Astronomy Picture of the Day

Explanation: Why was this collision so strange? In 2022, to develop Earth-saving technology, NASA deliberately crashed the DART spacecraft into the asteroid moonlet Dimorphos. The hope was that this collision would alter the trajectory of Dimorphos around its parent asteroid Didymos and so demonstrate that similar collisions could, in theory, save the Earth from being hit by (other) hazardous asteroids. But analyses of new results show that the effects of the collision are different than expected -- and we are trying to understand why. Featured here is the time lapse video taken by the ejected LICIACube camera LUKE showing about 250 seconds of the expanding debris field of Dimorphos after the collision, with un-impacted Didymos passing in the foreground. In 2026, Europe's Hera mission will reach the asteroids and release three spacecraft to better study the matter.