Walter M Harris
- Professor, Planetary Sciences
- Professor, Lunar and Planetary Laboratory
- Member of the Graduate Faculty
- Chief Scientist
- Associate Director, Community Engagement S4 Space Center
Contact
Degrees
- Ph.D. Astronomy & Atmospheric & Space Science
- University of Michigan, Ann Arbor, Michigan, USA
- B.S. Astronomy
- University of Illinois Champaign-Urbana, Urbana, Illinois, USA
- B.S. Physics Engineering
- University of Illinois Champaign-Urbana, Urbana, Illinois
Work Experience
- University of California-Davis (2007 - 2013)
- University of Washington, Seattle, Washington (2003 - 2007)
- University of Wisconsin-Madison, Madison, Wisconsin (2000 - 2003)
Interests
No activities entered.
Courses
2026-27 Courses
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Directed Research
PTYS 392 (Fall 2026)
2024-25 Courses
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Thesis
PTYS 910 (Fall 2024)
2021-22 Courses
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Dissertation
PTYS 920 (Spring 2022) -
Dissertation
PTYS 920 (Fall 2021)
2020-21 Courses
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Dissertation
PTYS 920 (Spring 2021) -
Directed Graduate Research
OPTI 792 (Fall 2020) -
Dissertation
PTYS 920 (Fall 2020)
2019-20 Courses
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Dissertation
PTYS 920 (Spring 2020) -
Research
PTYS 900 (Spring 2020) -
Astr,Comet,Kuipr Blt Obj
PTYS 416 (Fall 2019) -
Astr,Comet,Kuipr Blt Obj
PTYS 516 (Fall 2019) -
Dissertation
PTYS 920 (Fall 2019) -
Independent Study
PTYS 599 (Fall 2019)
2018-19 Courses
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Dissertation
PTYS 920 (Spring 2019) -
Research
PTYS 900 (Spring 2019) -
Dissertation
PTYS 920 (Fall 2018) -
Spec Tops in Planetary Science
PTYS 495B (Fall 2018) -
Spec Tops in Planetary Science
PTYS 595B (Fall 2018)
2017-18 Courses
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Directed Research
ASTR 492 (Summer I 2018) -
Dissertation
PTYS 920 (Spring 2018) -
Independent Study
PTYS 499 (Spring 2018) -
Astr,Comet,Kuipr Blt Obj
PTYS 416 (Fall 2017) -
Astr,Comet,Kuipr Blt Obj
PTYS 516 (Fall 2017) -
Dissertation
PTYS 920 (Fall 2017)
2016-17 Courses
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Research
PTYS 900 (Spring 2017) -
Spec Tops in Planetary Science
PTYS 495B (Spring 2017) -
Spec Tops in Planetary Science
PTYS 595B (Spring 2017) -
Research
PTYS 900 (Fall 2016) -
Spec Tops in Planetary Science
PTYS 495B (Fall 2016) -
Spec Tops in Planetary Science
PTYS 595B (Fall 2016)
Scholarly Contributions
Chapters
Journals/Publications
- More infoThe exospheres of all objects are mostly made of atomic hydrogen. Because the Sun is bright in Lyman α, the properties of the H atoms in the exospheres of certain terrestrial solar system objects can be studied by analyzing the resonantly scattered solar Lyman α emission by these exospheric H atoms. This emission is optically thick in the exospheres of all planets in our solar system except Mercury. This makes it complicated to derive the true characteristics (number density distribution, energy distribution) of the H atoms present in these exospheres. While radiative transfer (RT) models have been used extensively to derive the characteristics of exospheric H atoms by modeling the line-integrated Lyman α intensity measured by spacecrafts via remote sensing, the models often fail to resolve discrepancies between the observed emission intensity and the simulated value. This is because of the various assumptions that are made in the RT models about the inherent characteristics of the H atoms and the corresponding Lyman α lineshape. Our knowledge about the characteristics of the H atoms can be significantly improved by understanding what the true lineshape of the H Lyman α line may be for various conditions. This can then be used to resolve the discrepancies between the modeled and the observed intensities for planetary exospheres. Here we present a detailed study on the shape of the exospheric Lyman α emission line for various conditions like change in altitude, temperature, non-isothermality, asymmetry, and presence of non-thermal atoms. These detailed line profiles are being used to determine H density distribution in Earth’s exosphere from analysis of absorption of the solar Lyman α line by geocoronal H as measured by remote sensing satellites. This theoretical analysis also highlights the advantages of obtaining highly resolved H Lyman α emission line measurements from the exospheres of certain terrestrial objects in our solar system.
