Astronomers have filmed a small asteroid smashing into the dark side of the Moon, creating a flash bright enough to be seen with the naked eye.
The impact, caught on video camera, is the longest and brightest ever confirmed. Experts believe it was caused when an asteroid the size of a car hit the lunar surface.
Because the Moon has no discernible atmosphere, meteors do not burn up as they do over the Earth, so even small rocks hit the ground. In recent years astronomers have watched during known meteor showers and have recorded a handful of faint impacts.
But the explosion caught by Professor Jose Madiedo, from the south of Spain, and revealed this week in the UK journal Monthly Notices of the Royal Astronomical Society, is a record-breaker for recent times.
Through a telescope, the Moon shows it has undergone a violent history with its surface heavily scarred from major asteroid impacts. But most of these happened billions of years ago during a period called the Late Heavy Bombardment.
Today sizeable impacts are rare, with much less debris drifting around the inner Solar System, though the asteroid that exploded over Chelyabinsk, Russia, in February last year showed that the threat is ever present.
Professor Madiedo recorded the moonflash on 11 September 2013 as he was operating two telescopes near Seville, Spain, as part of the Moon Impacts Detection and Analysis System (MIDAS). The project monitors the Moon for tell-tale flashes.
At 20:07 UT, he detected a long and bright flash in Mare Nubium, the Sea of Clouds, which is an ancient lava-filled basin that makes up part of the face of the “Man in the Moon”. At the time it was on the side of the Moon that was in darkness, because the Moon was approaching First Quarter.
Professor Madiedo, from the University of Huelva, said: “At that moment I realised that I had seen a very rare and extraordinary event.” The flash, recorded through one of the telescopes on a video camera, was nearly as bright as the Pole Star and so could have been visible to anyone looking at the Moon at the time.
Prof Madiedo and colleague Dr Jose Ortiz, from the Institute of Astrophysics of Andalusia, think that the flash was produced by an asteroid up to 1.4 meters wide that struck Mare Nubium at about 38,000 mph (61,000 kph), with the explosive force of 15 tons of TNT, and created a new crater about 40 meters wide. The blast was at least three times higher than the largest previously seen event observed by NASA in March last year.
Video showing the flash caused by the asteroid impact. Credit: J. Madiedo / MIDAS