Showing papers by "Brett W. Denevi published in 2020"

Impact Melt Facies in the Moon's Crisium Basin: Identifying, Characterizing, and Future Radiogenic Dating.

Abstract: Both Earth and the Moon share a common history regarding the epoch of large basin formation, though only the lunar geologic record preserves any appreciable record of this Late Heavy Bombardment. The emergence of Earth's first life is approximately contemporaneous with the Late Heavy Bombardment; understanding the latter informs the environmental conditions of the former, which are likely necessary to constrain the mechanisms of abiogenesis. While the relative formation time of most of the Moon's large basins is known, the absolute timing is not. The timing of Crisium Basin's formation is one of many important events that must be constrained and would require identifying and dating impact melt formed in the Crisium event. To inform a future lunar sample dating mission, we thus characterized possible outcrops of impact melt. We determined that several mare lava-embayed kipukas could contain impact melt, though the rim and central peaks of the partially lava-flooded Yerkes Crater likely contain the most pure and intact Crisium impact melt. It is here where future robotic and/or human missions could confidently add a key missing piece to the puzzle of the combined issues of early Earth-Moon bombardment and the emergence of life.

A Mercury Lander Mission Concept Study for the Next Decadal Survey

Abstract: Mariner 10 provided our first closeup reconnaissance of Mercury during its three flybys in 1974 and 1975. MESSENGER’s 2011–2015 orbital investigation enabled numerous discoveries, several of which led to substantial or complete changes in our fundamental understanding of the planet. Among these were the unanticipated, widespread presence of volatile elements (e.g., Na, K, S); a surface with extremely low Fe abundance whose darkening agent is likely C; a previously unknown landform—hollows— that may form by volatile sublimation from within rocks exposed to the harsh conditions on the surface; a history of expansive effusive and explosive volcanism; substantial radial contraction of the planet from interior cooling; offset of the dipole moment of the internal magnetic field northward from the geographic equator by ~20% of the planet’s radius; crustal magnetization, attributed at least in part to an ancient field; unexpected seasonal variability and relationships among exospheric species and processes; and the presence in permanently shadowed polar terrain of water ice and other volatile materials, likely to include complex organic compounds. Mercury’s highly chemically reduced and unexpectedly volatile-rich composition is unique among the terrestrial planets and was not predicted by earlier hypotheses for the planet’s origin. As an end-member of terrestrial planet formation, Mercury holds unique clues about the original distribution of elements in the earliest stages of the Solar System and how planets (and exoplanets) form and evolve in close proximity to their host stars. The BepiColombo mission promises to expand our knowledge of this planet and to shed light on some of the mysteries revealed by the MESSENGER mission. However, several fundamental science questions raised by MESSENGER’s pioneering exploration of Mercury can only be answered with in situ measurements from the planet’s surface.

Shackleton — De Gerlache Ridge: A Strong Candidate for Important Lunar Science, Science Operations, and Polar Volatiles

Abstract: SCIENCE, SCIENCE OPEARTIONS, AND POLAR VOLATILES. J. E. Gruener, S. J. Lawrence, J. A. Hamilton, A. M. Jagge, A. W. Britton, S. R. Deitrick, C. R. Neal, B. W. Denevi, and J. D. Stopar. NASA JSC Astromaterials Division, Houston, TX. HX5 JETS Contract, NASA JSC Astromaterials Division, Houston, TX Jacobs JETS Contract, NASA JSC Astromaterials Division, Houston, TX. Dept. CEEES, University of Notre Dame, Notre Dame, IN. Johns Hopkins University Applied Physics Laboratory, Laurel, MD. Lunar Planetary InstituteUSRA, Houston, TX.