SAMPLE SCIENCE VERSUS REMOTE SENSING: BREAKING DOWN SILOS IN PLANETARY EXPLORATION

Among the most transformative events in the heritage of planetary exploration were opportunities to combine petrology/geochemistry/geochronology studies of samples in the laboratory with remote-sensing data for the same bodies obtained by orbiting or landed spacecraft. Prior to 1969, asteroid-sourced meteorites were the only known extraterrestrial samples, and spacecraft orbital remote-sensing focused primarily on planetary geomorphology and on rudimentary geophysics. Except for a handful of meteoriticists and astronomers studying telescopic spectra of asteroids, there was little or no interaction between the sample and planetary geology communities. Lunar samples returned by Apollo astronauts first breached these silos, with new discoveries about the Moon’s impact origin, an early magma ocean, later mare volcanism, and radiometric-age calibration for crater-distribution chronologies. Once martian meteorites were recognized in 1979, their mineralogy, geochemistry, and radioisotope chronology could be compared with analyses by instruments on Mars orbiters and rovers to constrain the planet’s magmatic evolution, surface sedimentary materials and processes, internal structure, and climate history. Organic compounds in one martian meteorite even prompted the search for life, a focus of current Mars exploration. For asteroid Vesta, meteorite samples were available long before spacecraft remote-sensing data. Vesta’s geologic evolution has been informed by analyses of HED meteorites, and by spectral and gravity mapping by the Dawn orbiter in 2011, which together have constrained its bulk composition, differentiation, chronology, internal structure, and impact history. These three bodies are now arguably the best understood extraterrestrial objects, in part because samples became available. The synergy between sample and remote-sensing data helped to transform these astronomical objects into worlds shaped by more or less familiar geologic processes.