Asteroids with tiny moons may be quietly trading material across space. Images from NASA’s DART mission revealed faint streaks on the moon Dimorphos—evidence of slow “cosmic snowballs” drifting from its parent asteroid, Didymos. The discovery provides the first direct visual proof that sunlight can spin asteroids fast enough to shed debris that lands on nearby companions. It also shows that near-Earth asteroids are much more active and constantly reshaped than scientists once believed.
