NASA/JPL-Caltech/Univ. of Ariz.
NASA's Spitzer Space Telescope captured this infrared image of a giant halo of very fine dust around the young star HR 8799, located 129 light-years away in the constellation Pegasus. The brightest parts of this dust cloud (yellow-white) likely come from the outer cold disk similar to our own Kuiper belt (beyond Neptune's orbit). The huge extended dust halo is seen as orange-red.
updated 11/10/2009 11:05:08 AM ET 2009-11-10T16:05:08

A young star observed by the Spitzer Space Telescope appears to be home to a wild — and young — planetary system that shares some of the frenetic dynamics thought to have shaped the early years of our own solar system.

The Spitzer observations suggest young planets circling the star are disturbing smaller comet-like bodies, causing them to collide and kick up a huge halo of dust.

The star, called HR 8799, became one of the first of two stars with planets that were directly imaged from Earth in November 2008. Ground-based telescopes at the W.M. Keck Observatory and the Gemini Observatory, both in Hawaii, took images of three planets orbiting in the far reaches of the system. Each of the three distant worlds is roughly 10 times the mass of Jupiter.

HR 8799 is younger and more massive than our sun, which is more than 4.5 billion years old and more than 300,000 times the mass of Earth. It is about 129 light-years from Earth, so scientists weren't sure if Spitzer would be able to snap a picture of its debris disk. But to their amazement, it succeeded.

The Spitzer team, led by Kate Su of the University of Arizona, Tucson, says the giant cloud of fine dust around the disk is very unusual. The researchers say this dust must be coming from collisions among small bodies similar to the comets or icy bodies that make up today's Kuiper Belt objects in our solar system.

"The system is very chaotic and collisions are spraying up a huge cloud of fine dust," Su said.

The gravity of the three large planets is throwing the smaller bodies off course, causing them to migrate around and collide with each other. Astronomers think the planets may have yet to reach their final stable orbits, so more violence could be in store.

A similar setup has also been seen by Spitzer and the Hubble Space Telescope around the star Fomalhaut, which sits about 25 light-years from Earth.

"What's exciting is that we have a direct link between a planetary disk and imaged planets," Su said. "We've been studying disks for a long time, but this star and Fomalhaut are the only two examples of systems where we can study the relationships between the locations of planets and the disks."

When our solar system was young, astronomers think it went through similar planet migrations. Jupiter and Saturn moved around quite a bit, throwing comets around, sometimes into Earth.

Some say the most extreme part of this phase, called the late heavy bombardment, explains how our planet got water. Wet, snowball-like comets are thought to have crashed into Earth, delivering life's favorite liquid.

The Spitzer results are detailed in the Nov. 1 issue of Astrophysical Journal.

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