[meteorite-list] Spitzer Telescope Sees Trail of Comet Crumbs (Schwassman-Wachmann 3)

[Ron Baalke]

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

Whitney Clavin (818) 354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

Image Advisory: 2006-075	           May 10, 2006

Spitzer Telescope Sees Trail of Comet Crumbs

NASA's Spitzer Space Telescope has snapped a picture of the 
bits and pieces making up Comet 73P/Schwassman-Wachmann 3, 
which is continuing to break apart on its periodic journey 
around the sun. The new infrared view shows several chunks 
of the comet riding along its own dusty trail of crumbs. 

"Spitzer has revealed a trail of meteor-sized debris filling 
the comet's orbit," said Dr. William T. Reach of NASA's 
Spitzer Science Center at the California Institute of 
Technology, Pasadena. Reach and his team recently observed the 
comet using Spitzer. The picture can be viewed at 

http://www.spitzer.caltech.edu/Media/releases/ssc2006-13/ssc2006-13a.shtml .

Comet 73P/Schwassman-Wachmann 3 consists of a collection of 
fragments that file along like ducks in a row around the sun 
every 5.4 years. This year, the bunch will pass by Earth beginning 
on May 12 before swinging by the sun on June 6. The fragments 
won't get too close to Earth, about 7.3 million miles, or 30 
times the distance between Earth and the moon, but they should 
be visible through binoculars in the countryside night skies. 

The icy comet began falling apart in 1995 during one of its 
tropical trips to the sun. Astronomers believe that its crusty 
outer layer cracked due to the heat, allowing fresh ice to 
evaporate and split the comet apart.  

During the past six weeks, amateur and professional astronomers 
have been watching the comet fall apart before their telescopes' 
eyes. Spitzer viewed the broken comet from its quiet perch up in 
space May 4 to May 6, covering a portion of the sky that allowed 
it to spot 45 of the 58 known fragments. 

The observatory's infrared view also provides the first look 
at the dusty trail left by the disintegrating comet after it 
splintered apart in 1995. The trail is made up of comet dust, 
pebbles and rocks that occasionally rain down on Earth in what 
is called the Tau Herculid meteor shower. From May 19 to June 19, 
as Earth passes through the outskirts of the trail, only a weak 
meteor shower is expected, with just a few "shooting stars" 
visible in the night sky. A larger meteor shower might occur in 
2022 if Earth crosses near the comet's wake as predicted.

Spitzer's infrared eyes were able to see the dusty comet bits 
lining the trail because the dust is warmed by sunlight and glows 
at infrared wavelengths. Most of the dust particles, specifically 
the millimeter-sized nuggets, had never been seen before. Reach 
said that these particles probably represent the natural 
deterioration of the comet over the years, a process commonly 
observed in intact comets.

The comet dust also adds up to more evidence for the "icy dirtball" 
theory of comets. In recent years, more and more astronomers are 
coming to think of comets not as snowballs coated in dust, but as 
dirtballs crusted with ice. 

"By measuring the brightness and extent of the debris trail, we 
are trying to find out whether most of the comet's mass 
disintegrates into vapors from evaporating ice, the house-sized 
chunks seen in images from the Hubble Space Telescope, or the 
meteor-sized debris seen in the Spitzer images," said Reach.

Reach and his team will continue to study the Spitzer data for 
clues to how the comet broke up. Their infrared data will tell 
them the sizes of the major fragments, which might indicate 
whether the comet did, as believed, crack under the thermal 
stress.

Comet 73P/Schwassman-Wachmann 3 should be dimly visible through 
binoculars on a clear night between the Cygnus and Pegasus 
constellations from May 12 to May 28. For more information 
about viewing the comet or the meteors, visit 

http://science.nasa.gov/headlines/y2006/24mar_73p.htm .  

None of the comet's fragments pose a danger to Earth. For more 
information, see 

http://www.nasa.gov/mission_pages/hubble/Comet_73P.html . 

Members of Reach's team include: Dr. Michael Kelley of the 
University of Minnesota, Twin Cities; Dr. Carey M. Lisse of 
the Johns Hopkins University's Applied Physics Laboratory, 
Laurel, Md.; Dr. Mark Sykes of Planetary Science Institute, 
Tucson, Ariz.; and Dr. Masateru Ishiguro of the Institute of 
Space and Astronautical Science, Japan.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages 
the Spitzer Space Telescope mission for NASA's Science 
Mission Directorate, Washington. Science operations are 
conducted at the Spitzer Science Center at the California 
Institute of Technology. Spitzer's multi-band imaging 
photometer, which made the observations, was built by Ball 
Aerospace Corporation, Boulder, Colo.; the University of 
Arizona, Tucson; and Boeing North American, Canoga Park, 
Calif. The instrument's principal investigator is Dr. George 
Rieke of the University of Arizona.

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

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

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