Antares, the bright star at the heart of Scorpius, huddles quite close to the Moon early this evening. They set not long after the sky gets dark, so there’s not a lot of time to look for them.
The Moon is a thin crescent now, so it’s night across most of the lunar disk. But on the bright sliver that’s in daylight, you can still make out some of the dark lunar “seas” – vast plains of volcanic rock. They formed long ago, when giant asteroids slammed into the Moon. Molten rock bubbled up from below, then cooled and hardened.
A recent study found evidence of an especially big impact three-and-a-half billion years ago. The hit would have been powerful enough to melt the surface across a wide area.
Researchers discovered the evidence in a meteorite known as Northwest Africa 12593. It was found in Mali, in 2017. It contained some tiny crystals that form only under extreme heat. The chemistry of the meteorite suggested the impact happened three-and-a-half billion years ago.
A later impact shattered the lava plain, jumbling up the rocks. And a third impact blasted some of the fragments into space, including the one that fell to Earth.
The initial impact happened at about the time of similar events on Earth and the asteroid Vesta. That suggests that the inner solar system was littered with many giant space rocks at the time – cosmic “missiles” that sometimes smashed into Earth and the other large worlds.
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