Paper No. 264-8
Presentation Time: 3:35 PM
THE DIMPLE EXPERIMENT TO INA: RESOLVING A CONUNDRUM IN LUNAR THERMAL EVOLUTION
ANDERSON, F1, LEVINE, J2, BRADEN, Sarah3, HEAD, James4, FAGAN, Amy5, JOY, Katherine6, TARTESE, Romain6, PERNET-FISHER, John6, YANT, Marcella7, BIERHAUS, E. Beau8, WURZ, Peter9, FAUSCH, Rico9 and OSTERMAN, Steven1, (1)Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, CO 80302, (2)Department of Physics and Astronomy, Colgate University, Hamilton, NY 13346, (3)Boulder, CO 80302, (4)Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, (5)Geosciences and Natural Resources, Western Carolina University, Cullowhee, NC 28723, (6)Department of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester, Manchester M13 9PL, United Kingdom, (7)Lockheed Martin Space, Littleton, CO 80127, (8)Lockheed Martin Space Systems Company, Littleton, CO 80120, (9)Physics Institute, University of Bern, 216 / Gesellschaftsstrasse 6, Bern, Switzerland
NASA has recently selected the DIMPLE payload (Dating an Irregular Mare Patch with a Lunar Explorer) for flight to the Moon. DIMPLE will land on Ina, a 2 x 3 km irregular mare patch characterized by low, smooth ~100-500 m wide meniscus-like mounds surrounded by lower rough terrain, situated in a volcanic summit pit crater in Lacus Facunditatis. Ina is an especially exciting target for study: its crater size-frequency distribution implies an extraordinarily young age of ~33 Ma. If it is indeed so young, then the Moon must have been volcanically active for at least 99% of its history. This would be a great surprise, since the youngest dated lunar basalts presently known are >1900 Ma old, and the lunar interior is thought to have long ago become too cold for volcanism. An alternative explanation for the scarcity of craters at Ina is that its host rocks are 3.5 Ga old and formed of a chilled vesicle-rich foamy extrusion that poorly records impact cratering over eons due to crushing of the porous substrate. If this is correct, then crater-based estimates of planetary surface ages throughout the inner Solar System cannot be secure without additionally assessing rock textures. DIMPLE will settle the question by determining the age, composition, and petrology of rocks at Ina.
The primary DIMPLE instrument is the Chemistry and Dating Experiment (CODEX), a resonance-ionization mass spectrometer developed for interference-free Rb and Sr isotopic measurements. CODEX also operates as a laser-ablation mass spectrometer for measuring elemental abundances. In both analyses, CODEX samples hundreds to thousands of ~35 μm spots on each rock specimen, producing a chemical map and an isochron age determination in as little as 5 hours. The rest of the payload includes a lander-mounted arm, gripper, and saw for obtaining rocks from the lunar surface and cutting flat faces into them, as well as a rover-mounted rake for collecting rocks within tens to hundreds of meters of the lander.
DIMPLE represents the first opportunity to employ a purpose-built radioisotopic dating instrument in situ on another planetary body. The technology can also be applied to address myriad other outstanding questions of Solar System chronology.
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