Last September, a pair of telescopes from a project called MIDAS (Moon Impacts Detection and Analysis System) did what they were designed for and monitored the blast from a meteoroid plowing into the lunar surface. This isn't the first time we've seen this happen, but this particular blast was the brightest ever detected, and the afterglow of the impact continued for eight seconds, as material that had vaporized in the blast cooled off. Now, the researchers have published a description of the event and placed video of it on YouTube.

The MIDAS project, which attempts to monitor the lunar surface for impacts, may seem like a dry academic pursuit. But it's actually relevant to human safety. We don't have a strong sense of the rate at which small bodies slam into the Earth, and it's difficult to monitor the entire Earth's atmosphere (done through projects called "fireball networks"). In contrast, it's relatively easy to monitor large areas of the unlit surface of the moon during many of its phases and to extrapolate from the rate of impacts to the rate at which the Earth must be getting struck.

(The MIDAS team uses two telescopes in case some form of noise causes a flash in one of the cameras, but they're less than a meter in size and are from a manufacturer that sells directly to consumers.)

When an object strikes the lunar surface, it creates a flash due to the vaporization of itself and material at the site of impact; larger bodies may have impacts that continue to glow a bit as the vaporized material cools off. But so far, the team had never detected anything like an eight-second glow.

Based on the amount of light emitted, the team was able to reconstruct two possible impact scenarios. Assuming the object was part of a then-recent meteor shower, it would have a very high velocity relative to the moon, and it wouldn't need as much mass to cause an impact with this energy. In this scenario, the rock was about 45kg and 36cm across. If it was a stray meteoroid, the velocity would be lower and the mass greater: 450kg, with a diameter that could be as large as 1.4 meters.

In either case, the resulting crater should be about 47m in diameter—big enough to be picked up by any orbiting lunar observatories. The impact site is near the western edge of Mare Nubium.

The MIDAS project has been running since 2009 and has an automated pipeline for identifying impacts. The statistics it has generated suggest that some early estimates of the rate at which Earth is bombarded may be low by as much as a factor of 10.

Monthly Notices of the Royal Astronomical Society, 2014. DOI: 10.1093/mnras/stu083 (About DOIs).