WISE Mission Spots 'Horseshoe' Asteroid

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Feature: 2011-112 April 08, 2011

WISE Mission Spots 'Horseshoe' Asteroid

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-112&cid=release_2011-112

An asteroid recently discovered by NASA's Wide-field Infrared Survey Explorer (WISE) may
be a bit of an oddball. Most near-Earth asteroids -- NEAs for short -- have eccentric, or egg-
shaped, orbits that take the asteroids right through the inner solar system. The new object,
designated 2010 SO16, is different. Its orbit is almost circular such that it cannot come close to
any other planet in the solar system except Earth.

However, even though the asteroid rides around with Earth, it never gets that close.

"It keeps well away from Earth," said Apostolos "Tolis" Christou, who, together with David
Asher of the Armagh Observatory in Northern Ireland, analyzed the orbit of the body after it
was discovered in infrared images taken by WISE. "So well, in fact, that it has likely been in this
orbit for several hundred thousand years, never coming closer to our planet than 50 times the
distance to the moon."

The asteroid is one of a few that trace out a horseshoe shape relative to Earth. As the asteroid
approaches Earth, the planet's gravity causes the object to shift back into a larger orbit that
takes longer to go around the sun than Earth. Alternately, as Earth catches up with the asteroid,
the planet's gravity causes it to fall into a closer orbit that takes less time to go around the sun
than Earth. The asteroid therefore never completely passes our planet. This slingshot-like effect
results in a horseshoe-shaped path as seen from Earth, in which 2010 SO16 takes 175 years to
get from one end of the horseshoe to the other.

"The origins of this object could prove to be very interesting," said Amy Mainzer of NASA's Jet Propulsion Laboratory, Pasadena, Calif., the principal investigator of NEOWISE, which is the asteroid- and comet-hunting portion of the WISE survey mission. "We are really excited that the astronomy community is already finding treasures in the NEOWISE data that have been released so far."

NEOWISE finished its one complete sweep of the solar system in early February of this year.
Data on the orbits of asteroids and comets detected by the project, including near-Earth
objects, are catalogued at the NASA-funded International Astronomical Union's Minor Planet
Center, at the Smithsonian Astrophysical Observatory in Cambridge, Mass.

A full story from the Armagh Observatory, including animations, is online at
http://www.arm.ac.uk/press/2011/aac_horseshoe_orbit.html .

JPL manages and operates the Wide-field Infrared Survey Explorer for NASA's Science
Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA. The
mission was competitively selected under NASA's Explorers Program managed by the
Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space
Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace &
Technologies Corp., Boulder, Colo. Science operations and data processing take place at the
Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena.
Caltech manages JPL for NASA. More information is online at http://www.nasa.gov/wise ,
http://wise.astro.ucla.edu and http://jpl.nasa.gov/wise .

#2011-112

-end-

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

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