It's an asteroid, no wait, a comet, no wait…

by Mary Caperton Morton
Thursday, December 14, 2017

NASA’s Hubble Space Telescope has spied a unique object in the debris-filled asteroid belt between Mars and Jupiter: a pair of asteroids — orbiting tightly around each other — that also show comet-like characteristics, including a bright halo of ice and dust known as a coma and a long tail of dust. The odd object, called 2006 VW139/288P, is the first known binary asteroid that is also classified as a main-belt comet.

The object was first seen in 2006 by Spacewatch, an asteroid survey project that is part of NASA’s Near-Earth Object (NEO) Observations Program; then, in 2011, it was identified as a comet by Pan-STARRS, another division of the NEO program. But it wasn’t until September 2016, when Hubble captured sharper images of the object, that scientists realized the singular space rock actually comprised two pieces of similar mass and size, orbiting each other at a distance of about 95 kilometers.

In a study published in Nature, a team led by Jessica Agarwal, of the Max Planck Institute for Solar System Research in Germany, estimated that the object has likely existed in binary form for about 5,000 years and may have resulted from a single asteroid breaking into equal fragments due to forces generated by its rapid rotation. It’s unknown how common such binary asteroid-comets may be.

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