¹J. R. Hill,¹P. R. Christensen
Journal of Geophysical Research: Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2026JE009775]
¹School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
Published by arrangement with John Wiley & Sons

Martian chloride salt deposits were first identified by Osterloo et al. (2008, https://doi.org/10.1126/science.1150690) and surveyed by Osterloo et al. (2010, https://doi.org/10.1029/2010je003613) primarily using thermal infrared data acquired by the Thermal Emission Imaging System (THEMIS) onboard the 2001 Mars Odyssey spacecraft. Over the subsequent 15 years, the THEMIS instrument has greatly expanded its areal and repeat coverage of the Martian surface. A principal component-based index was also developed to identify chloride salts and quantify the confidence level of their detection. Pairing the expanded data set with this improved analytical technique enabled a more accurate global survey of chloride salts, which identified 1,605 distinct deposits covering 11,974 km2. This includes 777 newly identified deposits, which represents a ∼20% increase in the surface area (∼1,997 km2) of identified chloride salts. The chloride salt deposits are primarily associated with Noachian-aged terrains, with a significant percentage occurring in Early Noachian terrains. A steep drop-off in chloride deposit occurrence was observed at the Noachian-Hesperian boundary. This pushes the period of chloride salt formation and deposition back to the earliest periods of Martian history, when the planet more closely resembled the Earth at the same time.