[meteorite-list] NASA's Spitzer Finds Possible Comet Dust Around Dead Star

[Ron Baalke]

Jan. 11, 2006

Erica Hupp/George Deutsch
Headquarters, Washington
(202) 358-1237/1324

RELEASE: 06-009

NASA'S SPITZER FINDS POSSIBLE COMET DUST AROUND DEAD STAR

NASA's Spitzer Space Telescope spotted what may be comet dust 
sprinkled around the white dwarf star G29-38 that died approximately 
500 million years ago.

The findings suggest the star, which most likely consumed its inner 
planets, is still orbited by a ring of surviving comets and possibly 
outer planets. This is the first observational evidence that comets 
can outlive their suns. 

"Astronomers have known for decades that stars are born, have an 
extended middle age, and then wither away or explode. Spitzer is 
helping us understand how planetary systems evolve in tandem with 
their parent stars," said David Leisawitz, NASA's Spitzer program 
scientist. 

Astronomers believe white dwarfs are shrunken skeletons of stars that 
were once similar to Earth's sun. As the stars aged over billions of 
years, they grew brighter and eventually swelled in size to become 
red giants. Millions of years later, the red giants shed their outer 
atmospheres, leaving behind white dwarfs. 

If any planets orbited in these systems, the red giants would have 
engulfed at least the inner ones. Only distant outer planets and an 
orbiting icy outpost of comets would have survived. 

"The dust seen by Spitzer around G29-38 was probably generated 
relatively recently when one such outlying comet may have been 
knocked into the inner region of the system and ripped into dust 
shreds by the tidal forces of the star," said astronomer William 
Reach of the Spitzer Science Center at the California Institute of 
Technology (Caltech) in Pasadena, Calif. 

Prior to the Spitzer findings, astronomers studying G29-38 noticed an 
unusual and unknown source of infrared light. Spitzer, with its 
powerful infrared spectrometer, was able to break this light apart 
revealing its molecular makeup. These data told astronomers the light 
was coming from the same types of dusty minerals found in comets in 
our solar system.

"We detected a large quantity of very small, dirty silicate grains," 
said astronomer Marc Kuchner of NASA's Goddard Space Flight Center, 
Greenbelt, Md. "The size of these grains tells us they are probably 
from comets and not other planetary bodies." 

In our own solar system, comets reside in the cold outer fringes in 
regions known as the Kuiper Belt and Oort Cloud. Only when something 
disturbs their orbits, such as another comet or an outer planet, do 
they begin periodic journeys into the sun's warmer neighborhood. 
However, these trips to the tropics often end in destruction. Comets 
slowly disintegrate as they pass close to the sun or they crash into 
it. They also occasionally crash into planets, as comet 
Shoemaker-Levy 9 did when it plunged into Jupiter.

Though the dust seen by Spitzer around the white dwarf is most likely 
the remains of such a torn-up comet, there may be other explanations. 
One possibility is a second wave of planets formed long after the 
death of the star, leaving a dusty construction zone. 

Kuchner presented his findings today at the 207th meeting of the 
American Astronomical Society in Washington. The findings were 
published in the December 20, 2005, issue of the Astrophysical 
Journal. 

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the 
Spitzer Space Telescope mission for the agency's Science Mission 
Directorate. Science operations are conducted at the Spitzer Science 
Center at Caltech. JPL is a division of Caltech.

For artists' concepts, other graphics and more information about 
Spitzer on the Web, visit: 

http://www.spitzer.caltech.edu/spitzer 

For more information about NASA and agency programs on the Web, visit: 

http://www.nasa.gov/home/ 

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