[meteorite-list] NASA's Space Eyes Focus on Deep Impact Target

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Jun 2 14:07:14 2005
Message-ID: <200506021806.j52I6Y718996_at_zagami.jpl.nasa.gov>

Dolores Beasley/Marta Metelko
Headquarters, Washington June 2, 2005
(Phone: 202/358-1753/1642)

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

RELEASE: 05-139

NASA'S SPACE EYES FOCUS ON DEEP IMPACT TARGET

On July 4, NASA's Deep Impact spacecraft will attempt an
extraordinarily daring encounter with the far-flung comet
Tempel 1 hurtling through space at tens of thousands of
miles per hour. As if that is not challenging enough, the
comet's size, shape and other characteristics are not
entirely known.

Two of NASA's eyes in the sky, the Spitzer and Hubble Space
Telescopes, helped scientists prepare for the comet encounter.
>From their orbits high above Earth, the telescopes watched
Tempel 1 in early 2004. Together they came up with the best
estimates of the comet's size, shape, reflectivity and
rotation rate. The data may help Deep Impact snap pictures
of the dramatic rendezvous and increase the probability of
making contact with the comet.

"Even tiny adjustments to our model of Tempel 1 are crucial
to hitting the target and setting camera exposure times," said
Dr. Carey Lisse, Johns Hopkins University Applied Physics
Laboratory, Laurel, Md. Lisse is team leader for the
Tempel 1 Spitzer studies.

Previous observations of Tempel 1 taken with ground-based
telescopes indicated the comet is dark and oblong, with a
width of a few miles. Spitzer and Hubble refined these
measurements, revealing a matte black comet approximately
8.7 by 2.5 miles, or roughly one-half the size of Manhattan
Island, N.Y.

"Spitzer was crucial in pinning down the comet's size," said
Dr. Michael A'Hearn, University of Maryland, College Park.
He is principal investigator for Deep Impact and the Hubble
observations. "We'll know exactly what it looks like when we
get there," he said.

The Deep Impact spacecraft was launched on January 12, 2005.
Its mission is to study the primordial soup of our solar
system, which is sealed away inside comets.

On July 3, as it approaches Tempel 1, the spacecraft will
separate into two parts. The impactor will attempt the tricky
task of placing itself in the path of the speeding snowball,
while the second part, the flyby spacecraft, swings around
for a ringside view.

After the impactor is released, its specialized software will
steer it toward the sunlit portion of Tempel 1's nucleus. To
program the software, mission planners at NASA's Jet Propulsion
Laboratory (JPL) needed to know the size and reflectivity of
Tempel 1's surface. Since its surface can't be observed
directly from Earth, scientists turned to Spitzer's infrared
eyes to measure its size.

When viewing a comet in visible light from very far away, only
reflected sunlight can be seen, so a big, dark comet can look
the same as a highly reflective, small comet. In infrared light,
a comet's radiated heat is measured, providing a direct look at
its size.

Once the size of Tempel 1 was known, scientists could calculate
surface reflectivity. They calculated the amount of reflected,
visible light observed by Hubble and found Tempel 1 reflects
only four percent of the sunlight that falls on it.

"Knowing the reflectivity also tells us how to set up our
cameras," Lisse said. "Like photographers, it's important for
us to know our subject before the shoot."

Tempel 1's shape and two-day rotation rate were derived from
long-term observations made by various telescopes, including
Hubble, Spitzer and the University of Hawaii's 2.2-meter
telescope at Mauna Kea.

In addition to the flyby spacecraft images, at least 30
telescopes around the world, including Spitzer, Hubble and the
Chandra X-ray Observatory, will be watching the dramatic impact.
By analyzing the material blown out of the interior of the comet,
this global network of telescopes will assemble a list of the raw
ingredients that went into making the planets in our solar system.

JPL manages the Deep Impact mission for NASA. For information
about NASA and the Deep Impact mission on the Web, visit:

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

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

http://hubblesite.org/news/

http://deepimpact.jpl.nasa.gov/

-end-
Received on Thu 02 Jun 2005 02:06:33 PM PDT