[meteorite-list] Comet Show Leaves NASA Speechless

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Jul 5 13:19:59 2005
Message-ID: <200507051719.j65HJCw11045_at_zagami.jpl.nasa.gov>

http://www.latimes.com/news/science/la-sci-deepimpact5jul05,1,4288858.story

Comet Show Leaves NASA Speechless

The debris field kicked up by the collision is so large, it will take
days to glean a clear image.

By Thomas H. Maugh II
Los Angeles Times
July 5, 2005

The collision of a probe from NASA's Deep Impact spacecraft with comet
Tempel 1 blew a plume of debris thousands of miles into space and
provided a spectacular first glimpse of the insides of a comet - ancient
bodies that may hold the key to the origins of the solar system -
scientists said Monday.

The collision - a carefully orchestrated dance at more than 20,000 mph
intended to expose the comet's interior - was much larger than anyone
had expected, said researchers at the Jet Propulsion Laboratory in La
Ca?ada Flintridge.

Telescopes on Earth showed that the light from the comet increased
fivefold in the aftermath of the collision at 10:52 p.m. PDT Sunday
before slowly fading over several hours.

"I was trying to think how to describe this, but I am just plain
speechless," said Andrew Dantzler, the director of NASA's solar system
program.

The eruption of debris from the impact was so large that principal
investigator Michael A'Hearn of the University of Maryland said it could
take scientists a week or more to tease out a reliable image of the
impact crater from behind the smokescreen of dust and gas that obscured
the comet's surface.

By Monday morning, project scientists had had little time to analyze the
information and images that were flooding into their databanks, but what
they saw was drawing back the veil from the composition and structure of
comets.

The high-resolution images taken before the impact show a comet surface
substantially different from that of previously observed comets, such as
Borrelly and Wild-2. Although the surface appears white because of
reflected sunlight, it is actually jet-black. Small bright patches on
the surface are most likely steep slopes that reflect more sunlight than
the surrounding landscape.

The surface of Tempel 1 is littered with what appear to be impact
craters - the first time such craters have been observed on a comet
surface, A'Hearn said.

There is also a large, flat area that curves around the surface of the
nucleus. The only flat area previously observed was a plateau on Borrelly.

"We don't understand the physics of what produces those flat surfaces,"
A'Hearn said. Tempel 1's "orbital history is very similar to Borrelly's,
but the surface looks totally different."

The impact surprised researchers in both its magnitude and its
structure. The sequence of images from the Deep Impact mother ship shows
a small flash, a slight delay and then a larger flash, said Peter
Schultz of Brown University, a project co-investigator.

That suggests that the 820-pound impactor, which struck the surface of
the comet at a speed of 6.3 miles per second, burrowed into a powdery
layer in the nucleus before encountering a solid surface of ice or rock
below it, Schultz said.

"We are getting an enormous wealth of data even though we can't yet see
the actual impact point," he said.

Late Monday, researchers from the University of Pennsylvania and
University College London said ultraviolet observations from NASA's
Swift satellite showed that the impactor struck a solid structure
beneath the powdery surface layer.

Although researchers are analyzing the spectra, "We don't know exactly
what we kicked up yet," said astronomer Keith Mason of University
College London.

Images of the impact taken by the mother ship clearly show the shadow of
the debris column spreading across the surface of the nucleus.

Initial imaging with Deep Impact's infrared spectrometer also showed big
changes in the composition of the comet's corona as the debris from the
impact was ejected, Mason said.

There are several unidentified materials in the spectra, strong evidence
that the interior of the comet is different from the surface, he said.

Telescopes on the ground reported changes in the abundance of gases
observed in the comet's corona, especially a large increase in water vapor.

Researchers believe that comets represent a kind of time capsule of the
materials that were present when the solar system was created 4.6
million years ago.
Received on Tue 05 Jul 2005 01:19:11 PM PDT