Although the Moon is Earth’s closest neighbor, some of its fundamental properties are not well understood. A better grasp of the composition and thermal structure of the lunar interior, for example, would help researchers trace the evolution of the Moon and the origins of its volcanic deposits and other surface features seen today. To help probe the Moon’s interior, two spacecraft with NASA’s GRAIL mission, Ebb and Flow, collected observations in lunar orbit in 2012. Small displacements in the orbits of the instruments were used to generate a map of the lunar gravitational field.
From early analyses, it appeared that the Moon’s deep interior was roughly spherically symmetric. Many researchers, therefore, assumed that the observed compositional and temperature asymmetries were too small to help explain how the Moon formed and evolved. That assumption, however, now seems to be overturned. Using GRAIL data, Ryan Park of the NASA Jet Propulsion Laboratory and colleagues found an unexpectedly large time-varying gravity signature that they report is consistent with uneven temperatures in the Moon’s deep interior.
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