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Science 13 February 2009:
Vol. 323. no. 5916, pp. 909 - 912
DOI: 10.1126/science.1165988
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Reports

Lunar Radar Sounder Observations of Subsurface Layers Under the Nearside Maria of the Moon

Takayuki Ono,1 Atsushi Kumamoto,1 Hiromu Nakagawa,1 Yasushi Yamaguchi,2 Shoko Oshigami,2 Atsushi Yamaji,3 Takao Kobayashi,4 Yoshiya Kasahara,5 Hiroshi Oya6

Observations of the subsurface geology of the Moon help advance our understanding of lunar origin and evolution. Radar sounding from the Kaguya spacecraft has revealed subsurface layers at an apparent depth of several hundred meters in nearside maria. Comparison with the surface geology in the Serenitatis basin implies that the prominent echoes are probably from buried regolith layers accumulated during the depositional hiatus of mare basalts. The stratification indicates a tectonic quiescence between 3.55 and 2.84 billion years ago; mare ridges were formed subsequently. The basalts that accumulated during this quiet period have a total thickness of only a few hundred meters. These observations suggest that mascon loading did not produce the tectonics in Serenitatis after 3.55 billion years ago. Global cooling probably dominated the tectonics after 2.84 billion years ago.

1 Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
2 Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan.
3 Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
4 Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, Korea.
5 Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, Japan.
6 Department of Space Science and Technology, Fukui University of Technology, Fukui 910-8505, Japan.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)