Exchangeable ice deposits are present today on the surface of Mars in polar caps and in the shallow subsurface in mid-latitudes. Geologic observations indicate these deposits waxed and waned in the past, at times, along with the emplacement and loss of equatorial glaciers. Here, we couple a climate model with an ice stability criterion, to self-consistently determine the distribution of the mid-latitude ground-ice deposits in diffusive equilibrium with the atmosphere, at present and under past orbital configurations. This new coupling and iteration between the short-term and long-term models improves upon past calculations that do not allow the ice table to evolve over timescales much longer than the annual climate dynamics. The model predictions for the extent of the equilibrium ice-table in the past match the latitudinal distribution of terrain softening geologic features previously mapped. At past times, thermally stable shallow ground ice is expected even in equatorial regions, in parts of Tharsis and Arabia Terra.

The Jupiter and Icy Moons Explorer (JUICE) mission of the European Space Agency (ESA) will investigate the Jovian system with multiple instruments over several years, beginning in early 2031. This paper describes the historical context and state of knowledge, as well as JUICE’s scientific goals and measurement techniques of the satellites that will not be encountered in close flybys. These include the large volcanically active moon Io, the four small inner moons Metis, Adrastea, Amalthea, and Thebe, and the numerous small Irregular (outer) moons. JUICE will provide multiple opportunities to observe Io from relatively remote distances of hundreds of thousands of kilometers. These observations will enable monitoring of Io’s surface for changes, and for the study of its neutral clouds and plasma torus. Io observations will be performed with the four optical remote sensing instruments and with the Particle Environment Package. For the small inner moons it is planned to obtain complete geographic longitude (scales up to 8 km/px), solar-phase and multi-color coverage, oblique polar views, and UV to near-IR spectra. Astrometric measurements will also be performed. The Irregular moons will mostly appear unresolved to the JUICE instruments. Nonetheless, long-duration disk-integrated lightcurves will be acquired to derive rotation periods, object dimensions, pole-axis orientations, and colors for most objects for the first time. From these data, convex-shape models will be generated and phase curves determined. Furthermore, the precision of the orbital elements will be improved via accurate astrometry. UV and near-IR measurements will be attempted for the largest of these objects.

Ice deposits at the lunar poles are concentrated within permanently shadowed regions where water molecules are thermally stable. The geographic distribution of the deposits has been predicted and observed. However, the timing of their formation remains poorly constrained. Owing to the gradual decrease in the lunar obliquity with time, the cold-trapping regions have expanded monotonically since the passage of the Moon through the Cassini state transition similar to 4 Gyr ago. Here, using reflected ultraviolet starlight, we show with observations from the Lyman-Alpha Mapping Project that there is a strong correlation between the exposed-ice fraction and the age of the permanent shadow within which it resides. A model of water delivery, burial and loss predicts such a correlation if these processes operate on timescales that are comparable with the ages of the permanently shadowed regions. The exposed-ice area ratio of similar to 3.4% in the youngest permanently shadowed regions aged similar to 100 Myr favours models with high proportional loss rates. The results indicate that polar ice has accumulated quasi-continuously at least over the last similar to 1.5 Gyr rather than from a discrete event.

IntroductionThe seasonal CO2 cycle on Mars is a key driver of the martian climate system. The cycle affects global energy balance and produces annual pressure variations of ~25% [1] that drive interhemispheric and local airflow [2]. In the southern hemisphere, the seasonal CO2 deposits are particularly enigmatic: ice properties change significantly between different regions; bright and fine-grained ice contrasts with areas of ice that remain dark and cold throughout the sublimation period [3].Existing studies on the southern seasonal CO2 cycle typically analyzed a few Mars years of data. Here, we analyze nearly two decades of continuous data acquired by the Mars Climate Sounder (MCS) [4], a visible and infrared radiometer onboard the Mars Reconnaissance Orbiter (MRO). While the instrument typically acquires limb observations for atmospheric characterization, high-emission-angle surface observations are regularly obtained. From these, we produce Lambert surface albedo values and explore the regional and temporal variations of ice reflectivity from a multi-annual average and an interannual perspective.MethodsWe use spectral radiance data, computed from band-integrated radiance obtained by the MCS A6 channel (spanning 0.3 - 3 μm), to derive the albedo of the surface CO2 deposits. We retain observations that are associated with surface temperatures below 160 K (brightness temperature at ~32 μm), which include normal frosted regions as well as the Cryptic region [5]. Since the instrument observes the surface at high phase angles (typically between 105° and 145°), radiance is typically elevated, producing non-physical Lambert albedo values. To correct for this, we divide the top-of-atmosphere (TOA) Lambert albedo into 3-degree bins of solar incidence; within each bin, we fit a scaled Henyey-Greenstein phase function. We produce an effective scene (surface + atmosphere) asymmetry parameter (g) versus incidence trend, which we apply to the raw TOA albedo to produce phase-corrected albedo. Next, we apply a delta-Eddington atmospheric correction [6] using MCS-derived aerosol column optical depth to obtain the Lambert surface albedo. We limit our analysis to incidence angles lower than 80°, above which albedo increases rapidly due to instrument noise.ResultsFig. 1 shows initial mapping results for the southern cap in polar stereographic projection. Prominent features of the southern cap are observed. Due to incidence angle constraints, we can observe the cap only in spring and summer. In mid-spring (Fig. 1a), we observe the cap in sublimation. High-albedo ice is seen in the Mountains of Mitchel (72° S, 330° E), while the Cryptic region (75° S - 85° S, 50° E - 210° E) is notably darker, as expected. Late spring cap (Fig. 1b) is notably asymmetric, with the Cryptic region completely defrosted. Ice remains in the western hemisphere, as well as the outliers at the Mountains of Mitchel. At mid-summer (Fig. 1c), after the sublimation of seasonal frost, the residual cap has a relatively lower albedo.Fig. 2 presents the multi-annual average CO2 albedo averaged over regions of interest (ROIs). The residual cap (Fig. 2a) is observable starting at Ls ~200°. The cap’s albedo initially fluctuates, and as seasonal ice sublimates to reveal residual ice, the albedo sharply drops to ~0.65. Byrne et al. [7] similarly found darkening during the seasonal frost sublimation. In the Cryptic region (Fig. 2b), ice albedo is initially similar to other regions, and subsequently decreases, showing the “cryptic” behavior presumably caused by slab transparency and/or surface dust accumulation [3]. Around Ls ~210°, a brightening phase is associated with temperatures increasing above the CO2 frost point, before the ice sublimates. In both regions, interannual variations are observed. Most prominently, the residual cap appears to have significant interannual albedo variations after Ls ~310°. We also highlight that ice albedo differs somewhat from other literature values (e.g., TES average albedo in the Cryptic region reaches values as low as ~0.2 in early spring, where our value is ~0.5). This may be due to errors in the atmospheric correction or non-Lambertian behavior of the ice.ConclusionsThe long observational baseline of MCS offers a unique opportunity to explore previously documented phenomena over multi-annual timescales and identify interannual variations over nearly a full martian decade. In addition, simultaneous MCS atmospheric and surface IR observations can be used to investigate relationships between visible ice albedo, atmospheric conditions, and ice metamorphic state. We are currently exploring several intriguing findings that could shed light on the seasonal evolution of southern CO2 ice.References[1] James, P. B., Kieffer, H. H., & Paige, D. A. (1992). 934-968. [2] Siili, T., Haberle, R. M., & Murphy, J. R. (1997). Advances in Space Research, 19(8), 1241-1244. [3] Kieffer, H. H., Christensen, P. R., & Titus, T. N. (2006). Nature, 442(7104), 793-796. [4] McCleese, D. J., Schofield, J. T., Taylor, F. W., Calcutt, S. B., Foote, M. C., Kass, D. M., ... & Zurek, R. W. (2007). Journal of Geophysical Research: Planets, 112(E5). [5] Kieffer, H. H., Titus, T. N., Mullins, K. F., & Christensen, P. R. (2000). Journal of Geophysical Research: Planets, 105(E4), 9653-9699. [6] Wiscombe, W. J., & Warren, S. G. (1980). Journal of Atmospheric Sciences, 37(12), 2712-2733. [7] Byrne, S., Zuber, M. T., & Neumann, G. A. (2008). Planetary and Space Science, 56(2), 194-211. Figure 1: Multi-annual (MY 29-37) average CO2 ice albedo. Data is obtained at ~3 PM local time, binned into 18 x 18 km cells and 15° Ls. Selected time frames include a) seasonal cap recession during mid-spring, b) late spring, and c) residual cap at mid-summer. ROIs shown in Fig. 2 are marked in (a); residual cap in cyan and the Cryptic region in red. Figure 2: ROI-average CO2 ice albedo for a) the residual cap and b) the Cryptic region. Multi-annual average albedo across MY 29 - 37 with standard error of the ROI mean (SEM).

A main source of bias in transmission spectroscopy of exoplanet atmospheres is magnetic activity of the host star in the form of stellar spots, faculae or flares. However, the fact that main-sequence stars have a chromosphere and a corona, and that these optically thin layers are dominated by line emission may alter the global interpretation of the planetary spectrum, has largely been neglected. Using a JWST NIRISS/SOSS data set of hot Jupiter HAT-P-18 b, we show that even at near-IR and IR wavelengths, the presence of these layers leads to significant changes in the transmission spectrum of the planetary atmosphere. Accounting for these stellar outer layers thus improves the atmospheric fit of HAT-P-18 b, and increases its best-fit atmospheric temperature from 536 K to 736 K, a value much closer to the predicted equilibrium temperature of 852 K. Our analysis also decreases the best-fit abundance of CO2 by almost an order of magnitude. The approach provides a new window to the properties of chromospheres/corona in stars other than our Sun.

The Martian South Polar Layered Deposits (SPLD) are composed mostly of ice and dust with a thin perennial CO2 cover and some internal CO2 ice layers. In the North, the seasonal CO2 cap is lost during summer, allowing H2O ice to sublimate into the atmosphere. In the South, the perennial CO2 cover prevents H2O ice sublimation. This work uses the Mars Planetary Climate Model to investigate how the H2O and CO2 cycles are affected if the thin perennial CO2 SPLD cover is lost. We find that during southern summer, the atmospheric water content will more than double in the south polar region. However, on a global scale, the NPLD is still the dominant source of humidity because of its larger surface area. When exposing some of the South Polar Cap buried water ice, the south polar cap becomes the dominant source of atmospheric humidity due to Mars's spin-orbital alignment.

We use PyDynamicaLC , a model using the least number of—and the least correlated—degrees of freedom needed to derive a photodynamical model, to describe some of the smallest—and lowest-transit-timing-variation-amplitude—of the Kepler planets. We successfully analyze 64 systems containing 218 planets, for 88 of which we were able to determine significant masses (to better than 3 σ ). We demonstrate consistency with literature results over 2 orders of magnitude in mass, and for the planets that already had literature mass estimations, we were able to reduce the relative mass error by ∼22% (median value). Of the planets with determined masses, 23 are new mass determinations, with no previous significant literature values, including a planet smaller and lighter than Earth (KOI-1977.02/Kepler-345 b). These results demonstrate the power of photodynamical modeling with the appropriately chosen degrees of freedom. This will become increasingly more important as smaller planets are detected, especially as the TESS mission gathers ever longer baseline light curves and for the analysis of the future PLATO mission data.

CO2 is the primary component of the martian atmosphere and its seasonal surface-atmosphere exchange is responsible for many of the climate phenomena on the planet. Near-surface ground water ice ('GI') has been found to inhibit seasonal CO2 ice accumulations. Previous studies concerning the response of the CO2 cycle to orbital variations did not take into account the redistribution of GI arising from the same orbital variations. This work aims to analyze the effect of GI redistribution on the CO2 cycle in past climates. We use the LMD Planetary Climate Model to simulate the full CO2 cycle at different orbital configurations and compare simulations with reference modern GI as observed by the Mars Odyssey Neutron Spectrometer ("MONS GI" scenario) to simulations with equilibrium GI produced by the Mars Subsurface Ice Model ("Eq. GI" scenario). In the Eq. GI scenario, equilibrium GI underlies 0.8-0.9 of the seasonal caps area at high obliquity periods, whereas in the reference MONS GI scenario, the overlap between GI and the seasonal cap is reduced, reaching less than 0.3 by obliquity 45 degrees. The mass and duration of seasonal CO2 ice are significantly reduced relative to the reference scenario, especially in the mid-latitudes, and the expected increase of seasonal pressure amplitude with obliquity is attenuated (by a factor of similar to 2 at obliquity 45 degrees). Interpolating the seasonal variations and mean annual pressure over the past 20,000 kyr, we highlight the influence of GI migration in attenuating both seasonal pressure variations and long-term oscillations of the martian atmospheric pressure.

Understanding Mars's water budget and distribution is crucial for evaluating its habitability and studying its evolution and past climate. Evidence for past and present glaciation includes geomorphological features: polar ice caps and subsurface ice. Among the most compelling evidence are Viscous Flow Features (VFFs), which suggest the presence of water ice due to surface patterns similar to Earth's rock glaciers and debris-covered glaciers. These features, including Lobate Debris Aprons (LDAs), are found in the mid-latitudes (30 degrees and 50 degrees) of both hemispheres. This study focuses on the composition of LDAs, which are large, ice-rich deposits found on slopes of massifs. Two hypotheses for their formation propose either low water ice content (30%) ("rock glaciers") or near-pure water ice under a debris layer ("debris-covered glaciers"). Using SHARAD (SHAllow RADar) data, we calculate two key parameters-dielectric constant (epsilon ') and loss tangent (tan delta)-to better understand the purity and composition of these deposits. Previous studies suggest LDAs consist of nearly pure water ice. Our work increases global coverage across the northern and southern hemispheres, examining five sites with enhanced data coverage and incorporating both epsilon ' and tans to improve the analysis. Our results indicate that LDAs are most likely part of a global population of features composed of >80% water ice, supporting the debris-covered glacier hypothesis. The results also point to the consistency of the debris cover across the globally distributed sites. This finding suggests that these features formed under similar climatic conditions, such as might occur under a specific orbital configuration. The high purity of the ice in LDAs has significant implications for understanding Mars's past climate and for future exploration, as LDAs represent accessible reservoirs of water ice at mid-latitudes. Additionally, our findings highlight the need for future radar-based studies to incorporate the calculation of the loss tangent, as this can alleviate the sensitivity to the topography of the LDA base inherent in epsilon '.

Introduction: A common outcome of a giant impact event is the formation of a circumplanetary debris disk, and in some cases, the capture of the surviving impactor, which results in a system composed of a primary, secondary, and a debris disk. The material in the debris disk may be accreted by the primary body (and secondary, if it exists), escape the system, or coalesce into larger clumps. A classic example of a system thought to originate by such an impact event is the Pluto-Charon binary system (Canup, 2005, 2011), in which all six bodies (including the other smaller satellites) lie approximately on the same plane and have nearly circular orbits. Such impacts are simulated using smoothed particle hydrodynamics (SPH) codes including self gravity. The equation of state (EOS) governs the relationship among the thermodynamic variables of the simulated material. The specific EOS used in the simulation may influence the final post-impact structure. In order to quantify the typical differences, we compare two approaches, one simple analytic and one tabulated EOS. Tillotson (Tillotson, 1962) is a widely used analytic EOS and is computationally fast, but it lacks important details such as the treatment of phase changes. Sesame (Bennett et al., 1978) is a commonly used tabulated EOS and is more accurate, but is computationally slower and may be poorly sampled in the required thermodynamic phase-space. Here we show a set of SPH impact simulations that assume similar geometric and dynamic initial conditions but different EOS. Methods: We performed ~100 SPH simulations using SWIFT code (Schaller et al., 2018), simulating Pluto-like impacts with 105-106 particles. The initial bodies are assumed to be differentiated, with target to impactor mass ratio of 1 or 7/3, impact angle, ξ, of 0, 30, 45, 60°. Impact velocity was chosen to be relatively small, 1-1.1 times the escape velocity. The impactor was either spin-less or rotating with a period of 5 or 10 hours. This parameter space was motivated by previous simulations (Canup, 2011) for the formation of the Pluto-Charon system. We compare results using the Tillotson and Sesame EOS. The simulations were stopped after 4 days, the typical time for the central body to relax to a stable spherical shape. We developed an algorithm to detect post-impact clumps. Two particles were considered in contact if their mutual distance was smaller than their combined smoothing lengths. The orbital elements of each clump (“satellitesimal”, defined as 100 particles in pairwise contact, equivalent to ~10-3Mpluto) were computed and studied.Results: Disk systems were formed for impact angles >30°, in using both EOSs. Satellitesimals, when formed, showed different properties. Figure 1 panels (a,b) show the final snapshots of an impact that produced a debris disk and several satellitesimals highlighted in color corresponding to their masses. In this example, a more massive debris disk with a larger number of satellitesimals is obtained when using Tillotson EOS than using Sesame. Moreover, in addition to the target body, at least one large satellitesimal was formed in each of the simulations, but their composition, mass, and orbital elements differ between the EOSs. In comparing the Sesame run to Tillotson, the largest satellitesimal has a mass of 0.015Mpluto (with water fraction of 0.16) and 0.008Mpluto (with water fraction of 0.30) respectively. Its orbital elements are e=0.67, a=10.07Rpluto for Sesame runs, and e=0.15, a=3.2Rpluto for Tillotson. At smaller masses, using Tillotson EOS produces a greater number of clumps, as seen in Figure 1c. Three more satellitesimals were formed (some beyond the plot limits of 1b), with e=0.86, 1.35, 0.10. Note that the satellitesimal mass is an order of magnitude smaller than Charon, so alone they do not predict Charon’s formation (Canup, 2011). In the final snapshot, a greater fraction of debris disk particles lie within the Roche limit (computed using present-day Charon’s density (McKinnon et al., 2017)) in the Sesame simulation, whereas the Tillotson disk extends to a greater distance. In terms of mass, angular momentum, and composition, the debris disks are similar (0.025 versus 0.033 of the total mass; 0.19 versus 0.25 of the total angular momentum; water fraction of 0.44 versus 0.37 for Sesame and Tillotson respectively). We note the execution time was 2-3 times longer for the simulations using Sesame than Tillotson, a factor which may be considered in choosing EOS.Exploring the parameter space, we note that head-on impacts (ξ~0°) produce a merged single body, with the vast majority of ejected particles accreted by the planet, and the rest ejected to space. Oblique, faster than escape velocity impacts (vimp/vesc=1.1 and ξ=60°) resulted in two unbound bodies, with little mass transfer between the two, consistent with previous studies of planetary impacts (Leinhardt & Stewart, 2012). References:Bennett, B. I., Johnson, J. D., Kerley, G. I., & Rood, G. T. (1978). Recent developments in the Sesame equation-of-state library. https://doi.org/10.2172/5150206Canup, R. M. (2005). A Giant Impact Origin of Pluto-Charon. Science, 307(5709), 546–550.Canup, R. M. (2011). On a Giant Impact Origin of Charon, Nix, and Hydra. The Astronomical Journal, 141(2), 35.Leinhardt, Z. M., & Stewart, S. T. (2012). Collisions Between Gravity-Dominated Bodies. I. Outcome Regimes and Scaling Laws. The Astrophysical Journal, 745(1), 79.McKinnon, W. B., Stern, S. A., Weaver, H. A., Nimmo, F., Bierson, C. J., Grundy, W. M., et al. (2017). Origin of the Pluto–Charon system: Constraints from the New Horizons flyby. Icarus. https://doi.org/10.1016/j.icarus.2016.11.019Schaller, M., Gonnet, P., Chalk, A. B. G., & Draper, P. W. (2018, May 1). SWIFT: SPH With Inter-dependent Fine-grained Tasking. Astrophysics Source Code Library. Retrieved from https://ui.adsabs.harvard.edu/abs/2018ascl.soft05020STillotson, J. H. (1962). Metallic equations of state for hypervelocity impact (No. Rep. GA-3216 ). General Dynamics San Diego CA.

The Ultraviolet Transient Astronomy Satellite (ULTRASAT) is scheduled to be launched to geostationary orbit in 2027. It will carry a telescope with an unprecedentedly large field of view (204 deg ^2 ) and near-ultraviolet (NUV; 230–290 nm) sensitivity (22.5 mag, 5 σ , at 900 s). ULTRASAT will conduct the first wide-field survey of transient and variable NUV sources and will revolutionize our ability to study the hot transient Universe. It will explore a new parameter space in energy and timescale (months-long light curves with minutes cadence), with an extragalactic volume accessible for the discovery of transient sources that is >300 times larger than that of the Galaxy Evolution Explorer (GALEX) and comparable to that of the Vera Rubin Observatory’s Legacy Survey of Space and Time. ULTRASAT data will be transmitted to the ground in real time, and transient alerts will be distributed to the community in <15 minutes, enabling vigorous ground-based follow up of ULTRASAT sources. ULTRASAT will also provide an all-sky NUV image to >23.5 AB mag, over 10 times deeper than the GALEX map. Two key science goals of ULTRASAT are the study of mergers of binaries involving neutron stars, and supernovae. With a large fraction (>50%) of the sky instantaneously accessible, fast (minutes) slewing capability, and a field of view that covers the error ellipses expected from gravitational-wave (GW) detectors beyond 2026, ULTRASAT will rapidly detect the electromagnetic emission following binary neutron star/neutron star–black hole mergers identified by GW detectors, and will provide continuous NUV light curves of the events. ULTRASAT will provide early (hour) detection and continuous high-cadence (minutes) NUV light curves for hundreds of core-collapse supernovae, including for rarer supernova progenitor types.

Planetary geologic maps are crucial tools for understanding the geological features and processes of solid bodies in the Solar System. Over the past six decades, best practices in planetary geologic mapping have emphasized clear and objective observation, geological interpretation, multi-sensor fusion, and iterative revision of maps based on new data. We summarize here four ways in which maps serve as indispensable instruments for scientific investigation, from enhancing observations to interrogating surface processes. With respect to space exploration, we underscore the role of planetary geologic maps as tools to link testable, hypothesis-driven science to exploration goals and provide actionable information for hazard identification, resource evaluation, sample collection, and potential infrastructure development. To further advance the field of planetary geologic mapping, international collaboration is essential. This includes sharing data and maps through FAIR (findable, accessible, interoperable, and reusable) platforms, establishing standardized mapping practices, promoting diverse nomenclature, and fostering continued cooperation in space exploration.

We fit a dynamical model to Kepler systems that contain four or more transiting planets using the analytic method AnalyticLC, and obtain physical and orbital parameters for 101 planets in 23 systems, of which 95 are of mass significance better than 3 sigma, and 46 are without previously reported mass constraints nor upper limits. In addition, we compile a list of 71 KOIs that display significant Impact Parameter Variations (TbVs), complementing our previously published work on two- and three-transiting planet systems. Together, these works include the detection of significant TbV signals of 130 planets, which is, to our knowledge, the largest catalog of this type to date. The results indicate that the typical detectable TbV rate in the Kepler population is of order 10^{-2} yr^{-1}, and that rapid TbV rates (>~0.05 yr^{-1}) are observed only in systems that contain a transiting planet of an orbital period less than ~20 days. The observed TbV rates are only weakly correlated with orbital period within Kepler's <~100 days-period planets. If this extends to longer periods, it implies a limit on the utility of the transit technique for long-period planets. The TbVs we find may not be detectable in direct impact parameter measurements but rather are inferred from the full dynamics of the system, encoded in all types of transit variations. Finally, we find evidence that the mutual inclinations distribution is qualitatively consistent with the previously suggested AMD (angular momentum deficit) model using an independent approach.

Mars harbors ice deposits in several forms, on the surface and in the subsurface, which exchange with each other on various timescales. We seek to study the pore ice evolution over millennial time scales and how it contributes to and affects the Polar cap's evolution. We calculate the evolution of SubSurface Ice (SSI) pore filling by coupling two models, the Mars LMD Global Climate Model, which calculates the atmospheric and surface evolution on an annual timescale, and the dynamical version of the Mars Subsurface Ice Model, which calculates the evolution of the SSI on a millennial timescale. The SSI latitudinal boundary fluctuates over more than 25° in one obliquity cycle, overall extending equatorward of latitude ±35° at high obliquity, and receding to about ±60° at low obliquity. In locations where the SSI is stable continuously over orbital cycles, the simulations predict layering caused by a sublimation front at the SSI top boundary. Between 5 and 2.5 Myr ago, the subsurface lost at least ∼95 m of polar equivalent layer ice. The SSI flux routinely reaches ∼1 mm/Mars year. In addition to the direct contribution to the growth of the North Polar Layered Deposits (NPLD), the SSI causes variations in the NPLD accumulation rate due to the changes in the SSI distribution that affect the seasonal energy budget. These variations are comparable to the change in rate due to variations in orbital elements. When running paleo‐climate simulations, particularly to reconstruct the NPLD profile, changes in the SSI distribution should be considered.

The Large Array Survey Telescope (LAST) is designed to survey the variable and transient sky at high temporal cadence. The array is comprised of 48 F/2.2 telescopes of 27.9 cm aperture, coupled to full-frame backside-illuminated cooled CMOS detectors with 3.76 μ m pixels, resulting in a pixel scale of 1.″25. A single telescope with a field of view of 7.4 deg 2 reaches a 5 σ limiting magnitude of 19.6 in 20 s. LAST 48 telescopes are mounted on 12 independent mounts—a modular design which allows us to conduct optimized parallel surveys. Here we provide a detailed overview of the LAST survey strategy and its key scientific goals. These include the search for gravitational-wave (GW) electromagnetic counterparts with a system that can cover the uncertainty regions of the next-generation GW detectors in a single exposure, the study of planetary systems around white dwarfs, and the search for near-Earth objects. LAST is currently being commissioned, with full scientific operations expected in mid 2023. This paper is accompanied by two complementary publications in this issue, giving an overview of the system and of the dedicated data reduction pipeline.

Estimation of planetary orbital and physical parameters from light-curve data relies heavily on the accurate interpretation of Transit Timing Variation (TTV) measurements. In this letter, we review the process of TTV measurement and compare two fitting paradigms—one that relies on making transit-by-transit timing estimates and then fitting a TTV model to the observed timings, and one that relies on fitting a global flux model to the entire light-curve data set simultaneously. The latter method is achieved either by solving for the underlying planetary motion (often referred to as “photodynamics”), or by using an approximate or empirical shape of the TTV signal. We show that, across a large range of the transit S/N regime, the probability distribution function of the mid-transit time significantly deviates from a Gaussian, even if the flux errors do distribute normally. Treating the timing uncertainties as if they are distributed normally leads, in such a case, to a wrong interpretation of the TTV measurements. We illustrate these points using numerical experiments and conclude that a fitting process that relies on a global flux fitting, rather than the derived TTVs, should be preferred.

Massive reservoirs of subsurface water ice in equilibrium with atmospheric water vapor are found poleward of 45 degrees latitude on Mars. The absence of CO2 frost on steep pole-facing slopes and simulations of atmospheric-soil water exchanges suggested that water ice could be stable underneath these slopes down to 25 degrees latitude. We revisit these arguments with a new slope microclimate model. Our model shows that below 30 degrees latitude, slopes are warmer than previously estimated as the air above is heated by warm surrounding plains. This additional heat prevents the formation of surface CO2 frost and subsurface water ice for most slopes. Our model suggests the presence of subsurface water ice beneath pole-facing slopes down to 30 degrees latitude, and possibly 25 degrees latitude on sparse steep dusty slopes. While unstable ice deposits might be present, our results suggest that water ice is rarer than previously thought in the +/- 30 degrees latitude range considered for human exploration. The presence of water ice near the equator is a key issue for future human exploration of Mars. In the current climate, this ice cannot exist near the equator but could be stable at accessible depths below pole-facing slopes down to latitudes of 25 degrees, that is, close enough to the equator for a crewed mission. Here, we study the possible presence of this subsurface ice with a new model that simulates the microclimates associated with slopes on Mars. Our results show that, contrary to the arguments put forward in the literature, the slopes close to the equator (20 degrees-30 degrees) may in fact be too warm to allow subsurface water ice to be stable, and that the observations that suggested the presence of ice under these slopes can be explained otherwise by our model. Thus, the widespread presence of water ice under these slopes at subtropical latitudes is not demonstrated. However, our model cannot rule out the presence of ancient ice reservoirs, that would be slowly sublimating today. We use a new model of steep slope microclimates to explore the stability of subsurface water ice on Mars at latitudes lower than 30 degrees Our model shows that warm plains and large-scale atmospheric dynamics heat these slopes, preventing ice from being stable Subsurface ice is predicted to be present down to 30 degrees of latitude, possibly down to 25 degrees but for sparse slopes with favorable conditions

We developed and provide AnalyticLC, a novel analytic method and code implementation for dynamical modeling of planetary systems, including non-coplanar interactions, based on a disturbing function expansion to fourth order in eccentricities and inclinations. AnalyticLC calculates the system dynamics in 3D and the resulting model light-curve, radial-velocity, and astrometry signatures, enabling simultaneous fitting of these data. We show that for a near-resonant chain of three planets, where the two super-periods are close to each other, the TTVs of the pair-wise interactions cannot be directly summed to give the full system TTVs because the super-periods themselves resonate. We derive the simultaneous three planets correction and include it in AnalyticLC. We compare the model computed by AnalyticLC to synthetic data generated by an N-body integrator, and evaluate its accuracy. Depending on the maximal order of expansion terms kept, AnalyticLC computation time can be up to an order of magnitude faster than the state-of-the-art published N-body integrator TTVFast, with a smaller enhancement seen at higher order. The advantage increases for long-term observations as our approach’s computation time does not depend on the time span of the data. Depending on the system parameters, the photometric accuracy is typically a few ppm, significantly smaller than Kepler’s and other observatories’ typical data uncertainty. Our highly efficient and accurate implementation allows full inversion of a large number of observed systems for planetary physical and orbital parameters, presented in a companion paper.

We apply AnalyticLC, an analytic model described in an accompanying paper, to interpret Kepler data of systems that contain two or three transiting planets. We perform tests to verify that the obtained solutions agree with full N-body integrations, and that the number of model parameters is statistically justified. We probe non-coplanar interactions via impact parameter variations (TbVs), enabled by our analytic model. The subset of systems with a valid solution includes 54 systems composed of 140 planets, more than half of which without previously reported mass constraints. Overall we provide: (1) Estimates on physical and orbital properties for all systems analyzed. (2) 102 planets with mass detections significant to better than 3 standard deviations, 43 of which are lighter than five Earth masses. (3) 35 TbVs significant to better than 3 standard deviations. We focus on select systems showing strong TbVs, which can result from either interaction among the known transiting planets, or with a non-transiting object, and provide: (4) a method to constrain the parameters of such unseen companions. These results are enabled by an accurate, 3D, photodynamical model, of a kind expected to become increasingly important for modeling multi-decade photometric and composite (RV, astrometry) data sets.

Impacts between planetary-sized bodies can explain the origin of satellites orbiting large (R > 500 km) transNeptunian objects. Their water rich composition, along with the complex phase diagram of water, make it important to accurately model the wide range of thermodynamic conditions material experiences during an impact event and in the debris disk. Since differences in the thermodynamics may influence the system dynamics, we seek to evaluate how the choice of an equation of state (EOS) alters the system's evolution. Specifically, we compare two EOSs that are constructed by different approaches: either by a simplified analytic description (Tillotson), or by interpolation of tabulated data (Sesame). Approximately 50 pairs of Smoothed Particle Hydrodynamics impact simulations were performed, with similar initial conditions but different EOSs, in the parameter space in which the Pluto-Charon binary is thought to form (slow impacts between Pluto-size, water rich bodies). Generally, we show that impact outcomes (e.g., circumplanetary debris disk) are consistent between EOSs. Some differences arise, importantly in the production of satellitesimals (large intact clumps) that form in the post-impact debris disk. When utilizing an analytic EOS, the emergence of satellitesimals is highly certain, while when using the tabulated EOS it is less common. This is because for the typical densities and energies experienced in these impacts, the analytic EOS predicts very low pressure values, leading to particles artificially aggregating by a tensile instability.