New study says left-over planetesimals, not asteroids, created the moon’s largest craters

The moon’s pock-marked surface tells the story of its history. It’s marked by over 9,000 impact craters, according to the International Astronomical Union (IAU.) The largest ones are called impact basins, not craters. Now, a new study published in The Astrophysical Journal Letters claims that asteroids didn’t create the basins; leftover planetesimals did.