Spitzer Teams Says Debris Disk Could Be Forming Infant Terrestrial Planets

SPITZER TEAM SAYS DEBRIS DISK COULD BE FORMING INFANT TERRESTRIAL
PLANETS
From Lori Stiles, UA, University Communications, 520-621-1877
Wednesday, December 14, 2005

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Contact and image information at the end of release
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Astronomers have found a debris disk around a sun-like star that may be
forming or has formed its terrestrial planets. The disk - a probable
analog
to our asteroid belt - may have begun a solar-system-scale demolition
derby,
where the rocky remains of failed planets collide chaotically.

"This is one of a very rare class of objects that may give us a glimpse
into what our solar system may have looked like during the formation of
our
terrestrial planets," said Dean C. Hines of the Space Science
Institute, a
leader of the team that discovered the rare objects with NASA's Spitzer
Space Telescope.

"The target is essentially a star similar to our sun, seen at a time
when
the terrestrial planets in our solar system were thought to have
formed,"
Hines said. "We see evidence that this star might have an asteroid
belt,
roughly at the distance Jupiter is from our sun."

"This object is very unusual in the context of all the others we've
looked
at," said University of Arizona assistant astronomy Professor Michael
R.
Meyer, a colleague in the discovery. Meyer directs a Spitzer Legacy
project
to study solar system formation and evolution in a sample of 328 young
sun-like stars in the Milky Way. The project turned up the unusual
system.

"This is the only such debris disk among the 33 sun-like stars we've
studied in our project so far, and one of only five such objects
known,"
Meyer said.

The star, named HD 12039, is about 30 million years old, or the age of
the
sun when the terrestrial planets are thought to have been 80 percent
complete and the Earth-moon system formed, the astronomers said. It is
roughly 137 light years away, or the distance light travels in 137
years.

HD 12039 is a "G" type star like our sun, a yellow star with surface
temperatures between 5,000 and 7,000 degrees Fahrenheit. It hasn't yet
settled into the "main sequence," or mature nuclear-burning phase as
our sun
has. It's eight percent brighter, just slightly cooler and a little
more
massive than our sun, or 1.02 solar masses.

The Spitzer team discovered that the star's debris disk temperature is
110
degrees Kelvin, or minus 262 degrees Fahrenheit. That's warmer than
temperatures of the frigid outer debris disks that Meyer's Spitzer team
commonly finds around sun-like stars. They've found that between 10 and
20
percent of the sun-like stars in their sample so far -- whether young,
middle-aged or old -- have outer disks like our Kuiper Belt beyond
Neptune.

"The temperature of the dust in HD 12039's strange, narrow debris ring
puts
it between four and six astronomical units from the star -- smack dab
where
Jupiter is in our solar system," Meyer said. (An astronomical unit, or
AU,
is the mean distance between Earth and the sun, about 93 million
miles.)

"What's curious about this disk is that there's little if any dust
inside
four AU and beyond six AU. It's a narrowly confined ring that could be
similar in some ways to the outer rings we see around Saturn," Meyer
said.

Just as small moons shepherd the ice grains orbiting Saturn into
discrete
rings, and just as Jupiter tends the outer edge of our solar system's
asteroid belt, an unseen giant planet may be nudging dust into the
narrow
debris ring around this star, the astronomers said.

"We think this is a tight, narrow ring of rocky objects similar to
those in
our asteroid belt, except this ring is five AU from its star, instead
of
two-to-three AU, the distance between our asteroid belt and the sun,"
Meyer
said.

"At 30 million years, the material we see in this star likely has to
come
from ground-up rocks in a zone where terrestrial planets could form,"
Hines
said.

NASA earlier this year announced a Spitzer telescope discovery of
another
of these alien asteroid belts. It orbits a two-billion-year-old
sun-like
star 35 light years away, at a distance comparable to that between
Venus and
the sun.

Based on Spitzer Telescope results to date, only one percent to three
percent of the young, sun-like stars in our Milky Way have massive
terrestrial debris disks, Meyer said.

"We could be witnessing a common, short-lived event through which all
systems pass, or we could be seeing a rare example of a massive warm
debris
disk surrounding an unusual, sun-like star," Meyer said.

The astronomers describe their work in an article to be published in
The
Astrophysical Journal.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope
mission
for NASA's Science Mission Directorate, Washington. Science operations
are
conducted at the Spitzer Science Center at Caltech. Caltech manages JPL
for
NASA. For information on the Spitzer Space Telescope visit:
http://www.spitzer.caltech.edu/spitzer

The Space Science Institute is a nonprofit organization that carries
out
world-class research in space and Earth science, together with
innovative
science education programs that inspire and deepen the public's
understanding of planet Earth and its place in the grander universe.
The
institute's integrated research and education programs span planetary
science, space physics, astrophysics, astrobiology and Earth science.

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Science contact Information
Dean C. Hines 505-239-6762
Michael R. Meyer 520-626-9199

Spitzer Telescope Media contact
Whitney Clavin, Jet Propulsion Lab, Pasadena, Calif.
818-354-4673

Spitzer Web site (downloadable images):
http://www.spitzer.caltech.edu/Media/
FEPS Legacy Project Website:
http://feps.as.arizona.edu/
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