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Pan-STARRS Telescope Discovers Main-Belt Comet

Comet P/2006 VW139

Long-exposure image of Comet P/2006 VW139 taken by the New Technology Telescope at La Silla Observatory in Chile. Sam Duddy and Stephen Lowry, University of Kent.

An unusual comet discovered by the Pan-STARRS1 telescope on Haleakalā, Maui, is helping astronomers understand how Earth got its water. Initially spotted on November 5, 2011, the comet was first thought to be an asteroid, since its orbit lies in the main asteroid belt between the orbits of Mars and Jupiter. But P/2006 VW139, as it is known, differs from almost all other asteroids in having a cometlike tail that almost certainly consists of water vapor and dust grains that are evaporating from the surface of the object.

“Regular comets are basically enormous snowballs that spend most of their lives in the cold outer regions of the solar system,” said IfA astronomer Henry Hsieh. “What makes P/2006 VW139 so unusual is that it is a comet that orbits within the relatively near asteroid belt. Of the half-million bodies currently known in the asteroid belt, just seven so-called “main-belt” comets are known.

Main-belt comets may be more than a mere curiosity: Astronomers are hoping that they will provide clues to one of the great unsolved mysteries of geophysics, namely, “Where did Earth’s water come from?” In its early days, Earth was so hot that any water it was born with would have evaporated into space. Main-belt comets colliding with the cooling Earth may well have been the source of some of the water in our oceans.

Comet P/2006 VW139 was found while searching the sky for potentially hazardous asteroids—ones that may someday hit Earth. Pan-STARRS software engineer Larry Denneau, with help from Pan-STARRS solar system team leader Richard Wainscoat, fellow IfA astronomer Robert Jedicke, Mikael Granvik of the University of Helsinki, and Tommy Grav of the Planetary Science Institute, designed software that searches each image taken by the Pan-STARRS 1 telescope for moving objects. The software designed to specifically search for comets was developed by Hsieh and Denneau.

The team’s investigation also includes studies of the comet’s composition, orbital properties, and brightness changes by IfA astronomers Bin Yang and Nader Haghighipour, and graduate student Heather Kaluna.