The terrestrial planetary bodies display a wide variety of surface expressions and histories of volcanic and tectonic, and magnetic activity, even those planets with apparently similar dominant modes of heat transport (e.g., conductive on Mercury, the Moon, and Mars). Each body also experienced differentiation in its earliest evolution, which may have led to density-stabilized layering in its mantle and a heterogenous distribution of heat-producing elements. We explore the hypothesis that mantle structure exerts an important control on the occurrence and timing of geological processes such as volcanism and tectonism. We investigate numerically the behavior of an idealized model of a planetary body where heat-producing elements are assumed to be sequestered in a stabilized layer at the top or bottom of the mantle. We find that the mantle structure alters patterns of heat flow at the boundaries of major heat reservoirs: the mantle and core. This modulates the way in which heat production influences geological processes. In the model, mantle structure is a dominant control on the relative timing of fundamental processes such as volcanism, magnetic field generation, and expansion/contraction, the record of which may be observable on planetary body surfaces. We suggest that Mercury exhibits characteristics of shallow sequestration of heat producing elements and that Mars exhibits characteristics of deep sequestration.

Exploration of Venus in the 1970–1990’s revealed that the geology of Venus, the most Earth-like of the terrestrial planets, was decidedly un-Earth-like, with no plate tectonics, and no record of the first 80% of its history. A major outstanding question is whether Venus is still volcanically active today. We find that regions of Ganis Chasma have low radar emissivity values, due to low volumes of high dielectric minerals formed by surface – atmosphere weathering on the timescales of around 10s Ma. This confirms the presence of geologically recent volcanism in association with this major tectonic rift zone. The spatial correspondence of this emissivity signature with transient thermal anomalies suggests that Venus has been volcanically active at this site for at least the last few decades, a prediction that can be tested with space missions to Venus in the coming decade.

One of the next giant leaps for humanity—inhabiting our neighbor planet Mars—requires enough water to support multi-year human survival and to create rocket fuel for the nearly 150-million-mile return trip to Earth. Water that is already on Mars, in the form of ice, is one of the leading in situ resources being considered in preparation for human exploration. Human missions will need to land in locations with relatively warm temperatures and consistent sunlight. But in these locations, ice (if present) is buried underground. Much of the ice known to exist in mid-latitude locations was likely emplaced under climate conditions (and orbital parameters) different from today. So in addition to providing an in-situ resource for human exploration, Martian ice also provides a crucial record of planetary climate change and the effects of orbital forcing.This presentation will highlight techniques and recent activities to characterize Mars’ underground ice, such as the Subsurface Water Ice Mapping (SWIM) Project (Morgan et al. 2021, Nature Astro.; Putzig et al. In Press, Handbook of Space Resources; Putzig et al. this AGU; Morgan et al. this AGU). We present outstanding questions that will be vital to address in the context of ISRU (in situ resource utilization) and connections between these questions and the climate in which the ice was emplaced and evolved (e.g., Bramson et al. 2020, Decadal White Paper). Lastly, we discuss how these science activities intersect with future exploration, particularly that enabled by collaborations between space agencies as well as industry partners (Heldmann et al. 2020, Decadal White Paper; Golombek et al. 2021, LPSC).High-priority future work includes better orbital characterization of shallow ice deposits, such as radar sounding at shallower scales (<~10m) than that of SHARAD, as proposed for the International Mars Ice Mapper. Also needed are detailed studies of the engineering required to build potential settlements at specific candidate locations; this includes characterization of the nature of the overburden above the ice, which will inform future resource extraction technology development efforts. Ideally, initial landing sites would be chosen with a long-term vision which includes preparation and development of the basic technologies and designs needed for human landing on Mars.