Fellow traveler: WISE satellite spots asteroid following Earth

By Kevin Opsahl
The Herald Journal
July 29, 2011

This artist's concept illustrates the first known Earth Trojan asteroid, discovered by WISE. The asteroid is gray and its extreme orbit is shown in green. Image credit: Paul Wiegert, University of Western Ontario, Canada.

Asteroid 2010 TK7 is circled in green, in this single frame taken by NASA's Wide-field Infrared Survey Explorer, or WISE. Image credit: NASA/JPL-Caltech/UCLA

NORTH LOGAN - A satellite built by Utah State University's Space Dynamics Laboratory has discovered an asteroid that has been following Earth for thousands of years, proving that the moon is not the planet's only travel companion.

NASA officials announced Thursday that astronomers studying observations taken by the agency's Wide-field Infrared Survey Explorer (WISE) satellite have found the first known "Trojan" asteroid orbiting the sun along with Earth.

"It's very exciting in the SDL community to say that we've been a part of this, to have built an instrument which has offered such fundamental knowledge of our solar system and of the universe," said John Elwell, program manager for WISE. "It's cool."

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 have long thought that Earth does have Trojans, but they've been hard to find because they are small and appear near the sun from Earth's point of view, according to NASA.

"It took so long because ... if you're looking for asteroids in your own orbit, you move closer towards the sun, so it's very hard to see," Elwell said. "The reason we were able to do it this time is because WISE is designed to look for the heat from the asteroid, rather than the reflective sunlight. ... It was designed just for this job."

Two of WISE's four cameras were designed to look for asteroids, Elwell said.

If other so-called Trojan asteroids are found, they could turn out to be ideal candidates for a visit from astronauts, something NASA hopes will be possible within the next 15 years.

However, Asteroid 2010 TK7 - the code name of the rock trailing the Earth - 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.

"It helps complete the painting of the picture of the physics of the solar system," Elwell said. "We thought we should see Trojans and no one ever found them. All of a sudden, we found one. So it helps solidify our theories about how the solar system works."

Martin Connors of Athabasca University in Canada, who recently authored a scientific journal entry on the discovery, called WISE "a game-changer," and SDL officials agree.

The discovery of the Trojan will more than likely "add fuel to the fire" for scientists to look for more of them, and to prove if their theories about the stability of the Trojan's orbit is correct, Elwell said.

The asteroid will not come closer to Earth than 15 million miles, according to NASA. In fact, Trojans are the least likely kind of asteroid to hit Earth.

WISE was launched in December of 2009 and collected data from January of 2010 to 2011. NASA only designated WISE to collect data for that period of time, and the instrument will most likely explode in space.

The data that's been collected and archived will take years for scientists to comb over, including thousands of pictures of asteroids, galaxies and stars. NASA released some of those images from WISE to the public back in April.

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