NASA's Wise Mission Finds First Trojan Asteroid Sharing Earth's Orbit

WASHINGTON -- Astronomers studying observations taken by NASA's
Wide-field Infrared Survey Explorer (WISE) mission have discovered
the first known "Trojan" asteroid orbiting the sun along with Earth.

Trojans are asteroids that share an orbit with a planet near stable
points in front of or behind the planet. Because they constantly lead
or follow in the same orbit as the planet, they never can collide
with it. In our solar system, Trojans also share orbits with Neptune,
Mars and Jupiter. Two of Saturn's moons share orbits with Trojans.

Scientists had predicted Earth should have Trojans, but they have been
difficult to find because they are relatively small and appear near
the sun from Earth's point of view.

"These asteroids dwell mostly in the daylight, making them very hard
to see," said Martin Connors of Athabasca University in Canada, lead
author of a new paper on the discovery in the July 28 issue of the
journal Nature. "But we finally found one, because the object has an
unusual orbit that takes it farther away from the sun than what is
typical for Trojans. WISE was a game-changer, giving us a point of
view difficult to have at Earth's surface."

The WISE telescope scanned the entire sky in infrared light from
January 2010 to February 2011. Connors and his team began their
search for an Earth Trojan using data from NEOWISE, an addition to
the WISE mission that focused in part on near-Earth objects, or NEOs,
such as asteroids and comets. NEOs are bodies that pass within 28
million miles (45 million kilometers) of Earth's path around the sun.
The NEOWISE project observed more than 155,000 asteroids in the main
belt between Mars and Jupiter, and more than 500 NEOs, discovering
132 that were previously unknown.

The team's hunt resulted in two Trojan candidates. One called 2010 TK7
was confirmed as an Earth Trojan after follow-up observations with
the Canada-France-Hawaii Telescope on Mauna Kea in Hawaii.

The asteroid is roughly 1,000 feet (300 meters) in diameter. It has an
unusual orbit that traces a complex motion near a stable point in the
plane of Earth's orbit, although the asteroid also moves above and
below the plane. The object is about 50 million miles (80 million
kilometers) from Earth. The asteroid's orbit is well-defined and for
at least the next 100 years, it will not come closer to Earth than 15
million miles (24 million kilometers). An animation showing the orbit
is available at:


"It's as though Earth is playing follow the leader," said Amy Mainzer,
the principal investigator of NEOWISE at NASA's Jet Propulsion
Laboratory (JPL) in Pasadena, Calif. "Earth always is chasing this
asteroid around."

A handful of other asteroids also have orbits similar to Earth. Such
objects could make excellent candidates for future robotic or human
exploration. Asteroid 2010 TK7 is not a good target because it
travels too far above and below the plane of Earth's orbit, which
would require large amounts of fuel to reach it.

"This observation illustrates why NASA's NEO Observation program
funded the mission enhancement to process data collected by WISE,"
said Lindley Johnson, NEOWISE program executive at NASA Headquarters
in Washington. "We believed there was great potential to find objects
in near-Earth space that had not been seen before."

NEOWISE data on orbits from the hundreds of thousands of asteroids and
comets it observed are available through the NASA-funded
International Astronomical Union's Minor Planet Center at the
Smithsonian Astrophysical Observatory in Cambridge, Mass.
JPL manages and operates WISE for NASA's Science Mission Directorate
in Washington. The principal investigator, Edward Wright, is a
professor at the University of California, Los Angeles. The mission
was selected under NASA's Explorers Program, which is managed by the
agency's Goddard Space Flight Center in Greenbelt, Md. The science
instrument was built by the Space Dynamics Laboratory in Logan, Utah.

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.

For more WISE information visit:



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