[meteorite-list] Hibernating Spacecraft Awakens for Comet Impact Mission (SWAS)

[Ron Baalke]

http://www.cfa.harvard.edu/press/pr0522.htmhttp://www.cfa.harvard.edu/press/pr0522.html

Harvard-Smithsonian Center for Astrophysics

Release No.: 05-22
For Release: Tuesday, June 28, 2005

Note to editors: High-resolution artwork to accompany this release is
online at http://www.cfa.harvard.edu/press/pr0522image.html.

Hibernating Spacecraft Awakens for Comet Impact Mission

Cambridge, MA--The Submillimeter Wave Astronomy Satellite (SWAS) has
been asleep on orbit for the past 11 months. SWAS operators placed it
into hibernation after a highly successful 5.5-year mission highlighted
by the discovery of a swarm of comets evaporating around an aging red
giant star. Now, they have awakened SWAS again for the first-ever
opportunity to study a comet on a collision course with a U.S. space probe.

"We knew there was life left in SWAS," said SWAS Principal Investigator
Gary Melnick (Harvard-Smithsonian Center for Astrophysics). "SWAS's
ability to detect emission from water convinced us that we could
contribute to the broader understanding of comets generated by this
event. This once-in-a-lifetime event was just too tempting to pass up."

NASA's Deep Impact mission will rendezvous with Comet Tempel 1 at the
end of June. Twenty-four hours before collision, on July 3rd, the flyby
spacecraft will deploy a 39-inch long by 39-inch wide, 802-pound
copper-reinforced impactor to strike the comet's nucleus. As the main
Deep Impact spacecraft watches from a safe distance, the impactor will
blast material out of the comet, excavating a football stadium-sized
crater of pristine ice from the interior. SWAS will measure the
abundance of water molecules as the icy comet debris vaporizes.

"Because a comet is composed mostly of ice and rock, water is the most
abundant molecule released by a comet. Everything else vaporizing from
the comet is measured relative to the amount of water," said Melnick.
"Water is the gold standard for comets, so knowing how much water is
being released per second is a very useful piece of information."

Current SWAS measurements indicate that Comet Tempel 1 is ejecting about
730 pounds of water per second, which is modest by cometary standards.
Deep Impact mission designers specifically selected the target for this
reason because the probe's mothership will have a better chance of
surviving the flyby. SWAS will watch closely for any changes to the
water production rate during and after the impact. Its measurements will
help constrain the nature of the comet's nucleus, including its chemical
makeup.

NASA and the SWAS team decided to reawaken the satellite because it
offers several unique advantages for observing the impactor-comet
collision. SWAS can determine the water production rate directly. It has
a large field of view that encompasses both the comet nucleus and the
surrounding envelope of vaporized gases known as the coma. And, it is
above the atmosphere and unaffected by weather, allowing SWAS to monitor
the comet almost continuously.

In early June, the satellite was powered up and its components
successfully tested. SWAS will remain active through the end of August,
watching Comet Tempel 1 for any long-term changes.

"It's gratifying that a satellite that has contributed so much during
its lifetime has been given one more opportunity," said Melnick.
"Helping to decipher the composition of material thought to be unchanged
since the birth of our solar system seems like a great last act."

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.

For more information, contact:

David Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7462 Fax: 617-495-7468
daguilar at cfa.harvard.edu 

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
cpulliam at cfa.harvard.edu