The unusual shapes of the tiny asteroids Dimorphos and Selam have perplexed astronomers for years, but a new study finally explains how they got so strange. It also suggests these bizarrely shaped "moonlets" may be more common than scientists thought.
Binary asteroids — pairs of asteroids that are essentially mini versions of the Earth-moon system — are pretty common in our cosmic neighborhood. These include the Didymos-Dimorphos duo that headlined NASA's 2022 Double Asteroid Redirection Test (DART) mission. Previous research suggests that such binary asteroids form when a rubble-pile "parent" asteroid — composed of loosely held rocks — spins so fast that it sheds some of its mass, which coalesces into the second, smaller satellite or "moonlet" asteroid.
