UA Scientist on Deep Impact Mission Ready for Spacecraft's Launch

UA Scientist on Deep Impact Mission Ready for Spacecraft's Launch
Lori Stiles
University of Arizona
January 3, 2005

N O T A E
Contact Information
H. Jay Melosh
520-621-2896


Animation (Beta format)
Contact Vern Lamplot, UA News Services
520-621-1877

Related Web site
Deep Impact
http://www.nasa.gov/mission_pages/de...ain/index.html


The scientist who wrote the book on planetary impact cratering will
join
NASA and other university researchers at Kennedy Space Center, Fla., to
watch the launch of Deep Impact this month.

If all goes as planned, Deep Impact will become the first mission to
slam
into a comet, giving astronomers worldwide something far better than
any
other fireworks show on July 4, 2005 the first look inside a comet at
the
most primitive material left in the solar system.

"The idea is that the best way to find what's inside a comet is to
blast a
hole in it," University of Arizona Regents' Professor and Deep Impact
science team member H. Jay Melosh said. "Other comet-rendezvous
missions
have proposed sampling less than a foot into the upper surface. But
that
doesn't get at the ices in the interior, which scientists believe are
early
solar system materials that have been kept in the deep freeze for the
past
4.5 billion years."

Melosh has done more than any other single scientist to explain how
impact
cratering has shaped the terrestrial planets, including Earth. His 1989
book
on the topic is still the universal reference for scholars, expert or
novice. Melosh's research interests relate to the origin and evolution
of
the early solar system. Deep Impact could add chapters to that story.

NASA's Deep Impact spacecraft is planned for liftoff Jan. 12, 2005, and
no
later than Jan. 28, to reach comet Tempel 1 beyond the orbit of Mars on
July
4. During the rendezvous, Deep Impact will deploy an 820 pound (372
kilogram) copper probe into the comet at about 23,000 mph (37,000 kph),
or
about a hundred times faster than a bullet fired from a .22 caliber
gun.

The probe carries a digital camera that will send images in real time
back
to the spacecraft as the projectile hurls through dust and debris
toward the
comet.

Powerful cameras and a spectrometer on the parent spacecraft, flying
about
300 miles (500 kilometers) away, will capture what happens on impact.
The
instruments will follow events for about 10 minutes after the
collision,
until the spacecraft goes into shield mode to survive flight through
the
comet's dusty orbital plane, where it will be blasted by
buckshot-to-gumball-sized particles.

"The impact may form a crater about the size of a football field and
deep
enough to swallow a 10-story building. The deeper the better, " Melosh
said.
"We're hoping to see the crater explosion and the ejecta plume. We'll
get
some idea of the strength of the interior of the comet as the crater
grows
and ejecta is blown out." The comet nucleus could be hard, Melosh said
-- or
fluffy as a bowl of cornflakes.

Impressive as the impact will be, it's only a minor hit as far as
Tempel 1
is concerned, Melosh said. The mass of the copper impactor is miniscule
compared the mass of the five-to-six-mile-long comet. An analogy would
be a
smash-up between an 18-wheeler and an armadillo crossing the road, or
even a
mosquito smashing into a windshield, he noted.

Scientists plan to get spectra that will tell them what molecules make
up
the comet ices.

"There'll be a flash of volatiles that we may see with the spectrometer
in
the early stage of impact, and that astronomers will see from the
ground and
with space-based telescopes like Hubble, Chandra and Spitzer."

A global network of professional and amateur astronomers will observe
the
comet for the next few days as it brightens after impact.

During mission design, Melosh carefully calculated the abundances of
"critical" elements scientists might expect to see vaporize on impact.
Critical elements are those which scientists want to measure because
they
are important in early solar system processes. Melosh also modeled how
much
mass of each of the different elements would be vaporized on impact so
scientists can know how much vaporized material comes from the comet
and how
much from the spacecraft.

The Deep Impact probe is made mostly of copper because "copper is an
element
that no geochemist or cosmochemist trying to work out the origin of the
solar system cares about. It's not characteristic of any particular
solar
system process," Melosh said.

University of Maryland astronomy professor Michael A'Hearn is principal
investigator for Deep Impact. He leads the mission from the University
of
Maryland, College Park. Kitt Peak National Observatory Astronomer
Emeritus
Michael Belton of Belton Space Exploration Initiatives, Tucson, is
another
member of the Deep Impact science team.

Ball Aerospace & Technologies in Boulder, Colo., built NASA's Deep
Impact
spacecraft. It was shipped to Florida in October for final launch
preparations. NASA's Jet Propulsion Laboratory in Pasadena, Calif.,
manages
the Deep Impact project for the Science Mission Directorate at NASA
Headquarters. Deep Impact is a mission in NASA's Discovery program of
moderately priced solar system exploration missions.

More information on Deep Impact is on the Internet at
http://www.nasa.gov/deepimpact