NASA scientists have observed an explosion on the moon. The blast, equal in energy to about 70 kg of TNT, occurred near the edge of Mare Imbrium (the Sea of Rains) on Nov. 7, 2005, when a 12-centimeter-wide meteoroid slammed into the ground traveling 27 km/s.
“What a surprise,” says Marshall Space Flight Center (MSFC) researcher Rob Suggs, who recorded the impact’s flash. He and colleague Wes Swift were testing a new telescope and video camera they assembled to monitor the moon for meteor strikes. On their first night out, “we caught one,” says Suggs.
The object that hit the moon was “probably a Taurid,” says MSFC meteor expert Bill Cooke. In other words, it was part of the same meteor shower that peppered Earth with fireballs in late October and early November 2005. (See “Fireball Sightings” from Science@NASA.)
The moon was peppered, too, but unlike Earth, the moon has no atmosphere to intercept meteoroids and turn them into harmless streaks of light. On the moon, meteoroids hit the ground–and explode.
“The flash we saw,” says Suggs, “was about as bright as a 7th magnitude star.” That’s two and a half times dimmer than the faintest star a person can see with their unaided eye, but it was an easy catch for the group’s 10-inch telescope.
Cooke estimates that the impact gouged a crater in the moon’s surface “about 3 meters wide and 0.4 meters deep.” As moon craters go, that’s small. “Even the Hubble Space Telescope couldn’t see it,” notes Cooke. The moon is 384,400 km away. At that distance, the smallest things Hubble can distinguish are about 60 meters wide.
This isn’t the first time meteoroids have been seen hitting the moon. During the Leonid meteor storms of 1999 and 2001, amateur and professional astronomers witnessed at least half-a-dozen flashes ranging in brightness from 7th to 3rd magnitude. Many of the explosions were photographed simultaneously by widely separated observers.