By Ron Cowen
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A tiny lump of ice and rock now near Neptune appears to have some very special properties. Astronomers have discovered that it came in from the cold — the frigid outermost limits of the solar system — and is now on its way back out there.
The roughly 40-kilometer-wide object, dubbed 2006 SQ372, may be the first known visitor to the planetary neighborhood that still makes return trips home to the remote Oort Cloud. This cloud is a proposed reservoir of long-period comets — those that visit the inner solar system no more than once every 200 years — and was first hypothesized to exist in 1950. It is likely thousands of times more distant from the sun than is Earth.
“We believe SQ372 is the first detected member of a comet population in the outer solar system that comes from the, up-until-now, unobserved inner Oort Cloud,” says codiscoverer Nathan Kaib of the University of Washington in Seattle. “Comets like SQ372 have the potential to tell us what the entire Oort Cloud looks like, which will test theoretical models of the cloud’s formation as well as provide clues about the environment that the solar system first formed in.” Kaib’s team reported the findings August 18 in Chicago at a meeting on the latest findings from the Sloan Digital Sky Survey.