DART finds binary asteroids exchange debris via slow 'cosmic snowballs'

NASA's DART mission captured the first direct evidence that debris can move between the binary asteroid pair Dimorphos and Didymos, with 2022-era imagery showing fan-shaped streaks likely produced by material shed from Didymos and landing on Dimorphos. The ejecta traveled about 30.7 centimeters per second (12.1 inches per second), slow enough to deposit material rather than creating craters, indicating active surface evolution in a binary asteroid system. The findings, published in The Planetary Science Journal, complement other results showing DART altered Dimorphos’ orbit and slightly shifted the binary system’s orbit around the sun; the ESA Hera mission is set to survey the system later this year to further study the aftermath and improve planetary-defense models.