Unique first-of-its-kind tail-less comet found in solar system

Astronomers have found a unique first-of-its-kind tail-less comet whose composition may offer clues into questions about the solar system's formation and evolution. The weakly active comet, C/2014 S3 (PANSTARRS), appears to be made of inner Solar System material from the time of Earth's formation.

Its current long orbital period (about 860 years) suggests that its source is in the Oort Cloud - an extended shell of icy objects that exist in the outermost reaches of the solar system, and it was nudged comparatively recently into an orbit that brings it closer to the Sun.

C/2014 S3 (PANSTARRS) is the first object to be discovered on a long-period cometary orbit that has the characteristics of a pristine inner Solar System asteroid, researchers said.

It may provide important clues about how the Solar System was formed. Researchers of the University of Hawaii concluded that the comet was ejected from the inner Solar System early in the planet formation process.

The comet was a potential building block of the rocky planets like Earth. "We already knew of many asteroids, but they have all been baked by billions of years near the Sun," said Karen Meech, from University of Hawaii.

"This one is the first uncooked asteroid we have found: it has been preserved in the best freezer there is," Meech said.

The team immediately noticed that the comet was unusual, missing the characteristic tail that most long-period comets sprout as they approach so close to the Sun.

They dubbed it a Manx comet, after the tail-less cat. Careful study of the spectra of the comet shows that it is typical of "S-type" asteroids, which are found in the inner asteroid main belt.

The comet's material has undergone very little processing, indicating that it has been deep frozen for a very long time, researchers said.

The very weak comet-like activity associated with C/2014 S3 (PANSTARRS), which is consistent with the vaporisation of water ice, is about a million times lower than active long-period comets at a similar distance from the Sun.

The researchers conclude that this object is probably made of fresh inner Solar System material that has been stored in the Oort Cloud and is now returning to its birthplace.

An important difference between these models is what they predict about the objects that make up the Oort Cloud.

Different models predict significantly different ratios of icy to rocky objects. This first discovery of a rocky object from the Oort Cloud is therefore an important test of the different predictions of the models. The study was published in the journal Science Advances.