MOON DIVER: DESCENDING INTO A LAVA PIT TO EXPLORE THE LUNAR MARE SEAS

Lunar basalts preserve a record of the chemical composition and thermal history of the Moon, yet significant questions remain unresolved regarding the dynamics and rates at which lava was emplaced on the lunar surface. While studies of the morphologies, chemistries, and spectral properties of mare basalts have yielded insights into the origin of lunar basalts, in situ analyses of a stratigraphic sequence of basalt layers are needed to constrain the eruption flux, eruption duration, and flow dynamics responsible for the emplacement of observed lava seas. Recent images returned by the Kaguya and Lunar Reconnaissance Orbiter missions reveal deep mare pits with meter-scale layered stratigraphy exposed in their walls, providing unprecedented access to mare bedrock stratigraphy. A mission to such an exposure would address numerous top priority lunar science goals as defined in the Lunar Exploration Roadmap, including understanding mare stratigraphy, exploring the regolith/bedrock interface, and accessing lava samples in context. Before now, limitations in traditional rover mobility have inhibited our ability to send a mission to such steep destinations. The Axel Extreme Terrain Rover, developed by JPL in collaboration with Caltech, has the mobility needed to approach and rappel into a lunar pit, revolutionizing our ability to explore the mare stratigraphy. The Axel rover consists of two wheels connected by a thick axle containing a winch and tether. Scientific instruments are inside the wheel well. Axel can traverse flat terrains like an ordinary rover, and it uses its tether for support to rappel down steep or vertical terrain. The rover receives communication and power through its tether, meaning that it can leave a solar panel and antenna on the surface while exploring the dark pit and cave below. The functionality of Axel enables examination and characterization of lava layers exposed in the wall of a mare pit crater during descent. Lava morphology and layer thicknesses (provided by a context imager), mineralogy and texture (provided by a multispectral microimager), and elemental chemistry (provided by an Alpha Particle X-Ray Spectrometer) would reveal how flood basalts are emplaced on one-plate bodies like the Moon, and how evolution of those deposits in the space environment creates regolith on an airless body.