The Habitable Worlds Observatory (HWO) is a future NASA flagship mission concept identified by the Astro2020 Decadal Survey as the highest priority for large space missions. HWO should conduct "transformative astrophysics" and search for biosignatures in the atmospheres of approximately 25 potentially Earth-like planets. To further the early-stage development of HWO, NASA formed the Science, Technology, Architecture Review Team (START). In turn, START invited the scientific community to join working groups to explore the potential discovery space. In this paper, we present 70 science cases that resulted from this process. The cases address four scientific pillars: growth of galaxies (15 cases), evolution of the elements (13 cases), solar systems in context (32 cases), and living worlds (10 cases). Combined, they would address 27 of the 30 science questions and discovery areas identified by Astro2020. The 140 observing programs needed for the 70 investigations encompass a rich variety of spectroscopic (for 87

At JGR: Planets, the peer review process is critical to ensuring that the published articles are based on sound scientific principles, follow state‐of‐the‐art techniques while acknowledging relevant prior results, and present exciting discoveries or novel understanding of the fundamental processes that affect solar system objects. JGR: Planets covers a broad range of topics addressing every aspect of geoscience with the only requirement that the work addresses planetary processes. The wide breadth of topics published is reflected by our editorial team composed in 2024 of associate editors Adrian Brown, Jun Cui, Joel Davis, Leigh Fletcher, Sierra Ferguson, Yang Liu, Ananya Mallik, Germán Martínez, Anna Mittelholz, Molly McCanta, Katarina Miljkovic, Naomi Murdoch, Ryan Park, Arianna Piccialli, Laura Schaefer, Mariek Schmidt, Yasuhito Sekine, Kelsi Singer, Michael Sori, Norihiko Sugimoto, Jamey Szalay, David Trang, and Zhiyong Xiao in addition to the editors who authored this note. We rely on the expertise of the community to vet the articles submitted to the journal. In 2024, JGR: Planets benefited from 1,269 reviews provided by 816 unique volunteer referees. We also received help from organizers and guest editors working on eight active special collections. To these volunteers: We are truly grateful that you chose to dedicate your time and energy to evaluate manuscripts and to advise us on the suitability of each manuscript for JGR: Planets, often suggesting ways to improve the papers. We know that all our volunteers juggle many duties, both professional and personal. On behalf of the entire editorial board of JGR: Planets, we express our heartfelt gratitude to the many scientists who support this journal. Thank you! You are performing a valued service to this journal and to the community.

We review the current state of understanding of Ceres as it relates to planetary protection policy for future landed missions, including for sample return, to the dwarf planet. The Dawn mission found Ceres to be an intriguing target for a mission, with evidence for the presence of regional, possibly extensive liquid at depth, and local expressions of recent and potentially ongoing activity. The Dawn mission also found a high abundance of carbon in the regolith, interpreted as a mix of carbonates and amorphous carbon, as well as locally high concentrations of organic matter. Key findings from this review are as follows: (1) outside of the region of Occator crater, Ceres shows no geological evidence for conduits from the surface to the interior; and (2) considering the biological potential of Ceres' deep interior, a surface sample return mission should be considered Category V restricted, unless it can be demonstrated that evaporites sourced from Ceres' deep brine region, and recently exposed in Occator crater, have not been scattered to the rest of Ceres' surface; in that case, the probability of returning an unsterilized particle to an acceptably low value is to be determined by a future study.

A strategy for planetary exploration using a rover capable of science autonomy is presented. We encoded into a rover a set of driving hypotheses pertaining to the geologic origin of a field site and equipped the rover with the instrumentation needed to measure the observables related to the hypotheses, as well as the software tools to analyze them to a relatively high level of confidence. We investigated the effects of different exploration strategies that make use of rover science autonomy and compared the operational efficiency and science yield of three geological exploration scenarios: (1) standard human-directed exploration, (2) rover-directed exploration, and (3) astronaut/rover collaborative exploration. We show that exploration with a rover capable of science autonomy is operationally more efficient than the human-directed strategy, resulting in higher rates of data collection and hence a greater science yield per command cycle. Additionally, we explored and developed astronaut/rover collaborative exploration strategies and present a basic framework for effective planetary exploration that leverages the expertise of a science team, the efficiency of a science-autonomous rover, and the contextual abilities of astronauts.

In JGR-Planets, the peer review process is critical to ensuring that the published articles are based on sound scientific principles, follow state-of-the-art techniques while acknowledging relevant prior results, and present exciting discoveries or novel understanding of the fundamental processes that affect solar system objects. JGR-Planets covers a broad range of topics addressing every aspect of geoscience with the only requirement that the work addresses planetary processes. The wide breadth of topics published is reflected by our editorial team composed in 2023 of associate editors Adrian Brown, Jun Cui, Joel Davis, Leigh Fletcher, Matthias Grott, Ananya Mallik, Germ & aacute;n Mart & iacute;nez, Molly McCanta, Katarina Miljkovic, Naomi Murdoch, Ryan Park, Arianna Piccialli, Andrew Poppe, Beatrix S & aacute;nchez-Cano, Laura Schaefer, Mariek Schmidt, Yasuhito Sekine, Kelsi Singer, Michael Sori, Norihiko Sugimoto, Sonia Tikoo, David Trang, and Zhiyong Xiao in addition to the editors who authored this note. We rely on the expertise of the community to vet the articles submitted to the journal. In 2023, JGR-Planets benefited from 1,184 reviews provided by 731 unique volunteer referees. We also received help from 19 guest editors working on four active special collections. To these volunteers: We are truly grateful that you chose to dedicate your time and energy to evaluate manuscripts and to advise us on the suitability of each manuscript for JGR-Planets, often suggesting ways to improve the papers. We know that all our volunteers juggle many duties, both professional and personal. On behalf of the entire editorial board of JGR-Planets, we express our heartfelt gratitude to the many scientists who support this journal. Thank you! You are performing a valued service to this journal and to the community.

OSIRIS-REx is a sample return mission to near-Earth Asteroid (101955) Bennu (Lauretta et al. 2017). The asteroid is spectrally classified as a B-type (Clark et al. 2011), and phyllosilicates similar to those found in carbonaceous chondrites have been detected on its surface (Hamilton et al. 2019). Bennu has a relatively flat (and blue) reflectance spectrum in the 0.4 to 3.7 micron spectral range and has a low albedo of ~4.5% (Golish et al. 2020).Bennu has a rough and rocky surface. Imaging data from the OSIRIS-REx Camera Suite (OCAMS; Rizk et al. 2018) reveals that boulders in the size range from 1 to 10 meters dominate the surface (Lauretta et al. 2019; DellaGiustina and Emery et al. 2019). Observed boulder textures range from smooth to hummocky and breccia-like (Walsh et al. 2019; DellaGiustina and Emery et al. 2019). The smoother rocks appear to be smaller, brighter, and more angular, while the rougher rocks appear to be larger, darker, and highly textured. Because spectral variations on Bennu are subtle and associated with albedo (Clark et al. 2019), the question arises: Could the observed color variations be due to texture variations alone, or are space-weathering variations required to explain the observations? To isolate the spectral effects of texture on the spectral properties of Bennu, we first simulate Bennu’s spectrum using a two-component mixture, then we check to see whether texture changes in this analog can account for the observed color and albedo trends. Simulated Bennu Spectral Analog: We synthesized physical mixtures of saponite (SAP105 with ~25 wt.% dolomite) with two forms of carbon:

A system for rapid analysis of spectroscopy data with emphasis on planetary surfaces, both imaging and single-spectrum data, is described. The system, called Tetracorder, is commanded by an expert system developed by expert spectroscopists. The Tetracorder and the expert system apply multiple algorithms to analyze a spectrum in segments, leveraging the advantages of each spectral region’s sensitivity to detecting different compounds, whether solid, liquid, or gas. The algorithms compare measured spectra to the spectral properties of materials in spectral libraries. The libraries include pure minerals, mineral mixtures that include areal mixtures, intimate mixtures, coatings, and molecular mixtures and other compounds such as organics, vegetation, liquids, and gases. Absorption bands of a particulate surface change shape with grain size, and shape changes are used in some cases to constrain grain size of each component in the surface. The different algorithm results are compared for each spectral region, and specific material composition and average grain size (when possible) are identified. The system is operational analyzing real-time data on a new generation of rovers for future planetary missions, as well as identifying materials using an imaging spectrometer on the International Space Station. Four abundance models are presented, each with increasing sophistication, that are computationally fast on imaging spectrometer data and use Tetracorder identifications to produce maps of mineral abundances. A fifth full radiative model that includes multilayer surfaces is presented but is computationally intensive. The system is open source and available on GitHub.

The Moon Mineralogy Mapper (M-3) on the Chandrayaan-1 spacecraft provided nearly global 0.5-3 mu m imaging-spectroscopy data at 140 m pixel-1 in 85 spectral bands. Targeted locations were imaged at 70 m pixel-1 and higher spectral resolution. These data enable a detailed look at the mineralogy, hydroxyl, and water signatures exposed on the lunar surface. We find evidence for multiple processes, including probable solar wind implantation, excavation of hydroxyl-poor and water-poor material in cratering events, excavation of hydroxyl and water-rich materials from depth and global trends with rock type and latitude. Some water-rich areas display sharp boundaries with water-poor rocks but have a diffuse halo of hydroxyl surrounding the water-rich rocks indicating a weathering process of destruction of water, probably due to a regolith gardening process. Mapping for specific mineralogy shows evidence for absorptions near 2.2 mu m, probably associated with smectites, and near 1.9 mu m due to water. Lunar swirls are confirmed to be OH-poor, but we also find evidence that swirls are water-poor based on a weak 1.9 mu m water band. Some swirls show enhanced pyroxene absorption. "Diurnal" signatures are found with stable minerals. Pyroxene is shown to exhibit strong band depth changes with the diurnal cycle, which directly tracks the solar incidence angle and is consistent with changing composition and/or grain size with depth. Mapping of M-3 data for the presence of iron oxides (e.g., hematite and goethite) is found to be a false signature in the M-3 data due to scattered light in the instrument.

The study of solar system bodies in the ultraviolet is often the study of extended sources, including vapor plumes, atmospheres, cometary tails, and planetary surfaces. These objects are traditionally studied with long-slit spectrographs that can sample one dimension of spatial information at a time - providing a cross section of the object in question. The Ultraviolet Micromirror Imaging Spectrograph (UMIS) is a new instrument concept that will bring integral-field spectroscopy to the field for the first time, effectively creating a two-dimensional image of the source at every wavelength in the spectral bandpass simultaneously. UMIS is designed around the concept of an image slicer, where a set of angled mirrors at the telescope focal plane dissect the image into sub-regions which are aligned to avoid overlap of spectra on the detector. Unlike conventional image slicers, however, UMIS employs a reconfigurable micromirror array at the focal plane instead of a fixed mirror slicer array. The UMIS micromirror array, provided by Bright Silicon Technologies, consists of 20 x 20 individual mirrors, each actuatable to any angle up to 15 degrees. This new concept overcomes the limitations of a conventional image slicer by enabling the sampling of various sized regions matched to different targets and spectral resolution requirements within a large field-of-view. This proceedings presents the UMIS optical design, concept and development schedule. UMIS is a collaboration of the Planetary Science Institute, The University of Colorado, Boulder, and BAE Systems (formerly Ball Aerospace).

Bombardment by solar wind ions is one of the main drivers of space weathering on airless bodies. Here, we simulate the solar-wind-driven spectral alteration of loosely packed olivine powders by irradiation with 1.2 keV helium ions (He+). We measured the reflectance spectra of the olivine powder in the ultraviolet-visible-near-infrared (UV-Vis-NIR) wavelength range (0.2-2 mu m) as a function of ion fluence. In the Vis-NIR range, we observed spectral darkening, absorption band shallowing, and spectral reddening, in agreement with lunar-style space weathering and previous laboratory studies. In the UV-Vis, spectral darkening was also observed. However, a spectral bluing took place at wavelengths below 400 nm. As the simulated space weathering progressed, the spectral slopes shifted from steep-UV/shallow-NIR slopes to shallow-UV/steep-NIR slopes. Moreover, the change in the UV slope was almost 10 times larger than in the NIR, supporting the hypothesis that the UV spectral slope could be an earlier indicator of space weathering.

This paper presents far-ultraviolet through mid-infrared (0.12–20 μ m) reflectance spectra of 27 fine-particulate (<10 μ m) terrestrial mineral samples, providing continuous spectra that cover an unusually broad spectral range and are of unusually fine particle size relative to most existing spectral libraries. These spectra of common geologic materials are useful for future applications that study the dust on various planetary bodies. Reflectance spectra were acquired of the samples at multiple laboratories at multiple wavelengths. All of the spectra were compared to one another to observe the general, common spectral characteristics (e.g., slope, band shape, and band depth), and the best segments of the spectra representing the mineral reflectance were scaled and spliced together to form a “Frankenspectrum” for each mineral that best represents the full wavelength range of far-ultraviolet, visible, near-infrared, and middle-infrared wavelengths. These scaled and spliced Frankenspectra, as well as the entire set of individual “original” reflectance spectra from each laboratory, are available in the Planetary Data System Geosciences Node.

Here we review the origin, evolution, and compositional properties of Saturn’s ring moons. This class of eleven small satellites includes objects orbiting near the outer edge of the main rings (Pan, Daphnis, Atlas, Prometheus, Pandora, Janus, Epimetheus) and “ring-embedded” moons (Aegeon, Methone, Anthe, Pallene) orbiting inward of Enceladus and associated with either diffuse or partial rings. We discuss current formation scenarios, according to which ring moons could originate either in the main rings from accretion onto original seeds denser than the ring material, or outside the A ring from spontaneous accretion of ring particles, and then evolve outwards due to gravitational torque from the rings. Remote sensing observations of the ring moons from the Cassini mission are analyzed in the broader context of Saturn’s icy moons and main rings observations. Spectroscopic data support a compositional paradigm similar to the main rings, dominated by water ice, and smaller amounts of two separate contaminants, in the form of a UV absorber and a spectrally neutral darkening material. Global radial trends in the spectral properties of the ring moons suggest that the surface composition is significantly affected by a complex interplay of exogenous processes, among which the contamination from nearby A ring particles, meteoritic bombardment, charged particle flux, and E ring particle accumulation, depending on the corresponding magnitude at the ring moon orbital distance and exposure time. These processes modify the original composition inherited by the rings and, coupled with the fact that the surface composition is likely representative only of the ring moon outer layers, make it difficult to trace back the present composition to a given ring moon formation scenario.

The origin and evolution of Saturn's rings is critical to understanding the Saturnian system as a whole. Here, we discuss the physical and chemical composition of the rings, as a foundation for evolutionary models described in subsequent chapters. We review the physical characteristics of the main rings, and summarize current constraints on their chemical composition. Radial trends are observed in temperature and to a limited extent in particle size distribution, with the C ring exhibiting higher temperatures and a larger population of small particles. The C ring also shows evidence for the greatest abundance of silicate material, perhaps indicative of formation from a rocky body. The C ring and Cassini Division have lower optical depths than the A and B rings, which contributes to the higher abundance of the exogenous neutral absorber in these regions. Overall, the main ring composition is strongly dominated by water ice, with minor silicate, UV absorber, and neutral absorber components. Sampling of the innermost D ring during Cassini's Grand Finale provides a new set of in situ constraints on the ring composition, and we explore ongoing work to understand the linkages between the main rings and the D ring. The D ring material is organic- and silicate-rich and water-poor relative to the main rings, with a large population of small grains. This composition may be explained in part by volatile losses in the D ring, and current constraints suggest some degree of fractionation rather than sampling of the bulk D ring material.

Visible/near-infrared narrowband spectroscopy (dispersion per element ∼ 6 Å) was obtained of the Jovian irregular satellites JVI Himalia, JVII Elara, JVIII Pasiphae, JIX Sinope, JX Lysithea, JXI Carme, JXII Ananke, and JXVII Callirrhoe in 2006, 2009, and 2010 using the MMT Observatory Red Channel spectrograph. These spectra sample three prograde ( i = 28°), four retrograde ( i = 149° and 165°), and one independent satellite. Our results suggest that the prograde cluster satellites represent fragments probing the cluster’s original parent body, with the largest satellite, Himalia, being the core of the parent body, while Elara preserves the geochemical/mineralogical transition between the core and an outer layer of the body, and Lysithea formed farther from the center of the parent body. The spectral signatures suggest that the prograde parent body fragmented in the early stages of aqueous alteration. This supports the change from more organic-rich material at Lysithea to more carbonized material at Himalia, consistent with weathering/processing of a carbon-bearing material at Himalia. At twice the distance from Jupiter, the retrograde cluster anchored by Pasiphae also suggests that Ananke preserves the transition between the core and an outer layer of a parent body. Both Sinope and Carme are similar to D-class asteroids. Bluing/flattening near 0.4–0.5 μ m in Carme’s spectrum suggests a carbonized component to Carme’s surface material, consistent with greater levels of weathering/processing. Sinope’s red spectrum is consistent with broadband photometry and does not confirm or negate the proposal that it had a common parent body with the Pasiphae cluster.

NASA’s Europa Clipper mission is designed to provide a diversity of measurements to further our understanding of the potential habitability of this intriguing ocean world. The Europa mission’s Ultraviolet Spectrograph (Europa-UVS), built at the Southwest Research Institute (SwRI), is primarily a “plume finder” and tenuous atmosphere investigation. The science objectives of Europa-UVS are to: 1) Search for and characterize any current activity, notably plumes; and 2) Characterize the composition and sources of volatiles to identify the signatures of non-ice materials, including organic compounds, in the atmosphere and local space environment. Europa-UVS observes photons in the 55–206 nm wavelength range at moderate spectral and spatial resolution along a 7.5° slit composed of 7.3°×0.1° and 0.2°×0.2° contiguous sections. A variety of observational techniques including nadir pushbroom imaging, disk scans, stellar and solar occultations, Jupiter transit observations, and neutral cloud/plasma torus stares are employed to perform a comprehensive study of Europa’s atmosphere, plumes, surface, and local space environment. This paper describes the Europa-UVS investigation’s science plans, instrument details, concept of operations, and data formats in the context of the Europa Clipper mission’s primary habitability assessment goals.

Nighttime Lyman Alpha Mapping Project (LAMP) observations are used to investigate condensed volatiles at the south polar region of the Moon. This study incorporates LAMP data from the first ∼7 years of the mission and Diviner annual maximum temperatures to search for volatile signatures associated with H 2 O, NH 3 , and CO 2 . Other stable potential species, for example, SO 2 and H 2 S, are not identifiable with the ultraviolet ratio‐temperature techniques and are not directly addressed in this study. We confidently detect a ∼20% increase in normalized Off‐band (175–190 nm) to On‐band (148–162 nm) albedo ratios (consistent with condensed surface volatiles) at temperatures below ∼115 K. Elevated normalized ratios extend to temperatures capable of supporting pure aforementioned ices over geologically long time scales. Although ∼115 K is consistent with H 2 O lifetimes of ∼1‐Myr, the presence of CO 2 and NH 3 are not uniquely delineated by the data trends with temperature. Future spectral modeling to appropriately identify the composition and abundance of these condensed volatiles remains necessary. Normalized albedo ratios are further analyzed for candidate species via maximum temperatures to inform the likelihood of ice signatures: H 2 O (70 K < T ≤ 115 K), NH 3 + H 2 O (60 K < T ≤ 70 K), and CO 2 + NH 3 + H 2 O ( T ≤ 60 K). We compare normalized albedo ratios across seven regions of interest (ROI), including Faustini, Shoemaker, Haworth, Cabeus, Amundsen, Nobile, and an unnamed region. Such comparisons allow for characterization of relative abundances of volatiles across the ROI important for their utilization in future crewed and robotic missions to the Moon.

We outline specific steps that NASA and the space science community can take to advance collaboration and coordination between the communities represented by the four NASA Science Mission Directorate Divisions. It is important to note that the only way that this effort can succeed is if NASA initiates and supports it through directed resources.

The bolometric Bond albedo is a fundamental parameter of planets and moons. Here, combined observations from the Cassini spacecraft and the Hubble Space Telescope are used to determine the bolometric Bond albedo of Enceladus. We provide the full-disk reflectance of Enceladus across all phase angles (0 degrees -180 degrees) from 150 nm to 5131 nm, a spectral range that accounts for nearly all incoming solar power. Considering the distribution of the monochromatic Bond albedo over wavelength, we find a value of 0.76 +/- 0.03 for Enceladus' bolometric Bond albedo. The corresponding optical characteristics (e.g., geometric albedo and phase function), which are closely related to Enceladus' surface properties, are also investigated. The wavelength-dependent nature of Enceladus' Bond albedo suggests that the bolometric Bond albedos of other icy moons, if they are mainly determined by the visible observations only, should be carefully considered. Our new measurements of bolometric Bond albedo can be used to better determine the radiant energy budget of Enceladus and further constrain the internal heat flow, a critical driving force for the water plumes on Enceladus.

Samples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed 17 Ryugu samples measuring 1 to 8 millimeters. Carbon dioxide-bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu's parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and calcium- and aluminum-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed through aqueous alteration reactions at low temperature, high pH, and water/rock ratios of <1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate that Ryugu's parent body formed ~2 million years after the beginning of Solar System formation.