[meteorite-list] To Strike a Comet: Astronomers Eager for Deep Impact's Cosmic Collision

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Jan 11 14:13:34 2005
Message-ID: <200501111913.LAA09247_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/scitues_deepimpact_050111.html

To Strike a Comet: Astronomers Eager for Deep Impact's Cosmic Collision
By Tariq Malik
space.com
11 January 2005

The two spacecraft of NASA's Deep Impact mission, dubbed Flyby and
Impactor by their makers, are set to launch Wednesday atop a Boeing
Delta 2 rocket, their mission: To unlock the inner secrets of comets. .

"All I can do now is worry and hope," said Deep impact principal
investigator Michael A'Hearn, of the University of Maryland, during a
telephone interview. "And then watch it go."

Deep Impact is currently scheduled for a 1:47 p.m. EST (1847 GMT)
liftoff from Launch Pad 17B at Cape Canaveral Air Force Station in
Florida. If all goes well, the mission's two spacecraft will tag team
Comet Tempel 1 on July 4, with Impactor set to slam into the icy
wanderer while Flyby looks on.

Built for NASA by Ball Aerospace and Technologies Corp., Deep Impact is
designed to give researchers their first glimpse of the inner workings
of a comet. By crashing Impactor into Tempel 1, thought to be a rather
typical example of comets, researchers hope to glimpse pristine material
that have not changed since the formation of the solar system.

"The interesting part of this mission is that we don't really know what
to expect," said Don Yeomans, a senior research scientist with the Deep
Impact mission at NASA's Jet Propulsion Laboratory (JPL). "But no matter
what happens, we'll observe the phenomena."

Digging into a comet

"We have a tremendous amount of Earth-based data on the composition of
gases that come out of a comet and the dust lifted off its surface,"
A'Hearn said, adding that the object's inner make up is still a mystery.
"But the [comet] interior is characteristic of what the solar system
formed from."

To measure that material, Deep Impact's Impactor probe -- an 820-pound
(372-kilogram), camera-equipped chunk of copper -- will be placed in
Tempel 1's path and ultimately slam into the comet at about 23,000 miles
an hour (37,014 kilometers an hour). Snapping images until the last,
Impactor is designed to give researchers their closest look yet at a
comet's surface.

"We hope to get 15 centimeters resolution," Yeomans told SPACE.com,
adding that extreme dust conditions could still limit Impactor's camera.
"That's unprecedented resolution."

Meanwhile, Flyby will record the event -- along with a myriad of
Earth-based and orbital instruments -- with telescopes capable of
two-meter resolution and an infrared spectrometer to determine the
mineral make-up of Tempel 1's innards.

Flyby should relay at least some data from its own sensors and
Impactor's camera during the event, but the spacecraft will continue to
send observations home until well after the initial impact.

"I really want to see the data as they come down," A'Hearn said, adding
that Deep Impact will allow researchers to look anew at previous comet
observations. "On the Fourth of July, we'll all be huddled around TV
screens at mission control."

Understanding impacts

Comet science aside, Deep Impact is also poised to give researchers a
ringside seat to what they hope will be a huge cometary smash-up.

When Deep Impact crashes into Comet Tempel 1, the size of its crater
remains will depend on the comet's structure and density. Size estimates
from mission scientists describe the crater as ranging from a meager 10
meters to the size of the Rose Bowl football stadium in Pasadena,
California.

"My personal estimate [for the crater] is at the large end of a
large-size football stadium, perhaps 150 meters in diameter," A'Hearn
said. "It could be larger."

Researchers are eager to compare Deep Impact's crater - granted the
spacecraft reaches Tempel 1 successfully in the first place - because of
the past comet craters observations.

Based on images taken by NASA's Stardust spacecraft, which swung by the
admittedly odd comet Wild 2, some astronomers believe that comet-based
craters differ from their planetary and moon-based cousins.

"They don't look like craters anywhere else in the solar system,"
A'Hearn said of Wild 2's surface features. "It's the lack of ejecta
around them that makes them unusual."

A'Hearn wants to see if Deep Impact's crater has the same attributes,
adding that the mission also has the benefit of creating at least one
crater on Tempel 1 that is unambiguously an impact feature.

A watery story

Some researchers are also interested in learning the amount of water in
Tempel 1, especially since some scientists believe comets may have been
the original vehicles for water to reach Earth.

"Comets are far more than an intellectual interest," Yeomans said,
adding if comets were Earth's water delivery system, they form a crucial
cog in life's beginnings. "These things affect us, and may have even
enabled us [to exist]."

And while they may have played a role in our beginnings, comets could
one day be tapped by future human space explorers as a source for water,
oxygen and hydrogen fuel for far-flung space missions, NASA researchers
said.

"They could be the watering holes and fuel stations for future
interplanetary exploration," Yeomans said.
Received on Tue 11 Jan 2005 02:13:23 PM PST