Solar systems like ours found
Two space telescopes capture evolving planetary systems.
December 10, 2004
In a phone-and-Internet news briefing yesterday, NASA scientists announced the Hubble Space Telescope and the Spitzer Space Telescope have produced fascinating and important images of dusty disks around Sun-like stars.
According to Charles Beichman, a Spitzer Space Telescope scientist, Spitzer found excess radiation coming from six systems known to have planets. "These systems have 2-15 times more heat than we expect from just the stars," Beichman says. He went on to explain a disk of dust and debris similar to the one that surrounds our solar system, which is known as the Kuiper Belt can account for this excess heat.
Alycia Weinberger, a staff research astronomer at the Carnegie Institution of Washington, says, "Prior to these observations, we didn't know of any systems that harbored both planets and disks other than our own. The reason I'm excited about the Spitzer images is that they close the loop. They show us both the planets and the disk."
David Ardila, a Hubble Space Telescope scientist from Johns Hopkins University, then shared two Hubble images that show debris disks around the stars AU Microscopii (AU Mic) and HD 107146. Both images were taken with Hubble's Advanced Camera for Surveys using a coronagraph — a device that blocks the light from the star only.
The disk around AU Mic is approximately 4 times the size of our solar system. The image shows the dust particles (blue) miniscule, only about 1/20,000 millimeter in diameter — much smaller than household dust.
The disk surrounding HD 107146 is slightly smaller than the one circling AU Mic, but it's still 3 times the size of our solar system. The red color in the image indicates dust grains 10 times larger than those imaged around AU Mic. One part of the HD 107146 ring is a bit brighter because that's the side closest to us.
Each image shows a central hole similar in size to the orbit of Uranus around the Sun. Such a hole often forms when a planet (or planets) there clears out all the dust.
These findings confirm the part of planet-formation theory that allows rocky planets to form by collision early in a solar system's history. The dust and debris seen in the Spitzer images were created as small planetary bodies crashed together. So, we're not observing the creation of solar systems, but older ones like ours. Also, these systems are not likely to have earthlike planets because of the masses and locations of the planets that have been found already.
The newly discovered systems contain 10-100 times as much dust as the Kuiper Belt. "Still," Beichman comments, "all the dust wouldn't equal the mass of the Moon."
"These systems will provide very exciting targets for future NASA missions," says Weinberger. "The Terrestrial Planet Finder will certainly be able to see the disks and to resolve them and tell us about their structure."