Ultramafic impact melt sheet beneath the South Pole–Aitken basin on the Moon

[1] The Spectral Profiler onboard the Japanese lunar explorer Kaguya conducted the first hyperspectral survey around the South Pole-Aitken basin (SPA) on the Moon that is one of the largest impact structures in the Solar System. The radiative transfer modeling revealed that fresh crater central peaks inside SPA are commonly composed of an ultramafic assemblage dominated by Magnesium rich orthopyroxene, suggesting a homogeneous layer buried under SPA. The extensive ultramafic layer could be a relic of a gigantic impact melt pool produced by the SPA-forming impact. The preponderance of orthopyroxene could have resulted from significant fractional crystallization of the lunar magma ocean prior to the onset of plagioclase floatation.