a suggestion that there may have been a transient increase in the global lunar impact flux at ∼800 Ma. Therefore, the Copernicus impact event could have been one of many. If correct, there should be evidence for this increased impact flux around 800 Ma ago in the age statistics of terrestrial impact samples. © 2009 Elsevier Ltd. All rights reserved.
• Plescia, J., & Swindle, T. (2008). Calibrating the martian cratering chronology: An in situ dating mission. International Astronautical Federation - 59th International Astronautical Congress 2008, IAC 2008, 3, 1356-1363.
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  Abstract: Perhaps the most critical aspect of understanding the geologic, climatological and biologic history of Mars is establishing the absolute timing of events. Presently, only a relative chronology has been established using the frequency of impact craters on different surfaces (higher frequencies indicate older ages). Attempts to extrapolate the lunar cratering chronology (established by dating Apollo and Luna samples from known locations with well-defined crater frequencies) to a martian crater rate have large uncertainties. For example, the youngest major volcanic surface (Cerberus Plains) has model ages ranging from a few million years to hundreds of millions of years. To calibrate the absolute cratering chronology for Mars, an absolute radiometric age must be determined for an igneous rock from a known location from a surface with a well-defined impact crater frequency. A promising approach to establishing the chronology is to determine the radio metric ages using an in situ experiment. While in situ techniques are less precise than terrestrial analyses, they have precisions of the order 10-20% which are sufficient for these objectives. Various techniques have been proposed and are under development in cluding K/Ar and Rb/Sr. A mission with the objective of determining a radiometric age would be relatively simple and need survive only a short time.
• Delano, J. W., Zellner, N. E., Barra, F., Olson, E., Swindle, T. D., Tibbetts, N. J., & Whittet, D. C. (2007). An integrated approach to understanding Apollo 16 impact glasses: Chemistry, isotopes, and shape. Meteoritics and Planetary Science, 42(6), 993-1004.
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  Abstract: The major- and minor-element abundances were determined by electron microprobe in 1039 glasses from regoliths and regolith breccias to define the compositional topology of lunar glasses at the Apollo 16 landing site in the central highlands of the Moon. While impact glasses with chemical compositions similar to local materials (i.e., Apollo 16 rocks and regoliths) are abundant, glasses with exotic compositions (i.e., transported from other areas of the Moon) account for up to ∼30% of the population. A higher proportion of compositionally exotic, angular glass fragments exists when compared to compositionally exotic glass spherules. Ratios of non-volatile lithophile elements (i.e., Al, Ti, Mg) have been used to constrain the original source materials of the impact glasses. This approach is immune to the effects of open-system losses of volatile elements (e.g., Si, Na, K). Four impact glasses from one compositionally exotic group (low-Mg high-K Fra Mauro; lmHKFM) were selected for 40Ar/39Ar dating. The individual fragments of 1mHKFM glass all yielded ages of ∼3750 ± 50 Ma for the time of the impact event. Based on the petrography of these individual glasses, we conclude that the likely age of the impact event that formed these 4 glasses, as well as the possible time of their ballistic arrival at the Apollo 16 site from a large and distant cratering event (perhaps in the Procellarum KREEP terrain) (Zeigler et al. 2004), is 3730 ± 40 Ma, close to the accepted age for Imbrium. © The Meteoritical Society, 2007.
• Barra, F., Swindle, T. D., Korotev, R. L., Jolliff, B. L., Zeigler, R. A., & Olson, E. (2006). ⁴⁰Ar/³⁹Ar dating of Apollo 12 regolith: Implications for the age of Copernicus and the source of nonmare materials. Geochimica et Cosmochimica Acta, 70(24), 6016-6031.
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  Abstract: Twenty-one 2-4 mm rock samples from the Apollo 12 regolith were analyzed by the 40Ar/39Ar geochronological technique in order to further constrain the age and source of nonmare materials at the Apollo 12 site. Among the samples analyzed are: 2 felsites, 11 KREEP breccias, 4 mare-basalt-bearing KREEP breccias, 2 alkali anorthosites, 1 olivine-bearing impact-melt breccia, and 1 high-Th mare basalt. Most samples show some degree of degassing at 700-800 Ma, with minimum formation ages that range from 1.0 to 3.1 Ga. We estimate that this degassing event occurred at 782 ± 21 Ma and may have been caused by the Copernicus impact event, either by providing degassed material or by causing heating at the Apollo 12 site. 40Ar/39Ar dating of two alkali anorthosite clasts yielded ages of 3.256 ± 0.022 Ga and 3.107 ± 0.058 Ga. We interpret these ages as the crystallization age of the rock and they represent the youngest age so far determined for a lunar anorthosite. The origin of these alkali anorthosite fragments is probably related to differentiation of shallow intrusives. Later impacts could have dispersed this material by lateral mixing or vertical mixing. © 2006 Elsevier Inc. All rights reserved.
• Cohen, B. A., Swindle, T. D., & Kring, D. A. (2005). Geochemistry and ⁴⁰Ar^-39Ar geochronology of impact-melt clasts in feldspathic lunar meteorites: Implications for lunar bombardment history. Meteoritics and Planetary Science, 40(5), 755-777.
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  Abstract: We studied 42 impact-melt clasts from lunar feldspathic regolith breccias MacAlpine Hills (MAC) 88105, Queen Alexandra Range (QUE) 93069, Dar al Gani (DaG) 262, and DaG 400 for texture, chemical composition, and/or chronology. Although the textures are similar to the impact-melt clasts identified in mafic Apollo and Luna samples, the meteorite clasts are chemically distinct from them, having lower Fe, Ti, K, and P, thus representing previously unsampled impacts. The 40Ar- 39Ar ages on 31 of the impact melts, the first ages on impact-melt samples from outside the region of the Apollo and Luna sampling sites, range from ∼4 to ∼2.5 Ga. We interpret these samples to have been created in at least six, and possibly nine or more, different impact events. One inferred impact event may be consistent with the Apollo impact-melt rock age cluster at 3.9 Ga. but the meteorite impact-melt clasts with this age are different in chemistry from the Apollo samples, suggesting that the mechanism responsible for the 3.9 Ga peak in lunar impact-melt clast ages is a lunar-wide phenomenon. No meteorite impact melts have ages more than 1 σ older than 4.0 Ga. This observation is consistent with, but does not require, a lunar cataclysm. © The Meteoritical Society, 2005.
• Swindle, T. D., Masarik, J., Kollár, D., Kim, K. J., & Reedy, R. C. (2005). Production of noble gases near the surface of Europa and the prospects for in situ chronology. Icarus, 174(1), 205-214.
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  Abstract: The age of the surface of Europa is probably tens of Myr or less, but is poorly constrained. Two different geochronology schemes could potentially be applied to near-surface samples to provide far more precise ages. First, the surface salts apparently contain enough potassium to make potassium-argon dating feasible. Second, the bombardment of the surface with both galactic cosmic rays and protons trapped within the jovian magnetosphere will cause nuclear reactions that can lead to measurable buildups of cosmogenic noble gases, which can be used to determine both cosmic-ray exposure ages and erosion, deposition, or mixing rates for surface modification. The major differences between Europa's salt-rich ice and the rocks (meteorites, lunar samples and terrestrial rocks) in which cosmogenic noble gases are normally measured are that the abundance of target elements for nuclear reactions creating neon and argon are lower (because of the high water content), but neutron-capture reactions, particularly 35Cl (n,γ)36Cl(β-)36Ar, are enhanced because of the thermalizing effects of the water. As well as presenting calculations of noble gas production near the surface of Europa, we also show that the measurements required to determine ages are within reach of technology in the near future, if an instrument can be landed on the surface of Europa. © 2004 Elsevier Inc. All rights reserved.
• Beaty, D. W., Miller, S., Zimmerman, W., Bada, J., Conrad, P., Dupuis, E., Huntsberger, T., Ivlev, R., Kim, S. S., Lee, B. G., Lindstrom, D., Lorenzoni, L., Mahaffy, P., McNamara, K., Papanastassiou, D., Patrick, S., Peters, S., Rohatgi, N., Simmonds, J. J., , Spray, J., et al. (2004). Planning for a Mars in situ sample preparation and distribution (SPAD) system. Planetary and Space Science, 52(1-3), 55-66.
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  Abstract: For Mars in situ landed missions, it has become increasingly apparent that significant value may be provided by a shared system that we call a Sample Preparation and Distribution (SPAD) System. A study was conducted to identify the issues and feasibility of such a system for these missions that would provide common functions for: receiving a variety of sample types from multiple sample acquisition systems; conducting preliminary characterization of these samples with non-destructive science instruments and making decisions about what should happen to the samples; performing a variety of sample preparation functions; and, finally, directing the prepared samples to additional science instruments for further analysis. Scientific constraints on the functionality of the system were identified, such as triage, contamination management, and various sample preparation steps, e.g., comminution, splitting, rock surfacing, and sieving. Some simplifying strategies were recommended and an overall science flow was developed. Engineering functional requirements were also investigated and example architectures developed. Preliminary conclusions are that shared SPAD facility systems could indeed add value to future Mars in situ landed missions if they are designed to respond to the particular requirements and constraints of those missions, that such a system appears feasible for consideration, and that certain standards should be developed for key SPAD interfaces. © 2003 Elsevier Ltd. All rights reserved.
• Doran, P. T., Clifford, S. M., Forman, S. L., Nyquist, L., Papanastassiou, D. A., Stewart, B. W., Sturchio, N. C., Swindle, T. D., Cerling, T., Kargel, J., McDonald, G., Nishiizumi, K., Poreda, R., Rice, J. W., & Tanaka, K. (2004). Mars chronology: Assessing techniques for quantifying surficial processes. Earth-Science Reviews, 67(3-4), 313-337.
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  Abstract: Currently, the absolute chronology of Martian rocks, deposits and events is based mainly on crater counting and remains highly imprecise with epoch boundary uncertainties in excess of 2 billion years. Answers to key questions concerning the comparative origin and evolution of Mars and Earth will not be forthcoming without a rigid Martian chronology, enabling the construction of a time scale comparable to Earth's. Priorities for exploration include calibration of the cratering rate, dating major volcanic and fluvial events and establishing chronology of the polar layered deposits. If extinct and/or extant life is discovered, the chronology of the biosphere will be of paramount importance. Many radiometric and cosmogenic techniques applicable on Earth and the Moon will apply to Mars after certain baselines (e.g. composition of the atmosphere, trace species, chemical and physical characteristics of Martian dust) are established. The high radiation regime may pose a problem for dosimetry-based techniques (e.g. luminescence). The unique isotopic composition of nitrogen in the Martian atmosphere may permit a Mars-specific chronometer for tracing the time-evolution of the atmosphere and of lithic phases with trapped atmospheric gases. Other Mars-specific chronometers include measurement of gas fluxes and accumulation of platinum group elements (PGE) in the regolith. Putting collected samples into geologic context is deemed essential, as is using multiple techniques on multiple samples. If in situ measurements are restricted to a single technique it must be shown to give consistent results on multiple samples, but in all cases, using two or more techniques (e.g. on the same lander) will reduce error. While there is no question that returned samples will yield the best ages, in situ techniques have the potential to be flown on multiple missions providing a larger data set and broader context in which to place the more accurate dates. © 2004 Elsevier B.V. All rights reserved.
• Grier, J. A., Kring, D. A., Swindle, T. D., Rivkin, A. S., Cohen, B. A., & Britt, D. T. (2004). Analyses of the chondritic meteorite Orvinio (H6): Insight into the origins and evolution of shocked H chondrite material. Meteoritics and Planetary Science, 39(9), 1475-1493.
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  Abstract: We have studied the petrography, reflectance spectra, and Ar-Ar systematics of the Orivinio meteorite. Orvinio is an H chondrite not an L chondrite as sometimes reported. The material in the meteorite was involved in several impact events. One impact event produced large swaths of impact melt from H chondrite material surrounding relict clasts of chondrule-bearing material. Not only were portions of a bulk H chondrite planestesimal melted during the impact event, but shock redistribution of metal and sulfide phases in the meteorite dramatically altered its reflectance spectra. Both the melt and relict clasts are darker than unshocked H chondrite material, bearing spectral similarities to some C-class asteroids. Such shock metamorphism, which lowers the albedo of an object without increasing its spectral slope, may partially explain some of the variation among S-class asteroids and some of the trends seen on asteroid 433 Eros. Noble gases record the evidence of at least two, and perhaps three, impact events in the meteorite and its predecessor rocks. The most significant evidence is for an event that occurred 600 Ma ago or less, perhaps ∼325 Ma ago or less. There is also a signature of 4.2 Ga in the Ar-Ar systematics, which could either reflect complete degassing of the rock at that time or partial degassing of even the most retentive sites in the more recent event. © Meteoritical Society, 2004.
• Swindle, T. D., & Campins, H. (2004). Do comets have chondrules and CAIs? Evidence from the Leonid meteors. Meteoritics and Planetary Science, 39(10), 1733-1740.
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  Abstract: Chondrules, silicate spheres typically 0.1 to 1 mm in diameter, are the most abundant constituents in the most common meteorites falling on Earth, the ordinary chondrites. In addition, many primitive meteorites have calcium-aluminum-rich inclusions (CAIs). The question of whether comets have chondrules or CAIs is relevant to understanding what the interior of a comet is like and what a cometary meteorite might be like. In addition, one prominent model for forming chondrules and CAIs, the X-wind model, predicts their presence in comets, while most other models do not. At present, the best way to search for chondrules and CAIs in comets is through meteor showers derived from comets, in particular, the Leonid meteor shower. Evidence potentially could be found in the overall mass distribution of the shower, in chemical analyses of meteors, or in light curves. There is no evidence for a chondrule abundance in the Leonid meteors similar to that found in chondritic meteorites. There is intriguing evidence for chondrule- or CAI-sized objects in a small fraction of the light curves, but further work is required to generate a definitive test. © Meteoritical Society, 2004.
• Swindle, T. D., & Olson, E. K. (2004). ⁴⁰Ar^-39Ar studies of whole rock nakhlites: Evidence for the timing of formation and aqueous alteration on Mars. Meteoritics and Planetary Science, 39(5), 755-766.
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  Abstract: 20-25 mg whole rock samples of the nakhlites Lafayette and Nakhla have been analyzed via the 40Ar39Ar technique, in part to verify their formation ages, but primarily, in an attempt to determine the timing of aqueous alteration in these martian meteorites. As in previous studies, plateaus in apparent age are observed at about 1300 Ma (1322 ± 10 for Lafayette, 1332 ± 10 and 1323 ± 11 for Nakhla), presumably corresponding to crystallization ages. The plateaus are not entirely flat, perhaps reflecting the effects of recoil during creation of 39Ar in the nuclear irradiation. The first 5-20% of the K-derived Ar released from all three samples give apparent ages
• Swindle, T. D., Plescia, J. B., & McEwen, A. S. (2004). Exploring a possible shergottite source crater and calibrating the martian cratering chronology. Meteoritics and Planetary Science, 39(SUPPL.), A102.
• Kring, D. A., Gleason, J. D., Swindle, T. D., Nishiizumi, K., Caffee, M. W., Hill, D. H., Jull, A. T., & Boynton, W. V. (2003). Composition of the first bulk melt sample from a volcanic region of Mars: Queen Alexandra Range 94201. Meteoritics and Planetary Science, 38(12), 1833-1848.
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  Abstract: Antarctic meteorite Queen Alexandra Range (QUE) 94201 is a 12 g basaltic achondrite dominated by plagioclase (now maskelynite) and zoned low- and high-Ca pyroxene. Petrologic, geochemical, and isotopic analyses indicate that it is related to previously described basaltic and lherzolitic shergottites, which are a group of igneous meteorites that are believed to be from Mars. Unlike previous shergottites, however, QUE 94201 represents a bulk melt rather than a cumulate fraction, meaning it can be used to infer magmatic source regions and the compositions of other melts on Mars. This melt has much more Fe and P than basaltic melts produced on Earth and formed at a much lower oxygen fugacity. This has altered the crystallization sequence of the melt, removing olivine from the liquidus to produce a plagioclase and 2-pyroxene assemblage. If the high-phosphorus and low-oxygen fugacity conditions represented by QUE 94201 are common in magmatic regions of Mars, then olivine may be rare in martian basalts. No solar cosmic ray effects were seen in the concentrations of 10Be, 26Al, and 36Cl with depth in the meteorite, implying at least 3 cm of ablation during entry to Earth. Significant excesses of neutron capture noble gas isotopes (80, 82Kr and 128,131Xe) suggest that the QUE 94201 sample came from a depth >22 cm in a meteoroid of at least that radius. The meteorite also has very low 21Ne/22Ne, which would often be interpreted to mean little ablation (contradicting above evidence) but, in this case, appears to reflect a very low abundance of Mg (the principal target element for Ne) in the meteorite, consistent with our bulk chemical analyses. The meteorite has a terrestrial 36Cl age of 0.29 ± 0.05 Myr and a 10Be exposure age of 2.6 ± 0.5 Myr in a 47π geometry, implying an ejection age of 2.9 ± 0.5 Myr. © Meteoritical Society, 2003. Printed in USA.
• Daubar, I. J., Kring, D. A., Swindle, T. D., & Jull, A. T. (2002). Northwest Africa 482: A crystalline impact-melt breccia from the lunar highlands. Meteoritics and Planetary Science, 37(12), 1797-1813.
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  Abstract: Northwest Africa 482 (NWA 482) is a crystalline impact-melt breccia from the Moon with highlands affinities. The recrystallized matrix and the clast population are both highly anorthositic. Clasts are all related to the ferroan anorthosite suite, and include isolated plagioclase crystals and lithic anorthosites, troctolites, and spinel troctolites. Potassium-, rare-earth-element-, and phosphorus-bearing (KREEP) and mare lithologies are both absent, constraining the source area of this meteorite to a highland terrain with little to no KREEP component, most likely on the far side of the Moon. Glass is present in shock veins cutting through the sample and in several large melt pockets, indicating a second impact event. There are two separate events recorded in the 40Ar-39Ar system: one at ∼3750 Ma, which completely reset the K-Ar system, and one at ≲2400 Ma, which caused only partial degassing. These events could represent, respectively, crystallization of the impact-melt breccia and later formation of the glass, or the formation of the glass and a later thermal event. The terrestrial age of the meteorite is 8.6 ± 1.3 ka. This age corresponds well with the modest amount of weathering in the rock, in the form of secondary phyllosilicates and carbonates. Based on terrestrial age and location, lithology, and chemistry, NWA 482 is unique among known lunar meteorites.
• Johnson, J. R., Feldman, W. C., Lawrence, D. J., Maurice, S., Swindle, T. D., & Lucey, P. G. (2002). Lunar prospector epithermal neutrons from impact craters and landing sites: Implications for surface maturity and hydrogen distribution. Journal of Geophysical Research E: Planets, 107(2), 3-1-3-8.
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  Abstract: Initial studies of neutron spectrometer data returned by Lunar Prospector concentrated on the discovery of enhanced hydrogen abundances near both lunar poles. However, the nonpolar data exhibit intriguing patterns that appear spatially correlated with surface features such as young impact craters (e.g., Tycho). Such immature crater materials may have low hydrogen contents because of their relative lack of exposure to solar wind-implanted volatiles. We tested this hypothesis by comparing epithermal* neutron counts (i.e., epithermal -0.057 × thermal neutrons) for Copernican-age craters classified as relatively young, intermediate, and old (as determined by previous studies of Clementine optical maturity variations). The epithermal* counts of the crater and continuous ejecta regions suggest that the youngest impact materials are relatively devoid of hydrogen in the upper 1 m of regolith. We also show that the mean hydrogen contents measured in Apollo and Luna landing site samples are only moderately well correlated to the epithermal* neutron counts at the landing sites, likely owing to the effects of rare earth elements. These results suggest that further work is required to define better how hydrogen distribution can be revealed by epithermal neutrons in order to understand more fully the nature and sources (e.g., solar wind, meteorite impacts) of volatiles in the lunar regolith.
• Lorenz, R. D., Jull, A. T., Swindle, T. D., & Lunine, J. I. (2002). Radiocarbon on Titan. Meteoritics and Planetary Science, 37(6), 867-874.
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  Abstract: We explore the likely production and fate of 14C in the thick nitrogen atmosphere of Saturn's moon Titan and investigate the constraints that measurements of 14C might place on Titan's photochemical, atmospheric transport and surface-atmosphere interaction processes. Titan's atmosphere is thick enough that cosmic-ray flux limits the production of 14C: absence of a strong magnetic field and the increased distance from the Sun suggest production rates of ~9 atom/cm2/s, ~4x higher than Earth. The fate and detectability of 14C depends on the chemical species into which it is incorporated: as methane it would be hopelessly diluted even in only the atmosphere. However, in the more likely case that the 14C attaches to the haze that rains out onto the surface (as tholin, HCN or acetylene and their polymers), haze in the atmosphere or recently deposited on the surface would be quite radioactive. Such radioactivity may lead to a significant enhancement in the electrical conductivity of the atmosphere which will be measured by the Huygens probe. Measurements with simple detectors on future missions could place useful constraints on the mass deposition rates of photochemical material on the surface and identity locations where surface deposits of such material are "freshest".
• Swindle, T. D. (2002). Martian noble gases. Reviews in Mineralogy and Geochemistry, 47.
• Swindle, T. D. (2002). Noble gases in the moon and meteorites: Radiogenic components and early volatile chronologies. Reviews in Mineralogy and Geochemistry, 47.
• Bridges, J. C., Catling, D. C., Saxton, J. M., Swindle, T. D., Lyon, I. C., & Grady, M. M. (2001). Alteration assemblages in Martian meteorites: Implications for near-surface processes. Space Science Reviews, 96(1-4), 365-392.
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  Abstract: The SNC (Shergotty-Nakhla-Chassigny) meteorites have recorded interactions between Martian crustal fluids and the parent igneous rocks. The resultant secondary minerals - which comprise up to ∼1 vol.% of the meteorites - provide information about the timing and nature of hydrous activity and atmospheric processes on Mars. We suggest that the most plausible models for secondary mineral formation involve the evaporation of low temperature (25 - 150 °C) brines. This is consistent with the simple mineralogy of these assemblages - Fe-Mg-Ca carbonates, anhydrite, gypsum, halite, clays - and the chemical fractionation of Ca-to Mg-rich carbonate in ALH84001 "rosettes". Longer-lived, and higher temperature, hydrothermal systems would have caused more silicate alteration than is seen and probably more complex mineral assemblages. Experimental and phase equilibria data on carbonate compositions similar to those present in the SNCs imply low temperatures of formation with cooling taking place over a short period of time (e.g. days). The ALH84001 carbonate also probably shows the effects of partial vapourisation and dehydration related to an impact event postdating the initial precipitation. This shock event may have led to the formation of sulphide and some magnetite in the Fe-rich outer parts of the rosettes. Radiometric dating (K-Ar, Rb-Sr) of the secondary mineral assemblages in one of the nakhlites (Lafayette) suggests that they formed between 0 and 670 Myr, and certainly long after the crystallisation of the host igneous rocks. Crystallisation of ALH84001 carbonate took place 0.5 Gyr after the parent rock. These age ranges and the other research on these assemblages suggest that environmental conditions conducive to near-surface liquid water have been present on Mars periodically over the last ∼1 Gyr. This fluid activity cannot have been continuous over geological time because in that case much more silicate alteration would have taken place in the meteorite parent rocks and the soluble salts would probably not have been preserved. The secondary minerals could have been precipitated from brines with seawater-like composition, high bicarbonate contents and a weakly acidic nature. The co-existence of siderite (Fe-carbonate) and clays in the nakhlites suggests that the pCO2 level in equilibrium with the parent brine may have been 50 mbar or more. The brines could have originated as flood waters which percolated through the top few hundred meters of the crust, releasing cations from the surrounding parent rocks. The high sulphur and chlorine concentrations of the Martian soil have most likely resulted from aeolian redistribution of such aqueously-deposited salts and from reaction of the Martian surface with volcanic acid volatiles. The volume of carbonates in meteorites provides a minimum crustal abundance and is equivalent to 50-250 mbar of CO2 being trapped in the uppermost 200-1000 m of the Martian crust. Large fractionations in δ18O between igneous silicate in the meteorites and the secondary minerals (≤30‰) require formation of the latter below temperatures at which silicate-carbonate equilibration could have taken place (∼400°C) and have been taken to suggest low temperatures (e.g. ≥150°C) of precipitation from a hydrous fluid.
• Musselwhite, D. S., & Swindle, T. D. (2001). Is release of martian atmosphere from polar clathrate the cause of nakhlite and ALH84001 Ar/Kr/Xe ratios?. Icarus, 154(1), 207-215.
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  Abstract: Variations in the Ar/Kr/Xe ratios of martian atmosphere trapped in martian meteorites correlate with the time of ejection of these meteorites from Mars. We suggest that these variations reflect actual differences in the Ar/Kr/Xe ratios of the martian atmosphere at the time of ejection of the meteorites. We propose that the variation of the Ar/Kr/Xe ratios of the martian atmosphere is caused by time varying uptake and release of these gases by CO2-H2O clathrate-hydrate in the polar caps. Nakhlites, martian meteorites representing cumulate magmatic rocks, contain evidence of atmosphere from the time of their ejection from Mars. We postulate that the martian atmosphere at that time had lower Ar/Xe and Kr/Xe ratios compared with the modern atmosphere because of the release of these and other gases from polar clathrate, possibly during a period of high (∼60°) obliquity. © 2001 Elsevier Science.
• Musselwhite, D. S., Swindle, T. D., & Lunine, J. I. (2001). Liquid CO₂ breakout and the formation of recent small gullies on Mars. Geophysical Research Letters, 28(7), 1283-1285.
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  Abstract: We show that the action of a CO2 suspended flow could have produced the recent small gullies on Mars, and, hence, that liquid water is not required. The model involves the build-up of a liquid-CO2 aquifer behind and below a dry-ice barrier (dam/cap rock) in the pore spaces a few meters into the rock from the cliff face and on order of a hundred meters below the top of the cliff brink surface. Seasonal for obliquity-cycle-seasonal) heating causes pinching out of the dry-ice barrier and rapid release of the liquid CO2. Erosion of the gullies occurs as the rapid vaporization of the liquid CO2 with entrainment of rock and clathrate-hydrate ice produces a density flow analogous to a terrestrial nue ardente.
• SWINDLE, T., CAFFEE, M., & HOHENBERG, C. (1986). XENON AND OTHER NOBLE-GASES IN SHERGOTTITES. GEOCHIMICA ET COSMOCHIMICA ACTA, 50(6), 1001-1015.
• Cohen, B. A., Swindle, T. D., & Kring, D. A. (2000). Support for the lunar cataclysm hypothesis from lunar meteorite impact melt ages. Science, 290(5497), 1754-1756.
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  PMID: 11099411;Abstract: Lunar meteorites represent a more random sampling of lunar material than the Apollo or Luna collections and, as such, lunar meteorite impact melt ages are the most important data in nearly 30 years with which to reexamine the lunar cataclysm hypothesis. Within the lunar meteorite breccias MAC 88105, QUE 93069, DaG 262, and DaG 400, seven to nine different impact events are represented with 40Ar-39Ar ages between 2.76 and 3.92 billion years ago (Ga). The lack of impact melt older than 3.92 Ga supports the concept of a short, intense period of bombardment in the Earth-moon system at ~3.9 Ga. This was an anomalous spike of impact activity on the otherwise declining impact-frequency curve.
• Musselwhite, D., Swindle, T., & Lunine, J. (2000). Liquid CO2 breakout and the formation of recent small gullies on Mars. GEOPHYSICAL RESEARCH LETTERS, 28(7), 1283-1285.
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  We show that the action of a CO2 suspended flow could have produced the recent small gullies on Mars, and, hence, that liquid water is not required. The model involves the build-up of a liquid-CO2 aquifer behind and below a dry-ice barrier (dam/cap rock) in the pore spaces a few meters into the rock from the cliff face and on order of a hundred meters below the top of the cliff brink surface. Seasonal (or obliquity-cycle-seasonal) heating causes pinching out of the dry-ice barrier and rapid release of the liquid CO2. Erosion of the gullies occurs as the rapid vaporization of the liquid CO2 with entrainment of rock and clathrate-hydrate ice produces a density flow analogous to a terrestrial nue ardente.
• Swindle, T. D., Treiman, A. H., Lindstrom, D. J., Burkland, M. K., Cohen, B. A., Grier, J. A., Li, B., & Olson, E. K. (2000). Noble gases in iddingsite from the Lafayette meteorite: Evidence for liquid water on Mars in the last few hundred million years. Meteoritics and Planetary Science, 35(1), 107-115.
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  Abstract: We analyzed noble gases from 18 samples of weathering products ('iddingsite') from the Lafayette meteorite. Potassium-argon ages of 12 samples range from near zero to 670 ± 91 Ma. These ages confirm the martian origin of the iddingsite, but it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration or incorporation of martian atmospheric 40Ar. In any case, because iddingsite formation requires liquid water, this data requires the presence of liquid water near the surface of Mars at least as recently as 1300 Ma ago, and probably as recently as 650 Ma ago. Krypton and Xe analysis of a single 34 μg sample indicates the presence of fractionated martian atmosphere within the iddingsite. This also confirms the martian origin of the iddingsite. The mechanism of incorporation could either be through interaction with liquid water during iddingsite formation or a result of shock implantation of adsorbed atmospheric gas.
• Grier, J. A., Swindle, T. D., Kring, D. A., & Melosh, H. J. (1999). Argon-40/argon-39 analyses of samples from the Gardnos impact structure, Norway. Meteoritics and Planetary Science, 34(5), 803-807.
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  Abstract: We have conducted 40Ar/39Ar age dating on a sample of impact melt from the Gardnos impact structure in Norway in an attempt to better constrain the formation age of the crater. Current estimates of the age of the Gardnos crater cover a wide range and are as old as 900 Ma (Dons and Naterstad, 1992; French et al., 1997). The age spectra that we obtained from three samples are consistent with a thermal event at 385 ± 5 Ma (1σ). Because this differs greatly from the best stratigraphic age of ~600 Ma, and because the minerals present in the dated sample are a metamorphic assemblage, we believe we have not dated the formation age of the crater. Instead we have probably dated the effect of the early Devonian collapse of the late Caledonian (Scandian) orogeny on these materials (Dons and Naterstad, 1992; French et al., 1997). Although it may be possible, it will be difficult to determine the age of the impact by isotopic means alone because of this widespread metamorphism. Detailed stratigraphic analyses of the crater fill sediments may be the most promising method for constraining the crater age.
• Johnson, J. R., Swindle, T. D., & Lucey, P. G. (1999). Estimated solar wind-implanted helium-3 distribution on the Moon. Geophysical Research Letters, 26(3), 385-388.
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  Abstract: Among the solar wind-implanted volatiles present in the lunar regolith, 3 He is possibly the most valuable resource because of its potential as a fusion fuel. The abundance of 3 He in the lunar regolith at a given location depends on surface maturity, the amount of solar wind fluence, and titanium content, because ilmenite (FeTiO3) retains helium much better than other major lunar minerals. Surface maturity and TiO2 maps from Clementine multispectral data sets are combined here with a solar wind fluence model to produce a 3He abundance map of the Moon. Comparison of the predicted 3He values to landing site observations shows good correlation. The highest 3He abundances occur in the farside maria (due to greater solar wind fluence received) and in higher TiO2 nearside mare regions.
• Krot, A. N., Brearley, A. J., Ulyanov, A. A., Biryukov, V. V., Swindle, T. D., Keil, K., Mittlefehldt, D. W., Scott, E. R., Clayton, R. N., & Mayeda, T. K. (1999). Mineralogy, petrography, bulk chemical, iodine-xenon, and oxygen-isotopic compositions of dark inclusions in the reduced CV3 chondrite Efremovka. Meteoritics and Planetary Science, 34(1), 67-89.
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  Abstract: We studied the petrography, mineralogy, bulk chemical, I-Xe, and O-isotopic compositions of three dark inclusions (E39, E53, and E80) in the reduced CV3 chondrite Efremovka. They consist of chondrules, calcium-aluminum-rich inclusions (CAIs), and fine-grained matrix. Primary minerals in chondrules and CAIs are pseudomorphed to various degrees by a mixture largely composed of abundant (>95%), fine-grained (>0.2 μm) fayalitic olivine (Fa(35-42)) and minor amounts of chlorite, poorly-crystalline Si-Al-rich material, and chromite; chondrule and CAI shapes and textures are well-preserved. Secondary Ca-rich minerals (Ti-andradite, kirschsteinite, Fe-diopside) are common in chondrule pseudomorphs and matrices in E39 and E80. The degree of replacement increases from E53 to E39 to E80. Fayalitic olivines are heavily strained and contain abundant voids similar to those in incompletely dehydrated phyllosilicates in metamorphosed CM and CI chondrites. Opaque nodules in chondrules consist of Ni- and Co-rich taenite, Co-rich kamacite, and wairauite; sulfides are rare; magnetite is absent. Bulk O-isotopic compositions of E39 and E53 plot in the field of aqueously altered CM chondrites, close to the terrestrial fractionation line; the more heavily altered E39 is isotopically heavier than the less altered E53. The apparent I-Xe age of E53 is 5.4 Ma earlier than Bjurbole and 5.7 ± 2.0 Ma earlier than E39. The I-Xe data are consistent with the most heavily altered dark inclusion, E39 having experienced either longer or later alteration than E53. Bulk lithophile elements in E39 and E53 most closely match those of CO chondrites, except that Ca is depleted and K and As are enriched. Both inclusions are depleted in Se by factors of 3-5 compared to mean CO, CV, CR, or CK chondrites. Zinc in E39 is lower than the mean of any carbonaceous chondrite groups, but in E53 Zn is similar to the means in CO, CV, and CK chondrites. The Efremovka dark inclusions experienced various degrees of aqueous alteration, followed by low degree thermal metamorphism in an asteroidal environment. These processes resulted in preferential oxidation of Fe from opaque nodules and formation of Ni- and Co-rich metal, metasomatic alteration of primary minerals in chondrules and CAIs, and the formation of fayalitic olivine and secondary Ca-Fe-rich minerals. Based on the observed similarities of the alteration mineralization in the Efremovka and Allende dark inclusions, we infer that the latter may have experienced similar alteration processes.
• Swindle, T. D. (1999). Polar endeavours. Nature, 399(6738), 738-.
• Campins, H., & Swindle, T. D. (1998). Expected characteristics of cometary meteorites. Meteoritics and Planetary Science, 33(6), 1201-1211.
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  Abstract: Recent developments in our understanding of comets provide insights into the topic of cometary meteorites. These developments include the identification of comet-asteroid transition objects (such as 4015 Wilson-Harrington and 3200 Phaethon), information on the composition of cometary solids, and new ideas on the collisional history of Jupiter-family comets. In this work, we revisit this question, and we conclude that comets do indeed yield macroscopic meteorites, which either have not been found or have not been recognized. We also consider the expected characteristics of cometary meteorites, with an emphasis on those that may help identify and differentiate them from other types of meteorites. If cometary meteorites have preserved the main characteristics of cometary dust, the mineralogy would be dominated by highly unequilibrated anhydrous silicates, and the chemistry would be nearly chondritic but with a high abundance of C and N. On the other hand, if an unknown process produced extensive aqueous alteration in the material that formed cometary meteorites, they would resemble (or could even be) CI carbonaceous chondrites. We do not expect cometary meteorites to have chondrules. So far, no single meteorite looks unequivocally cometary. However, we have identified xenoliths in ordinary chondrite regolith breccias that meet most of our criteria for a cometary origin and deserve further study.
• Goswami, J. N., Sahijpal, S., Kehm, K., Hohenberg, C. M., Swindle, T., & Grossman, J. N. (1998). In situ determination of iodine content and iodine-xenon systematics in silicates and troilite phases in chondrules from the LL3 chondrite Semarkona. Meteoritics and Planetary Science, 33(3), 527-534.
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  Abstract: Iodine concentrations in small domains (~10 μm) of silicates and troilite (FeS) phass in three chondrules from the Semarkona (LL3) meteorite were determined by an ion microprobe. Independent determination of I content in some of these phases was accomplished by in situ laser probe mass spectrometric analysis of I-derived 12Xe in one of these neutron-irradiated chondrules. The ion microprobe data suggest low I content for olivines (20-45 ppb) and relatively higher values for pyroxene and glass (mesostasis) (40-160 ppb). The broad similarity in the measured I contents in pyroxenes in a porphyritic pyroxene chondrule by ion microprobe (42-138 ppb) and by laser probe (37-76 ppb) demonstrate the feasibility of in situ determination of I content in silicate phases via ion microprobe. The I contents in troilite measured by ion microprobe, however, are prone to uncertainty because of the lack of a sulfide standard. The ion microprobe data suggest I content of >1 ppm in troilite, if the calibration from our silicate standard is used. However, teh noble gas data suggest that the content in troilite is comparable to that in silicates. We attribute this apparent discrepancy to an enhanced sputter ion yield of I from sulfides. Iodine-derived 129Xe excesses were observed in both pyroxene and troilite within this chondrule. The I-Xe model ages of these selected phases are consistent with the I-Xe studies of the bulk chondrule. The individual data points fall on or near the isochron obtained from the bulk chondrule, although all except the most radiogenic data point contain evidence of low-temperature uncorrelated iodine.
• Kring, D. A., Swindle, T. D., Gleason, J. D., & Grier, J. A. (1998). Formation and relative ages of maskelynite and carbonate in ALH84001. Geochimica et Cosmochimica Acta, 62(12), 2155-2166.
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  Abstract: The morphology and stoichiometry of feldspathic glass in the Martian meteorite ALH84001 indicates it is maskelynite (a diaplectic glass) rather than a flowed glass, although this glass was heterogeneously affected by a tertiary set of processes. An impact event with shock pressures in excess of 31 GPa was needed to convert the original plagioclase (An36Ab60Or4) to maskelynite. Carbonate is intimately associated with the maskelynite, and the carbonate's radiating crystalline fabric and globular forms suggest it was produced after plagioclase was converted to maskelynite. Textures also suggest carbonate was produced at the expense of maskelynite in a dissolution-precipitation reaction that involved a carbonic fluid. This fluid system is tentatively estimated to have been active for at least a few years at temperatures
• Swindle, T. D. (1998). Implications of iodine-xenon studies for the timing and location of secondary alteration. Meteoritics and Planetary Science, 33(5), 1147-1155.
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  Abstract: Iodine-xenon ages (based on 15.7 Ma 129I) of meteoritic samples are highly susceptible to secondary alteration processes, so they have the potential to determine both the timing, and in some cases the location, of those secondary processes. Iodine-xenon studies can determine the location in two cases. First, if the length of time required is greater than the lifetime of the nebula, then the process must have occurred on a parent body. Ages from sodalite in Allende, dark inclusions in Efremovka (CV3), and some samples from CM chondrites all suggest durations of several million years, in some cases marginally longer than the predicted duration of the nebula. Second, in some cases the evolution of the 129Xe/132Xe ratio can be used to determine the I/Xe elemental ratio of the reservoir in which the evolution occurred. For chondrules from the unequilibrated ordinary chondrites Chainpur and Tieschitz, the isotopic evolution is quantitatively consistent with evolution in a chondritic (parent body), rather than nebular, reservoir.
• Swindle, T. D. (1998). Lunar exploration: Water amongst the rock. Nature, 395(6702), 549-550.
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  PMID: 9783579;
• Swindle, T. D., Kring, D. A., Burkland, M. K., Hill, D. H., & Boynton, W. V. (1998). Noble gases, bulk chemistry, and petrography of olivine-rich achondrites Eagles Nest and Lewis Cliff 88763: Comparison to brachinites. Meteoritics and Planetary Science, 33(1), 31-48.
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  Abstract: Eagles Nest and Lewis Cliff (LEW) 88763 are olivine-rich achondrites that have been suggested to be related to Brachina and ALH 84025. Both are ultramafic, although LEW 88763 has ∼10% plagioclase, which Eagles Nest lacks. Olivine in Eagles Nest (Fo68) is virtually identical in composition to that in Brachina (Fo68-70), and that in LEW 88763 is only slightly different (Fo63-64). The meteorites' cosmic-ray exposure ages differ from each other and from Brachina and ALH 84025. Like Brachina, Eagles Nest has a substantial amount of radiogenic 129Xe and an apparent K-Ar age of
• Swindle, T. D., & Jones, J. H. (1997). The xenon isotopic composition of the primordial Martian atmosphere: Contributions from solar and fission components. Journal of Geophysical Research E: Planets, 102(E1), 1671-1678.
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  Abstract: Previous models of the evolution of the isotopic composition of Xe in the Martian atmosphere have little room for any Xe produced by fission of 244Pu, although there is a contribution from the decay of shorter-lived 129I. We find that the previously calculated ratios of I-derived to Pu-derived Xe can only be matched if Mars accreted very early and outgassing of I-derived Xe after atmospheric loss was much stronger than outgassing of Pu-derived Xe. Alternatively, we find that if we assume that primordial Xe on Mars had the isotopic composition of the solar wind, rather than the previously assumed chondritic Xe, a larger contribution from 244Pu is allowed, and it is much easier to generate models of outgassing and atmospheric loss that match the present atmosphere. Furthermore, the isotopic composition of solar wind Xe matches that of the Chassigny meteorite (widely considered to represent a sample of Martian interior Xe), so it is not necessary to postulate separate sources of Xe for the interior and atmosphere of Mars. Copyright 1997 by the American Geophysical Union.
• Swindle, T. D., & Kring, D. A. (1997). Implications of small comets for the noble gas inventories of Earth and Mars. Geophysical Research Letters, 24(24), 3113-3116.
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  Abstract: Frank et al. [1986a,b] proposed the possibility of large numbers of small comets impacting the Earth. Using the parameters for the small cornets suggested by Frank and Sigwarth [1993], we find that, over the lifetime of the solar system, such small comets would deliver far more Ar, Kr, and Xe to the atmospheres of Earth and Mars than those atmospheres presently contain if, as Frank and Sigwarth [1993] assumed, the small comets formed in very cold regions far from the Sun. Comets can be greatly depleted in noble gases if they form relatively close to the Sun (for example, near Jupiter), but this source region is inconsistent with other features of the proposed model. Alternatively, if the comets did form in very cold regions far from the Sun, the current flux would have to be at least a factor of 30,000 higher than the long-term average. Copyright 1997 by the American Geophysical Union.
• Kring, D. A., Swindle, T. D., Britt, D. T., & Grier, J. A. (1996). Cat Mountain: A meteoritic sample of an impact-melted asteroid regolith. Journal of Geophysical Research E: Planets, 101(E12), 29353-29371.
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  Abstract: Cat Mountain is a new ordinary chondrite impact melt breccia that contains several shocked chondrule-bearing clasts of L5 material. These clasts are surrounded by a total impact melt of similar composition material which appears to have cooled over a period of a few thousand years, probably within a melt breccia lens in the bottom of a large (>1 km diameter) crater on an L chondrite asteroid. Noble gas isotopes indicate that the sample was involved in at least two different impact events, approximately 880 and 20 Myr ago, followingGA the 4.55 Ga accretion of primitive chondritic material. The 880 Ma event is responsible for the impact breccia texture of the sample, and the 20 Ma event reduced the sample to a meter-sized object. We also infer that another impact occurred between 880 and 20 Ma (possibly the ∼500 Ma event recorded in many other L chondrites) to jettison the material from the asteroid belt into an orbit that evolved into an Earth-crossing trajectory. The shock-metamorphic processes that occurred at 880 Ma redistributed the opaque phases in the meteorite and altered the crystalline characteristics of silicate phases. This reduced the reflectance of the L5 material and decreased the amplitude of its spectral absorption features. These characteristics are consistent with the spectral characteristics of some C class asteroids and suggest that some dark asteroids that appear to belong to the C class could be covered with shocked ordinary chondrite material. If one assumes that Cat Mountain came from the same asteroid as other L chondrites with the same cosmic ray exposure age, then the juxtaposition of these different materials suggests asteroids are rubble piles which are heterogeneous on a scale less than 100 m. Furthermore, the structural integrity of Cat Mountain and other L chondrites suggests the strengths of asteroid rubble piles are limited by fractures and contrasting material properties and are thus inherently weak in a ram pressure regime produced when they enter a planetary atmosphere. However, in a regime where the asteroid is the target of impact fragmentation rather than the projectile, the added porosity of a rubble pile structure will compensate for the presence of fractures and absorb a large amount of the impact energy. In this case the structural integrity of the asteroid may appear to be the same as a previously unshocked chondritic material. Copyright 1996 by the American Geophysical Union.
• Warren, P. H., Drake, B. G., Lofgren, G. E., & Swindle, T. D. (1996). Designing a robotic sampler to collect Moon rocks. Eos, 77(5), 33+37+41.
• Burkland, M. K., Swindle, T. D., & Baldwin, S. L. (1995). Isothermal heating experiments on Bjurböle: Implications for the release mechanisms of radiogenic ¹²⁹Xe. Geochimica et Cosmochimica Acta, 59(10), 2085-2094.
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  Abstract: To understand the response of the IXe system to thermal events, isothermal heating experiments were performed on the Bjurböle (L4) standard used for IXe dating. The time dependence of the release of radiogenic 129Xe was determined by analyzing Bjurbole heated for various times at temperatures of I000, 1100, and 1200°°C using noble gas mass spectrometry. Results indicate that a single domain (site of radiogenic 129Xe) model is insufficient to describe the release. At least two, and possibly more, domains are present in Bjurböle. At least one domain outgasses in one hour at a temperature ≤ 1000°C by a mechanism which is not indicative of volume diffusion. For the 1100°C heating one domain containing the majority of radiogenic 129Xe in Bjurböle is seen to outgas in a manner suggestive of volume diffusion. Release characteristics at 1200°C indicate the presence of at least one high temperature domain. In domains which contain I-correlated Xe, assuming loss by volume diffusion, Dodson closure temperatures are at least as high as, and perhaps much higher than, the peak metamorphic temperature experienced by Bjurböle. Based on diffusion parameters, the diffusion length of radiogenic 129Xe, at peak metamorphic temperatures, is much less than a characteristic domain size of 10-3 cm. Therefore, if the release is governed by volume diffusion, then the IXe system has remained unaltered by thermal metamorphism. Loss of radiogenic 129Xe by mechanisms other than volume diffusion, such as a phase transformation or the melting of a host mineral phase, is possible, but is not indicated in the release of the majority of the gas. If the release is by melting of highly retentive domains then the IXe system has remained unaltered by thermal metamorphism. © 1995.
• Swindle, T. D., Grier, J. A., & Burkland, M. K. (1995). Noble gases in orthopyroxenite ALH84001: A different kind of martian meteorite with an atmospheric signature. Geochimica et Cosmochimica Acta, 59(4), 793-801.
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  Abstract: Meteorite ALH84001, a recently identified martian orthopyroxenite, has xenon with higher ratios of 129Xe 132Xe (up to 2.15) than any previously identified martian sample except the glass in EETA79001, suggesting that it has incorporated a relatively large amount of martian atmosphere. As such, it should be a fruitful sample to study in order to try to determine incorporation mechanisms, but it is petrogenetically very different from other martian meteorites with similar noble gas signatures. We determine a cosmic-ray exposure age of 15.8±1.6 Ma, longer than any other martian meteorites, requiring either another impact event on Mars, or another breakup of a martian fragment en route to Earth. Argon systematics suggest an age much older than the other martian meteorites and may indicate a substantial amount of martian atmospheric argon as well. Excesses of 80Kr and 82Kr in one sample are consistent with neutron capture on bromine in situ, but not with an atmosphere rich in Br-derived isotopes. © 1995.
• Drake, M. J., Swindle, T. D., Owen, T., & Musselwhite, D. S. (1994). Fractionated Martian atmosphere in the nakhlites?. Meteoritics, 29(6), 854-859.
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  PMID: 11539475;Abstract: Considerable evidence points to a martian origin of the SNC meteorites. Noble gas isotopic compositions have been measured in most SNC meteorites. The 129Xe/132Xe vs. 84Kr/132Xe ratios in Chassigny, most shergottites, and lithology C of EETA 79001 define a linear array. This array is thought to be mixing line between martian mantle and martian atmosphere. One of the SNC meteorites, Nakhla contains a leachable component that has an elevated 129Xe/132Xe ratio relative to its 84Kr/132Xe ratio when compared to this approximately linear array. The elevated Xe isotopic ratio may represent a distinct reservoir in the martian crust or mantle. More plausibly, it is elementally fractioned martian atmosphere. -from Authors
• Swindle, T. D. (1994). "{Book Review: Resources of near-earth space / U Arizona Press, 1993}". nat, 371, 484.
• Swindle, T. D. (1994). "{Book Review: Resources of near-earth space / U Arizona Press, 1993}". skytel, 87, 60.
• Swindle, T. D. (1993). Noble gases in ancient asteroidal atmospheres. Journal of Geophysical Research, 98(E8), 15,069-15,077.
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  Abstract: The atmospheres of rocky asteroids are unlikely to have ever been anything more than tenuous exospheres. However, it is possible that the densities of radiogenic heavy noble gases might have once been high enough to have implanted observable quantities in the regoliths that became meteorites. Analytical and numerical results suggest that acceleration of photoions by the solar wind motional field is a significant loss process for Xe on asteroids about 200 km in radius or larger, if the Xe is thermalized by its interactions with the surface. For Ar, photoion acceleration can only become important for asteroids nearly 500 km in radius. Thus photoion acceleration, previously invoked for lunar samples, could be responsible for excess fission-produced Xe found associated with solar wind Xe in howardite meteorites. -from Author
• Musselwhite, D. S., Drake, M. J., & Swindle, T. D. (1991). Early outgassing of Mars supported by differential water solubility of iodine and xenon. Nature, 352(6337), 697-699.
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  Abstract: THE martian atmosphere has a high 129Xe/132Xe ratio compared with any on Earth and most meteorites. The 129Xe/132Xe ratio in the martian atmosphere is also high relative to the martian mantle1. In contrast, Earth's upper mantle has a higher 129Xe/132Xe ratio than its atmosphere2. As 129Xe is the daughter product of the extinct nuclide 129I, a means of fractionating iodine from xenon early in martian history appears necessary to account for the 129Xe/132Xe ratios of its known reservoirs. Crystal/melt partitioning will fractionate iodine from xenon in the right sense, but the fractionation is probably inadequate in magnitude; differences in the silicate melt solubilities of iodine and xenon would cause fractionation in the wrong direction. Here we present a model to account for the martian xenon data which relies on the very different solubilities of the two elements in water to fractionate them after outgassing. Atmospheric xenon is lost by impact erosion during heavy bombardment, followed by release of 129Xe produced from 129I decay in the crust.
• Swindle, T., Caffee, M., Hohenberg, C., Lindstrom, M., & Taylor, G. (1991). Iodine-xenon studies of petrographically and chemically characterized Chainpur chondrules. Geochimica et Cosmochimica Acta, 55(3), 861-880.
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  Abstract: We have performed petrographie, instrumental neutron activation analysis (INAA) and noble gas studies on samples of 18 chondrules and matrix from the Chainpur (LL3) meteorite to study variations in R0, the ratio of 129I to 129I at the time of xenon isotopic closure. R0 varies by more than a factor of 10 among the chondrules, corresponding to a span of more than 50 Ma in apparent I-Xe ages, including the latest apparent I-Xe ages ever observed for a chondritic sample. Variations are not closely related to any pétrographie properties, although low values of R0 (late apparent ages) may be associated with high sulfide abundances and/or non-porphyritic textures. Similarly, R0 is not closely related to any chemical components, but does seem to correlate with abundance of refractory lithophile elements. Also, R0is correlated with 244Pu 238U and anticorrelated with trapped 129Xe 132Xe, as might be expected if the variations in iodine isotopic composition are dominated by decay of 129I. We have not found a completely satisfying explanation of the variations in R0. Models involving gas-dust mixing or nebular heterogeneity cannot satisfactorily explain the Chainpur data. However, there are also difficulties with explanations attributing the variations to differences in formation age, metamorphic age, or time of aqueous alteration. We believe the most plausible explanation is that the variations represent times of low-grade shock events. © 1991.
• Swindle, T., Grossman, J., Olinger, C., & Garrison, D. (1991). Iodine-xenon, chemical, and petrographie studies of Semarkona chondrules: Evidence for the timing of aqueous alteration. Geochimica et Cosmochimica Acta, 55(12), 3723-3734.
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  Abstract: We have performed INAA, petrographie, and noble gas analyses on seventeen chondrules from the Semarkona meteorite (LL3.0) primarily to study the relationship of the I-Xe system to other measured properties. We observe a range of ≥10 Ma in apparent I-Xe ages. The three latest apparent ages fall in a cluster, suggesting the possibility of a common event. The initial 129I/127I ratio (R0) is apparently related to chondrule type and/or mineralogy, with nonporphyritic and pyroxene-rich chondrules showing evidence for lower R0'S (later apparent I-Xe ages) than porphyritic and olivine-rich chondrules. In addition, chondrules with sulfides on or near the surface have lower R0S than other chondrules. The 129Xe/132Xe ratio in the trapped Xe component anticorrelates with R0, consistent with evolution of a chronometer in a closed system or in multiple similar systems. On the basis of these correlations, we conclude that the variations in R0 represent variations in ages, and that later event(s), possibly aqueous alteration, preferentially affected chondrules with nonporphyritic textures and/or sulfide-rich exteriors about 10 Ma after the formation of the chondrules. © 1991.
• Swindle, T. D., Garrison, D. H., Goswami, J. N., Hohenberg, C. M., Nichols, R. H., & Olinger, C. T. (1990). Noble gases in the howardites Bholghati and Kapoeta. Geochimica et Cosmochimica Acta, 54(8), 2183-2194.
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  Abstract: Analyses of noble gases in whole rock samples of the howardites Bholghati and Kapoeta and grain-size separates of Kapoeta yield evidence for excesses of the Xe isotopes 129Xe, 131Xe, 132Xe, 134Xe, and 136Xe in a low-temperature component, similar to lunar excess fission Xe. Such a component may be able to provide Chronometric information if the relative abundances of radioactive progenitors (129I, 244Pu, and 238U) can be determined, but the isotopic spectra we obtain are not sufficiently precise to do so. Eucritic clast BH-5 in Bholghati contains Xe produced in situ by the decay of 244Pu. Calculated fission Xe retention ages are 30-70 Ma after the formation of the solar system, consistent with the apparent presence of 146Sm decay products. Both the clast and the matrix of Bholghati have K-Ar ages of about 2 Ga, suggesting a common thermal event at least that recently. © 1990.
• McKay, D. S., Swindle, T. D., & Greenberg, R. (1989). Asteroidal regoliths: what we do not know. Asteroids II, 617-642.
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  Abstract: Most of our knowledge of asteroidal regoliths is indirect. It comes primarily from extensive studies of the lunar regolith and meteorite regolith breccias, and from theroretical models which try to match some characteristics of these two types of samples. There is evidence that at least some were assembled in their present form more than 4Gyr ago. Also, since regoliths can change with time because of changes in the flux and velocity of impactors, the properties of meteorite breccias may not reflect those of modern asteroidal regoliths. In addition, some meteorite breccias may come from either accretional regoliths or the megaregoliths predicted to result from catastrophic disruption of an asteroid followed by re-accretion. -from Authors
• Bernatowicz, T., Podosek, F., Swindle, T., & Honda, M. (1988). I-Xe systematics in LL chondrites. Geochimica et Cosmochimica Acta, 52(5), 1113-1121.
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  Abstract: We report Ar and Xe data from stepwise heating analysis of five neutron-irradiated whole rock LL chondrites (Soko Banja, Alta Ameen, Tuxtuac, Guidder and Olivenza). None of these meteorites yields a well-defined 40Ar-39Ar apparent age plateau comprised of more than two release fractions, although in some cases intermediate-temperature apparent ages may provide significant lower limits to the age of initial Ar retention. Possibly excepting Guidder, these samples yield well-defined high-temperature correlations between 129Xe 130Xe and 128Xe 130Xe, and thus determinations of 129I 127I and 129Xe 130Xe at the time of isotopic closure for Xe. Nominal 129I-129Xe formation ages range from 2.7 Ma before to 8.2 Ma after Bjurbole. Considered in isolation, the present I-Xe results can be viewed in a coherent chronological framework, although possible isotopic heterogeneity of I cannot be excluded. I-Xe systematics do not correlate with metamorphic grade for the LL chondrites, however, nor with chronologies based on other methods (40Ar-39Ar, initial 87Sr 86Sr, metallographic or fission track retention cooling rates). The LL chondrites are, in this respect, like the other ordinary chondrites (H and L groups). Barring serious unrecognized flaws in essentially all the relevant Chronometrie methodologies, the primary conclusion is that the thermal history of the ordinary chondrites, including the LL chondrites, is very complicated. © 1988.
• Podosek, F. A., & Swindle, T. D. (1988). Extinct radionuclides. Meteorites and the early solar system, 1093-1113.
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  Abstract: "Extinct radionuclides' are radioactive isotopes with lifetimes of the order of 106 to 108 yr, long enough to survive the interval between nucleosynthesis and the formation of solids in the solar system but short enough so that they are essentially fully decayed and now extinct in the solar system. There is good evidence for the presence of several such radionuclides in the early solar system: 26Al, 53Mn, 107Pd, 129I, 244Pu, 146Sm. Together with longer-lived radionuclides the abundances of these short-lived species provide significant constraints on nucleosynthetic time scales and the history of solar system materials before they became the solar system. -from Authors
• Podosek, F. A., & Swindle, T. D. (1988). Nucleocosmochronology. Meteorites and the early solar system, 1114-1126.
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  Abstract: The relative abundances of radioactive nuclides can be used to determine the time scale for nucleosynthesis of those nuclides and, by extension, of many other nuclides in the solar system. Such time scales can also yield estimates for the age of the universe, and information about the time scale for protosolar collapse. -Authors
• Swindle, T. D. (1988). Trapped noble gases in meteorites. Meteorites and the early solar system, 535-564.
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  Abstract: The most volatile elements in meteorites are the noble (or inert) gases. Although they are far less abundant than condensible elements, they are present in measurable quantities in virtually all meteorites. The trapped noble gases in meteorites come in two main varieties, usually referred to as "solar' and "planetary'. The solar noble gases are implanted solar-wind or solar-flare materials, and thus their relative elemental abundances provide a good estimate of those of the Sun. The planetary noble gases have relative elemental abundances similar to those in the terrestrial atmosphere, but there are also important distinctions: At least one other elemental pattern ("subsolar') and several isotopic patterns have also been identified. Understanding the relationship among all these components continues to be a challenging problem. -Author
• Swindle, T. D., & Podosek, F. A. (1988). Iodine-xenon dating. Meteorites and the early solar system, 1127-1146.
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  Abstract: The most readily and widely studied of the extinct radionuclides in meteorites is 129I, and there is an extensive data base for meteorite chronology based on this isotope, but also significant uncertainty about how to interpret many of the data. If the data are interpreted as a straightforward chronology, a time span is inferred for most meteorite classes that appears too long for the events being dated to have taken place in the nebula. -Authors
• Swindle, T., Caffee, M., & Hohenberg, C. (1988). Iodine-xenon studies of Allende inclusions: Eggs and the Pink Angel. Geochimica et Cosmochimica Acta, 52(9), 2215-2227.
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  Abstract: The iodine-xenon systems of six Allende inclusions (five Eggs and the Pink Angel) appear to have been altered by non-nebular secondary processes. Evidence for this includes temperature-ordered variations in the initial I isotopic composition within several objects (with older apparent I-Xe ages associated with higher extraction temperatures) and the absence of primitive I-Xe ages. The span of apparent ages seen in Allende objects (10 Ma or more) is probably too long to reflect any nebular process, so at least some alteration probably occurred on the parent body. The range in initial 244Pu 238U ratios for the Eggs (3-14 × 10-3) includes the current best estimates of the bulk solar system value (4-7 × 10-3). For Egg 3, the Pu U ratio varies by a factor of two between extractions, probably the result of fractionation of Pu from U among different phases. © 1988.
• Cohen, B., Swindle, T., & Kring, D. (1986). Support for the lunar cataclysm hypothesis from lunar meteorite impact melt ages. SCIENCE, 290(5497), 1754-1756.
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  Lunar meteorites represent a more random sampling of Lunar material than the Apollo or Luna collections and, as such, Lunar meteorite impact melt ages are the most important data in nearly 30 years with which to reexamine the Lunar cataclysm hypothesis. Within the lunar meteorite breccias MAC 88105, QUE 93069, DaG 262, and DaG 400, seven to nine different impact events are represented with Ar-40-Ar-39 ages between 2.76 and 3.92 billion years ago (Ca). The Lack of impact melt older than 3.92 Ca supports the concept of a short, intense period of bombardment in the Earth-moon system at similar to3.9 Ca. This was an anomalous spike of impact activity on the otherwise declining impact-frequency curve.
• Caffee, M. W., Goswami, J. N., Hohenberg, C. M., & Swindle, T. D. (1983). COSMOGENIC NEON FROM PROCOMPACTION IRRADIATION OF KAPOETA AND MURCHISON.. Journal of Geophysical Research, 88 Suppl, 267-273.
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  Abstract: Neon from hand-picked Murchison and Kapoeta grains, selected on the basis of the presence or absence of solar flare particle tracks, was analyzed in order to delineate the precompaction history of this material. The irradiated grains showed large enrichments of cosmogenic neon relative to the unirradiated grains. Galactic cosmic ray (GCR) exposure ages for the unirradiated grains yield the nominal values reported for the recent exposure history of these meteorites.
• Swindle, T. D., Caffee, M. W., Hohenberg, C. M., & Lindstrom, M. M. (1983). I-Xe studies of individual Allende chondrules. Geochimica et Cosmochimica Acta, 47(12), 2157-2177.
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  Abstract: Iodine-xenon studies have been performed on nine Allende chondrules and a sample of oxidized Allende matrix material. The chondrules are all very rich in radiogenic xenon relative to trapped xenon, making it possible to determine a relatively precise model initial iodine composition for each temperature extraction. These model compositions show a total range in variation of about 20 percent, spanning the compositions seen in Bjurbole chondrules. One of the chondrules (chondrule 6) gives a well-defined isochron, with an apparent age .53 ±. 15 m.y. later than Bjurbole whole rock. The rest of the chondrules show a pattern of increasing apparent antiquity with increasing extraction temperature, which could be interpreted as relatively slow cooling (100-200°C/m.y.). Alternatively, poorly-defined plateaus in composition can be seen, perhaps indicative of a few phases with distinct initial iodine compositions (but also temperature-ordered), as has been previously suggested for Allende inclusions. Possible consequences of these interpretations are discussed. Elemental abundances were determined for some elements several months after the irradiation by INAA, and suggest that all the chondrules except chondrule 6 might be pyroxene- or mesostasis-rich. The oxidized matrix sample gives a well-defined isochron with an initial 129I 127I ratio higher than any plateaus seen in the chondrules, suggesting that, if this sample is representative of matrix, the matrix pre-dates the chondrules. The initial 244Pu 238U ratios of the Allende chondrules and 10 Bjurbole chondrules irradiated earlier appear to be consistent with. 004-.007 values quoted for unfractionated material in the early solar nebula. © 1983.
• Caffee, M. W., Hohenberg, C. M., Horz, F., Hudson, B., Kennedy, B. M., Podosek, F. A., & Swindle, T. D. (1982). Shock disturbance of the I-Xe system.. Journal of Geophysical Research, 87(Supplement), A318-A330.
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  Abstract: Samples of the Bjurbole chondrite were artifically shocked at 70, 200 and 400 kbar. Analyses of Xe released in stepwise heating show progressively greater alteration of the I-Xe system with increasing shock intensity; it was no longer possible to infer an age or trapped Xe composition for the 400 kbar sample. Interpretations of the I-Xe and 40Ar/39Ar systems for the naturally shocked chondrites Kota-Kota, McKinney and Arapahoe are presented. The data for Arapahoe do not confirm the reported age and trapped Xe composition. -B.M.
• Caffee, M. W., Hohenberg, C. M., Swindle, T. D., & Hudson, B. (1982). I-Xe ages of individual Bjurbole chondrules.. Journal of Geophysical Research, 87(Supplement), A303-A317.
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  Abstract: Initial iodine isotopic compositions for 10 individual chondrules show a total range of 6.5%, corresponding with an age difference of 1.6 m.y. Possible interpretations are distinct formation ages, metamorphic ages, or isotopic inhomogeneities in the early solar system, and constrain models for chondrule formation. Two chondrules show evidence of either isotopic inhomogeneities or disturbances of their I-Xe systems. -B.M.

Proceedings Publications

• Beard, S., Swindle, T., Kring, D., & Lapen, T. (2020, mar). Chelyabinsk's Impact Chronology: New Interpretations. In Lunar and Planetary Science Conference.
• Cohen, B., Curran, N., Fassett, C., Jolliff, B., Kendall, J., Moriarty, D., Petro, N., Swindle, T., Valencia, S., Yingst, R., Young, K., & Zellner, N. (2020, may). Dating Key Lunar Events with Artemis. In Lunar Surface Science Workshop, 2241.
• Nesnas, I., Swindle, T., & Castillo-Rogez, J. (2020, mar). Design Reference Mission (DRM) Scenarios for Small Bodies Enabled by Advances in Autonomy. In Lunar and Planetary Science Conference.
• Beard, S., Swindle, T., Kring, D., & Lapen, T. (2019, Jul). Impact Chronology of Chelyabinsk. In 82nd Annual Meeting of The Meteoritical Society, 82.
• Nolau, J., Swindle, T., Campins, H., & Connolly, H. (2019, Jul). How Unique is Almahata Sitta and How Relevant is it to Bennu?. In 82nd Annual Meeting of The Meteoritical Society, 82.
• Beard, S., Weimer, D., Busemann, H., Maden, C., & Swindle, T. (2018, mar). Cosmic-Ray Exposure Ages of Brachinites and Brachinite-Like Achondrites. In Lunar and Planetary Science Conference, 49.
• Bridges, J., Hicks, L., Miller, M., Schwenzer, S., Ott, U., Filiberto, J., Chavez, C., Smith, H., Treiman, A., Kelley, S., Moore, J., Swindle, T., Bullock, M., McIntosh, R., & Craig, P. (2018, mar). Amazonian Hydrothermal Alteration: Comparing Nakhlite Secondary Mineralogy to Water-Rock Reaction Experiments. In Lunar and Planetary Science Conference, 49.
• Cohen, B., Petro, N., Lawrence, S., Clegg, S., Denevi, B., Dyar, M., Elardo, S., Grinspoon, D., Hiesinger, H., Liu, Y., McCanta, M., Moriarty, D., Norman, M., Runyon, K., Schwenzer, S., Swindle, T., Bogert, C., & Wiens, R. (2018, mar). Curie: Constraining Solar System Bombardment Using In Situ Radiometric Dating. In Lunar and Planetary Science Conference, 49.
• Miller, M., Schwenzer, S., Bridges, J., Hicks, L., Ott, U., Filiberto, J., Chavez, C., Smith, H., Treiman, A., Kelley, S., Moore, J., Swindle, T., Bullock, M., & McIntosh, R. (2018, mar). Mineral Surface and Fluid Chemistry in Nakhlite Analog Water-Rock Reactions. In Lunar and Planetary Science Conference, 49.
• Schwenzer, S., Ott, U., Hicks, L., Bridges, J., Filiberto, J., Bart, G., Swindle, T., Miller, M., Treiman, A., Crowther, S., Gilmour, J., Herrmann, S., Mohapatra, R., Seidel, R., Kelley, S., Bullock, M., Chavez, C., Smith, H., & Moore, J. (2018, mar). Fractionated Martian Atmosphere \mdash The Case of the Nakhlites, Revisited with Experiments. In Lunar and Planetary Science Conference, 49.
• Team, i., Beaty, D., Grady, M., McSween, H., Sefton-Nash, E. .., Carrier, B., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Benning, L., Bishop, J., Borg, L., Boucher, D., Brucato, J., Busemann, H., Campbell, K., Czaja, A., Debaille, V., , Des, M. D., et al. (2018, apr). Introduction to the 2018 iMOST Study. In Second International Mars Sample Return, 2071.
• Team, i., Bishop, J., Horgan, B., Benning, L., Carrier, B., Hausrath, E., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Beaty, D., Borg, L., Boucher, D., Brucato, J., Busemann, H., Campbell, K., Czaja, A., Debaille, V., Des, M. D., , Dixon, M., et al. (2018, apr). Potential High Priority Subaerial Environments for Mars Sample Return. In Second International Mars Sample Return, 2071.
• Team, i., Campbell, K., Farmer, J., Van, K. M., Fernandez-Remolar, D., Czaja, A., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Beaty, D., Benning, L., Bishop, J., Borg, L., Boucher, D., Brucato, J., Busemann, H., Carrier, B., Debaille, V., , Des, M. D., et al. (2018, apr). Seeking Signs of Life on Mars: A Strategy for Selecting and Analyzing Returned Samples from Hydrothermal Deposits. In Second International Mars Sample Return, 2071.
• Team, i., Des, M. D., Grady, M., Shaheen, R., Steele, A., Westall, F., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Beaty, D., Benning, L., Bishop, J., Borg, L., Boucher, D., Brucato, J., Busemann, H., Campbell, K., Carrier, B., , Czaja, A., et al. (2018, apr). Seeking the Signs of Life: Assessing the Presence of Biosignatures in the Returned Sample Suite. In Second International Mars Sample Return, 2071.
• Team, i., Ehlmann, B., Mayhew, L., Mustard, J., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Beaty, D., Benning, L., Bishop, J., Borg, L., Boucher, D., Brucato, J., Busemann, H., Campbell, K., Carrier, B., Czaja, A., Debaille, V., , Des, M. D., et al. (2018, apr). High Priority Samples to Characterize the Habitability of Groundwaters and Search for Rock-Hosted Life on Mars. In Second International Mars Sample Return, 2071.
• Team, i., Harrington, A., Carrier, B., Fernandez-Remolar, D., Fogarty, J., McCoy, J., Rucker, M., Spry, J., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Beaty, D., Benning, L., Bishop, J., Borg, L., Boucher, D., Brucato, J., Busemann, H., , Campbell, K., et al. (2018, apr). The Importance of Returned Martian Samples for Constraining Potential Hazards to Future Human Exploration. In Second International Mars Sample Return, 2071.
• Team, i., Herd, C., Ammannito, E., Anand, M., Debaille, V., Hallis, L., McCubbin, F., Schmitz, N., Usui, T., Weiss, B., Altieri, F., Amelin, Y., Beaty, D., Benning, L., Bishop, J., Borg, L., Boucher, D., Brucato, J., Busemann, H., , Campbell, K., et al. (2018, apr). The Importance of Mars Samples in Constraining the Geological and Geophysical Processes on Mars and the Nature of its Crust, Mantle, and Core. In Second International Mars Sample Return, 2071.
• Team, i., Humayun, M., Kleine, T., Amelin, Y., Borg, L., Herd, C., Moser, D., Moynier, F., Shuster, D., Wadhwa, M., Werner, S., Zipfel, J., Altieri, F., Ammannito, E., Anand, M., Beaty, D., Benning, L., Bishop, J., Boucher, D., , Brucato, J., et al. (2018, apr). What Could be Learned About the Geochronology of Mars from Samples Collected by M-2020. In Second International Mars Sample Return, 2071.
• Team, i., Kate, I., Mackelprang, R., Rettberg, P., Smith, C., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Beaty, D., Benning, L., Bishop, J., Borg, L., Boucher, D., Brucato, J., Busemann, H., Campbell, K., Carrier, B., Czaja, A., , Debaille, V., et al. (2018, apr). The Use of Returned Martian Samples to Evaluate the Possibility of Extant Life on Mars. In Second International Mars Sample Return, 2071.
• Team, i., Kleinhenz, J., Beaty, D., Boucher, D., Dixon, M., Niles, P., Wheeler, R., Zorzano, M., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Benning, L., Bishop, J., Borg, L., Brucato, J., Busemann, H., Campbell, K., Carrier, B., , Czaja, A., et al. (2018, apr). The Relevance of Mars Samples to Planning for Potential Future In-Situ Resource Utilization. In Second International Mars Sample Return, 2071.
• Team, i., Mangold, N., McLennan, S., Czaja, A., Ori, G., Tosca, N., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Beaty, D., Benning, L., Bishop, J., Borg, L., Boucher, D., Brucato, J., Busemann, H., Campbell, K., Carrier, B., , Debaille, V., et al. (2018, apr). Seeking Signs of Life on Mars: The Importance of Sedimentary Suites as Part of Mars Sample Return. In Second International Mars Sample Return, 2071.
• Team, i., Sephton, M., Siljestrom, S., Glavin, D., Brucato, J., Raulin, F., Altieri, F., Amelin, Y., Ammannito, E., Anand, M., Beaty, D., Benning, L., Bishop, J., Borg, L., Boucher, D., Busemann, H., Campbell, K., Carrier, B., Czaja, A., , Debaille, V., et al. (2018, apr). The Search for Life's Organic Carbon in Returned Samples from Mars. In Second International Mars Sample Return, 2071.
• Team, i., Swindle, T., Altieri, F., Busemann, H., Niles, P., Shaheen, R., Zorzano, M., Amelin, Y., Ammannito, E., Anand, M., Beaty, D., Benning, L., Bishop, J., Borg, L., Boucher, D., Brucato, J., Campbell, K., Carrier, B., Czaja, A., , Debaille, V., et al. (2018, apr). Constraining Our Understanding of the Actions and Effects of Martian Volatiles Through the Study of Returned Samples. In Second International Mars Sample Return, 2071.
• Zellner, N., Nguyen, P., Swindle, T., Beard, S., & Isachsen, C. (2018, mar). Apollo 17 Lunar Impact Glasses: Ages Evaluated via Statistical and Compositional Studies. In Lunar and Planetary Science Conference, 49.
• Asphaug, E., Baker, J., Choukroun, M., Furfaro, R., Sava, P., Scheeres, D., Schwartz, S., Swindle, T., & Thangavelautham, J. (2017, mar). Spacecraft Penetrator for Increasing Knowledge of NEOs (SPIKE). In Lunar and Planetary Science Conference, 48.
• Cohen, B., Arevalo, R., Bottke, W., Conrad, P., Farley, K., Fasset, C., Jolliff, B., Lawrence, S., Mahaffy, P., Malespin, C., Swindle, T., & Wadhwa, M. (2017, feb). Geochronology as a Framework for Planetary History Through 2050. In Planetary Science Vision 2050 Workshop, 1989.
• Hope, D., Hart, M., Swindle, T., & Jefferies, S. (2017). Image Restoration from Limited Data. In Advanced Maui Optical and Space Surveillance (AMOS) Technologies Conference.
• Schwenzer, S., Bridges, J., Miller, M., Hicks, L., Ott, U., Filiberto, J., Chavez, C., Smith, H., Treiman, A., Kelley, S., Moore, J., Swindle, T., & Bullock, M. (2017, mar). Diagenesis on Mars: Insights Into Noble Gas Pathways and Newly Formed Mineral Assemblages from Long Term Experiments. In Lunar and Planetary Science Conference, 48.
• Seifert, L., Kring, A., & Swindle, T. (2017, mar). 40Ar-39Ar Dating of Lunar Impact Melts - Searching for Imbrium. In Lunar and Planetary Science Conference, 48.
• Swindle, T., & Weirich, J. (2017, mar). The Effect of Partial Thermal Resetting on 40Ar-39Ar ``Plateaus''. In Lunar and Planetary Science Conference, 48.
• Swindle, T., Chabot, N., Barbee, B., Bauer, J., Bierhaus, B., Britt, D., Castillo-Rogez, J. .., Chodas, P., Feaga, L., Hartzell, C., Mercer, C., & Stickle, A. (2017, feb). Small Bodies Exploration in the Next 35 Years. In Planetary Science Vision 2050 Workshop, 1989.
• Zellner, N., Nguyen, P., Vesa, O., Cook, R., Blachut, S., Delano, J., Swindle, T., Beard, S., & Isachsen, C. (2017, mar). Only Specific Lunar Impact Glasses Record Episodic Events on the Moon. In Lunar and Planetary Science Conference, 48.
• {Schmieder}, M., {Kring}, D., {Swindle}, T., {Carter-Bond}, J., , C. (2016, mar). The Gao-Guenie (Burkina Faso) Impact Melt Breccia {\mdash} A Piece of an Impact Melt Injection Dike on an H-Chondrite Asteroid. In Lunar and Planetary Science Conference, 47.
• {Schwenzer}, S., {Bullock}, M., {Bridges}, J., {Chavez}, C., {Filiberto}, J., {Hicks}, L., {Kelley}, S., {Miller}, M., {Moore}, J., {Smith}, H., {Swindle}, T., , A. (2016, mar). Noble Gas Fractionation in Hydrous Rock Alteration Under Diagenetic Pressure and Temperature Conditions. In Lunar and Planetary Science Conference, 47.
• {Bullock}, M., {Schwenzer}, S., {Bridges}, J., {Chavez}, C., {Filiberto}, J., {Kelley}, S., {Miller}, M., {Moore}, J., {Smith}, H., {Swindle}, T., , A. (2015, mar). Noble Gas Fractionation During Low Temperature Alteration {\mdash} An Experimental Approach. In Lunar and Planetary Science Conference, 46.
• Lapen, T., Kring, D., Zolensky, M., Andreasen, R., Righter, M., Swindle, T., & Beard, S. (2014, March). Uranium-Lead Isotope Evidence in the Chelyabinsk LL5 Chondrite Meteorite for Ancient and Recent Thermal Events. In 45th Lunar and Planetary Science Conference, 2561.
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  LPI Contribution No.: 1777
• {Beard}, S., {Kring}, D., {Isachsen}, C., {Lapen}, T., {Zolensky}, M., , T. (2014, mar). "{Ar-Ar Analysis of Chelyabinsk: Evidence for a Recent Impact}". In Lunar and Planetary Science Conference, 45.
• {Bottke}, W., {Swindle}, T., {Marchi}, S., {Scott}, E., {Vokrouhlicky}, D., , J. (2014, sep). "{Using Meteorites to Find the Age of the Moon-Forming Event}". In 77th Annual Meeting of the Meteoritical Society, 1800.
• {Bottke}, W., {Vokrouhlicky}, D., {Marchi}, S., {Swindle}, T., {Scott}, E., , J. (2014, mar). "{The Evolution of Giant Impact Ejecta and the Age of the Moon}". In Lunar and Planetary Science Conference, 45.
• {Cohen}, B., {Swindle}, T., , S. (2014, mar). "{In Situ Geochronology on the Mars 2020 Rover with KArLE (Potassium-Argon Laser Experiment)}". In Lunar and Planetary Science Conference, 45.
• {Lapen}, T., {Kring}, D., {Zolensky}, M., {Andreasen}, R., {Righter}, M., {Swindle}, T., , S. (2014, mar). "{Uranium-Lead Isotope Evidence in the Chelyabinsk LL5 Chondrite Meteorite for Ancient and Recent Thermal Events}". In Lunar and Planetary Science Conference, 45.
• Weirich JR, ., Wittmann, A., Isachsen, C., Rumble, D., Swindle, T., & Kring, D. (2013, August). Miller Range 05029: Evidence for a Large Impact on the L Chondrite Parent Body >4.5 Ga Large Meteorite Impacts and Planetary Evolution V. In Proceedings of the conference held 5-8 August 2013, in Sudbury, Canada, 3062.
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  LPI Contribution No. 1737

Presentations

• Bottke, W., Vokrouhlicky, D., Marchi, S., Jackson, A., Levison, H., & Swindle, T. (2015, feb). The Earliest Lunar Bombardment Produced by Moon-Forming Impact Ejecta. Early Solar System Impact Bombardment III.
• Swindle, T., & Kring, D. (2015, feb). Was There a Concentration of Lunar and Asteroidal Impacts at ~4000 Ma?. Early Solar System Impact Bombardment III.
• {Beard}, S., , T. (2015, jul). 21Ne Cosmic-Ray Exposure Ages of Ureilites. 78th Annual Meeting of the Meteoritical Society.
• {Beard}, S., {Swindle}, T., , K. (2015, mar). Searching for Potassium Host Phases in Preparation for Ar-Ar Analysis of Brachinite and Brachinite-Like Achondrites. Lunar and Planetary Science Conference.
• Swindle, T. D. (2014, February). Review of Ordinary Chondrite Collisional Ages. Center for Lunar Science and Exploration of the Solar System Virtual Institute (SSERVI) seminar. Houston.
• Swindle, T. D. (2014, March). Review of Existing Collisional Ages among Ordinary Chondrites. Colloquium. Houston: Center for Lunar Science and Exploration of the Solar System Exploration Virtual Institute.

Poster Presentations

• Beard, S., Kring, D., Solensky, M., & Swindle, T. (2014, 17-21 March). Ar-Ar Analysis of Chelyabinsk: Evidence for a Recent Impact. 45th Lunar and Planetary Science Conference. The Woodlands, Texas.
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  LPI Contribution No. 1777
• Bottke, W., Vokrouhlicky, D., Marchi, S., Swindle, T., Scorr, E., & Weirich JR, . (2014, 17-21 March). The Evolution of Giant Impact Ejecta and the Age of the Moon. 45th Lunar and Planetary Science Conference. The Woodlands, Texas.
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  LPI Contribution No. 1777
• Cohen, B., Swindle, T., & Roark, S. (2014, 17-21 March). In Situ Geochronology on the Mars 2020 Rover with KArLE (Potassium-Argon Laser Experiment). 45th Lunar and Planetary Science Conference. The Woodlands, Texas.
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  LPI Contribution No. 1777
• Kring, D., Swindle, T., & Zolensky, M. (2014, Fall). Meteoritic and Geologic Context of the Chelyabinsk Near-Earth Asteroid Air Burst. American Geophysical Union.
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  abstract #NH21D-01
• Lapen, T., Kring, D., Zolensky, M., Andreasen, R., Righter, M., Swindle, T., & Beard, S. (2014, 17-21 March). Uranium-Lead Isotope Evidence in the Chelyabinsk LL5 Chondrite Meteorite for Ancient and Recent Thermal Events. 45th Lunar and Planetary Science Conference. The Woodlands, Texas.
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  LPI Contribution No. 1777
• Beard, S., Swindle, T., Isachsen, C., Jenniskens, P., & Shaddad, M. (2013, March 18-22). Ar-Ar Analysis of Almahata Sitta Ordinary Chondrites. 44th Lunar and Planetary Science Conference. The Woodlands, Texas.
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  LPI Contribution No. 1719
• Cohen, B., Li, Z., Miller, J., Brinckerhoff, W., Clegg, S., Mahaffy, P., Swindle, T., & Wiens, R. (2013, March 18-22). UpDates on Development of the Potassium-Argon Laser Experiment (KArLE) Instrument for In Situ Geochronology. 44th Lunar and Planetary Science Conference. The Woodlands, Texas.
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  LPI Contribution No. 1719
• Fagan, A., Neal, C., Beard, S., & Swindle, T. (2013, March 18-22). Bulk Composition and ^40Ar-^39Ar Age Dating Suggests Impact Melt Sample 67095 may be Exotic to the Apollo 16 Site. 44th Lunar and Planetary Science Conference. The Woodlands, Texas.
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  LPI Contribution No. 1719
• Kring, D., Swindle, T., & Zolensky, M. (2013, July 29- August 7). Brecciated Chelyabinsk Near-Earth Asteroid and its Catastrophic Air Burst. 76th Annual Meeting of the Meteoritical Society. Edmonton, Canada.
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  id.5224
• Niihara, T., Beard, S., Swindle, T., & Kring, D. (2013, March 18-22). Evidence for Multiple Impact Events from Centimeter-Sized Impact Melt Clasts in Apollo 16 Ancient Regolith Breccias: Support for Late Stage Heavy Bombardment of the Moon. 44th Lunar and Planetary Science Conference. The Woodlands, Texas.
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  LPI Contribution No. 1719
• Cohen, B., Li, Z., Miller, J., Brinckerhoff, W., Clegg, S., Mahaffy, P., Swindle, T., & Wiens, R. (2012, October 10-12). Development of the Potassium-Argon Laser Experiment (KArLE) Instrument for In Situ Geochronology. International Workshop on Instrumentation for Planetary Missions. Greenbelt, Maryland.
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  LPI Contribution No. 1683
• Friedrich, J., Rubin, A., Swindle, T., Isachsen, C., & Beard, S. (2012, March 19-23). Impact Histories of Incompletely Compacted Ordinary Chondrites from Petrographic Examination and ^4^0Ar/^3^9Ar Analysis. 43rd Lunar and Planetary Science Conference. The Woodlands, Texas.
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  LPI Contribution No. 1659
• Glavin, D., Malespin, C., ten, K. I., Getty, S., Holmes, V., Mumm, E., Franz, H., Noreiga, M., Dobson, N., Southard, A., Feng, S., Kotecki, C., Dworkin, J., Swindle, T., Bleacher, J., Rice, J., & Mahaffy, P. (2012, October 10-12). Volatile Analysis by Pyrolysis of Regolith (VAPoR) for Planetary Resource Exploration. International Workshop on Instrumentation for Planetary Missions. Greenbelt, Maryland.
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  LPI Contribution No. 1683
• Gombosi, D., Baldwin, S., Watson, E., Swindle, T., Delano, J., & Roberge, W. (2012, March 19-23). Diffusion in Lunar Impact Glass. 43rd Lunar and Planetary Science Conference. The Woodlands, Texas.
• Swindle, T., Beard, S., Isachsen, C., & Kring, D. (2012, August 12-17). 40Argon-39Argon Ages of Centimeter-Sized Impact Melt Clasts from Ancient Regolith Breccia 60016. 75th Annual Meeting of the Meteoritical Society. Cairns, Australia.