Projectile remnants in central peaks of lunar impact craters

• Published in: Nature geoscience Vol. 6; no. 6; pp. 435 - 437
• Main Authors: Yue, Z., Johnson, B. C., Minton, D. A., Melosh, H. J., Di, K., Hu, W., Liu, Y.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2013; Nature Publishing Group
• Subjects: 704/445/847; Earth Sciences; Earth System Sciences; Excavation; Geochemistry; Geology; Geophysics/Geodesy; letter; Magnesium; Mathematical models; Minerals
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/ngeo1828

Unusual minerals observed in lunar craters were thought to originate from beneath the Moon’s surface. Numerical simulations show that rather than being vaporized, much of the impactor material can survive in the crater, implying that the unusual minerals come from the impactor and may not be indigenous to the Moon. The projectiles responsible for the formation of large impact craters are often assumed to melt or vaporize during the impact, so that only geochemical traces 1 , 2 or small fragments 3 , 4 remain in the final crater. In high-speed oblique impacts, some projectile material may survive 5 , 6 , 7 , but this material is scattered far down-range from the impact site. Unusual minerals, such as magnesium-rich spinel 8 , 9 and olivine 10 , 11 , observed in the central peaks of many lunar craters are therefore attributed to the excavation of layers below the lunar surface. Yet these minerals are abundant in many asteroids, meteorites and chondrules 12 , 13 , 14 , 15 . Here we use a numerical model to simulate the formation of impact craters and to trace the fate of the projectile material. We find that for vertical impact velocities below about 12 km s −1 , the projectile may both survive the impact and be swept back into the central peak of the final crater as it collapses, although it would be fragmented and strongly deformed. We conclude that some unusual minerals observed in the central peaks of many lunar impact craters could be exogenic in origin and may not be indigenous to the Moon.