The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter (MRO) collected hyperspectral images of the Martian surface and atmosphere from September 27, 2006, through May 7, 2022. Over that time, nearly twenty scientific investigations were completed, most of which arose as a result of the findings from previous investigations. Two review papers published in 2009 (Murchie et al., 2009a, b) described the initial two-year investigation during MRO's Primary Science Phase, its key findings, and the CRISM data products that were developed and released to the community through that time. Here we describe the conduct and evolution of the CRISM investigation since then, which includes MRO's Extended Science Phase and first five Extended Missions. We document the physical changes in the instrument as it aged, including capabilities that were lost as well as new modes of operation not initially envisioned; the new science questions that were investigated and their key findings; anatomy of the extensive collection of data products that have been released to the Planetary Data System; the "final" radiometric calibration; high-order derived products produced from high-resolution targeted observations and global mapping campaigns; and data processing and analysis tools which have been developed and released by the CRISM team.

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. 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. 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 Water ice in the Martian mid‐latitudes has advanced and retreated in response to variations in the planet's orbit, obliquity, and climate. A 150 m‐diameter new impact crater near 35°N provides the lowest‐latitude impact exposure of subsurface ice on Mars. This is the largest known ice‐exposing crater and provides key constraints on Martian climate history. This crater indicates a regional, relatively pure ice deposit that is unstable and has nearly vanished. In the past, this deposit may have been tens of meters thick and extended equatorward of 35°N. We infer that it is overlain by pore ice emplaced during temporary stable intervals, due to recent climate variability. The marginal survival of ice here suggests that it is near the edge of shallow ice that regularly exchanges with the atmosphere.

A dark‐toned, indurated, smooth horizon, and (or) bed (herein called “marker horizon”) is exposed across much of the northwestern, southwestern, and southeastern portions of Mount Sharp in Gale crater. Compact Reconnaissance Imaging Spectrometer for Mars spectra taken from the marker horizon exhibit evidence for the presence of high calcium pyroxene and other basaltic minerals in contrast to the hydrated sulfate signatures associated with strata above and below it. Mean dips for the marker horizon and sulfate‐bearing strata are 1–5° with almost all azimuths radially away from the center of Mount Sharp. The marker horizon thickness varies between <1 and 3 m and its elevation changes by 1.6 km across the mound. Surface slopes along the sulfate‐bearing strata above and below the marker horizon are typically 20°–40° compared to <5° surface slopes on the marker horizon. Features observed on the marker horizon include ridges, fractures, faults, layering, oval depressions, small craters, and possible yardangs/indurated bedforms. We interpret the marker horizon to be a single unit that formed contemporaneously across Mount Sharp during the same depositional sequence that created the sulfate‐bearing strata. Plausible formation mechanisms for the marker horizon include (1) emplacement of a more indurated sulfate unit, either from (a) primary deposition or (b) secondary diagenesis; (2) deposition of a more resistant sandstone unit during a brief drier period; (3) emplacement of a volcanic ash deposit laid down in the midst of the sulfate formation period; or (4) a lag deposit created during a drier period. Based on our observations, origins (1a) and (3) are the most plausible.

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.

Introduction: Aeolis Mons (Fig. 1a) is a ~5 kmhigh stack of layered materials superposed on the floor and central peak of Gale crater (5.3°S, 137.8°E). Since landing in 2012, the Mars Science Laboratory (MSL) Curiosity rover is investigating the crater floor and the lower units of Aeolis Mons in the northwestern portion of Gale crater [e.g., 1]. However, studies of the remainder of Gale consists largely orbital identification of minerals such as hematite, monoand polyhydrated sulfates, Fe/Mg-phyllosilicates, and hydrated silica [e.g., 2–7]. These minerals indicate significant past aqueous activity under variable geochemical conditions. We are constructing a geologic map of the western portion of the Gale mound at 1:60K scale. The overarching goal of the project is to better understand the origin(s) of mound-forming and mound-draping layers. Coupled with the geomorphic mapping efforts, we correlate mapped units to Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) [4] near-infrared spectral data in order to assess the primary and secondary mineral budgets. The lower units of Gale are the subject of considerable interest because they capture a transition from an environment that appears to have favored phyllosilicatebearing layers to an environment that favored the deposition of sulfate-bearing layers [2,5,6]. More detailed mapping of this transition zone will reveal if the transition was one-sided and irreversible [e.g., 8,9], or if simultaneous or near-contemporaneous deposition of phyllosilicates and sulfate occurred [10]. We here present the results of geologic mapping in the southwestern region of Aeolis Mons, where geomorphic units are closely related to mineralogic detections, and can be mapped for significant distances around the mound. Methods: The geomorphic map has been created using traditional geomorphic mapping principles, but also informed by the addition of CRISM compositional data. The basemap was a 5 m/pixel Context Camera (CTX) mosaic; a ~25 cm/pixel HiRISE merged orthophoto mosaic [11] was also used for the northern part of the map region (Fig. 1). HRSC and HiRISE stereo-derived topography (post spacing 1 m and 50 m, respectively) were also utilized. Units contacts have been drawn throughout the map region. Different team members mapped in three different regions (Fig. 1); these contacts are being reconciled now. Unit descriptions are also ongoing. Figure 1. CTX mosaic of western Aeolis Mons overlain by darker HiRISE mosaic (upper center). Inner black box marks map region. Red diagonal lines mark the map areas of 3 team members, with contacts in yellow, green or pink. Some overlap was purposely mapped.

FUTURE EXPLORATION BY THE CURIOSITY ROVER. C. M. Weitz, J. L. Bishop, B. J. Thomson, K. D. Seelos, K. Lewis, I. Ettenborough, and R. E. Arvidson. Planetary Science Institute, 1700 East Fort Lowell, Tucson, AZ (weitz@psi.edu); SETI Institute, Carl Sagan Center, Mountain View, CA; Dept. of Earth and Planetary Sciences, Univ. Tennessee, Knoxville, TN; Planetary Exploration Group, JHU Applied Physics Laboratory, Laurel, MD; Dept Earth and Planetary Sciences, John Hopkins University, Baltimore, MD; Dept Earth and Planetary Sciences, Washington University, St. Louis, Missouri.

Introduction: Launched in 2005, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) [1] is an instrument that measures the composition of Mars’s surface and allows scientists to understand climate patterns that relate to the presence of water on the planet. Our effort consisted of assisting in ongoing mapping by validating and compositionally mapping using CRISM images in three unique areas: Northwest Noachis Terra (this work), Terra Sabaea, and Central Valles Marineris. Spectral analysis utilizing image analysis software of each regions of interest were compared with reference spectra in the MICA library [2], a compilation of the best CRISM end member mineral detections, in order to identify and label minerals in the regions of interest. Compositionally, the NW Noachis Terra region revealed large amounts of low calcium and high calcium pyroxene (LCP and HCP, respectively), magnesium smectite, and iron smectite. This concentration of minerals suggests an aqueous past, as smectite phyllosilicates generally form as a result of aqueous alteration. Methodology: CRISM can detect visible and infrared wavelengths ranging from 0.4 4 microns [1] and is sensitive to absorption features due to primary and secondary minerals. For this project we utilize CRISM “tiles”, 5 by 5 degree mosaics of ~200-m/pixel mapping-mode data (Fig. 1 upper). Absorption bands from mineral signatures are parametrized and derived RedGreen-Blue false color composites of these parameters are used to highlight where detectable minerals are present (Fig. 1 lower). A variety of programs were utilized in order to compare these parameter composites to observable surface features. Java Missionplanning and Analysis for Remote Sensing (JMARS) [3], a geospatial information system (GIS), was used to pinpoint areas of interest in the provided tiles by observing different RGB parameter composites. Once areas of interest were pinpointed, the Environment for Visualizing Images (ENVI) [4], a geospatial imaging program, was used to ratio spectra from these areas against other more spectrally-bland regions along the same image strip in the mosaic. These ratios were then plotted with the reference spectra of potential mineral matches from the MICA library for comparison (Fig. 2). By plotting these ratios, the spectrally-dominant component of each area of interest was able to be classified. The location of these mineral outcrops were then compared to the USGS Geologic Map of Mars (Fig. 3) [5], to determine the age of the units the materials formed in. Five tiles were analyzed in NW Noachis Terra (Fig. 1).

Mars Polar Science is an integrated, compelling system that serves as a nearby analogue to numerous other planets, supports human exploration, and habitability. Mars possesses the closest and most easily accessible layered ice deposits outside of Earth, and accessing those layers to read the climate record would be a triumph for planetary science.

Introduction: The “cryptic region” is a large area in the retreating southern seasonal cap of Mars that develops a low albedo, but retains the cold temperature of CO2 ice in equilibrium with the atmosphere [1]. Calvin et al. [2] observed the seasonal retreat in four Mars Years (MY 28 to 31) using MARCI and found the largescale boundary of this area was similar in all MY, with many small scale variations from year to year. Why the cryptic area occurs where it does and not throughout the retreating seasonal cap remains puzzling and not easily explained by elevation, deposition, or topography and may depend on subsurface or surface properties. While there have been a number of coordinated campaigns by MRO imaging and spectral instruments to observed small, localized regions as they evolve with season [3-8], we noticed several regional scale phenomena in MARCI mosaics at ~2 km/pixel that we wished to explore at higher spatial resolution using CTX (~6 m/pix) and CRISM (up to 18 m/pix). The hemisphere opposite the cryptic region (“anti-cryptic”) develops redder-hued material as compared to the classic low albedo cryptic region. Near the margins of the cryptic area there is a complex interplay of dark (presumably sand), red (dust), and retreating frost. MARCI data show clear defrosting of crater rims well within the seasonal cap boundary over Reynolds Crater (Figure 1).

Viviano, 1K. D. Seelos, 2M. S. Phillips, 3S. F. A. Cartwright, 4A. W. Beck, 1F. P. Seelos, 1S. L. Murchie, 5A. M. Dapremont, 1K. R. Frizzell, and 6,7I. B. Smith. 1Johns Hopkins University Applied Physics Laboratory , 2University of Tennessee, Knoxville, 3University of Nevada, Reno, 4Marietta College, 5Georgia Institute of Technology, 6York University, Toronto, 7Planetary Science Institute.