Moon Gets Slammed by Cosmic Bullet

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On March 17, scientists monitoring the moon for meteorite impacts spotted the biggest impact event to date: a space rock the size of a basketball slammed into the lunar surface at a speed of 56,000 miles per hour (90,000 km/hr), creating a new crater around 20 meters wide.

“On March 17, 2013, an object about the size of a small boulder hit the lunar surface in Mare Imbrium,” said Bill Cooke of NASA’s Meteoroid Environment Office in a statement over the weekend. “It exploded in a flash nearly 10 times as bright as anything we’ve ever seen before.”

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Indeed, the flash was impressive — it unleashed the equivalent energy of 5 tons of TNT exploding and would have been visible to anyone casually looking at the moon, no telescope required.

The impact was captured by a NASA program monitoring impact events during “lunar meteor showers.” When small pieces of rock — meteoroids — hit the Earth’s atmosphere, they produce a bright streak of light as they burn up. These are “meteors.” On the moon, however, there is no atmosphere, so the meteoroids directly hit the lunar surface, creating an energetic flash.

These impact events occur with more regularity than expected.

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For the past eight years, NASA telescopes have been surveying the moon’s surface, cataloging every event. But the March 17 event was the biggest impact spotted to date.

Interestingly, the lunar impact coincided with an uptick of meteor detections in the Earth’s atmosphere — a factor that has led program scientists to believe that both events stemmed from debris originating from the asteroid belt between the orbits of Mars and Jupiter. This could signify a previously unknown stream of debris that could supply more impact events in the future.

“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,” said Cooke. “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. Meanwhile, our analysis of the March 17th event continues.”

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It is hoped that NASA’s Lunar Reconnaissance Orbiter (LRO) will fly over the impact site in the near future to image the fresh crater.

The rationale behind understanding the frequency of meteoroid impacts is to safeguard an extended human presence on the lunar surface. Rocks of any size traveling 56,000 mph with no atmosphere to slow them down would place spacewalking astronauts in a cosmic shooting gallery.

Since 2005, the lunar observation program has registered over 300 impact events. By identifying periods of intensified meteoroid impacts could signify that the Earth-moon system is passing through streams of interplanetary debris, similar to seasonal meteor showers. This could help mitigate the risks that moonwalkers would face in the future and may even aid lunar habitat designs.

Watch a video of the impact event.

Image: A photograph of the lunar surface taken by Apollo 12 astronauts. Credit: NASA

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