September 8, 2017
In the spring of 2015, the MESSENGER Mercury orbiter was running low on fuel and gravitational perturbations were pulling the spacecraft toward an inevitable impact on the surface. With end of the mission in sight, the MESSENGER team conceived an ambitious plan to to observe the planet from altitudes as low as a few km, orders of magnitude closer than previously achieved. This low-altitude observation campaign provided unprecedented views of Mercury’s surface. One target of these observations was the mysterious “low-reflectance material”, irregular dark patches of the surface that were expected to provide the answer to an important outstanding question – why is Mercury’s surface as dark as coal? The answer to this question provided an unexpected view of Mercury’s original, 4.5 billion-year-old crust and transformed our understanding of the planet’s formation and early evolution.
Patrick Peplowski is a research scientist with the Johns Hopkins University Applied Physics Laboratory’s Solar System Exploration group. He specializes in using nuclear spectroscopy of planetary surfaces to map the surface compositions of airless solar system bodies, including Mercury, the Moon, and asteroids. He served as the instrument scientist for the MESSENGER Gamma-Ray Spectrometer, and will reprise that role for the upcoming Psyche mission to explore the metallic asteroid 16 Psyche.
Rachel Klima is a research scientist at the Johns Hopkins University Applied Physics Laboratory. Her research focuses on linking infrared reflectance spectra to the mineralogical composition of solid bodies in the solar system. She has been involved with the Moon Mineralogy Mapper, Dawn, and MESSENGER science teams, and is now serving as a member of the Europa Clipper Mission project science team.