[meteorite-list] Stardust Reveals Surprising Anatomy Of A Comet

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Jun 17 16:09:47 2004
Message-ID: <200406172009.NAA11538_at_zagami.jpl.nasa.gov>

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

Jane Platt/DC Agle (818) 354-0880
Jet Propulsion Laboratory, Pasadena, Calif.

Dwayne Brown (202) 358-1726
NASA Headquarters, Washington

NEWS RELEASE: 2004-154 June 17, 2004

NASA Spacecraft Reveals Surprising Anatomy Of A Comet

Findings from a historic encounter between NASA's Stardust spacecraft
and a comet have revealed a much stranger world than previously
believed. The comet's rigid surface, dotted with towering pinnacles,
plunging craters, steep cliffs, and dozens of jets spewing violently,
has surprised scientists.

"We thought Comet Wild 2 would be like a dirty, black, fluffy
snowball," said Stardust Principal Investigator Dr. Donald Brownlee of
the University of Washington, Seattle. "Instead, it was mind-boggling
to see the diverse landscape in the first pictures from Stardust,
including spires, pits and craters, which must be supported by a
cohesive surface."

Stardust gathered the images on Jan. 2, 2004, when it flew 236
kilometers (about 147 miles) from Wild 2. The flyby yielded the most
detailed, high-resolution comet images ever.

"We know Wild 2 has features sculpted by many processes. It may turn
out to be typical of other comets, but it is unlike any other type of
solar system body," Brownlee said. He is lead author of one of four
Stardust papers appearing in the Fri., June 18, issue of Science.
"We're fortunate that nature gave us such a rich object to study."

Stardust images show pinnacles 100 meters tall (328 feet), and craters
more than 150 meters deep (492 feet). Some craters have a round
central pit surrounded by ragged, ejected material, while others have
a flat floor and straight sides. The diameter of one large crater,
called Left Foot, is one fifth of the surface of the comet. Left Foot
is one kilometer (.62 miles) across, while the entire comet is only
five kilometers (3.1 miles) across.

"Another big surprise was the abundance and behavior of jets of
particles shooting up from the comet's surface. We expected a couple
of jets, but saw more than two dozen in the brief flyby," said Dr.
Benton Clark, chief scientist of space exploration systems, Lockheed
Martin Space Systems, Denver.

The team predicted the jets would shoot up for a short distance, and
then be dispersed into a halo around Wild 2. Instead, some
super-speedy jets remained intact, like blasts of water from a
powerful garden hose. This phenomenon created quite a wild ride for
Stardust during the encounter.

"Stardust was absolutely pummeled. It flew through three huge jets
that bombarded the spacecraft with about a million particles per
second," said Thomas Duxbury, Stardust project manager at NASA's Jet
Propulsion Laboratory, Pasadena, Calif. Twelve particles, some larger
than a bullet, penetrated the top layer of the spacecraft's protective
shield.

The violent jets may form when the Sun shines on icy areas near or
just below the comet's surface. The solid ice becomes a gas without
going through a liquid phase. Escaping into the vacuum of space, the
jets blast out at hundreds of kilometers per hour.

The Stardust team theorizes sublimation and object hits may have
created the comet's distinct features. Some features may have formed
billions of years ago, when life began on Earth, Brownlee said.
Particles collected by Stardust during the Wild 2 encounter may help
unscramble the secrets of how the solar system formed.

Stardust was launched in 1999. It is zooming back to Earth with
thousands of captured particles tucked inside a capsule. The capsule
will make a soft landing in the Utah desert in January 2006. The
samples will be analyzed at the planetary material curatorial facility
at NASA's Johnson Space Center, Houston.

Comets have been objects of fascination through the ages. Many
scientists believe they delivered carbon and water, life's building
blocks, to Earth. Yet their destructive potential is illustrated by
the widely held theory that a comet or asteroid wiped out the
dinosaurs.

To view Stardust images on the Internet, visit:

http://stardust.jpl.nasa.gov

or

http://photojournal.jpl.nasa.gov/ .

Stardust, part of NASA's Discovery Program of low-cost, highly focused
science missions, was built by Lockheed Martin Space Systems and is
managed by JPL for NASA. JPL is a division of the California
Institute of Technology in Pasadena.

-end-
Received on Thu 17 Jun 2004 04:09:35 PM PDT