Ejecta
Rock and debris thrown out of a crater during an impact.
Ejecta is everything blasted out of a crater as it forms, from house-sized blocks to dust and droplets of melted rock. Close to the crater, ejecta piles up as a thick, continuous ejecta blanket, roughly out to one crater radius from the rim. Further out it becomes patchy. Large blocks thrown far away can make smaller secondary craters of their own, and on airless bodies bright streaks called rays can stretch for hundreds of kilometres.
Ejecta is important because it carries deep material to the surface, and its layers record the order of events. On Earth, distant ejecta helps date impacts: a thin layer of debris from Chicxulub is found around the world at the boundary marking the end of the age of dinosaurs. Meteorites from Mars and the Moon are themselves ejecta, flung off with enough speed to escape and later land on Earth.
On the Moon, the rays of Tycho crater are easy to see with binoculars near full Moon, spreading across the southern half of the disc. Around the Ries crater in Germany, a widespread ejecta deposit of jumbled, colourful rock called Bunte Breccia is exposed in quarries. Ejecta usually forms an apron of broken rock thinning away from a crater.
Related terms
Level: Explorer Ages 10 and up