Unique Type of Asteroid Discovered

Many astronomers set their telescopes on distant galaxies, but they still have much to learn about Earth's own backyard.

Earlier this month, the Deep Ecliptic Survey Team, which includes UC Berkeley astronomy professor Eugene Chiang, announced the discovery of the first Neptunian Trojan.

The asteroid, an estimated 230 kilometers in diameter, orbits the Sun along the same path as Neptune.

Because the asteroid's unique orbit has left it relatively unscathed by the Sun, it may offer clues to how the solar system formed.

"Neptune Trojans are likely direct remnants from the planet formation era of our solar system," Chiang said. "Understanding their composition and internal structure might give us direct clues as to how the first large bodies formed."

About 500 Trojan asteroids, the vast majority of which lie along Jupiter's orbit, have been found since the first discovery in 1906.

"If you were to mark (the Jupiter Trojans') positions in space, they would appear as two clusters of points lying on the nearly circular orbit of the planet," Chiang said.

The strategic location of these asteroids has inspired the imagination of their discoverers.

"These two populations evoke the two warring camps in Homer's Iliad, the Greeks and the Trojans," Chiang said. "Bodies shifted forward of Jupiter's position have been named after the Greeks, and bodies shifted backwards have been named after the Trojans."

The Neptunian Trojan was initially observed by astronomers from Lowell Observatory in Flagstaff, Arizona.

"We have a program searching for asteroidal objects with orbits beyond Pluto. The Trojan was accidentally picked up during this study," said Larry Wasserman, a Lowell astronomer. "However, our search technique is sensitive to objects that are in the outer part of the solar system, so it is not surprising that we found this object."

Despite no previous observations of Neptunian Trojans, astronomers have long suspected their existence.

"It would seem a little odd if only Jupiter were to harbor a Trojan population," Chiang said. "It is the most massive planet in the solar system, but Saturn, Uranus, and Neptune are not that far behind in mass."

After the suspected Neptunian Trojan was observed, the team spent over a year tracking its movements through the sky to confirm that it was indeed a Trojan.

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