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Multispectral mapping data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) provide a unique opportunity to characterize south polar ice deposits at higher spectral sampling, spatial resolution, or spatiotemporal coverage than previous work. This new perspective can help constrain the nature and distribution of different mixtures of CO2 ice, H2O ice, and dust that influence the formation, evolution, and preservation of Mars climate records. We processed 1,103 CRISM observations spanning the southern summer of six Mars Years (MYs) through a combination of k‐means clustering and random forest classification. Using a set of 12 spectral endmembers directly tied to previous work with high‐resolution CRISM targeted data, we made a series of temporally restricted mosaics showing surface spectral variation over time. The mosaics show the effects of the MY 28 dust storm on the removal of the seasonal CO2 ice cap that year and reveal how this process differed from the years that followed. A mosaic showing residual ice surfaces displays broad agreement with previous compositional maps while resolving new details in the distribution of H2O ice‐rich material around the periphery of the bright CO2 ice cap. By showing how surface composition varies across a broad swath of the south polar region through time, the endmember set and classified mosaics produced in this work can provide critical context for future studies of the dynamic processes that shape south polar ice deposits. Plain Language Summary: At the south pole of Mars, different mixtures of CO2 ice, water ice, and dust on the surface influence interactions with the atmosphere. These influences affect how polar ice deposits are formed, how they change over time, and how they are preserved as records of past climates. Existing maps of ice and dust in the region have limitations in how accurately they can describe mixtures and how much detail they can show on the ground. Using data from an orbiting spectrometer that measures sunlight reflected from the surface, we made new maps that reveal important details not seen in previous work. For example, these maps show how surface composition changes through time, which can be used to study CO2 frost that forms on the surface every winter and is removed in the summer. We observe how a dust storm in 1 year affected the composition and/or thickness of seasonal frost compared with other years. The maps also reveal how composition varies in different permanent ice deposits. Compared to previous work, it is easier to see how CO2 ice and dust are mixed with water ice in enigmatic exposures that may be linked to the formation of new climate records. Key Points: Variable mixtures of CO2 and H2O ice with dust are linked to the formation of south polar climate recordsTo better understand these mixtures, we mapped 12 endmembers across multispectral data spanning 6 south polar summersWe made a series of mosaics to explore compositional variation in both seasonal and residual ice deposits [ABSTRACT FROM AUTHOR]

Current maps of compositional variation across south polar ice exposures on Mars do not resolve the meter‐scales at which erosional processes are most active, ultimately limiting our understanding of how the deposits form and evolve and how they can be used to interpret long‐term climate records. In this study, we use k‐means clustering and random forest classification to identify and map a set of universal spectral endmembers across 167 high‐resolution observations acquired during southern summer by the Compact Reconnaissance Imaging Spectrometer for Mars. The 21 endmembers show distinct combinations and strengths of key infrared absorption features reflecting diverse mixtures of CO2 ice, H2O ice, and dust. The resulting compositional framework can be used to characterize the nature of both seasonal CO2 frost and the residual ices it overlies across a variety of terrains. Following the large dust event of Mars Year 28, the residual CO2‐ice deposits (RCD) were covered by an unusually thick or long‐lived deposit of seasonal frost. Within the RCD, low‐albedo material around erosional features display H2O ice absorptions consistent with exposures around the outer margins of the RCD. These peripheral water‐ice deposits show unexpected variation in CO2 ice and dust content. Most notably, regions within several km of the edge of the RCD display spectral contributions from CO2 ice even after seasonal frost has been removed. These results can inform investigations focused on the dynamics of seasonal CO2 deposition, the development of erosional morphologies, and the creation of climate records in south polar stratigraphy. Plain Language Summary: Ice deposits near the south pole of Mars contain varied mixtures of CO2 ice, water ice, and dust. These mixtures influence interactions with solar heating and atmospheric cycling that affect the formation, evolution, and preservation of different ice deposits. However, ice composition in this region has not been mapped in sufficient detail to fully understand these dynamic processes. We used high‐resolution data gathered from an orbiting spectrometer that measured sunlight reflected from the surface. Through automated and manual techniques, we identified the most typical reflectance signatures in the data set and generated maps showing where those materials are located. These results reveal unprecedented detail in the nature of both seasonal (removed during summer) and residual (remaining on the surface throughout each year) ice deposits. The most compelling findings are that (a) increased seasonal CO2 ice thickness or retention appeared following a large dust storm, (b) residual CO2 ice is found to extend beyond the brightest deposits, and (c) water ice‐rich exposures reveal more varied CO2 ice and dust content than previously understood. The compositional framework provided by the study can help guide future investigations into a variety of processes that shape south polar ices and the climate records they preserve. Key Points: One hundred sixty‐seven south polar observations by the Compact Reconnaissance Imaging Spectrometer for Mars images were mapped with a set of 21 spectral endmembers representing a range of CO2 ice, H2O ice, and dust mixturesSeasonal CO2 ice cover was thicker or more prolonged in Mars Year 28, linking dust storms to cold‐trapping of CO2 on the bright residual iceCO2 ice signatures extend beyond the bright residual ice and into surrounding material, even in late summer after seasonal frost removal [ABSTRACT FROM AUTHOR]

Carbonate minerals have been detected in Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, and within the regional olivine‐bearing (ROB) unit in the Nili Fossae region surrounding this crater. It has been suggested that some carbonates in the margin fractured unit, a rock unit within Jezero crater, formed in a fluviolacustrine environment, which would be conducive to preservation of biosignatures from paleolake‐inhabiting lifeforms. Here, we show that carbonate‐bearing rocks within and outside of Jezero crater have the same range of visible‐to‐near‐infrared carbonate absorption strengths, carbonate absorption band positions, thermal inertias, and morphologies. Thicknesses of exposed carbonate‐bearing rock cross‐sections in Jezero crater are ∼75–90 m thicker than typical ROB unit cross‐sections in the Nili Fossae region, but have similar thicknesses to ROB unit exposures in Libya Montes. These similarities in carbonate properties within and outside of Jezero crater is consistent with a shared origin for all of the carbonates in the Nili Fossae region. Carbonate absorption minima positions indicate that both Mg‐ and more Fe‐rich carbonates are present in the Nili Fossae region, consistent with the expected products of olivine carbonation. These estimated carbonate chemistries are similar to those in martian meteorites and the Comanche carbonates investigated by the Spirit rover in Columbia Hills. Our results indicate that hydrothermal alteration is the most likely formation mechanism for non‐deltaic carbonates within and outside of Jezero crater. Plain Language Summary: Spacecraft orbiting Mars can measure the composition of rocks that make up its surface. Understanding rock composition allows us to interpret past environmental conditions on Mars, including their likelihood to be habitable. Using data acquired from orbit, researchers have found carbonate minerals in Jezero crater and the surrounding region—called the Nili Fossae region. Jezero crater is the landing site of NASA's Mars 2020 Perseverance rover and once contained a lake. The discovery of carbonates is exciting because on Earth they sometimes form in habitable environments and preserve fossils. In this study, we used all available high resolution orbital datasets to look at similarities and differences between carbonate‐bearing rocks within and outside of Jezero crater. We found that carbonate‐bearing rocks within and outside of Jezero crater have similar orbital properties, implying that they formed by the same processes. We found that the range in chemistries (magnesium‐rich vs. iron‐rich) for carbonates within and outside of Jezero crater is similar to carbonate chemistries found in martian meteorites and by other rovers on Mars. The carbonates within and outside of Jezero crater could have formed by the same water‐rock interactions that formed carbonates discovered in martian meteorites and by other rovers on Mars. Key Points: Carbonates within and outside of Jezero crater have similar spectra, thermal inertias, morphologies, and thicknessesCarbonates within and outside of Jezero crater likely formed via the same processesHydrothermal alteration and evaporation are the most likely processes for carbonate formation within and outside of Jezero crater [ABSTRACT FROM AUTHOR]