We have built a prototype instrument of the Small All-range LIdar (SALI) for altimetric mapping of planetary bodies and real-time measurements of spacecraft altitude during touchdown or landing. SALI uses a return-to-zero pseudo-noise (RZPN) code laser modulation, which enables the use of optical fiber laser amplifiers for long-distance range measurement. The receiver uses a 2 & times;8 pixel HgCdTe avalanche photodiode (APD) array in linear single-photon detection mode to give the highest receiver sensitivity at the infrared laser wavelength. The receiver measures the laser pulse time-of-flight and target reflectance by correlating the received signal with a patented three-state RZPN kernel. A field programable gate array processes the signal in real time at up to 120-Hz measurement rate for eight independent receiver channels. The laser output power, the APD gain, and the receiver integration time are all programable in orbit. The instrument can range continuously to planetary surfaces from >100-km orbit altitude to <1 m during descent and sample collection or landing. SALI uses electro-optic components from the terrestrial optic communications industry and can be built at a fraction of the cost of conventional planetary LiDARs. SALI is also modular and can use different fiber lasers and detectors at different wavelengths and modified receiver optics to best fit the specific mission requirements. The prototype instrument is 31 & times;30 & times;11 cm in size, <60 W in electrical power, and 9.2 kg in mass. A vibration and a partial thermal-vacuum test have been conducted. The measured ranging performance is close to the predictions given in our earlier publications. We described the detailed instrument design and the test results.

The lunar polar regions are high-priority targets for scientific investigation and exploration. To aid these endeavors, we produced enhanced altimetry data from the Lunar Orbiter Laser Altimeter for the north polar region, from which we computed new maps of surface height and slope as well as topographic roughness on horizontal baselines of 100–1600 m. We also produced a new map of permanently shadowed regions (PSRs) that contains fewer artifacts and is higher resolution than previous maps. These new maps were then compared to an analogous set previously produced for the south polar region. Generally, in both polar regions, more steeply sloped terrain is rougher at baselines ≲200 m and has a bluer roughness spectrum, a behavior hypothesized to be due to downslope mass transport. Roughness in the polar regions is also correlated with regolith temperature, and we discuss several possible causes including surface ice in unresolved cold traps, subsurface ice outside cold traps, and changes in the regolith’s geotechnical properties. In the north, there are more PSRs with areas ∼0.1–1.0 km ^2 and fewer with areas >100 km ^2 , which may be due to the north having a higher number of craters with diameters of hundreds of meters to ∼3 km. The new maps presented here have many applications in the scientific study and exploration of the lunar north polar region, such as geologic mapping, modeling of cold traps, landing-site characterization, traverse planning, and the interpretation of in situ and remote-sensing data.

Numerous space agencies are planning sustainable human presence at the lunar south pole. Understanding the nature of the lunar crust, particularly its three-dimensional density structure, is important, for example, for the search for water ice predicted to be present. The paucity of in situ measurements requires that we exploit the knowledge obtained through orbital measurements. Two data sets, gravity and topography, in combination with local geology, can provide constraints on the density of the crust. We analyzed the radial component of the gravity field to determine the density of the crust, which we relate to depth using a point-mass spherical harmonic approach. Our investigation provides estimates of density and density gradient at 20 sites in the south polar region: the original 13 Artemis sites, 5 permanently shadowed regions (PSRs), the south pole, and a site on the floor of the Amundsen crater. We find that the mean density in the top 2–10 km for the six PSRs (2475 ± 108 kg m ^−3 ) is comparable to that (2483 ± 147 kg m ^−3 ) for the 14 non-PSRs. The weighted mean gradient for the five PSRs and the Amundsen floor is 3 times greater than that for the 14 non-PSRs in the 2–4 km depth range; the average density increases with depth at 25 kg m ^−3 km ^−1 . To investigate whether a relationship exists between inferred areal coverage of ice and our density results, we compared densities with results for reflectance in several common PSR localities. We find lower densities and higher gradients for areas characterized by greater areal coverage of ice.

We report on the design, measurement capabilities, and measured performance of a new Small All-range LIdar (SALI). The lidar transmitter uses a 1.55-mu m Erbium-Doped Fiber-Amplifier (EDFA) laser modulated with a return-to-zero pseudo-noise (RZPN) code. The receiver uses a 2x8-pixel HgCdTe avalanche photodiode (APD) array in linear single photon detection mode of operation. The receiver electronics calculate the target range by correlating the received signal with a patented 3-state RZPN kernel. A field programmable gate array (FPGA) processes the signal in real time up to a 120 Hz measurement rate for eight parallel receiver channels. The output power of the fiber laser, the detector gain, and the receiver integration time are all adjustable so that it can measure planetary surface at range from more than 100 kilometers down to a fraction of a meter without saturation. SALI is primarily designed for mapping planetary bodies from orbit but can also be used as a guidance sensor for sample collection or landing. The instrument uses all standard components from the fiber optic communications industry except for the detector and it can be built at a much lower cost compared to previous planetary lidars. SALI is also modular and can use different lasers and detectors at different wavelengths and different receiver telescope sizes to best fit the specific mission requirements. We have recently completed the instrument integration and performed function and performance testing. The measured performance is close to the prediction given in our earlier publications. We will soon conduct a vibration and thermal-vacuum tests to demonstrate its readiness for use in a space mission.

The results of geomorphological mapping and survey of Lateglacial and Holocene displaced shorelines in the Clyde estuary and around Loch Lomond, western central Scotland are described. On the basis of morphology, sedimentology, altitude and radiocarbon dating, four discrete shorelines are identified and are correlated with previously identified Scottish displaced shorelines. The shoreline formerly referred to as the Main Postglacial Shoreline is renamed the Menteith Shoreline. This body of data, combined with data on displaced shorelines for Scotland as a whole has been analysed using Gaussian quadratic trend surface analysis in order to determine the centre of glacio‐isostatic displacement for each shoreline. These Gaussian models of palaeo‐relative sea‐level suggest that the zone of greatest displacement lay NNW of Loch Lomond in the Lateglacial then moved SSE to the region of Loch Lomond during the Holocene and the Clyde in the Late Holocene. The factors responsible for the movement of the zone of greatest uplift are discussed, including temporal variations in the ice‐sheet thickness, variations in water load in the adjacent sea‐lochs and neotectonic processes. Comparison is made with glacial isostatic adjustment (GIA) models. A sensitivity analysis has been carried out on the use of Gaussian trend surface analysis glacio‐isostatic modelling and this is included in the research evaluation, and reported in full in the Supporting Information files, along with the raw data used throughout this study.

Based on previous applications of laser altimetry to planetary geodesy at GSFC [Mazarico et al. (2014)], we use the recently developed PyXover software package to analyze altimetric crossovers from the Mercury Laser Altimeter (MLA) and improve geodetic parameters via least squares (LS) minimization of crossover discrepancies.We simultaneously solve for orbital corrections for each MESSENGER track, for the geodetic parameters of the IAU recommended orientation model for Mercury [Archinal et al, 2018], and for the Mercury Love number h2.We calibrate the formal errors of our solution based on closed-loop simulations and on the level of independence from \emph{a priori values and data selection.Data description:From March 2011 to April 2015, the MESSENGER spacecraft orbited Mercury in a highly elliptical, near-polar orbit with a periapsis of ~200-400 km, an apoapsis between ~1.5-2 x 10^4 km, and an orbital period of 12 hrs initially and reduced to 8 hrs after one year. The spacecraft was within ranging distance for the onboard MLA over 15-45 min periods near periapsis, typically at latitudes > 30 deg N.MLA collected over 22 million measurements of surface height with a vertical precision of ~1 m and an accuracy of ~10 m. The total MLA dataset contains ~3,200 tracks and ~3 million crossovers, i.e., instances where two ground-tracks intersect. Because of the elliptical orbit, the laser spot size on the surface varied between ~10 - 100 m, while the average distance between each crossover and its bracketing observations was ~200 m.These crossovers provide an opportunity to measure Mercury’s orientation and rotation (see Fig.1).Independent confirmation and refinement of the IAU libration model, developed from ground-based radar measurements [Margot et al. 2009], is important as it has implications for the moment of inertia of the outer solid shell and thus the mass distribution, internal structure, and thermal evolution of Mercury [Phillips et al. (2018), Genova et al. (2019)].Processing and solution strategy:Each crossover is the intersection of two separate ground-tracks. It can be thought of as a differential measurement between two distinct observations of the same surface location at two different times. Any difference in height at the crossover point is mainly due to the following effects: (1) Errors in the spacecraft orbit and attitude, or MLA boresight orientation, (2) interpolation errors of the surface topography between MLA footprints, and (3) geophysical signal due, e.g., to mismodeled time-varying planetary rotation or to tidal vertical motions.We perform the analysis of MLA data with the PyXover python code, whose modular structure is sketched in Fig.2.Laser altimetry ranges are geolocated to the planetary surface and partial derivatives of the ground-tracks are computed with respect to the chosen parameters by finite differencing. Initial geolocation is based on the MESSENGER orbit navigation reconstruction by KinetX and on the values provided by the IAU for Mercury orientation [Archinal et al, 2018]. Values for the Love numbers h2 and l2 are set to 0 in our a priori tidal model.Horizontal coordinates of crossover points are recovered in local stereographic projection in a two-step process, to balance computational time.Expected elevations at intersection points are then interpolated from neighbouring points on each track. Their discrepancies w constitute the observation residuals to be minimized in the LS procedure.Huber weighting is then applied to the crossovers depending on the reliability of the orbital tracks involved, on the off-nadir angle of the spacecraft and on inter-point distances. Crossovers with abnormally large discrepancies are strongly down-weighted in our analysis. We minimize the total RMSE of crossover discrepancies within a penalised LS with weights determined by Variance Component Estimation (VCE). The resulting corrections to MESSENGER orbits and Mercury geodetic parameters are then applied to update the a priori for the subsequent iteration, until convergence is reached.Parametrization and error assessment:Formal errors provided by LS and VCE are notoriously under-estimated. We thus perform additional analysis to consider systematic error sources, such as the chosen apriori values and data selection. In particular, we measure the stability of the solutions resulting from different Doppler reconstructions of MESSENGER orbits (KinetX and [Genova et al, 2018]) and from both IAU [Archinal et al, 2018] and [Genova et al, 2019] values for Mercury rotational parameters. Also, we process multiple sub-samples of 500,000 crossovers (max 20% in common, stratified by latitude to conserve the overall geographical distribution) and we verify the dispersion of the solutions at convergence.Moreover, we conduct extensive simulations with time-of-flight ranges consistently generated from realistic topography to analyze the impact of the interpolation error and the reliability of the recovery in different scenarios and parametrizations. Processing of MLA crossovers:Finally, we perform a weighted LS solution of orbit corrections and geodetic parameters based on the presented processing setup.We base our solution on a set of 106 crossovers selected according to their computed weight (i.e., their quality) and to ensure a balanced geographical distribution. We iterate the solution until convergence is reached, i.e., parameters changes are well below formal errors (

Examining the reflectance of the Moon's surface across a broad range of viewing geometries through photometric analysis can reveal physical and geological properties of its regolith. Since 2013 December, the Lunar Orbiter Laser Altimeter (LOLA) on board the Lunar Reconnaissance Orbiter (LRO) has been operating as a near-infrared (1064 nm) passive radiometer when its laser is turned off. We present a new analysis of this data set spanning roughly 8 yr and covering the surface up to high latitudes in both hemispheres. We apply semiempirical phase functions to find a lower photometric slope and a narrower opposition effect for the highlands than the maria, consistent with theoretical expectations given the higher albedo of the highlands. Examining various geological properties at global scales shows that, in the highlands, iron abundance (FeO) and optical maturity (OMAT) are the dominant factors affecting the phase function, with a smaller influence from surface slope. In the maria, FeO is the dominant factor, with smaller influences from OMAT, surface slope, and TiO2. Submicroscopic iron abundance (SMFe) has a similar effect to OMAT in both highlands and maria. Analysis at specific sites, including the Reiner Gamma swirl and several silicic anomalies, indicates that the phase functions are consistent with the global data for similar FeO and OMAT. Thermophysical properties inferred from surface temperature observations by the Diviner Lunar Radiometer Experiment on board LRO do not affect the 1064 nm phase function, possibly due to a difference between their depth scale and LOLA's sensing depth.

Introduction: The Here to Observe (H2O) program was established in 2021 to pair mission teams with institutions with large populations of underrepresented and historically marginalized students, to provide an opportunity for participants in the program an insider’s view of how NASA missions operate, as well as one-on-one mentorship of the students by science team members [1]. By pairing a mission team directly with faculty and student leads, the goal was to co-create a program that is tailored to the students’ needs, schedules, and interests, without adding significant additional burden to the mission’s science team. For the initial pilot program, the Europa Clipper team was paired with the University of Puerto Rico. With the formal announcement of the program in ROSES, Europa Clipper is now paired with a partnership between the Ohio Space Grant and Puerto Rico Space Grant Consortia.H2O Program History: The initial concept of inviting students to observe a science team meeting was piloted in 2020, when graduate students were invited to submit short statements of interest and several missions agreed to invite them to attend a virtual science team meeting. This initial pilot has mixed success, as there was little time for engagement before the meetings, and students who were not already familiar with mission work had little frame of reference to understand a lot of the jargon and technical details that they observed.Based on feedback from this process, NASA initiated a formal pilot program in 2021, championed by David Smith. The pilot aimed to co-create the program with specific institutions, specifically targeting those without active involvement with NASA missions. Unlike the initial formulation, in this pilot, the goal was to pair undergraduate, rather than graduate, students with mentors from missions. Although faculty contacts were involved, the university side of project was spearheaded by student leaders, who helped coordinate the student teams and provide input on how to tailor program activities to meet students’ needs and interests. On the mission side, the goal was to provide a welcoming environment and direct interactions with scientists, but, importantly, to be non-intrusive to mission activities.Three mission teams agreed to participate in the formal pilot: Europa Clipper, Dragonfly, and Lucy, and their university partners were the University of Puerto Rico, Virginia State University, and Howard University. For this pilot, teams worked to design a school-year-long program that would provide background sessions to prepare the students before the science team observing opportunities, and, ideally, also provide additional opportunities to the students to sit in on mission activities throughout the year.Europa Clipper H2O Pilot Results: The H2O cohort in Puerto Rico was initially led by two students, Jorge Y. Coppin-Massanet and Andrea Ortiz-Cana. With contacts at the university and within the Puerto Rico Space Grant, student applications were solicited, with over 100 student applications received each year. The student leaders worked to down-select to 10 students, plus alternates, in case students became overburdened and needed to withdraw from the program. Likewise, the list of mission mentors included backup mentors, to ensure that each student would have a mentor, even if their assigned mentor was no longer able to support meetings.Mentors and students were asked to expect to meet one-on-one for ~1 hour per month, and students were also provided one organized event per month, as well. In addition, science-team-wide activities, including monthly mission updates as well as a bi-weekly lecture series, which is often focused on discussing science topics, were made open to students, whenever possible. The organized events each month included open discussions with team members, a career panel in Spanish, introductory presentations about NASA missions as well as the Europa Clipper mission.Each year, two students from the past year stepped into the role as student leads, providing continuity and experience as the team worked to improve the program. The program was very successful, largely in part to the hard work and dedication of the original student leaders, who remained involved in an advisory capacity throughout the program.Local Engagement: In 2023, the decision was made by the Clipper Project to host a Europa Clipper science team meeting in San Juan, Puerto Rico, to provide an opportunity for students and alumni of the H2O program to meet the scientists they had interacted with in person (Fig. 1). The team worked with the contacts at the University of Puerto Rico and Puerto Rico Space Grant to design and run a number of public engagement activities, which were attended by hundreds of students from middle school through university (Fig. 2).Further Evolution of the H2O Program: Beginning in 2023, the H2O program was formalized in the NASA ROSES call, with applicants funded to support student involvement. The new program, described in detail in [1], includes additional infrastructure for mentoring, formal program evaluation, and mission advocate support. Students are also provided self-guided modules with additional background information about planetary exploration. NASA is committed to the success of this program, and supportive of additional mission involvement.Europa Clipper is currently officially partnered with both the Ohio and Puerto Rico Space Grant Consortia, with six students participating from each consortium. Activities are similar to those offered in the past, but with the goal of at least one visit to each home institution. The team looks forward to interacting with students from both regions, to share the excitement of Europa exploration. Acknowledgments: We are grateful to NASA and Europa Clipper for enduring support of the H2O program. References: [1] D. Smith et al. (2024), Updates from Planetary Science Division’s Here to Observe (H2O) Program. LPSC 55th, this volume.

Abstract The formation and evolution of the South Pole‐Aitken (SPA) basin is critical to relating large impact basin formation and modification to lunar geophysical evolution. Most prior models of the SPA impact were conducted in 2D, making it difficult to compare model output to the 3D crustal structure and ejecta distribution. In order to better constrain the parameters of the SPA impactor and the expected post impact distribution of crust and ejecta, we conducted numerical simulations of the SPA impact in 3D. We tested a wide range of impact parameters and constrained model results with recent geophysical data. We found the crustal structure of the SPA basin is best fit by an oblique impact (30–45°) of a 350–400 km diameter projectile impacting at 12–16 km/s. The impact excavated material from as deep as 80–120 km, and ejecta was deposited in a butterfly pattern with a forbidden region uprange of the impact.

The lunar gravity field is used to estimate and constrain the depth of mass anomalies under 19 major lunar impact basins. We use radial gravitational spectra, consisting of accelerations computed either per spherical harmonic degree or cumulatively, at surface locations to obtain the distribution of the gravity signal with spherical harmonic degree and, by implication, to the likely depth below the surface. The results provide estimates for the maximum likely depths of the primary component to the mass anomalies under 19 basins. We find that the maximum depths of the primary source of mascon gravity on the lunar nearside are deeper than the depths for those on the farside when South Pole–Aitken (SPA) is excluded. All basin mass anomalies on the lunar nearside are in the mantle. The maximum depth of the primary source of the mass anomalies is <80 km, with the exception of SPA, whose dominant mass signature lies at a maximum depth of >200 km beneath the surface. The upper 20 km under all basins is largely devoid of anomalies, reflecting predominantly mixing and relaxation associated with impact melt combined with ejecta fallback, as well as homogenization associated with post-basin formation impact bombardment. Except for SPA, all basin anomalies merge with the deep interior at ∼150 km or below, indicating the depth penetration of disruption of the density structure of the lunar interior associated with impact bombardment.

Upcoming missions to the lunar south pole require detailed maps over large areas to fully characterize landing sites locally and regionally and to place their data into proper geologic context. To that end, we enhanced the Lunar Orbiter Laser Altimeter altimetry data set for the south polar region, from which we produced new maps of topography, topographic roughness, and permanently shadowed regions (PSRs). The roughness maps reveal a diversity of terrains characterized by hectometer-scale roughness that is controlled in this region primarily by cratering and downslope mass transport. The south polar region is littered with linear roughness features of order ∼1–10 km wide and approximately tens to hundreds of kilometers long hypothesized to be secondary impacts within extended ejecta rays. Nonuniformities in these features could reflect variations in secondary impactor properties and/or target terrain properties. Poleward of 80° S, the PSR cumulative size–frequency distribution (CSFD) shows an approximately power-law behavior whose exponent has a spatial variation of ∼10%. PSRs with areas <1 km 2 contain 15% ± 5% of the total PSR area. Finally, we studied the effect of false positives and false negatives on the accuracy of the measured PSR CSFD and on the area for any individual PSR. The new maps presented here have many applications in the science and exploration of the lunar south polar region, such as geologic mapping and traverse planning.

SUMMARYRelationships between the degree of a spherical harmonic model of the gravitational field of a body and the depth of a source expressed as a density contrast can be used to study the structure of features. Here, we show that the gravitational acceleration per spherical harmonic degree of a constant density source has an extremum that depends on the depth of the source. Using the spherical harmonics expansion for a point mass source, we use this to derive a degree–depth relationship. Our relationship resembles an earlier one derived by Bowin, with substantial differences at the lower degrees. We also find that a recent relationship derived by Deng et al. overestimates the source depth. The relationship that we derive relates spherical harmonic degree n to depth d for a planet of radius R according to $d = (1-e^{\frac{-1}{n+1}})R$, which simplifies to d = R/(n + 1) for high degrees. We support our new relationship with synthetic models of a density contrast in a planet. We also show how the differences between our relationship and that of Bowin affect band-filtered gravity, for example when inspecting the upper 100 km of the Moon. Using point masses in our modelling results in an approximate relationship where in reality sources can be deeper than estimated, since any source contributes to all spherical harmonic degrees. The use of the contribution per individual degree however provides an intuitive relationship between spherical harmonic degree and depth that can be used to place relative bounds on source depths or to determine the bounds on spherical harmonic expansions when band-filtering gravity field models.

The 8.2 ka climate event is the most significant North Atlantic cooling event during the Holocene. Freshwater pulses from the melting Laurentide Ice Sheet draining into the North Atlantic Ocean are commonly thought to be its cause by perturbing the Atlantic Meridional Overturning Circulation. The timing, magnitude and number of freshwater pulses, however, remain uncertain. This is problematic for predicting future climate scenarios because it prevents rigorous testing of coupled ocean-atmosphere climate models against an otherwise excellent test case of climate effects of meltwater inputs into the North Atlantic. To address this knowledge gap, we present a highresolution relative sea-level record from the Ythan Estuary, Scotland, spanning the centuries leading into the 8.2 ka climate event. The results show a 'sea-level event' with two distinct stages between 8,530 and 8,240 cal yr BP when rates of sea-level rise departed from the background rates of around 2 mm yr-1 and reached around 13 mm yr-1 and 4 mm yr-1, respectively. The maximum probable magnitude of local sea-level rise during the stages was 1.67 and 0.41 m, which equate to barystatic magnitudes of 2.39 and 0.58 m respectively after considering the geographic location relative to the source. For the first time, we demonstrate that Lake Agassiz-Ojibway drainage alone is insufficient to explain the large volumes of North Atlantic freshwater input, and that the collapse of the Hudson Bay Ice Saddle appears to have been the main source of meltwater in to the North Atlantic. By comparing the Ythan sea-level record with other sources of evidence, we hypothesise that an initial thinning of the Laurentide Ice Sheet enabled subglacial drainage of Lake Agassiz and subsequent collapse of the Hudson Bay Ice Saddle. This was followed by the terminal drainage of Lake Agassiz completing a sequence of events that likely forced the shift in the Atlantic Meridional Overturning Circulation and hence the 8.2 ka climate event.

Geodetic and geophysical investigations of the Galilean moon Callisto address fundamental questions regarding the formation and evolution of the Jovian system. Callisto's evolution and internal structure appear to significantly differ from the other Jovian satellites. Similarly-sized Ganymede is a highly evolved ice-rock moon with a differentiated interior, intrinsic magnetic field, and abundant surface evidence of internal activity. In contrast, Callisto's surface is ancient, and Galileo spacecraft data suggest its interior is only incompletely differentiated, despite the presumed presence of a sub-surface ocean. These properties make Callisto uniquely able to constrain the timing and nature of the Jovian system formation. The Magnetics, Altimetry, Gravity, and Imaging of Callisto (MAGIC) mission concept is conceived to fully characterize the properties of this enigmatic moon from its deep interior to the icy shell. Three main instruments are included as a scientific payload. Highly accurate measurements of Callisto's topography, magnetic field, and morphology are obtained by the onboard laser altimeter, magnetometer, and camera, respectively. The telecommunication system supports an additional gravity and radio science investigation. Long- and short-wavelength gravity anomalies afford powerful constraints on internal differentiation and the properties of the hydrosphere (water and ice). Comprehensive numerical simulations and covariance analyses of MAGIC mission scenarios presented in this paper show that the gravitational degree-2 normalized coefficients and the pole obliquity enable the determination of the moment of inertia with an accuracy better than 0.015%. The combination of gravity and altimetry measurements acquired by MAGIC are essential to the characterization of Callisto's interior if - as is likely - the degree-2 gravity includes non-hydrostatic terms. MAGIC's radio science data yield the estimation of Callisto's gravity field with spatial resolutions of <100 km. The combination of gravitational and deformation tides that are retrieved by the radio science and altimetry investigations, respectively, leads to the recovery of the rigid ice shell thickness to within similar to 3 km. Together these datasets would resolve ambiguities inherent in Galileo flyby data, revealing Callisto's interior structure as well as the existence and properties of its postulated internal ocean.

The International Space Station (ISS) is a unique and complex built environment with the ISS surface microbiome originating from crew and cargo or from life support recirculation in an almost entirely closed system. The Microbial Tracking 1 (MT-1) project was the first ISS environmental surface study to report on the metagenome profiles without using whole-genome amplification. The study surveyed the microbial communities from eight surfaces over a 14-month period. The Microbial Tracking 2 (MT-2) project aimed to continue the work of MT-1, sampling an additional four flights from the same locations, over another 14 months. Eight surfaces across the ISS were sampled with sterile wipes and processed upon return to Earth. DNA extracted from the processed samples (and controls) were treated with propidium monoazide (PMA) to detect intact/viable cells or left untreated and to detect the total DNA population (free DNA/compromised cells/intact cells/viable cells). DNA extracted from PMA-treated and untreated samples were analyzed using shotgun metagenomics. Samples were cultured for bacteria and fungi to supplement the above results. Staphylococcus sp. and Malassezia sp. were the most represented bacterial and fungal species, respectively, on the ISS. Overall, the ISS surface microbiome was dominated by organisms associated with the human skin. Multi-dimensional scaling and differential abundance analysis showed significant temporal changes in the microbial population but no spatial differences. The ISS antimicrobial resistance gene profiles were however more stable over time, with no differences over the 5-year span of the MT-1 and MT-2 studies. Twenty-nine antimicrobial resistance genes were detected across all samples, with macrolide/lincosamide/streptogramin resistance being the most widespread. Metagenomic assembled genomes were reconstructed from the dataset, resulting in 82 MAGs. Functional assessment of the collective MAGs showed a propensity for amino acid utilization over carbohydrate metabolism. Co-occurrence analyses showed strong associations between bacterial and fungal genera. Culture analysis showed the microbial load to be on average 3.0 × 105 cfu/m2 Utilizing various metagenomics analyses and culture methods, we provided a comprehensive analysis of the ISS surface microbiome, showing microbial burden, bacterial and fungal species prevalence, changes in the microbiome, and resistome over time and space, as well as the functional capabilities and microbial interactions of this unique built microbiome. Data from this study may help to inform policies for future space missions to ensure an ISS surface microbiome that promotes astronaut health and spacecraft integrity.

Changes in mass distribution affect the gravitational figure and reorient a planetary body’s surface with respect to its rotational axis. The mass anomalies in the present-day lunar gravity field can reveal how the figure and pole position have evolved over the Moon’s history. By examining sequentially each individual crater and basin, working backward in time order through the catalog of nearly 5200 craters and basins between 1200 and 20 km in diameter, we investigate their contribution to the lunar gravitational figure and reconstruct the evolution of the pole position by extracting their gravitational signatures from the present-day Moon. We find that craters and basins in this diameter range, which excludes South Pole–Aitken, have contributed to nearly 25% of the present-day power from the Moon’s degree-2 gravitational figure and resulted in a total displacement of the Moon’s pole by ∼10° along the Earth–Moon tidal axis over the past ∼4.25 billion years. This also implies that the geographical location of the Moon’s rotational pole has not moved since ∼3.8 Ga by more than ∼2° in latitude owing to impacts, and this has implications for the long-term stability of volatiles in the polar regions.

Europa is a premier target for advancing both planetary science and astrobiology, as well as for opening a new window into the burgeoning field of comparative oceanography. The potentially habitable subsurface ocean of Europa may harbor life, and the globally young and comparatively thin ice shell of Europa may contain biosignatures that are readily accessible to a surface lander. Europa's icy shell also offers the opportunity to study tectonics and geologic cycles across a range of mechanisms and compositions. Here we detail the goals and mission architecture of the Europa Lander mission concept, as developed from 2015 through 2020. The science was developed by the 2016 Europa Lander Science Definition Team (SDT), and the mission architecture was developed by the preproject engineering team, in close collaboration with the SDT. In 2017 and 2018, the mission concept passed its mission concept review and delta-mission concept review, respectively. Since that time, the preproject has been advancing the technologies, and developing the hardware and software, needed to retire risks associated with technology, science, cost, and schedule.

We present a case for the exploration of Venus as an astrobiology target-(1) investigations focused on the likelihood that liquid water existed on the surface in the past, leading to the potential for the origin and evolution of life, (2) investigations into the potential for habitable zones within Venus' present-day clouds and Venus-like exo atmospheres, (3) theoretical investigations into how active aerobiology may impact the radiative energy balance of Venus' clouds and Venus-like atmospheres, and (4) application of these investigative approaches toward better understanding the atmospheric dynamics and habitability of exoplanets. The proximity of Venus to Earth, guidance for exoplanet habitability investigations, and access to the potential cloud habitable layer and surface for prolonged in situ extended measurements together make the planet a very attractive target for near term astrobiological exploration.

A global COVID-19 pandemic, rising asthma and allergies, along with climate change impacting storm intensity and frequency, point to an urgent need to unify U.S. atmospheric biology research. To this end, we briefly define atmospheric biology, summarize its fragmented history, and then outline how to unify the field to provide benefits for the U.S. science community and its citizens. Atmospheric biology refers to the study of concentrations, sources, sinks, transformation, and impacts of airborne microorganisms inclusive of pollen, fungal spores, algae, lichens, bacteria, viruses, cellulose fibers, and other biomolecules or fragments of cells. Here our focus is biological particles, both respirable (PM10) and systemic (PM2.5). Due to its interdisciplinary dependencies and broadness of scales from nanometers to kilometers, atmospheric biology research is highly fragmented in the U.S. science community. It lacks shared paradigms and common vocabulary. This deficit calls for recognizing atmospheric biology as a research community in its own right, thereby linking human health to climate change. We need to recognize atmospheric biology's importance to national security and science diplomacy. Advanced atmospheric biology research is being conducted in Europe, Russia, and China, not in the United States.