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Crash or Coincidence?
An odd-looking impact feature raises an intriguing, Apollo-era trivia question › View larger image
An odd-looking impact feature raises an intriguing, Apollo-era trivia question (3.02°N, 119.15°E). NAC image number M141485413; incidence angle 12°; Sun is from the east; north is up; image is ~600 meters across [NASA/GSFC/Arizona State University].

What caused this peculiar-looking impact? The "butterfly"-shaped ejecta pattern is diagnostic of a low-angle collision (see another example here). The dark/light contrasting tones are indicative of compositional or maturity differences among the target materials (see another example here). This much we understand. But was it created by a chunk of space debris or from the crash landing of a space probe? The LROC NAC resolution is so high that small features from Apollo-era landed or crashed spacecraft are often visible. Today's Featured Image is a fitting topic for the 42nd anniversary of the Apollo 11 landing, which landed safely in Mare Tranquillitatis on July 20, 1969.

Lunar Orbiter 2 was an unmanned imaging spacecraft used in November and early December 1966 to aid with Apollo and Surveyor landing site selection. The spacecraft became famous in 1967 with the public release of an oblique image of Copernicus crater (one of only four obliques collected), which was hailed as the "Picture of the Century" by the news media of the day. According to the 2007 International Atlas of Lunar Exploration, the Lunar Orbiter 2 spacecraft was commanded to crash into the lunar farside surface on October 11, 1967. The coordinates of the Lunar Orbiter 2 impact are given as 119.1° east longitude and 3.0° north latitude, which match those of the feature in the NAC image (measured at 119.149° east longitude, and 3.020° north latitude). However, the published Lunar Orbiter 2 numbers are given as a rough estimate because the impact occurred on the farside of the Moon, out of direct radio contact. So the match with the NAC coordinates could be a coincidence. The impact appears much too large (~85 m in diameter) to be the result of an impact from a spacecraft only a few meters tall, but with a solar incidence angle of only 12 degrees, it is difficult to see the crater rim and find out the true diameter. Perhaps the ejecta pattern extends far beyond the immediate impact. The truth is that we are not sure what caused this impact feature. We are currently re-targeting the area under a higher incidence angle to help with crater rim measurements. Stay tuned!

What additional clues would you look for to satisfy this mystery? The feature is very asymmetrical. Would it help to know the orientation of Lunar Orbiter 2's final orbit? Why? Here is a good discussion for the classroom!

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