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Posted by baalke on March 30, 2007, 1:45 pm
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NASA'S SPITZER TELESCOPE FINDS PLANETS THRIVE AROUND STELLAR TWINS
(Forwarded by Lori Stiles, University Communications, 520-626-4402)
- Thursday, March 29, 2007
--------------------------------------------------------------
SUMMARY: Our universe could be packed with worlds with two or more
suns,
University of Arizona Steward Observatory astronomers and their
colleagues
conclude from new research with NASA's Spitzer Space Telescope. They
will
publish their findings in the Astrophysical Journal. Spitzer is flying
UA
Steward Observatory's multiband imaging photometer. The following
release is
forwarded from the Jet Propulsion Laboratory Media Relations Office in
Pasadena, Calif. Contact information is listed at the end.
---------------------------------------------------------------
The double sunset that Luke Skywalker gazed upon in the film "Star
Wars"
might not be a fantasy.
Astronomers using NASA's Spitzer Space Telescope have observed that
planetary systems ? dusty disks of asteroids, comets and possibly
planets ?
are at least as abundant in twin-star systems as they are in those,
like our
own, with only one star. Since more than half of all stars are twins,
or
binaries, the finding suggests the universe is packed with planets
that have
two suns. Sunsets on some of those worlds would resemble the ones on
Luke
Skywalker's planet, Tatooine, where two fiery balls dip below the
horizon
one by one.
"There appears to be no bias against having planetary system
formation in
binary systems," said David Trilling of the University of Arizona,
Tucson,
lead author of a new paper about the research appearing in the April 1
issue
of the Astrophysical Journal. "There could be countless planets out
there
with two or more suns."
Previously, astronomers knew that planets could form in exceptionally
wide
binary systems, in which stars are 1,000 times farther apart than the
distance between Earth and the sun, or 1,000 astronomical units. Of
the
approximately 200 planets discovered so far outside our solar system,
about
50 orbit one member of a wide stellar duo.
The new Spitzer study focuses on binary stars that are a bit more
snug,
with separation distances between zero and 500 astronomical units.
Until
now, not much was known about whether the close proximity of stars
like
these might affect the growth of planets. Standard planet-hunting
techniques
generally don't work well with these stars, but, in 2005, a NASA-
funded
astronomer found evidence for a planet candidate in one such multiple-
star
system (http://www.jpl.nasa.gov/news/news.cfm?release=2005-115).
Trilling and his colleagues used Spitzer's infrared, heat-seeking
eyes to
look not for planets, but for dusty disks in double-star systems.
These
so-called debris disks are made up of asteroid-like bits of leftover
rock
that never made it into rocky planets. Their presence indicates that
the
process of building planets has occurred around a star, or stars,
possibly
resulting in intact, mature planets.
In the most comprehensive survey of its kind, the team looked for
disks in
69 binary systems between about 50 and 200 light-years away from
Earth. All
of the stars are somewhat younger and more massive than our middle-
aged sun.
The data show that about 40 percent of the systems had disks, which is
a bit
higher than the frequency for a comparable sample of single stars.
This
means that planetary systems are at least as common around binary
stars as
they are around single stars.
In addition, the astronomers were shocked to find that disks were
even more
frequent (about 60 percent) around the tightest binaries in the study.
These
coziest of stellar companions are between zero and three astronomical
units
apart. Spitzer detected disks orbiting both members of the star pairs,
rather than just one. Extra-tight star systems like these are where
planets,
if they are present, would experience Tatooine-like sunsets.
"We were very surprised to find that the tight group had more disks,"
said
Trilling. "This could mean that planet formation favors tight binaries
over
single stars, but it could also mean tight binaries are just dustier.
Future
observations should provide a better answer."
The Spitzer data also reveal that not all binary systems are friendly
places for planets to form. The telescope detected far fewer disks
altogether in intermediately spaced binary systems, between three to
50
astronomical units apart. This implies that stars may have to be
either very
close to each other, or fairly far apart, for planets to arise.
"For a planet in a binary system, location is everything," said co-
author
Karl Stapelfeldt of NASA's Jet Propulsion Laboratory in Pasadena,
Calif.
"Binary systems were largely ignored before," added Trilling. "They
are
more difficult to study, but they might be the most common sites for
planet
formation in our galaxy."
Other authors on the paper include: John Stansberry, George Rieke and
Kate
Su of the University of Arizona; Richard Gray of the Appalachian State
University, Boone, N.C.; Chris Corbally of the Vatican Observatory,
Tucson;
Geoff Bryden, Andy Boden and Charles Beichman of JPL; and Christine
Chen of
the National Optical Astronomical Observatory, Tucson.
JPL manages Spitzer for NASA's Science Mission Directorate,
Washington.
Science operations are conducted at the Spitzer Science Center at the
California Institute of Technology, also in Pasadena. The multiband
imaging
photometer for Spitzer was built by Ball Aerospace Corporation,
Boulder,
Colo.; the University of Arizona; and Boeing North American, Canoga
Park,
Calif. Co-author Rieke is the principal investigator.
For more information and graphics, visit www.spitzer.caltech.edu/Media
and
http://www.nasa.gov/spitzer .
-----------------------------------------------
Science Contact Information
David Trilling UA Steward Observatory
(520) 626-1600 trilling@as.arizona.edu
Media Contact Information
Whitney Clavin, Media Relations
Jet Propulsion Laboratory, Pasadena (818) 354-4673
-----------------------------------------------
Related Web sites
www.spitzer.caltech.edu/Media
http://www.nasa.gov/spitzer
---------------------------
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