Astronomers believe they have witnessed a cosmic fender bender in the asteroid belt. Asteroid (493) Griseldis was hit by a small object, and the impact released materials from its surface.
On March 17, 2015, astronomers using the 8-meter Subaru Telescope in Hawaii, noticed that (493) Griseldis showed an extended feature which was not present in previous observations of the object in 2010 and 2012.
Follow-up observations four nights later were able to detect the extension weakening. By March 24 the feature had completely disappeared, with no further sightings on April 18 or May 21. As the phenomenon was so short-lived, the researchers concluded in a statement that “the observations are consistent with the occurrence of an impact event on this asteroid.”
(493) Griseldis is an asteroid residing in the main belt, between Mars and Jupiter. It has an average diameter of 46.41 kilometers (28.84 miles) and it orbits the Sun in 5.5 years.
The main asteroid belt contains only 200 objects larger than 100 kilometers (62 miles) and scientists estimate that there are 750,000 to almost two million objects larger than one kilometer (0.62 miles).
Although the number of asteroids is large they are very spread out. The average distance between two asteroids is over 10 times the distance between the Earth and the Moon. Even if all the asteroids were on the same orbit of (493) Griseldis, which is almost 29 billion kilometers (just over 18 billion miles) long, they would still have a gap of 15,000 kilometers (9,300 miles) between them. For this reason, collisions between asteroids like the one observed in March are very rare.
The astronomers who made the discovery are David Tholen, from the Institute for Astronomy, University of Hawaii at Manoa, Scott Sheppard from the Carnegie Institution for Science in Washington, and Chad Trujillo from the Gemini Observatory.
The results were presented on November 12 at the annual meeting of the Division for Planetary Sciences of the American Astronomical Society.