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Rachel Sheppard

Photo of Rachel Sheppard


4800 Oak Grove Drive

Pasadena, CA 91109

Curriculum Vitae:

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Member of:

Planetary Geosciences


As a JPL postdoc, I work within the Planetary Geosciences and Laboratory Studies groups, carrying out simulations of the martian subsurface groundwater environment in the Origins and Habitability Lab. I have a background in mineralogy, geophysics, geochemistry, and spectroscopy.


  • Ph.D., Earth & Planetary Sciences, Brown University (2020)
  • M.Sc., Earth & Planetary Sciences, Brown University (2017)
  • B.A., Earth Science, Columbia University (2013)

Professional Experience

  • 2020-present JPL postdoctoral associate
  • 2015-2020 Graduate research fellow, Brown University
  • 2013-2015 Gemological Institute of America, research laboratory
  • 2011-2013 Research Assistant, Lamont-Doherty Earth Observatory, Columbia University

Community Service

  • Recurring professional service: NASA review panel member, journal reviewer, conference session convener and chair, diversity and inclusion panel member, undergraduate student mentor.
  • Recurring public outreach: Girl Scouts of America workshop leader, Skype a Scientist participant, other high school student outreach lectures.

Research Interests

I am interested in the feedback between planetary surface processes and the preserved mineralogical and chemical records. Using visible-near infrared spectroscopy, mineral analysis under changing environmental conditions, and statistical methods, my research focuses on water-rock interaction, crystallinity, and distinguishing between surface and subsurface processes.

Research Grants
  • 2022-2025 Mars Science Laboratory Participating Scientist Program (MSL-PSP). Science PI. “Understanding Mg-sulfate distribution, hydration state, and crystallinity in Mt. Sharp.”
  • 2022 Spontaneous Research and Technology Development Program, Jet Propulsion Laboratory. Co-I. “Novel reaction design to test martian weathering.”
  • 2020-2022 Strategic Research and Technology Development Program, Jet Propulsion Laboratory. Science PI. “Experimental constraints on groundwater driven redox gradients on Mars.”

Selected Awards

  • 2019 Dissertation fellowship, Brown University Graduate School
  • 2015-2018 Presidential Fellowship, Brown University Graduate School.
  • 2013 Walter C. Pitman III Award for excellence in thesis research and presentation, Columbia University.

Selected Publications

  • R. Y. Sheppard, R. E. Milliken, K. M. Robertson. Presence of clay minerals can obscure spectral evidence of Mg sulfates: Implications for orbital observations of Mars. Under review at Icarus.
  • C. Lee, J. M. Weber, L. E. Rodriguez, R. Y. Sheppard, L. M. Barge, E. L. Berger, & A. S. Burton. The effects of binding and release during alteration on the chirality of organics and minerals. Submitted to Symmetry special issue Chirality, Prebiotic Chemistry, and the Origins of Life.
  • R. Vachula, R. Y. Sheppard, A. Cheung. Preservation biases are pervasive in Quaternary paleofire records. Under review at Sedimentology.
  • M. Prakash, J. M. Weber, L. E. Rodriguez, R. Y. Sheppard, L. M. Barge. Database on carbon reduction: Implications for future research. Under review at International Journal of Astrobiology.
  • 2021 R. Y. Sheppard, M. T. Thorpe, A. A. Fraeman, V. K. Fox, R. E. Milliken. Merging perspectives on secondary minerals on Mars: A review of ancient water-rock interactions in Gale crater inferred from orbital and in situ observations. Minerals special issue Expanding Views of Clays, Oxides, and Evaporites on Aquaplanets in the Solar System, 11(986).
  • 2021 R. Y. Sheppard, R. E. Milliken, J. M. Russell, M. D. Dyar, E. Sklute, H. Vogel, M. Melles, S. Bijaksana, A. K. M. Hasberg, & M. A. Morlock. Iron mineralogy and sediment color in a 100 m drill core from Lake Towuti, Indonesia reflect catchment and diagenetic conditions. Geochemistry, Geophysics, Geosystems. 22, e2020GC009582.
  • 2020 R. Y. Sheppard, R. E. Milliken, Y. Itoh, & M. Parente. Updated perspectives and hypotheses on the mineralogy of Lower Mt. Sharp, Mars, as seen from orbit. Journal of Geophysical Research: Planets. 26.
  • 2020 Russell, J., Vogel, H., Bijaksana, S., Melles, M., Deino, A., Hafidz, A., Hasberg, A., Morlock, M., von Rintelen, T., Sheppard, R. Y., Stelbrink, B., & Stevenson, J. The Late Quaternary tectonic, biogeochemical, and environmental evolution of ferruginous Lake Towuti, Indonesia. Palaeogeography, Palaeoclimatology, Palaeoecology. 556, pp. 109905.
  • 2019 Sheppard, R. Y., Milliken, R. E., Russell, J. M., Dyar, M. D., Sklute, E., Vogel, H., Melles, M., Bijaksana, S, Hasberg, A. K. M., & Morlock, M. A. Characterization of iron in Lake Towuti sediment. Chemical Geology. 512, pp. 11-30.
  • 2017 Johnson, B. C., Sheppard, R. Y., Pascuzzo, A. C., Fisher, E. A., & Wiggins, S. E. Porosity and salt content determine if subduction can occur in Europa’s ice shell. Journal of Geophysical Research: Planets. 122.
  • 2015 Sheppard, R. E., Polissar, P. J., & Savage, H. M. Organic thermal maturity as a proxy for fric- tional fault heating: experimental constraints on methylphenanthrene kinetics at earthquake timescales. Geochimica et Cosmochimica Acta. 151, pp. 103-116.
  • 2014 Savage, H. M., Polissar, P. J., Sheppard, R., Rowe, C. D., & Brodsky, E. E. Biomarkers heat up during earthquakes: New evidence of seismic slip in the rock record. Geology. 42(2), pp. 99-102.