Several remote observations have indicated that water ice may be presented in permanently shadowed craters of the Moon. The Lunar Crater Observation and Sensing Satellite (LCROSS) mission was designed to provide direct evidence. On 9 October 2009, a spent Centaur rocket struck the persistently shadowed region within the lunar south pole crater Cabeus, ejecting debris, dust, and vapor. This material was observed by a second "shepherding" spacecraft, which carried nine instruments, including cameras, spectrometers, and a radiometer. Near-infrared absorbance attributed to water vapor and ice and ultraviolet emissions attributable to hydroxyl radicals support the presence of water in the debris. The maximum total water vapor and water ice within the instrument field of view was 155 ± 12 kilograms. Given the estimated total excavated mass of regolith that reached sunlight, and hence was observable, the concentration of water ice in the regolith at the LCROSS impact site is estimated to be 5.6 ± 2.9% by mass. In addition to water, spectral bands of a number of other volatile compounds were observed, including light hydrocarbons, sulfur-bearing species, and carbon dioxide.

The martian valley networks formed near the end of the period of heavy bombardment of the inner solar system, about 3.5 billion years ago. The largest impacts produced global blankets of very hot ejecta, ranging in thickness from meters to hundreds of meters. Our simulations indicated that the ejecta warmed the surface, keeping it above the freezing point of water for periods ranging from decades to millennia, depending on impactor size, and caused shallow subsurface or polar ice to evaporate or melt. Large impacts also injected steam into the atmosphere from the craters or from water innate to the impactors. From all sources, a typical 100-, 200-, or 250-kilometers asteroid injected about 2, 9, or 16 meters, respectively, of precipitable water into the atmosphere, which eventually rained out at a rate of about 2 meters per year. The rains from a large impact formed rivers and contributed to recharging aquifers.

[1] We have modeled the effects of moderate-sized (30-100 km diameter) impacts on Mars using a one-dimensional radiative-convective model. The model computes the evolution of temperature following an impact and includes a subsurface model to compute the evolution of the ground temperature; a hydrological cycle to follow the evaporation, condensation, and precipitation of injected and surface-evaporated water; a radiative transfer code to compute greenhouse warming by CO 2 , water vapor, and water clouds; and an atmospheric thermodynamics module to compute the latent heating due to cloud formation/dissipation. We have found that parts of the Martian regolith may be kept above freezing for 95 days to decades by the modeled events. However, if we include the radiative effects of water clouds, a sustained greenhouse climate is computed for impactors 50 km in size that could be centuries long. The amount of water precipitated out of the atmosphere from vaporization of impactor, target, and polar caps yields global rainfall totals ranging from 40 to 18 m depending on the size of the impactor and assumed background CO 2 atmosphere. We also estimate the surface erosion following precipitation events and find that the total erosion done by all impactors in time is the same order of magnitude as the total erosion estimated to have occurred on early Mars.

A new Mars Global Digital Dune Database (MGD3) constructed using Thermal Emission Imaging System (THEMIS) infrared (IR) images provides a comprehensive and quantitative view of the geographic distribution of moderate‐ to large‐size dune fields (area >1 km2) that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of Mars. MGD3 extends from 65°N to 65°S latitude and includes ∼550 dune fields, covering ∼70,000 km2, with an estimated total volume of ∼3,600 km3. This area, when combined with polar dune estimates, suggests moderate‐ to large‐size dune field coverage on Mars may total ∼800,000 km2, ∼6 times less than the total areal estimate of ∼5,000,000 km2 for terrestrial dunes. Where availability and quality of THEMIS visible (VIS) or Mars Orbiter Camera narrow‐angle (MOC NA) images allow, we classify dunes and include dune slipface measurements, which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification. For dunes located within craters, the azimuth from crater centroid to dune field centroid (referred to as dune centroid azimuth) is calculated and can provide an accurate method for tracking dune migration within smooth‐floored craters. These indicators of wind direction are compared to output from a general circulation model (GCM). Dune centroid azimuth values generally correlate to regional wind patterns. Slipface orientations are less well correlated, suggesting that local topographic effects may play a larger role in dune orientation than regional winds.

As its detached upper-stage launch vehicle collided with the surface, instruments on the trailing Lunar Crater Observation and Sensing Satellite (LCROSS) Shepherding Spacecraft monitored the impact and ejecta. The faint impact flash in visible wavelengths and thermal signature imaged in the mid-infrared together indicate a low-density surface layer. The evolving spectra reveal not only OH within sunlit ejecta but also other volatile species. As the Shepherding Spacecraft approached the surface, it imaged a 25- to-30-meter-diameter crater and evidence of a high-angle ballistic ejecta plume still in the process of returning to the surface--an evolution attributed to the nature of the impactor.