A team of international scientists, including astronomers from Hawaii, have confirmed the existence of an asteroid that shares the same orbit with Earth.

The existence of the first known Trojan asteroid associated with Earth was confirmed by Martin Connors of Athabasca University in Canada, Christian Veillet of the Canada-France-Hawaii Telescope on Hawaii island, and Paul Wiegert of the University of Western Ontario in Canada.

The discovery of the asteroid, which measures only about 300 yards across, is the cover story of the July 28 edition of Nature magazine.

Asteroids are giant space rocks that orbit the sun, and those that share an orbit with a planet are called Trojans. Scientists had previously found a few for Mars and Neptune and nearly 5,000 for Jupiter.

Veillet, who is in Thailand at an Asia-Pacific astronomy conference, told the Star-Advertiser by email that scientists had postulated such objects for Earth.

"But they are hard to find as they are always not very far from the sun seen from Earth," Veillet said.

The Trojan asteroid, called 2010 TK7, was first tentatively identified by the team from observations made with NASA’s Wide-field Infrared Survey Explorer, or WISE, satellite and follow-up observations from ground-based telescopes in October 2010, according to the Canada-France-Hawaii Telescope website. The team confirmed the Trojan nature of the asteroid using observations by the Canada-France-Hawaii Telescope in April.

Veillet said 2010 TK7’s orbit is stable for at least 10,000 years.

"More Earth Trojans are likely to be found in the coming years, allowing for a better understanding of their dynamics and the characteristics of their population," Veillet added.

"The discovery is significant because it shows that some asteroids can share the orbit of the Earth and stay around its leading or trailing Lagrangian points for a relatively long amount of time (though 10,000 years is short on astronomical time scales)," Veillet added.

A Lagrangian point is an orbital position in which the gravitational forces of the Earth and another object, in this case the sun, are equal.

"A Trojan asteroid is potentially a good candidate for a space mission landing, as its motion is not very different from the Earth’s. The orbit of 2010 TK7 is, however, significantly inclined with respect to the Earth’s orbit, which does not make it an attractive target.

"Now that one has been found, the hunt is open to finding more: a difficult task from Earth, which could be eased in the future from space missions dedicated to the search for near-Earth asteroids."

Donald Yeomans, manager of NASA’s Near-Earth Object Program Office, who didn’t participate in the discovery, agreed that the asteroid is a Trojan. Most scientists suspected Earth had them, he said, and "I would guess there’s others."

The Associated Press contributed to this report.

On the Net: www.cfht.hawaii.edu/en/news/EarTro/