If you were looking up at the Moon on March 17, 2013 at 03:50:55 UTC, you might have seen one of the brightest “lunar flashes” ever witnessed. And it would have been visible with just the naked eye.
“On March 17, 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.”
The scientists estimate that the flash came from a 40 kg meteoroid measuring 0.3 to 0.4 meters wide hitting the Moon, likely traveling about 90,000 km/hr (56,000 mph.) The resulting explosion packed as much punch as 5 tons of TNT.
Lunar meteors hit the ground with so much kinetic energy that they don’t require an oxygen atmosphere to create a visible explosion. The flash of light comes not from combustion but rather from the thermal glow of molten rock and hot vapors at the impact site.
When researchers looked back at their records from March, they found that the moon meteor might not have been an isolated event.
“On the night of March 17, NASA and University of Western Ontario all-sky cameras picked up an unusual number of deep-penetrating meteors right here on Earth” said Cooke. “These fireballs were traveling along nearly identical orbits between Earth and the asteroid belt.”
Though Earth’s atmosphere protected our planet’s surface from being hit by these meteors, the moon has no such luck. Its lack of an atmosphere exposes it to all incoming space rocks, and the NASA monitoring program has spotted more than 300 meteor strikes that reached its surface since 2005.
Part of the motivation for the program is NASA’s eventual intent to send astronauts back to the moon. When they arrive, they’ll need to know how often meteors impact the surface, and whether certain parts of the year, coinciding with the moon’s passage through crowded bits of the solar system, pose special dangers.
“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,” Cooke said. “Meanwhile, our analysis of the March 17th event continues.”
The scientists also hope to use NASA’s Lunar Reconnaissance Orbiter to photograph the impact site to learn more about how the crash occurred.