In hypervelocity impact events, substantial kinetic energy of the impactor undergoes conversion into internal energy, where shock-induced high pressures and temperatures generate impact melt1, 2. On water-bearing or icy planets3, 4, and even on asteroids5, the ensuing propagation of heat and water after meteoric impact culminates in the development of impact-induced hydrothermal systems, which have the potential to support diverse forms of life6.
Numerical simulations have also predicted impact-generated hydrothermal systems on Mars driven by heat from impact melt, triggering basin-wide groundwater percolation7, 8, 9 and subsequent chemical alteration10, 11. These sites potentially fulfill important requirements for habitability, i.e., liquid water, nutrients and energy3, 12, 13. Moreover, potential biosignatures on Mars, if present, were likely to be preserved in chemically precipitated minerals (e.g., carbonates and silica) from various settings, particularly in association with hydrothermal activity3, 14, 15. However, the extent, mechanism and distribution of such hydrothermal systems in impact craters on Mars are unclear. Most previous research has searched for signatures of hydrothermal alteration within central peaks, where a series of alteration minerals associated with vein-16, 17 or mound-like features18, 19 have been identified in orbital datasets. Less commonly, alteration minerals at crater rims were detected in many craters20, 21, 22 including Jezero crater23, but no clear relationship with the impact or impact-related hydrothermal alteration was established. As the Mars 2020 Perseverance rover is approaching the crater rim of Jezero, it is crucial to scrutinize the origin of alteration minerals for potential links to post-impact hydrothermal systems. One challenge of making this link is that ancient Martian craters like Jezero are often heavily eroded, so interpreting the alteration and impactite stratigraphy is difficult. A sufficiently large, young, and well-preserved impact crater would reveal more about the nature of impact-induced hydrothermal alterations within crater rims.
Ritchey crater is located ~ 200 km south of Valles Marineris and is a complex crater 78 km in diameter, with exceptionally well-preserved central uplift, terraces, rim, and ejecta. Crater counting on the Ritchey ejecta yields a retention age of 3.46 Ga (Early Hesperian21). At the crater center, a smooth, coherent layer and a dark, rough unit were speculated to be a preserved impact melt deposit21. Although the crater floor is covered by aeolian deposits, the inner-rim exhibits well-exposed and intact bedrock. Fluvial channels and related fan deposits emanating from the wall indicate at least some post-impact aqueous activity occurred21.
The well-preserved state of Ritchey crater offers a unique opportunity to study impactite-alteration stratigraphy on the rim for large, complex craters on Mars. Here we use Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) hyperspectral visible/near-infrared24 and High Resolution Imaging Science Experiment (HiRISE25) images to identify alteration minerals, impactite stratigraphy, and post-impact geological processes on the rim of Ritchey, in order to investigate their relationship to impact-induced hydrothermal activity. Through these observations, we seek to provide an important framework to understand alteration processes and astrobiological potential of martian crater rims.