493 Griseldis

Griseldis (minor planet designation: 493 Griseldis) is a fairly dark main-belt asteroid 46 km in diameter.

Overview
Griseldis is suspected of having been impacted by another asteroid in March 2015. Other asteroids suspected of an asteroid-on-asteroid impact include 354P/LINEAR and 596 Scheila which also showed extended features (tails).

The asteroid was observed with the Subaru Telescope (8m), the Magellan Telescopes (6.5), and also the University of Hawaii 2.2 m telescope in early 2015. The activity was detected on the Subaru in late March, and confirmed on the Magellan telescope a few days later (which is in Chile), but no activity was seen by April. Also, no activity was seen in archived images from 2010 or 2012 according to a University of Hawaii press release.