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2.3.1 One 'big' impact

Watch this NASA video reporting the event of 17 March 2013. The commentary for the video omits to point out that the video of the flash was made by imaging the part of the Moon that was in darkness and that the faintly visible Moon in the video is illuminated only by light reflected onto the Moon from the Earth. Faint flashes occurring on the sunlit part of the Moon would be almost impossible to see. The video refers to ‘explosions’, which is not strictly true – the crater is excavated by a shock wave generated at the point of impact. The flash is the sudden glow caused by the incoming energy being turned into heat. Listen out for the estimated size of the crater in the video commentary.

The new crater has now been imaged, and you can swipe across a before and after comparison [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] captured by the Lunar Reconnaissance Orbiter Camera. (This can be a little fiddly on small screens and will work best on desktops/tablets.)

Download this video clip.
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Bright Explosion on the Moon. Presented by Science @ NASA. For the past eight years, NASA astronomers have been monitoring the Moon for signs of explosions caused by meteoroids hitting the lunar surface. Lunar meteor showers have turned out to be more common than anyone expected-- with hundreds of detectable impacts occurring every year. They've just seen the biggest explosion in the history of the programme.
On March 17th, 2013, an object about the size of a small boulder hit the lunar surface in Mare Imbrium says Bill Cooke of NASA's Meteoroid Environment Office. It exploded in a flash nearly 10 times as bright as anything we've ever seen before. Anyone looking at the Moon at the moment of impact could have seen the explosion - no telescope required. For about one second, the impact site was glowing like a fourth-magnitude star.
Ron Suggs - an analyst at the Marshall Space Flight Centre - was the first to notice the impact in a digital video recorded by one of the monitoring programmes' 14-inch telescopes. "It jumped right out at me. It was so bright," he recalls. The 40 kg meteoroid-- measuring 0.3 to 0.4 metres wide - hit the Moon travelling 56,000 miles per hour. The resulting explosion packed as much punch as five tonnes of TNT. Cooke believes the lunar impact might have been part of a much larger event.
'On the night of March 17th, NASA and University of Western Ontario all-sky cameras picked up an unusual number of deep-penetrating meteors right here on Earth,' he says. 'These fireballs were travelling along nearly identical orbits between Earth and the asteroid belt. This means Earth and the Moon were pelted by meteoroids at about the same time. My working hypothesis is that the two events are related and that this constitutes a short-duration cluster of material encountered by the Earth/Moon system.' says Cooke.
One of the goals of the lunar monitoring programme is to identify new streams of space debris that pose a potential threat to the Earth/Moon system. The March 17th event seems to be a good candidate. Controllers of NASA's Lunar Reconnaissance Orbiter have been notified of the strike. The crater could be as wide as 20 m, which would make it an easy target for LRO the next time the spacecraft passes over the impact site. Comparing the size of the crater to the brightness of the flash would give researchers a valuable ground truth measurement to validate lunar impact models.
Unlike Earth - which has an atmosphere to protect it - the Moon is airless and exposed. Lunar meteors crash into the ground with fair frequency. Since the monitoring programme began in 2005, NASA's lunar impact team has detected more than 300 strikes - most, orders of magnitude fainter than the March 17th event. Statistically speaking, more than half of all lunar meteors come from known meteoroid streams - such as the Perseids and Leonids. The rest are sporadic meteors, random bits of comet and asteroid debris of unknown parentage.
US space exploration policy eventually calls for extended astronaut stays on the lunar surface. Identifying the sources of lunar meteors and measuring their impact rates gives future lunar explorers an idea of what to expect. Is it safe to go on a Moon walk or not? The middle of March might be a good time to stay inside.
'We'll be keeping an eye out for signs of a repeat performance next year when the Earth/Moon system passes through the same region of space,' says Cooke. Meanwhile, our analysis of the March 17th event continues. For updates about explosions on the Moon and elsewhere in the cosmos stay tuned to
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