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ToSeek
2004-Jun-17, 06:09 PM
Almost forgot about this and got into it late.

Looking at comet Wild 2: "Almost every spot has a feature."

Named largest crater Shoemaker.

Showing spires and shadows.

Seeing vertical cliffs, columns, overhanging cliffs. Means comet's surface is strong, not just dust or loose material. Likens it to astronaut ice cream: strong but brittle.

ToSeek
2004-Jun-17, 06:13 PM
Talking about instrument "Comet and Interstellar Dust Analyzer."

Materials from this comet are very enriched in organic material, looks like comets are richest bodies in the solar system in organics. Earth may have gotten much of its organics from comets. Astrobiologists want to get material back and look at it.

Many jets of gas and dust emanating from comet, not just the one that it seems to be from Earth. Jet is very rough, "very bumpy ride" going through it, very uneven quantities of dust.

ToSeek
2004-Jun-17, 06:19 PM
Claudia Alexander, comet expert. Been modeling comets for years, not at all what was expected.

Rubble pile model more the classic model, doesn't fit observations. Geyser model implies more gravity, more force, chamber in which gases are forcibly brought out. Comet definitely more cohesive than a rubble pile.

Slide showing Wild 2 next to Cassini image of Phoebe. Phoebe may be a Kuiper Belt object, Wild 2 definitely is. No resemblance: no cliffs, overhangs on Phoebe. Must have different histories.

Future missions: Deep Impact, drop impactor July 4, 2005 on Comet Tempel and see what happens. See what kind of hole is made, should tell us about composition of comet's surface. Likewise, European Rosetta mission will be informative.

ToSeek
2004-Jun-17, 06:28 PM
Back in about two years with discussion of actual samples returned by Stardust.

Question time:

Any idea how pinnacles were formed?

Erosion features like Monument Valley on Earth. If so, means comet has lost something like 100 meters of surface.

Why do Wild 2 and Phoebe look so different? Both from Kuiper Belt?

Phoebe may have been captured by Saturn a long time ago, subject to different environment. Wild 2 in outer solar system longer. Wild 2 definitely from Kuiper Belt, not so confident about Phoebe. But Phoebe has been in orbit around Saturn for a long time. Don't know much about comets yet - only seen 3 up close.

Wild 2 a comparatively fresh comet, only been in present orbit for 30 years, was in Jupiter-Uranus orbit before, but could have been in close Sun orbit even before then.

Deeper insights from study last few months?

Seeing types of features "we haven't even named." Amazed at variety. Seeing downslope falls with nothing at bottom, seeing dozens of jets, a big surprise. First time seeing how a comet's tail is formed.

Was able to take about 20 of the jets and trace them back to spots on surface. Stardust went through many of the jets.

Deep holes called "Left Foot," "Right Foot," kilometers-wide, very deep holes, but no jets currently coming out. Perhaps completely outgassed by now.

END. I'm sure I missed some good stuff at the beginning.

01101001
2004-Jun-17, 06:33 PM
Pictures of Comet Wild-2 (http://stardust.jpl.nasa.gov/photo/cometwild2.html)

Craters and pinnacles and mesas.

01101001
2004-Jun-17, 06:41 PM
Almost forgot about this and got into it late.
I wasn't taking notes, but from the opening I enjoyed the sample "bullet-proof vest" material. It had a grape-sized hole in its mylar and carbon fiber shell, and grapefruit sized holes in the layers of fabric underneath, where energy was disipated.

They actually wound up getting impacts of small-grape size, around 20 of them. I guess the shield got a pretty good workout and did its job well.

The Bad Astronomer
2004-Jun-17, 08:12 PM
Expect nonsense from Jim McCanney to follow soon... :o

R.A.F.
2004-Jun-17, 08:34 PM
Dag gummit!

Not only did I miss the press conference, I was going to post the new images and now I see that's already been done!! :)

Those new images are amazing!

ToSeek
2004-Jun-18, 12:24 AM
Associated press release:


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.