“We already knew of many asteroids, but they have all been baked by billions of years near the Sun,” says Karen Meech of the University of Hawaii’s Institute for Astronomy. “This one is the first uncooked asteroid we could observe: it has been preserved in the best freezer there is.”
C/2014 S3 (aka PANSTARRS) was formed about 4.5 billion years ago, close to Earth when it was formed. But PANSTARRS traveled far from the sun, “preserved in the deep freeze of the Oort Cloud for billions of years.” Now it is headed back, and astronomers are excited to see what fresh frozen ancient asteroid looks like.
Careful study of the light reflected by C/2014 S3 (PANSTARRS) indicates that it is typical of asteroids known as S-type, which are usually found in the inner asteroid main belt. It does not look like a typical comet, which are believed to form in the outer Solar System and are icy, rather than rocky. It appears that the material has undergone very little processing, indicating that it has been deep frozen for a very long time. The very weak comet-like activity associated with C/2014 S3 (PANSTARRS), which is consistent with the sublimation of water ice, is about a million times lower than active long-period comets at a similar distance from the Sun.
The authors conclude that this object is probably made of fresh inner Solar System material that has been stored in the Oort Cloud and is now making its way back into the inner Solar System.