Over nearly 60 years of spacecraft exploration of the Moon, lots of spacecraft have crashed on the lunar surface. Some were accidental impacts, like the NASA robotic lander Surveyor 2 which failed during its flight to the Moon, or the Soviet Union’s Luna 15 which was attempting a sample return even while the Apollo 11 astronauts were on the lunar surface. Others were deliberate crashes. Some of those crashed as part of the mission, like Ranger 7 or LCROSS, the first taking pictures all the way down to the point of impact and the second using its crash to excavate a plume of debris and volatile substances for analysis by a companion spacecraft. Others were simply commanded to hit the Moon at the end of a mission, like the gravity-mapping GRAIL spacecraft or the Apollo Lunar Module ascent stages. Some of those still did useful work, like the Apollo ascent stages which generated seismic signals for equipment deployed by the astronauts. A few other spacecraft such as the Soviet orbiter Luna 19 and the Indian Chandrayaan 1 orbiter were abandoned in orbit and will have crashed later as their orbits evolved, at unknown locations.

For many of these crashes tracking or imaging data allowed the impact site to be located fairly precisely, and often an impact crater can been found in the spectacular high resolution images from NASA’s Lunar Reconnaissance Orbiter. The LRO camera team have a great website in which these craters and their ejecta deposits (and lots of successful landers) can be seen under different illumination conditions, sometimes with before and after images for recent impacts.

But some impact sites are missing from this site. In some cases we don’t know the location well enough to look for it—Surveyor 2 and Luna 15 both fall into that category. Others should be easier to find but have not been located. In particular the Apollo LM ascent stage impacts have proven elusive, despite prolonged efforts by several researchers. The Apollo Lunar Module ascent stage was massive enough (2300 kg) to make its mark on the lunar surface but the large hollow structure and the very low angle oblique impact (about 3°) make it hard to estimate what sort of feature might mark the impact site.

Four impact sites which have not been identified previously are described here based on recent work I have been doing in the Centre for Planetary Science and Exploration at Western University in London, Ontario. Two are Apollo Lunar Module ascent stages, from Apollo 12 and Apollo 14. The third site is that of the Chinese orbiter Chang’E 1, whose impact site was previously imaged by Apollo 16 for comparison with LRO images, forming a before-and-after pair which conclusively demonstrates that the correct location has been found. The fourth is SMART-1, the European mission to the Moon launched in 2003 and crashed at the end of its mission in September 2006.

Apollo 12

The Apollo 12 impact site was discovered by means of a very unusual (in fact apparently unique) field of small dark markings suggestive of shrapnel strikes, located at 3.90° S, 21.23° W just west of the tracking location of the impact. By following this line back along the orbit path the impact site was discovered. The expected fan-shaped spray of ejecta which LRO has also seen at the GRAIL and LADEE impact sites was visible and seems to originate from a linear gouge oriented along track (C in the figure below). The gouge is roughly 25 m long and 2 to 3 m wide at 3.920° S, 21.172° W. Topographically, the gouge is on the crest of a small rise in topography, and the shrapnel markings commence 800 m to the west and extend for about 1500 m. The gap between those markings and the impact site is a shallow depression in LRO laser altimeter (LOLA) topography. It seems that the cloud of debris from the impact, which was probably generated when a grazing impact induced catastrophic rotation in the spacecraft, flew over the depression before striking the surface downrange.