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North Ray crater is a small crater in the Descartes Highlands of the moon visited by the astronauts of Apollo 16. The name of the crater was formally adopted by the IAU in 1973.〔 It is the largest crater sampled by astronauts during the Apollo program. The Apollo 16 Lunar Module (LM) ''Orion'' landed between North Ray and South Ray craters on April 21, 1972. The astronauts John Young and Charles Duke explored the area between the craters over the course of three EVAs using a Lunar Roving Vehicle, or rover. They visited North Ray on EVA 3, at station 11, about 4.4 km north of the landing site. On the way, they drove along the rim of the similar sized but older crater Palmetto, which is approximately 3 km south of North Ray. North Ray crater is approximately 1 km in diameter and approximately 240 m deep.〔(Apollo 16 Landing Area ), 78D2S1(50), NASA Lunar Topophotomap. Published by The Defense Mapping Agency, November 1974. Available from Lunar and Planetary Institute.〕 The astronauts observed that the upper 50 m of the slope is gentle, but that it becomes steep below 50 m, and they could not observe the bottom. The inner slopes are covered by boulders up to 5 m across. A huge (10 m high x 20 m long) boulder, known as House Rock, lies near the southeastern rim. A smaller boulder that is almost certainly a fragment of House Rock is officially known as South Boulder, but unofficially known as Outhouse Rock.〔(Apollo 16 Preliminary Science Report ) (NASA SP-315), 1972〕 The ray system, which can be seen from orbit, was not obvious on the ground. North Ray cuts into the Cayley Formation of Imbrian age,〔(Geologic Map of the Apollo 16 (Descartes) Landing Area ) by Apollo Field Geology Investigation Team (D. P. Elston, E. L. Boudette, J. P. Schafer), United States Geological Survey, April 1972〕 but the crater itself is much younger, of Copernican age, based on the presence of rays. (See also section on age below.) ==Age== Based on sample 67955,〔(67955 ) Summary Sheet available from Lunar and Planetary Institute〕 a noritic anorthosite collected from Outhouse Rock, the impact that created North Ray crater was about 50 million year ago. This is based on the measured duration of the rock's exposure to cosmic rays.〔Drozd R.J., Hohenberg C.M., Morgan C.J. and Ralston C.E. (1974) Cosmic-ray exposure history at the Apollo 16 and other lunar sites: lunar surface dynamics. Geochim. Cosmochim. Acta 38, 1625-1642.〕 The rock itself is dated at 4.20 ± 0.07 b.y. by Sm/Nd radiometric dating.〔Norman M.D., Shih C.-Y., Nyquist L.E., Bogard D.D. and Taylor L.A. (2007) Early impacts on the moon: Crystallization ages of Apollo 16 melt breccias ((abs#1991 )). Lunar Planet. Sci. XXXVIII Lunar & Planetary Institute, Houston. ((LPSC 2007 web page ))〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「North Ray (crater)」の詳細全文を読む スポンサード リンク
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