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NASA Spacecraft Reveals Surprising Anatomy Of A Comet
06.17.04 

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. 

Image above: This image and diagram show the comet Wild 2, 
which NASA's Stardust spacecraft flew by on Jan. 2, 2004. The 
picture on the left is the closest short exposure of the 
comet. The listed names on the right are those used by the 
Stardust team to identify features. "Basin" does not imply an 
impact origin. 

Animation: This movie strings together a series of still 
images of comet Wild 2 taken during Stardust's historic flyby 
of the comet. Animation credit: NASA/JPL-Caltech. 

"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/ 







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            Last Updated: June 28, 2004
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