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Emily LakdawallaJune 15, 2010

Is this SMART-1's impact site?

Speaking of spacecraft crashing...I was reading the May 2010 issue of Icarus and came across a paper tersely titled "The SMART-1 lunar impact," by M.J. Burchell, R. Robin-Williams, and B.H. Foing. It was an interesting paper because there wasn't a lot of data available. The SMART-1 team knew exactly when and approximately where the spacecraft hit, and they saw a weak flash from Earth. But they have not been able to locate an impact crater on the Moon. This is not too surprising, since it was such a small spacecraft and hit the ground at such a shallow angle (only 1 degree), so the paper goes into great detail on theoretical models of what the crater should look like.

SMART-1 lunar impact as seen from Earth

Canada-France-Hawaii Telescope Corporation

SMART-1 lunar impact as seen from Earth
The 3.6-meter optical/infrared Canada-France-Hawaii Telescope (CFHT) in Hawaii captured this impressive sequence of SMART-1 impact images showing before, during, and after the impact. The impact flash -- which lasted only about 1 millisecond -- may have been caused by the thermal emission from the impact itself or by the release of spacecraft volatiles, such as the small amount of hydrazine fuel remaining on board.

Well, it may be possible that Phil Stooke has found the real thing in recent Lunar Reconnaissance Orbiter images (which would not have been available before the Icarus article went to print). But I emphasize "maybe." The thing that makes this impact site hard to locate also makes it very hard to be certain that Phil's found the real thing; it could just be another relatively recent low-angle impact of a low-mass object. Still, it'd be worth a long look by the authors of that paper! If it's the right thing, then, Phil says, SMART-1's crash didn't end with an impact into the north slope mountain identified by the mission team; it would have skimmed that peak and came to ground slightly to the south. "I don't know how plausible that is, but I don't see another candidate site yet," he says.

Is this where SMART-1 hit?

NASA / GSFC / ASU / Phil Stooke

Is this where SMART-1 hit?
Planetary cartographer Phil Stooke tentatively identified a tiny splat visible in a Lunar Reconnaissance Orbiter image as the place where ESA's lunar orbiter SMART-1 crashed. SMART-1 was traveling from north to south, and the mission previously identified a small mountain (top image) as being the likely crash location based upon its ground track and the time of its impact (which produced a detectable flash, seen from Earth). SMART-1 hit at 33°S and 46.2°W on September 3, 2006 at 05:42 UTC. When it crashed, it did so at an exceedingly shallow angle of only about 1 degree. The resulting crater should be elongate and should have a butterfly-like spray of ejecta. Stooke looked at Lunar Reconnaissance Orbiter Camera images of the mountain, progressively zooming in from the top image, to left center, to right center, to the bottom image, identifying a bright (hence, fresh) splat as the possible impact site. This identification is far from certain; it's just a possible candidate.

Read more: citizen science, Lunar Reconnaissance Orbiter, SMART-1, spacecraft, the Moon, optical telescopes

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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