Key Points1. We link Mars's orbital elements with the stratigraphy and isotopic composition of its ice by modeling the exchange among its reservoirs.2. The precession period of 50 kyr dominates the isotopic composition during epochs of low and nearly constant obliquity such as at present.3. Isotopic sampling of the top 100 meters may reveal climate oscillations unseen in the layer thicknesses. AbstractThe layered polar caps of Mars have long been thought to be related to variations in orbit and axial tilt. We dynamically link Mars's past climate variations with the stratigraphy and isotopic composition of its ice by modeling the exchange of H2O and HDO among three reservoirs. The model shows that the interplay among equatorial, mid-latitude, and north-polar layered deposits (NPLD) induces significant isotopic changes in the cap. The diffusive properties of the sublimation lags and dust content in our model result in a cap size consistent with current Mars. The layer thicknesses are mostly controlled by obliquity variations, but the precession period of 50 kyr dominates the variations in the isotopic composition during epochs of relatively low and nearly constant obliquity such as at present. Isotopic sampling of the top 100 meters may reveal climate oscillations unseen in the layer thicknesses and would thus probe recent precession-driven climate cycles.

Exposed scarps images and ice‐penetrating radar measurements in the North Polar Layered Deposits (NPLD) of Mars show alternating layers that provide an archive of past climate oscillations, that are thought to be linked to orbital variations, akin to Milankovitch cycles on Earth. We use the Laboratoire de Météorologie Dynamique Martian Global Climate Model to study paleoclimate states to enable a better interpretation of the NPLD physical and chemical stratigraphy. When a tropical ice reservoir is present, water vapor transport from the tropics to the poles at low obliquity is modulated by the intensity of summer. At times of low and relatively constant obliquity, the flux still varies due to other orbital elements, promoting polar layer formation. Ice migrates from the tropics toward the poles in two stages. First, when surface ice is present in the tropics, and second, when the equatorial deposit is exhausted, from ice that was previously deposited in mid‐high latitudes. The polar accumulation rate is significantly higher when tropical ice is available, forming thicker layers per orbital cycle. However, the majority of the NPLD is sourced from ice that temporary resided in the mid‐high latitudes and the layers become thinner as the source location moves poleward. The migration stages imprint different D/H ratios in different sections in the PLDs. The NPLD is isotopically depleted compared to the South Polar Layered Deposits in all simulations. Thus we predict the D/H ratio of the atmosphere in contact with NPLD upper layers is biased relative to the average global ice reservoirs.

Knowledge of both the mass and radius of an exoplanet allows us to estimate its mean density, and therefore its composition. Exoplanets seem to fill a very large parameter space in terms of mass and composition, and unlike the solar-system's planets, exoplanets also have intermediate masses (∼5 -50 M ⊕ ) with various densities. In this letter, we investigate the behavior of the Mass-Radius relation for methane (CH 4 ) planets and show that when methane planets are massive enough (M p 15 M ⊕ ), the methane can dissociate and lead to a differentiated planet with a carbon core, a methane envelope, and a hydrogen atmosphere. The contribution of a rocky core to the behavior of CH 4 planet is considered as well. We also develop interior models for several detected intermediate-mass planets that could, in principle, be methane/methane-rich planets. The example of methane planets emphasizes the complexity of the Mass-Radius relation and the challenge involved in uniquely inferring the planetary composition.

This list includes many of the hundreds of current students and scientists who have made significant contributions to Mars Polar Science in the past decade. Every name listed represents a person who asked to join the white paper or agreed to be listed and provided some comments.