Last month, Earth passed through a “minefield” of debris from Comet 55P/Tempel-Tuttle. This happens every year in mid-November and results in the annual Leonid meteor shower. From Nov. 17th to Nov. 19th both Earth and the Moon were peppered with meteoroids.
Meteoroids that hit Earth disintegrate harmlessly (and beautifully) in the atmosphere. But the Moon has no atmosphere to protect it, so meteoroids don’t stop in the sky. They hit the ground. The vast majority of these meteoroids are dust-sized, and their impacts are hardly felt. But bigger debris can gouge a crater in the lunar surface and explode in a flash of heat and light. Some flashes can be seen from Earth.
During the passage through Tempel-Tuttle’s debris field, Cooke’s team trained their telescopes (two 14-inch reflectors located at the Marshall Space Flight Center) on the dark surface of the Moon. On Nov. 17th, after less than four hours of watching, they video-recorded two impacts: a 9th magnitude flash in Oceanus Procellarum (the Ocean of Storms) and a brighter 8th magnitude flash in the lunar highlands near crater Gauss.
“The flashes we saw were caused by Leonid meteoroids 2 to 3 inches (5 to 8 cm) in diameter,” says Cooke. “They hit with energies between 0.3 and 0.6 Giga-Joules.” In plain language, that’s 150 to 300 pounds of TNT.