Two flashes eerily illuminated the moon last week; what caused them?

Last week, some sharp-eyed telescopes captured something crashing into the moon. Then, over the weekend, a second object pierced its silvery surface.

The two incidents were a reminder that the moon is not quite the serene orb we clearly see in the night sky a few nights a month, but rather a noisy battlefield, constantly gaining new craters.

The two lunar impacts were detected by Daichi Fujii, curator at the Hiratsuka City Museum in Japan, who keeps his telescopes focused on the lunar surface. On Thursday, at 8:33 pm local time, he spotted a brief burst of light in the darkness. Then, on Saturday, at 8:49 p.m., “I caught another bright glow,” he said.

These flashes may have occurred around Halloween, but there’s nothing scary going on here. Both were the result of asteroids colliding with the lunar surface.

Without an atmosphere to slow them down, these two space rocks hit the moon’s volcanic soil at speeds of up to 96,500 km/h, approximately 30 times faster than a fighter jet. The size of the objects is unknown, but even an asteroid just a few meters long traveling at that speed would release a powerful explosion, equivalent to a modest stash of dynamite — a fleeting firestorm that can be seen hundreds of thousands of kilometers from Earth.

These lunar impact events are important to astronomers, who use them to figure out how often the moon is bombarded by smaller asteroids. This way, they can refine their estimates of how many larger asteroids there are — those that could pass through our planet’s atmosphere with potentially devastating effect.

Fujii, an astronomy enthusiast, is fascinated by the ever-changing nature of the night sky. “I want the public to enjoy science,” he said. And one way to do this is to show how often the moon is hit by rocky missiles.

Fujii uses multiple telescopes at two locations—Fuji and Hiratsuka—to watch Earth’s white companion. Software automatically detects movements and explosions on the lunar surface.

This setup has worked very well: It has documented about 60 lunar impacts since 2011. Seeing two impacts in a row, however, is less common.

The first flash, on Thursday, appeared east of the Gassendi crater, which is 113 km wide. The second appeared west of the Oceanus Procellarum, or “Ocean of Storms” — a colossal plain 2,575 km long, filled with crystallized magma.

Sometimes flashes on the moon are illusions: cosmic rays that appear as strange sparks in telescopes. Were those two flashes real?

When asked, the American space agency was unable to comment. “NASA is currently closed due to a lack of government funding,” a spokesperson responded via email. (NASA-funded planetary defense observatories continue to operate during the shutdown.)

The European Space Agency’s telescopes did not see the flashes, as the moon was too bright as seen from Europe at the time they occurred. But because multiple telescopes in Japan captured the same glows from different angles, it’s easy to classify them as asteroid impacts.

“These impact flashes look real,” said Juan Luis Cano, an aerospace engineer at ESA’s Near-Earth Object Coordination Center. “What caught my attention is that they both appear to be a little above average in terms of flash size” — suggesting they may have been more energetic impacts than usual.

The origin of these asteroids is not certain. But Fujii suspects they may have come from the Taurid meteor shower, which breaks off from comet Encke. The Taurids, which peak this month, are known for featuring meteors that are larger than average and move at particularly high speeds. It wouldn’t be surprising, then, if some had crashed into the moon instead of disintegrating in Earth’s atmosphere.

Fujii hopes his surveillance will help improve lunar security. Space agencies and private companies seek to make the moon an inhabited place — something that is not without risks, including possible impacts from space rocks.

“Understanding the frequency and energy of impact flashes can be used to inform the design and operation of lunar bases,” he said.