¹Stephen R. Kane,²Giada N. Arney,³Paul K. Byrne,^1,4Paul A. Dalba,⁵Steven J. Desch,⁶Jonti Horner,⁷Noam R. Izenberg,⁷Kathleen E. Mandt,⁸Victoria S. Meadows,⁹Lynnae C. Quick
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2020JE006643]
¹Department of Earth and Planetary Sciences, University of California, Riverside, CA, 92521 USA
²Planetary Systems Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, 20771 USA
³Planetary Research Group, Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, NC, 27695 USA
⁴NSF Astronomy and Astrophysics Postdoctoral Fellow
⁵School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 85287 USA
⁶Centre for Astrophysics, University of Southern Queensland, Toowoomba, QLD, 4350 Australia
⁷Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723 USA
⁸Department of Astronomy, University of Washington, Seattle, WA, 98195 USA
⁹Planetary Geology, Geophysics and Geochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, 20771 USA
Published by arrangement with John Wiley & Sons

Over the past several decades, thousands of planets have been discovered outside of our Solar System. These planets exhibit enormous diversity, and their large numbers provide a statistical opportunity to place our Solar System within the broader context of planetary structure, atmospheres, architectures, formation, and evolution. Meanwhile, the field of exoplanetary science is rapidly forging onward towards a goal of atmospheric characterization, inferring surface conditions and interiors, and assessing the potential for habitability. However, the interpretation of exoplanet data requires the development and validation of exoplanet models that depend on in‐situ data that, in the foreseeable future, are only obtainable from our Solar System. Thus, planetary and exoplanetary science would both greatly benefit from a symbiotic relationship with a two‐way flow of information. Here, we describe the critical lessons and outstanding questions from planetary science, the study of which are essential for addressing fundamental aspects for a variety of exoplanetary topics. We outline these lessons and questions for the major categories of Solar System bodies, including the terrestrial planets, the giant planets, moons, and minor bodies. We provide a discussion of how many of these planetary science issues may be translated into exoplanet observables that will yield critical insight into current and future exoplanet discoveries.

¹A.S.Yen et al. (>10)
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2020JE006569]
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, 91109Published by arrangement with John Wiley & Sons

In August 2015, the Curiosity Mars rover discovered tridymite, a high‐temperature silica polymorph, in Gale crater. The existing model for its occurrence suggests erosion and detrital sedimentation from silicic volcanic rocks in the crater rim or central peak. The chemistry and mineralogy of the tridymite‐bearing rocks, however, are not consistent with silicic volcanic material. Using data from Curiosity, including chemical composition from the Alpha Particle X‐ray Spectrometer, mineralogy from the CheMin instrument, and evolved gas and isotopic analyses from the Sample Analysis at Mars instrument, we show that the tridymite‐bearing rocks exhibit similar chemical patterns with silica‐rich alteration halos which crosscut the stratigraphy. We infer that the tridymite formed in‐place through hydrothermal processes and show additional chemical and mineralogical results from Gale crater consistent with hydrothermal activity occurring after sediment deposition and lithification.

¹Rachel Y. Sheppard,¹Ralph E. Milliken,²Mario Parente,²Yuki Itoh
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2020JE006372]
¹Department of Earth, Environmental and Planetary Sciences, Brown University
²Department of Electrical and Computer Engineering, University of Massachusetts, Amherst
Published by Arrangement with John Wiley & Sons

Previous studies have shown that Mt. Sharp has stratigraphic variation in mineralogy that may record a global transition from a climate more conducive to clay mineral formation to one marked by increased sulfate production. To better understand how small‐scale observations along the traverse path of NASA’s Curiosity rover might be linked to such large‐scale processes, it is necessary to understand the extent to which mineral signatures observed from orbit vary laterally and vertically. This study uses newly processed visible‐shortwave infrared CRISM data and corresponding visible images to re‐examine the mineralogy of lower Mt. Sharp, map mineral distribution, and evaluate stratigraphic relationships. We demonstrate the presence of darker‐toned strata that appears to be throughgoing with spectral signatures of monohydrated sulfate. Strata above and below this zone are lighter‐toned and contain polyhydrated sulfate and variable distribution of Fe/Mg clay minerals. Clay minerals are observed at multiple stratigraphic positions; unlike the kieserite zone these units cannot be traced laterally across Mt. Sharp. The kieserite zone appears to be stratigraphically confined, but in most locations the orbital data do not provide sufficient detail to determine whether mineral signatures conform to or cut across stratigraphic boundaries, leaving open the question as to whether the clay minerals and sulfates occur as detrital, primary chemical precipitates, and/or diagenetic phases. Future observations along Curiosity’s traverse will help distinguish between these possibilities. Rover observations of clay‐bearing strata in northwest Mt. Sharp may be more reflective of local conditions that could be distinct from those associated with other clay‐bearing strata.

^1,2C.D.Neish,³K.M.Cannon,^1,2L.L.Tornabene,^1,2R.L.Flemming,⁴M.Zanetti,^1,2E.Pilles
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114392]
¹Department of Earth Sciences, The University of Western Ontario, London, ON N6A 5B7, Canada
²Institute for Earth and Space Exploration, The University of Western Ontario, London, ON N6A 5B7, Canada
³Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401, United States of America
⁴NASA Marshall Space Flight Center, Huntsville, AL 35808, United States of America
Copyright Elsevier

Lunar impact melt deposits have unusual surface properties, unlike any measured terrestrial lava flow. Radar observations suggest that they are incredibly rough at decimeter scales, but they appear smooth in high-resolution, meter-scale optical images. The cause of their unusual surface roughness is unknown. In this work, we investigate the properties of impact melt deposits from seven lunar craters, ranging in size from 7.5 to 96 km in diameter, in an effort to understand the cause of their unique surface texture. We use data from the Lunar Reconnaissance Orbiter’s (LRO) Mini-RF instrument to characterize the small-scale roughness of the deposits, data from the LRO Camera (LROC) to characterize their meter-scale morphology, and data from Chandrayaan-1’s Moon Mineralogy Mapper (M3) to characterize their composition. This represents the most comprehensive study of the composition of lunar melt deposits completed to date. In particular, we applied a customized spectral unmixing model to the M3 data using laboratory spectra acquired from a range of possible lunar endmembers: pyroxene, olivine, fast-quenched lunar glass simulants, and impact melts and breccias (both synthetic and natural). We found that spectra derived from lunar melt deposits are typically modeled as a mix of the pyroxene and/or impact melts and breccias endmembers. Our modeled results suggest that lunar melt deposits are either crystalline deposits of pyroxene-rich rocks, or a mixture of glassy material and pyroxene minerals. The latter interpretation could explain the roughness observed in the Mini-RF data, if the melt deposits have a glassy surficial layer that shatters during impact gardening to produce decimeter scale blocks.