Freaky ‘Active’ Object in Jupiter’s Orbit Is First of Its Kind Seen by Astronomers - Gizmodo

Say hello to 2019 LD2, the only active Jupiter Trojan known to science.

Trojans are a large group of asteroids located in the same orbital path as Jupiter, and they’re all dead, inert asteroids—well, except apparently this one, which now boasts a very comet-like tail, according to a press release put out by the University of Hawaii’s Institute for Astronomy.

Active asteroids are rare, but the discovery of an active Jupiter Trojan is unprecedented.

2019 LD2 is located in the Trojan clump ahead of the planet.

They should be dead and boring like the vast majority of other asteroids, but the discovery of a lone active Trojan suggests something else might be going on—namely the sudden exposure of deeper materials to the surface.

“We have believed for decades that Trojan asteroids should have large amounts of ice beneath their surfaces, but never had any evidence until now,” said Alan Fitzsimmons, an astronomy professor at Queen’s University Belfast who’s been studying 2019 LD2, in the press release.