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*Web Extra Tuesday, July 5, 2005*
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Deep Impact strikes back
The scientists at NASA's Jet Propulsion Laboratory (JPL) cheered
yesterday as they received confirmation that the Deep Impact probe
successfully hit its target, comet Tempel 1, after six months' and
hundreds of millions of miles' worth of journey. The images the mother
ship spacecraft sent back are stunning, showing a bright curtain of
materials surrounding the impact site, and giving the science team an
Independence Day to remember.
"The impact was spectacular, much brighter than I expected," said Mike
A'Hearn, principal investigator for Deep Impact, speaking in the early
morning hours yesterday from JPL via teleconference to a group of fellow
colleagues and friends at his home institution, the University of
Maryland. After the successful 1:52 a.m. EDT impact on July 4, A'Hearn
said that it will take days to years for the scientists to wade through
all the images and data. "There's a lot of image processing to be done,"
he said.
The mission's aim was to ram a spacecraft into a comet to dig up the
volatile materials buried below the body's surface. The materials
ejected in the impact, researchers hope, will shed light on the origins
of the solar system, as the volatile ices and gases are believed to be
some of the oldest and coldest materials left over from when the sun and
planets formed 4.5 billion years ago.
*
When NASA's Deep Impact probe collided with Tempel 1, a bright, small
flash was created, which rapidly expanded above the surface of the
comet. This flash lasted for more than a second. Its overall brightness
is close to that predicted by several models. This image was taken by
Deep Impact's medium-resolution camera. All images courtesy of
NASA/JPL-Caltech/UMD.*
Deep Impact achieved its goals, by re-creating a naturally occurring
event, common throughout the solar system. As Derek Richardson,
astronomy professor at the University of Maryland, explained to eager
Deep Impact partygoers yesterday, Earth has experienced many significant
impacts of asteroids and comets, including the infamous one, 65 million
years ago, that scientists think spelled the dinosaurs' demise. Deep
Impact, he said, is going to bring some karma to the solar system.
"Tonight, hopefully we got our revenge," he said. It's the "Earth
strikes back."
And it did. At 2 a.m. EDT on July 3, almost a full day before impact,
the washing machine-sized Deep Impact probe separated from its mother
ship, and began its own journey to the nucleus of Tempel 1, about 14 by
4 by 4 kilometers in dimensions. From a distance, all the probe could
see of the comet was its coma ? the cloud of gas that surrounds the
comet. But as the probe got closer, it began to discern the heart of the
comet ? its nucleus ? and sent back pictures in real-time of what
appeared to be a pear-like structure.
*This image shows the view from Deep Impact's probe 90 seconds before it
vaporized after impact with comet Tempel 1. The image was taken by the
probe's impactor targeting sensor. *
"The resolution [on the photos] is really quite extraordinary," said Don
Yeomans, co-investigator for Deep Impact, also at JPL for the event. The
pictures show a comet that has perhaps experienced impacts before, with
crater-like structures on the surface.
"There's a lot of structure on the comet, which is a bit surprising,"
Richardson said. "That could mean there's some strength to the comet." *
*
As the probe neared its target, it began to experience comet conditions,
with gases and debris bombarding it. "Our brave little spacecraft is now
in a very hostile environment," Yeomans said, as the probe's pictures
were sent back to Earth. The impactor spacecraft, however, survived much
longer than expected, delivering images right up until its demise. "The
last image we got was three seconds before impact," A'Hearn said. The
mother ship fared well too, sending back the first images of the impact
itself, a cosmic explosion of sorts.
*
* After the initial flash from impact, a bright plume quickly extended
above the comet's surface. The debris from the impact eventually cast a
long shadow across the surface, indicating a narrow plume, rather than a
wide cone. A preliminary analysis of the data indicate that the upper
surface of the comet may be fluffy, or highly porous. Based on lab
experiments with highly porous targets, rich in volatile substances, the
crater is likely to be large. In the end, the scientists hope that
analyzing the crater left behind by the impact will tell them more about
what holds these mysterious bodies together.
While the Deep Impact team analyzes the images from the mother ship, it
will have help from the many scientists who were watching the impact
from telescopes around the world. Immediately after impact, observers on
the ground had already seen an increase in the comet's total brightness.
*
The view from Deep Impact's probe 30 minutes before it hit comet Tempel
1 highlights the comet's coma, the cloud of gases and dust that
surrounds all comets. The picture's brightness has been enhanced to show
the jets of dust streaming away from the comet. Only as the probe got
nearer could it see the comet's nucleus. The image was taken by the
probe's impact targeting sensor. *
As to whether the impact would affect the comet and its path through the
solar system, Lee Mundy, head of astronomy at the University of
Maryland, said "it's like a mosquito hitting a 747." Although the
outgassing from the impact could cause a small shift in orbit, it is
unlikely, and so far, it looks like the comet is doing just fine.
*Lisa Pinsker
*/For more background information on Deep Impact, read this month's
feature story <#>. /
*Links:*
Deep Impact home page <#>
Collision Course: Deep Impact <#>, /Geotimes/, July 2005
*Order your free trial
copy of /Geotimes/ !*
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