The lunar burst was caused by a 40-kilogram boulder-sized rock slamming into the surface at about 90,000 kph. It generated a flash 10 times brighter than anything seen before, which came from the thermal glow of molten rock at the point of impact.
The moon, like most bodies in the solar system, is subject to relatively frequent bombardment by small space rocks. Most of these objects are fairly tiny, pebble-sized or smaller, but in 2005 NASA set up a specific program to identify how often they occur. The lunar impact team has since identified more than 300 explosions, most of them faint and usually happening at the same time as a meteor shower on Earth. Researchers want to know how often they can expect such impacts, which could come in handy when planning moonwalks during future astronaut trips to our satellite.
The March 17 impact created a blast that was bright enough to be seen from Earth with the naked eye. It may have generated a crater roughly 20 meters wide, which could be imaged by the Lunar Reconnaissance Orbiter next time it passes over the area, allowing researchers to see a very fresh impact on the moon.
From Wired Science