Sukrit Ranjan

Interests

Research

Astrobiology, Earth, Early Earth, Exoplanets; Planetary Formation and Evolution, Origin of Life, Planetary Atmospheres, Photochemistry, Theoretical Astrophysics

Courses

Scholarly Contributions

Journals/Publications

• Abac, A., Abbott, R., Abouelfettouh, I., Acernese, F., Ackley, K., Adhicary, S., Adhikari, N., Adhikari, R., Adkins, V., Agarwal, D., Agathos, M., Aghaei Abchouyeh, M., Aguiar, O., Aguilar, I., Aiello, L., Ain, A., Ajith, P., Akutsu, T., Albanesi, S., , Alfaidi, R., et al. (2025). Search for Continuous Gravitational Waves from Known Pulsars in the First Part of the Fourth LIGO-Virgo-KAGRA Observing Run. \apj, 983(2), 99.
• Abac, A., Abbott, R., Abouelfettouh, I., Acernese, F., Ackley, K., Adhicary, S., Adhikari, N., Adhikari, R., Adkins, V., Agarwal, D., Agathos, M., Aghaei Abchouyeh, M., Aguiar, O., Aguilar, I., Aiello, L., Ain, A., Akutsu, T., Albanesi, S., Alfaidi, R., , Al-Jodah, A. .., et al. (2025). Search for Gravitational Waves Emitted from SN 2023ixf. \apj, 985(2), 183.
• Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., Aguiar, O., Ahrend, I., Aiello, L., , Ain, A., et al. (2025). All-sky search for short gravitational-wave bursts in the first part of the fourth LIGO-Virgo-KAGRA observing run. \prd, 112(10), 102005.
• Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., Aguiar, O., Ahrend, I., Aiello, L., , Ain, A., et al. (2025). GW231123: A Binary Black Hole Merger with Total Mass 190???265 M$_{\ensuremath{\odot}}$. \apjl, 993(1), L25.
• Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., Aguiar, O., Ahrend, I., Aiello, L., , Ain, A., et al. (2025). GW241011 and GW241110: Exploring Binary Formation and Fundamental Physics with Asymmetric, High-spin Black Hole Coalescences. \apjl, 993(1), L21.
• Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., Aguiar, O., Ahrend, I., Aiello, L., , Ain, A., et al. (2025). GW250114: Testing Hawking's Area Law and the Kerr Nature of Black Holes. \prl, 135(11), 111403.
• Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agarwal, D., Agathos, M., Aghaei Abchouyeh, M., Aguiar, O., Ahmadzadeh, S., Aiello, L., Ain, A., Ajith, P., Akcay, S., , Akutsu, T., et al. (2025). GWTC-4.0: An Introduction to Version 4.0 of the Gravitational-Wave Transient Catalog. \apjl, 995(1), L18.
• Arora, R., Ranjan, S., Moitra, P., & Mallik, A. (2025). Thin H$_2$-dominated Atmospheres as Signposts of Magmatic Outgassing on Tidally-Heated Terrestrial Exoplanets. arXiv e-prints, arXiv:2510.07378.
• Broussard, W., , ., Schwieterman, E. W., Sousa-Silva, C., Sanger-Johnson, G., Ranjan, S., & Venot, O. (2025). The Impact of Extended CO2 Cross Sections on Temperate Anoxic Planet Atmospheres. Astrophysical Journal, 980(Issue 2). doi:10.3847/1538-4357/adaaf0
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  Our interpretation of terrestrial exoplanet atmospheric spectra will always be limited by the accuracy of the data we use as input in our forward and retrieval models. Ultraviolet molecular absorption cross sections are one category of these essential model inputs; however, they are often poorly characterized at the longest wavelengths relevant to photodissociation. Photolysis reactions dominate the chemical kinetics of temperate terrestrial planet atmospheres. One molecule of particular importance is CO2, which is likely present in all terrestrial planet atmospheres. The photolysis of CO2 can introduce CO and O, as well as shield tropospheric water vapor from undergoing photolysis. This is important because H2O photolysis produces OH, which serves as a major reactive sink to many atmospheric trace gases. Here, we construct CO2 cross-section prescriptions at 195 K and 300 K extrapolated beyond 200 nm from measured cross sections. We compare results from the implementation of these new cross sections to the most commonly used CO2 prescriptions for temperate terrestrial planets with Archean-like atmospheres. We generally find that the observational consequences of CO2 dissociation beyond 200 nm are minimal so long as our least conservative (highest opacity) prescription can be ruled out. Moreover, implementing our recommended extended CO2 cross sections does not substantially alter previous results that show the consequential photochemical impact of extended H2O cross sections.
• Broussard, W., Schwieterman, E. W., Sousa-Silva, C., Sanger-Johnson, G., Ranjan, S., & Venot, O. (2025). The Impact of Extended CO$_2$ Cross Sections on Temperate Anoxic Planet Atmospheres. \apj, 980(2), 198.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). All-sky search for continuous gravitational-wave signals from unknown neutron stars in binary systems in the first part of the fourth LIGO-Virgo-KAGRA observing run. arXiv e-prints, arXiv:2511.16863.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). All-sky search for long-duration gravitational-wave transients in the first part of the fourth LIGO-Virgo-KAGRA Observing run. arXiv e-prints, arXiv:2507.12282.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). Constraints on gravitational waves from the 2024 Vela pulsar glitch. arXiv e-prints, arXiv:2512.17990.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). Cosmological and High Energy Physics implications from gravitational-wave background searches in LIGO-Virgo-KAGRA's O1-O4a runs. arXiv e-prints, arXiv:2510.26848.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). Direct multi-model dark-matter search with gravitational-wave interferometers using data from the first part of the fourth LIGO-Virgo-KAGRA observing run. arXiv e-prints, arXiv:2510.27022.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). Directed searches for gravitational waves from ultralight vector boson clouds around merger remnant and galactic black holes during the first part of the fourth LIGO-Virgo-KAGRA observing run. arXiv e-prints, arXiv:2509.07352.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). Directional Search for Persistent Gravitational Waves: Results from the First Part of LIGO-Virgo-KAGRA's Fourth Observing Run. arXiv e-prints, arXiv:2510.17487.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). GWTC-4.0: Constraints on the Cosmic Expansion Rate and Modified Gravitational-wave Propagation. arXiv e-prints, arXiv:2509.04348.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). GWTC-4.0: Updating the Gravitational-Wave Transient Catalog with Observations from the First Part of the Fourth LIGO-Virgo-KAGRA Observing Run. arXiv e-prints, arXiv:2508.18082.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). Open Data from LIGO, Virgo, and KAGRA through the First Part of the Fourth Observing Run. arXiv e-prints, arXiv:2508.18079.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). Search for planetary-mass ultra-compact binaries using data from the first part of the LIGO--Virgo--KAGRA fourth observing run. arXiv e-prints, arXiv:2511.19911.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agapito, A., Agarwal, D., Agathos, M., Aggarwal, N., Aggarwal, S., , Aguiar, O., et al. (2025). Upper Limits on the Isotropic Gravitational-Wave Background from the first part of LIGO, Virgo, and KAGRA's fourth Observing Run. arXiv e-prints, arXiv:2508.20721.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adamcewicz, C., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agarwal, D., Agathos, M., Aghaei Abchouyeh, M., Aguiar, O., Ahmadzadeh, S., , Aiello, L., et al. (2025). GWTC-4.0: Population Properties of Merging Compact Binaries. arXiv e-prints, arXiv:2508.18083.
• Collaboration, T., Collaboration, ., Collaboration, ., Abac, A., Abouelfettouh, I., Acernese, F., Ackley, K., Adhicary, S., Adhikari, D., Adhikari, N., Adhikari, R., Adkins, V., Afroz, S., Agarwal, D., Agathos, M., Aghaei Abchouyeh, M., Aguiar, O., Ahmadzadeh, S., Aiello, L., , Ain, A., et al. (2025). GWTC-4.0: Methods for Identifying and Characterizing Gravitational-wave Transients. arXiv e-prints, arXiv:2508.18081.
• Espinoza, N., , ., Allen, N. H., Glidden, A., Lewis, N. K., Seager, S., Cañas, C. I., Grant, D., Gressier, A., Courreges, S., Stevenson, K. B., Ranjan, S., Colón, K., Morris, B. M., MacDonald, R. J., Long, D., Wakeford, H. R., Valenti, J. A., Alderson, L., , Batalha, N. E., et al. (2025). JWST-TST DREAMS: NIRSpec/PRISM Transmission Spectroscopy of the Habitable Zone Planet TRAPPIST-1 e. Astrophysical Journal Letters, 990(Issue 2). doi:10.3847/2041-8213/adf42e
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  TRAPPIST-1 e is one of the very few rocky exoplanets that is both amenable to atmospheric characterization and resides in the habitable zone of its star—located at a distance from its star such that it might, with the right atmosphere, sustain liquid water on its surface. Here, we present a set of four JWST/NIRSpec PRISM transmission spectra of TRAPPIST-1 e obtained in mid-to-late 2023. Our transmission spectra exhibit similar levels of stellar contamination as observed in prior works for other planets in the TRAPPIST-1 system but over a wider wavelength range, showcasing the challenge of characterizing the TRAPPIST-1 planets even at relatively long wavelengths (3-5 μm). While we show that current stellar modeling frameworks are unable to explain the stellar contamination features in our spectra, we demonstrate that we can marginalize over those features instead using Gaussian processes, which enables us to perform novel exoplanet atmospheric inferences with our transmission spectra. In particular, we are able to rule out cloudy, primary H2-dominated (≳80% by volume) atmospheres at better than a 3σ level. Constraints on possible secondary atmospheres on TRAPPIST-1 e are presented in a companion paper. Our work showcases how JWST is breaking ground in the precision needed to constrain the atmospheric composition of habitable-zone rocky exoplanets.
• Glidden, A., Ranjan, S., Seager, S., Espinoza, N., MacDonald, R. J., Allen, N. H., Ca{\~nas}, C. I., Grant, D., Gressier, A., Stevenson, K. B., Batalha, N. E., Lewis, N. K., Long, D., Wakeford, H. R., Alderson, L., Challener, R. C., Col{\'on}, K., Huang, J., Lin, Z., , Louie, D. R., et al. (2025). JWST-TST DREAMS: Secondary Atmosphere Constraints for the Habitable Zone Planet TRAPPIST-1 e. \apjl, 990(2), L53.
• Krissansen-Totton, J., Ulses, A. G., Frissell, M., Gilbert-Janizek, S., Young, A., Lustig-Yaeger, J., Robinson, T., Olson, S., Alei, E., Arney, G., Hagee, C., Harman, C., Hinkel, N., Lafleche, E., Latouf, N., Mandell, A., Moussa, M. M., Parenteau, N., Ranjan, S., , Russell, B., et al. (2025). Wavelength Requirements for Life Detection via Reflected Light Spectroscopy of Rocky Exoplanets. arXiv e-prints, arXiv:2507.14771.
• Raman, G., Ronchini, S., Delaunay, J., Tohuvavohu, A., Kennea, J. A., Parsotan, T., Ambrosi, E., Grazia, B. M., Campana, S., Cusumano, G., D'A{\`\i}, A., D'Avanzo, P., D'Elia, V., De, P. M., Dichiara, S., Evans, P., Hartmann, D., Kuin, P., Melandri, A., , O'Brien, P., et al. (2025). Swift-BAT GUANO Follow-up of Gravitational-wave Triggers in the Third LIGO\textendashVirgo\textendashKAGRA Observing Run. \apj, 980(2), 207.
• Ranjan, S., Adams, D., Wong, M., Schlecker, M., Wogan, N., & Weber, J. M. (2025). Prebiosignatures with the Habitable Worlds Observatory (HWO). arXiv e-prints, arXiv:2507.00165.
• Ranjan, S., Kumar, V., Kanti, S., Sahoo, B., & Deb, S. (2025). Thermo-Mechanical Investigation on Hot Deformation Behavior of Cast Magnesium-Aluminum Alloy: Experimental and Constitutive Analysis. Journal of Materials Engineering and Performance.
• Ranjan, S., Schlecker, M., Wogan, N., & Wong, M. (2025). Testing Origin-of-Life Theories with the Habitable Worlds Observatory (HWO). arXiv e-prints, arXiv:2507.00164.
• Ranjan, S., Wogan, N. F., Glidden, A., Wang, J., Stevenson, K. B., Lewis, N., Koskinen, T., Seager, S., Wakeford, H. R., & Marel, R. P. (2025). The Photochemical Plausibility of Warm Exo-Titans Orbiting M Dwarf Stars. \apjl, 993(2), L39.
• Schlecker, M., Apai, D., Affholder, A., Ranjan, S., Ferrière, R., Hardegree-Ullman, K. K., Lichtenberg, T., & Mazevet, S. (2025). Bioverse: Potentially Observable Exoplanet Biosignature Patterns under the UV Threshold Hypothesis for the Origin of Life. Astrophysical Journal, 987(Issue 1). doi:10.3847/1538-4357/adc8a9
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  A wide variety of scenarios for the origin of life have been proposed, with many influencing the prevalence and distribution of biosignatures across exoplanet populations. This relationship suggests these scenarios can be tested by predicting biosignature distributions and comparing them with empirical data. Here, we demonstrate this approach by focusing on the cyanosulfidic origins-of-life scenario and investigating the hypothesis that a minimum near-ultraviolet (NUV) flux is necessary for abiogenesis. Using Bayesian modeling and the Bioverse survey simulator, we constrain the probability of obtaining strong evidence for or against this “UV Threshold Hypothesis” with future biosignature surveys. Our results indicate that a correlation between past NUV flux and current biosignature occurrence is testable for sample sizes of ≳50 planets. The diagnostic power of such tests is critically sensitive to the intrinsic abiogenesis rate and host star properties, particularly maximum past NUV fluxes. Surveys targeting a wide range of fluxes, and planets orbiting M dwarfs enhance the chances of conclusive results, with sample sizes ≳100 providing ≳80% likelihood of strong evidence if abiogenesis rates are high and the required NUV fluxes are moderate. For required fluxes exceeding a few hundred erg s−1 cm−2, both the fraction of inhabited planets and the diagnostic power sharply decrease. Our findings demonstrate the potential of exoplanet surveys to test origins-of-life hypotheses. Beyond specific scenarios, this work underscores the broader value of realistic survey simulations for future observatories (e.g., Habitable Worlds Observatory, LIFE, Extremely Large Telescopes, Nautilus) in identifying testable science questions, optimizing mission strategies, and advancing theoretical and experimental studies of abiogenesis.
• Singh, D., Biennier, L., Simon, A., Chakraborty, S., Dartois, E., Georges, R., Kassi, S., Chandrasekaran, V., Sabbah, H., Joblin, C., Ranjan, S., Suwas, S., Gopalan, J., & Arunan, E. (2025). Shock-induced evolution: Tracing the fate of coronene in astrophysical environments. \aap, 704, A345.
• Broussard, W., Schwieterman, E. W., Ranjan, S., Sousa-Silva, C., Fateev, A., & Reinhard, C. T. (2024). The Impact of Extended H$_2$O Cross Sections on Temperate Anoxic Planet Atmospheres: Implications for Spectral Characterization of Habitable Worlds. \apj, 967(2), 114.
• Broussard, W., Schwieterman, E., Ranjan, S., Sousa-Silva, C., Fateev, A., & Reinhard, C. (2024). The Impact of Extended H2O Cross Sections on Temperate Anoxic Planet Atmospheres: Implications for Spectral Characterization of Habitable Worlds. Astrophysical Journal, 967(2). doi:10.3847/1538-4357/ad3a65
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  JWST has created a new era of terrestrial exoplanet atmospheric characterization, and with it, the possibility to detect potential biosignature gases like CH4. Our interpretation of exoplanet atmospheric spectra, and the veracity of these interpretations, will be limited by our understanding of atmospheric processes and the accuracy of input modeling data. Molecular cross sections are essential inputs to these models. The photochemistry of temperate planets depends on photolysis reactions whose rates are governed by the dissociation cross sections of key molecules. H2O is one such molecule; the photolysis of H2O produces OH, a highly reactive and efficient sink for atmospheric trace gases. We investigate the photochemical effects of improved H2O cross sections on anoxic terrestrial planets as a function of host star spectral type and CH4 surface flux. Our results show that updated H2O cross sections, extended to wavelengths >200 nm, substantially impact the predicted abundances of trace gases destroyed by OH. The differences for anoxic terrestrial planets orbiting Sun-like host stars are greatest, showing changes of up to 3 orders of magnitude in surface CO levels, and over an order of magnitude in surface CH4 levels. These differences lead to observable changes in simulated planetary spectra, especially important in the context of future direct-imaging missions. In contrast, the atmospheres of planets orbiting M-dwarf stars are substantially less affected. Our results demonstrate a pressing need for refined dissociation cross-section data for H2O, where uncertainties remain, and other key molecules, especially at mid-UV wavelengths >200 nm.
• Initiative, T., Wit, J., Doyon, R., Rackham, B. V., Lim, O., Ducrot, E., Kreidberg, L., Benneke, B., Ribas, I., Berardo, D., Niraula, P., Iyer, A., Shapiro, A., Kostogryz, N., Witzke, V., Gillon, M., Agol, E., Meadows, V., Burgasser, A. J., , Owen, J. E., et al. (2024). A roadmap for the atmospheric characterization of terrestrial exoplanets with JWST. Nature Astronomy, 8, 810-818.
• Jiang, H. J., Underwood, T. C., Bell, J. G., Lei, J., Gonzales, J. C., Emge, L., Tadese, L. G., Abd, E., Wilmouth, D. M., Brazaca, L. C., Ni, G., Belding, L., Dey, S., Ashkarran, A. A., Nagarkar, A., Nemitz, M. P., Cafferty, B. J., Sayres, D. S., Ranjan, S., , Crocker, D. R., et al. (2024). Mimicking lightning-induced electrochemistry on the early Earth. Proceedings of the National Academy of Science, 121(32), e2400819121.
• Jiang, H., Underwood, T., Bell, J., Lei, J., Gonzales, J., Emge, L., Tadese, L., Abd El-Rahman, M., Wilmouth, D., Brazaca, L., Ni, G., Belding, L., Dey, S., Ashkarran, A., Nagarkar, A., Nemitz, M., Cafferty, B., Sayres, D., Ranjan, S., , Crocker, D., et al. (2024). Mimicking lightning-induced electrochemistry on the early Earth. Proceedings of the National Academy of Sciences of the United States of America, 121(32). doi:10.1073/pnas.2400819121
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  To test the hypothesis that an abiotic Earth and its inert atmosphere could form chemically reactive carbon- and nitrogen-containing compounds, we designed a plasma electrochemical setup to mimic lightning-induced electrochemistry under steady-state conditions of the early Earth. Air-gap electrochemical reactions at air–water–ground interfaces lead to remarkable yields, with up to 40 moles of carbon dioxide being reduced into carbon monoxide and formic acid, and 3 moles of gaseous nitrogen being fixed into nitrate, nitrite, and ammonium ions, per mole of transmitted electrons. Interfaces enable reactants (e.g., minerals) that may have been on land, in lakes, and in oceans to participate in radical and redox reactions, leading to higher yields compared to gas-phase-only reactions. Cloud-to-ground lightning strikes could have generated high concentrations of reactive molecules locally, establishing diverse feedstocks for early life to emerge and survive globally.
• Petkowski, J. J., Seager, S., Grinspoon, D. H., Bains, W., Ranjan, S., Rimmer, P. B., Buchanan, W. P., Agrawal, R., Mogul, R., & Carr, C. E. (2024). Astrobiological Potential of Venus Atmosphere Chemical Anomalies and Other Unexplained Cloud Properties. Astrobiology, 24(4), 343-370.
• Petkowski, J. J., Seager, S., Grinspoon, D. H., Bains, W., Ranjan, S., Rimmer, P. B., Buchanan, W. P., Agrawal, R., Mogul, R., & Carr, C. E. (2024). Astrobiological Potential of Venus Atmosphere Chemical Anomalies and Other Unexplained Cloud Properties. Astrobiology, 24(4), 343-370. doi:10.1089/ast.2022.0060
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  Long-standing unexplained Venus atmosphere observations and chemical anomalies point to unknown chemistry but also leave room for the possibility of life. The unexplained observations include several gases out of thermodynamic equilibrium (e.g., tens of ppm O2, the possible presence of PH3 and NH3, SO2 and H2O vertical abundance profiles), an unknown composition of large, lower cloud particles, and the “unknown absorber(s).” Here we first review relevant properties of the venusian atmosphere and then describe the atmospheric chemical anomalies and how they motivate future astrobiology missions to Venus.
• Todd, Z. R., Lozano, G. G., Kufner, C. L., Ranjan, S., Catling, D. C., & Sasselov, D. D. (2024). UV Transmission in Prebiotic Environments on Early Earth. Astrobiology, 24(5), 559-569.
• Todd, Z. R., Lozano, G., Kufner, C., Ranjan, S., Catling, D., & Sasselov, D. (2023).

  UV Transmission in Prebiotic Environments on Early Earth

  . Astrobiology, n/a.
• Todd, Z., Lozano, G., Kufner, C., Ranjan, S., Catling, D., & Sasselov, D. (2024). UV Transmission in Prebiotic Environments on Early Earth. Astrobiology, 24(5). doi:10.1089/ast.2023.0077
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  Ultraviolet (UV) light is likely to have played important roles in surficial origins of life scenarios, potentially as a productive source of energy and molecular activation, as a selective means to remove unwanted side products, or as a destructive mechanism resulting in loss of molecules/biomolecules over time. The transmission of UV light through prebiotic waters depends upon the chemical constituents of such waters, but constraints on this transmission are limited. Here, we experimentally measure the molar decadic extinction coefficients for a number of small molecules used in various prebiotic synthetic schemes. We find that many small feedstock molecules absorb most at short (∼200 nm) wavelengths, with decreasing UV absorption at longer wavelengths. For comparison, we also measured the nucleobase adenine and found that adenine absorbs significantly more than the simpler molecules often invoked in prebiotic synthesis. Our results enable the calculation of UV photon penetration under varying chemical scenarios and allow further constraints on plausibility and self-consistency of such scenarios. While the precise path that prebiotic chemistry took remains elusive, improved understanding of the UV environment in prebiotically plausible waters can help constrain both the chemistry and the environmental conditions that may allow such chemistry to occur.
• de Wit, J., Doyon, R., Rackham, B., Lim, O., Ducrot, E., Kreidberg, L., Benneke, B., Ribas, I., Berardo, D., Niraula, P., Iyer, A., Shapiro, A., Kostogryz, N., Witzke, V., Gillon, M., Agol, E., Meadows, V., Burgasser, A., Owen, J., , Fortney, J., et al. (2024). A roadmap for the atmospheric characterization of terrestrial exoplanets with JWST. Nature Astronomy, 8(7). doi:10.1038/s41550-024-02298-5
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  Ultracool dwarf stars are abundant, long-lived and uniquely suited to enable the atmospheric study of transiting terrestrial companions with the JWST. Among them, the most prominent is the M8.5V star TRAPPIST-1 and its seven planets. While JWST Cycle 1 observations have started to yield preliminary insights into the planets, they have also revealed that their atmospheric exploration requires a better understanding of their host star. Here we propose a roadmap to characterize the TRAPPIST-1 system — and others like it — in an efficient and robust manner with JWST. We notably recommend that — although more challenging to schedule — multi-transit windows be prioritized to mitigate the effects of stellar activity and gather up to twice more transits per JWST hour spent. We conclude that, for such systems, planets cannot be studied in isolation by small programmes but rather need large-scale, joint space- and ground-based initiatives to fully exploit the capabilities of JWST for the exploration of terrestrial planets.
• Bains, W., Pasek, M. A., Ranjan, S., Petkowski, J. J., Omran, A., & Seager, S. (2023). Large Uncertainties in the Thermodynamics of Phosphorus (III) Oxide (P4O6) Have Significant Implications for Phosphorus Species in Planetary Atmospheres. ACS Earth and Space Chemistry, 7(6), 1219-1226.
• Grant, D., Lewis, N. K., Wakeford, H. R., Batalha, N. E., Glidden, A., Goyal, J., Mullens, E., MacDonald, R. J., May, E. M., Seager, S., Stevenson, K. B., Valenti, J. A., Visscher, C., Alderson, L., Allen, N. H., Ca{\~nas}, C. I., Col{\'on}, K., Clampin, M., Espinoza, N., , Gressier, A., et al. (2023). JWST-TST DREAMS: Quartz Clouds in the Atmosphere of WASP-17b. \apjl, 956(2), L32.
• Initiative, T., Wit, J., Doyon, R., Rackham, B. V., Lim, O., Ducrot, E., Kreidberg, L., Benneke, B., Ribas, I., Berardo, D., Niraula, P., Iyer, A., Shapiro, A., Kostogryz, N., Witzke, V., Gillon, M., Agol, E., Meadows, V., Burgasser, A. J., , Owen, J. E., et al. (2023). A roadmap to the efficient and robust characterization of temperate terrestrial planet atmospheres with JWST. arXiv e-prints, arXiv:2310.15895.
• Ranjan, S., Abdelazim, K., Lozano, G. G., Mandal, S., Zhou, C. Y., Kufner, C. L., Todd, Z. R., Sahai, N., & Sasselov, D. D. (2023). Geochemical and Photochemical Constraints on S[IV] Concentrations in Natural Waters on Prebiotic Earth. AGU Advances, 4(6), e2023AV000926.
• Ranjan, S., Nayak, P. K., Pineda, J. S., & Narang, M. (2023). UV Spectral Characterization of Low-mass Stars with AstroSat UVIT for Exoplanet Applications: The Case Study of HIP 23309. \aj, 166(2), 70.
• Ranjan, S., Schwieterman, E. W., Leung, M., Harman, C. E., & Hu, R. (2023). The Importance of the Upper Atmosphere to CO/O$_2$ Runaway on Habitable Planets Orbiting Low-mass Stars. \apjl, 958(1), L15.
• Bains, W., Petkowski, J. J., Seager, S., Ranjan, S., Sousa-Silva, C., Rimmer, P. B., Zhan, Z., Greaves, J. S., & Richards, A. M. (2022). Venusian phosphine: a ‘wow!’signal in chemistry?. Phosphorus, Sulfur, and Silicon and the Related Elements, 197(5-6), 438--443.
• Bains, W., Shorttle, O., Ranjan, S., Rimmer, P. B., Petkowski, J. J., Greaves, J. S., & Seager, S. (2022). Constraints on the production of phosphine by Venusian volcanoes. Universe, 8(1), 54.
• Bains, W., Shorttle, O., Ranjan, S., Rimmer, P. B., Petkowski, J. J., Greaves, J. S., & Seager, S. (2022). Only extraordinary volcanism can explain the presence of parts per billion phosphine on Venus. Proceedings of the National Academy of Sciences, 119(7), e2121702119.
• Glidden, A., Seager, S., Huang, J., Petkowski, J. J., & Ranjan, S. (2022). Can Carbon Fractionation Provide Evidence for Aerial Biospheres in the Atmospheres of Temperate Sub-Neptunes?. The Astrophysical Journal, 930(1), 62.
• Greaves, J. S., Rimmer, P. B., Richards, A. M., Petkowski, J. J., Bains, W., Ranjan, S., Seager, S., Clements, D. L., Silva, C. S., & Fraser, H. J. (2022). Low levels of sulphur dioxide contamination of Venusian phosphine spectra. Monthly Notices of the Royal Astronomical Society, 514(2), 2994--3001.
• Huang, J., Seager, S., Petkowski, J. J., Ranjan, S., & Zhan, Z. (2022). Assessment of Ammonia as a Biosignature Gas in Exoplanet Atmospheres. Astrobiology, 22(2), 171--191.
• Huang, J., Seager, S., Petkowski, J. J., Zhan, Z., & Ranjan, S. (2022). Methanol—A Poor Biosignature Gas in Exoplanet Atmospheres. The Astrophysical Journal, 933(1), 6.
• Lin, Z., Seager, S., Ranjan, S., Kozakis, T., & Kaltenegger, L. (2022). H2-dominated Atmosphere as an Indicator of Second-generation Rocky White Dwarf Exoplanets. The Astrophysical Journal Letters, 925(1), L10.
• Ranjan, S., Kufner, C. L., Lozano, G. G., Todd, Z. R., Haseki, A., & Sasselov, D. D. (2022). UV Transmission in Natural Waters on Prebiotic Earth. Astrobiology, 22(3), 242--262.
• Ranjan, S., Seager, S., Zhan, Z., Koll, D. D., Bains, W., Petkowski, J. J., Huang, J., & Lin, Z. (2022). Photochemical Runaway in Exoplanet Atmospheres: Implications for Biosignatures. Astrophysical Journal, 930(2), 131.
• Zhan, Z., Huang, J., Seager, S., Petkowski, J. J., & Ranjan, S. (2022). Organic Carbonyls Are Poor Biosignature Gases in Exoplanet Atmospheres but May Generate Significant CO. The Astrophysical Journal, 930(2), 133.
• An, S., Ranjan, S., Yuan, K., Yang, X., & Skodje, R. T. (2021). The Role of the Three Body Photodissociation Channel of Water in the Evolution of Dioxygen in Astrophysical Applications. Physical Chemistry Chemical Physics.
• Bains, W., Petkowski, J. J., Seager, S., Ranjan, S., Sousa-Silva, C., Rimmer, P. B., Zhan, Z., Greaves, J. S., & Richards, A. M. (2021). Phosphine on Venus cannot be explained by conventional processes. Astrobiology, 21(10), 1277--1304.
• Greaves, J. S., Richards, A. M., Bains, W., Rimmer, P. B., Sagawa, H., Clements, D. L., Seager, S., Petkowski, J. J., Sousa-Silva, C., Ranjan, S., & others, . (2021). Addendum: Phosphine gas in the cloud deck of Venus. Nature Astronomy, 5(7), 726--728.
• Greaves, J. S., Richards, A. M., Bains, W., Rimmer, P. B., Sagawa, H., Clements, D. L., Seager, S., Petkowski, J. J., Sousa-Silva, C., Ranjan, S., & others, . (2021). Phosphine gas in the cloud decks of Venus. Nature Astronomy, 5(7), 655--664.
• Greaves, J. S., Richards, A., Bains, W., Rimmer, P. B., Clements, D. L., Seager, S., Petkowski, J. J., Sousa-Silva, C., Ranjan, S., & Fraser, H. J. (2021). Reply to: No evidence of phosphine in the atmosphere of Venus from independent analyses. Nature Astronomy, 5(7), 636--639.
• Rimmer, P. B., Ranjan, S., & Rugheimer, S. (2021). Life’s origins and the search for life on rocky exoplanets. Elements: An International Magazine of Mineralogy, Geochemistry, and Petrology, 17(4), 265--270.
• Seager, S., Petkowski, J. J., Gao, P., Bains, W., Bryan, N. C., Ranjan, S., & Greaves, J. (2021). The Venusian lower atmosphere haze as a depot for desiccated microbial life: A proposed life cycle for persistence of the Venusian aerial biosphere. Astrobiology, 21(10), 1206--1223.
• Zhan, Z., Seager, S., Petkowski, J. J., Sousa-Silva, C., Ranjan, S., Huang, J., & Bains, W. (2021). Assessment of isoprene as a possible biosignature gas in exoplanets with anoxic atmospheres. Astrobiology, 21(7), 765--792.
• G"unther, M. N., Zhan, Z., Seager, S., Rimmer, P. B., Ranjan, S., Stassun, K. G., Oelkers, R. J., Daylan, T., Newton, E., Kristiansen, M. H., & others, . (2020). Stellar flares from the first TESS data release: exploring a new sample of M dwarfs. The Astronomical Journal, 159(2), 60.
• Ranjan, S., Schwieterman, E. W., Harman, C., Fateev, A., Sousa-Silva, C., Seager, S., & Hu, R. (2020). Photochemistry of Anoxic Abiotic Habitable Planet Atmospheres: Impact of New H2O Cross Sections. The Astrophysical Journal, 896, 2.
• Sousa-Silva, C., Seager, S., Ranjan, S., Petkowski, J. J., Zhan, Z., Hu, R., & Bains, W. (2020). Phosphine as a biosignature gas in exoplanet atmospheres. Astrobiology, 20(2), 235--268.
• Todd, Z. R., Fahrenbach, A. C., Ranjan, S., Magnani, C. J., Szostak, J. W., & Sasselov, D. D. (2020). Ultraviolet-driven deamination of cytidine ribonucleotides under planetary conditions. Astrobiology, 20(7), 878--888.
• Ranjan, S., Todd, Z. R., Rimmer, P. B., Sasselov, D. D., & Babbin, A. R. (2019). Nitrogen oxide concentrations in natural waters on early Earth. Geochemistry, Geophysics, Geosystems, 20(4), 2021--2039.
• Ranjan, S., Todd, Z. R., Sutherland, J. D., & Sasselov, D. D. (2018). Sulfidic anion concentrations on early earth for surficial origins-of-life chemistry. Astrobiology, 18(8), 1023--1040.
• Todd, Z. R., Fahrenbach, A. C., Magnani, C. J., Ranjan, S., Bj"orkbom, A., Szostak, J. W., & Sasselov, D. D. (2018). Solvated-electron production using cyanocuprates is compatible with the UV-environment on a Hadean--Archaean Earth. Chemical Communications, 54(9), 1121--1124.
• Xu, J., Ritson, D. J., Ranjan, S., Todd, Z. R., Sasselov, D. D., & Sutherland, J. D. (2018). Photochemical reductive homologation of hydrogen cyanide using sulfite and ferrocyanide. Chemical Communications, 54(44), 5566--5569.
• Ranjan, S., & Sasselov, D. D. (2017). Constraints on the early terrestrial surface UV environment relevant to prebiotic chemistry. Astrobiology, 17(3), 169--204.
• Ranjan, S., Wordsworth, R., & Sasselov, D. D. (2017). Atmospheric constraints on the surface UV environment of Mars at 3.9 Ga relevant to prebiotic chemistry. Astrobiology, 17(8), 687--708.
• Ranjan, S., Wordsworth, R., & Sasselov, D. D. (2017). The surface UV environment on planets orbiting M dwarfs: implications for prebiotic chemistry and the need for experimental follow-up. The Astrophysical Journal, 843(2), 110.
• Ranjan, S., & Sasselov, D. D. (2016). Influence of the UV environment on the synthesis of prebiotic molecules. Astrobiology, 16(1), 68--88.
• Ranjan, S., Charbonneau, D., D'esert, J., Madhusudhan, N., Deming, D., Wilkins, A., & Mandell, A. M. (2014). Atmospheric characterization of five hot Jupiters with the wide field camera 3 on the Hubble space telescope. The Astrophysical Journal, 785(2), 148.
• Wilkins, A. N., Deming, D., Madhusudhan, N., Burrows, A., Knutson, H., McCullough, P., & Ranjan, S. (2014). The emergent 1.1--1.7 $mu$m spectrum of the exoplanet COROT-2b as measured using the Hubble Space Telescope. The Astrophysical Journal, 783(2), 113.
• Deming, D., Wilkins, A., McCullough, P., Burrows, A., Fortney, J. J., Agol, E., Dobbs-Dixon, I., Madhusudhan, N., Crouzet, N., Desert, J., & others, . (2013). Infrared transmission spectroscopy of the exoplanets HD 209458b and XO-1b using the Wide Field Camera-3 on the Hubble Space Telescope. The Astrophysical Journal, 774(2), 95.
• Nicolls, M. J., Heinselman, C. J., Hope, E. A., Ranjan, S., Kelley, M. C., & Kelly, J. D. (2007). Imaging of polar mesosphere summer echoes with the 450 MHz poker flat advanced modular incoherent scatter radar. Geophysical Research Letters, 34(20).

Proceedings Publications

• Allen, N., Espinoza, N., Agol, E., Batalha, N., Boehm, V., Ca{\~nas}, C., Colon, K., Diamond-Lowe, H., Glidden, A., Grant, D., Gressier, A., Huang, J., Lewis, N., Lin, Z., Long, D., Louie, D., MacDonald, R., Moran, S., Morris, B., , Pueyo, L., et al. (2025, jan). Characterizing the atmosphere of TRAPPIST-1 e in the face of stellar contamination. In American Astronomical Society Meeting Abstracts \#245, 245.
• Branco, A., Sousa-Silva, C., Broussard, W., Ranjan, S., Schwieterman, E., & Machado, P. (2025, sep). Assessing the Impact of Varying HSO and HNO Cross-Sections on Photochemical Models: Implications for Spectral Characterization of Terrestrial Exoplanets. In EPSC-DPS Joint Meeting 2025, 2025.
• Glidden}, A., Ranjan, S., Espinoza, N., MacDonald, R., Allen, N., Lewis, N., & Team, {. (2025, jan). JWST-TST DREAMS: Preliminary Reconnaissance of TRAPPIST-1e with JWST NIRSpec PRISM. In American Astronomical Society Meeting Abstracts \#245, 245.
• Pineda, J. S., Ranjan, S., N{\'u\~nez}, A., Youngblood, A., & France, K. (2025, jan). Diminished Chromospheres Around the Lowest-mass Stars: Implications for Planetary Atmospheres and Biosignature False Positives. In American Astronomical Society Meeting Abstracts \#245, 245.
• Schlecker, M., Apai, D., Lichtenberg, T., Bergsten, G., Salvador, A., Hardegree-Ullman, K., Affholder, A., Ranjan, S., Ferriere, R., Mazevet, S., & Heng, K. (2024, sep). Bioverse: Probing the Habitable Zone Inner Edge Discontinuity and the Origins of Life. In European Planetary Science Congress.
• Cosgrove, R., Nicolls, M., Dahlgren, H., Ranjan, S., Sanchez, E., & Doe, R. (2010). Radar detection of a localized 1.4 Hz pulsation in auroral plasma, simultaneous with pulsating optical emissions, during a substorm. In Annales Geophysicae, 28.

Presentations

• Ranjan, S. (2023).

  A Re-Examination of Photochemical False Positives for O2 as a Biosignature Gas on Temperate Terrestrial Exoplanets

  . Origins 2023. Quito, Ecuador: International Society for the Study of the Origins of Life (ISSOL).
• Ranjan, S. (2023). Experimental Constraints for Improving Terrestrial Exoplanet Photochemical Models
  (ExCITE-PM). NASA Lab Astro PI Program Review. Washington, D. C.: National Aeronautics & Space Administration (NASA).
• Ranjan, S. (2023). Life in the Light: Photochemical Insights Towards Life as a Planetary Phenomenon. Alien Earths Origins Seminar.
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  Invited Seminar
• Ranjan, S. (2023). Life in the Light: Photochemical Insights Towards Life as a Planetary Phenomenon. CU Boulder Physical Chemistry/Chemical Physics Colloquium.
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  Invited Colloquium
• Ranjan, S. (2023). Life in the Light: Photochemical Insights Towards Life as a Planetary Phenomenon. JHU/StSci Joint Astrobiology Seminar. Baltimore, MD: Johns Hopkins University & Space Telescope Science Institute.
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  Invited Seminar
• Ranjan, S. (2023). Life in the Light: Photochemical Insights Towards Life as a Planetary Phenomenon. MIT Planetary Science Lunch Seminar.
• Ranjan, S. (2023). Life in the Light: Photochemical Insights Towards Life as a Planetary Phenomenon. Northern Arizona University Astronomy & Planetary Science Colloquium. Flagstaff, AZ: Northern Arizona University.
• Ranjan, S. (2023). Life in the Light: Photochemical Insights Towards Life as a Planetary Phenomenon. Penn State Astrobiology Hour. State College, PA: Pennsylvania State University.
• Ranjan, S. (2023). Photochemical Controls on Biosignature Gas Accumulation in Habitable Planet Atmospheres. Oxygen In Planetary Biospheres. Green Bank, WV: Green Bank Observatory.
• Ranjan, S. (2023). Photolytic Controls on Accumulation of Precursor Chemicals for Prebiotic Chemistry. BMSIS SeminarBlue Marble Space Institute of Science.
• Ranjan, S. (2023). Re-Assessment of CO/O2 Runaway in Temperate Terrestrial Planet Atmospheres. Alien Earths Team Meeting.
• Ranjan, S. (2023). Reduced Scope for Abiotic False Positives for Oxygen as a Biosignature Gas on Habitable Exoplanets. Steward Observatory Internal SymposiumSteward Observatory, UA.
• Ranjan, S. (2023). Sulfite In Natural Waters on Prebiotic Earth. NSF Workshop “Life in the Universe”. Cambridge, MA: National Science Foundation.
• Ranjan, S. (2023). The M-Dwarf Opportunity for Understanding Life as a Planetary Phenomenon. StSci Conference “Planetary Systems and the Origins of Life in the Era of JWST”. Baltimore, MD: Space Telescope Science Institute.
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  Invited Talk
• Ranjan, S. (2023). [S[IV]] In Natural Waters On Prebiotic Earth. LPL Science Conference (LPLSC).

Others

• Allen, N., Espinoza, N., Agol, E., Batalha, N., Canas, C., Colon, K., Glidden, A., Goyal, J., Grant, D., Gressier, A., Huang, J., Lewis, N., Lin, Z., Long, D. R., Louie, D. R., MacDonald, R., Morris, B. M., Pueyo, L., Rackham, B., , Ranjan, S., et al. (2025). Using stellar contamination proxy TRAPPIST-1 b to search for an atmosphere on TRAPPIST-1 e.
• Allen, N., Espinoza, N., Agol, E., Batalha, N., Canas, C., Colon, K., Glidden, A., Goyal, J., Grant, D., Gressier, A., Huang, J., Lewis, N., Lin, Z., Long, D. R., Louie, D. R., MacDonald, R., Morris, B. M., Pueyo, L., Rackham, B., , Ranjan, S., et al. (2024). Using stellar contamination proxy TRAPPIST-1 b to search for an atmosphere on TRAPPIST-1 e.