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Last updated on April 16, 2014 at 1:21 EDT

Astronomers Discovery Earth’s Trojan Asteroid

July 28, 2011

Astronomers have discovered the first known “Trojan” asteroid orbiting the sun along with Earth.

Trojan asteroids share an orbit with a planet near stable points in front of or behind a planet, according to NASA.

Trojans constantly lead or follow in the same orbit as the planet, which means they will never collide with it.  These asteroids share orbits with Neptune, Mars and Jupiter.

Astronomers used NASA’s Wide-field Infrared Survey Explorer (WISE) mission to discover Earth’s first Trojan.  Scientists have had a difficult time finding these asteroids 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,” Martin Connors of Athabasca University in Canada said in a press release.

“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 team began their search for the Trojan using data from NEOWISE, an addition to the WISE mission that focused in part on near-Earth objects (NEOs) like asteroids and comets.

The Earth Trojan is about 1,000 feet in diameter and has an unusual orbit that traces a complex motion near a stable point in the plane of Earth’s orbit.  The object is about 50 million miles from Earth.

“It’s as though Earth is playing follow the leader,” Amy Mainzer, the principal investigator of NEOWISE at NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a press release. “Earth always is chasing this asteroid around.”

Connor is the lead author of a new paper on the discovery in the July 28 issue of the journal Nature.

Image Caption: This artist’s concept illustrates the first known Earth Trojan asteroid, discovered by NEOWISE, the asteroid-hunting portion of NASA’s WISE mission. The asteroid is shown in gray and its extreme orbit is shown in green. Earth’s orbit around the sun is indicated by blue dots. Image credit: Paul Wiegert, University of Western Ontario, Canada

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