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The Honolulu Advertiser
Posted on: Friday, May 7, 2004

Planetary satellites get closer look here

By Kevin Dayton
Advertiser Big Island Bureau

HILO, Hawai'i — Astronomers using the Gemini North Telescope on Mauna Kea have found evidence suggesting that clusters of satellites circling Jupiter and Saturn may be pieces of asteroid-like objects that were shattered in collisions early in the existence of the solar system.

In this illustration provided by the Gemini observatory atop Mauna Kea, irregular satellites of Jupiter are unlike the Jovian moons. One possibility is that they may be asteroid-like debris captured by Jupiter's gravitational pull.

Gemini observatory

The astronomers, Tommy Grav and Matthew J. Holman of the Harvard-Smithsonian Center for Astrophysics, used the Near Infrared Imager on the telescope to observe 10 objects circling Jupiter and four others circling Saturn.

The objects studied were all considered "irregular satellites" that followed odd orbits unlike the moons of the two planets. Scientists theorized that the irregular satellites formed differently from the way the moons did.

One possibility is the irregular satellites may be pieces of asteroid-like objects that were captured by the gravitational pull of Jupiter and Saturn about 4.5 billion years ago. Those satellites may have been broken in collisions with other asteroids, with some pieces thrown away from the planets and others left to circle the planets in clusters.

In research published in the April 20 issue of The Astrophysical Journal, Grav and Holman reported that infrared observations of the surface colors of the satellites last year revealed they can be grouped into families with common "ancestry."

That supports the theory that each "family" of satellites probably came from a larger "parent body" that shattered, said Chad Trujillo, a science fellow with the Gemini observatory who specializes in study of the solar system.

"This is another piece of evidence that this fragmentation-collision (theory) is responsible for the satellites being there," Trujillo said.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com or (808) 935-3916.