First Trojan asteroid found in gravitational ‘dead zone’

WASHINGTON - The first Trojan asteroid, 2008 LC18, has been found in a difficult-to-detect stability region at Neptune, called the Lagrangian L5 point.

There are places in space where the gravitational tug between a planet and the Sun balance out, allowing other smaller bodies to remain stable. These places are called Lagrangian points.

So-called Trojan asteroids have been found in some of these stable spots near Jupiter and Neptune.

Trojans share their planet’s orbit and help astronomers understand how the planets formed and how the solar system evolved.

Now Scott Sheppard at the Carnegie Institution’s Department of Terrestrial Magnetism and Chad Trujillo have made the above discovery to estimate the asteroid population there and find that it is similar to the asteroid population at Neptune’s L4 point.

“The L4 and L5 Neptune Trojan stability regions lie about 60 degrees ahead of and behind the planet, respectively. Unlike the other three Lagrangian points, these two areas are particularly stable, so dust and other objects tend to collect there. We found 3 of the 6 known Neptune Trojans in the L4 region in the last several years, but L5 is very difficult to observe because the line-of-sight of the region is near the bright center of our galaxy,” explained Sheppard.

The scientists devised a unique observing strategy.

Using images from the digitized all-sky survey they identified places in the stability regions where dust clouds in our galaxy blocked out the background starlight from the galaxy’s plane, providing an observational window to the foreground asteroids.

They discovered the L5 Neptune Trojan using the 8.2-meter Japanese Subaru telescope in Hawaii and determined its orbit with Carnegie’s 6.5-meter Magellan telescopes at Las Campanas, Chile.

“We estimate that the new Neptune Trojan has a diameter of about 100 kilometers and that there are about 150 Neptune Trojans of similar size at L5,” said Sheppard.

“It matches the population estimates for the L4 Neptune stability region. This makes the Neptune Trojans more numerous than those bodies in the main asteroid belt between Mars and Jupiter. There are fewer Neptune Trojans known simply because they are very faint since they are so far from the Earth and Sun,” he added.

The research is published in the latest online issue of Science Express. (ANI)