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NASA probe leaves crater, debris trail
(Agencies)
Updated: 2005-07-05 06:29
PASADENA, Calif - A spectacular collision between a spacecraft and a comet
has freed a huge plume of primordial material from the comet's nucleus that
could unlock the secret of how life arrived on Earth, NASA scientists said on
Monday.
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A
NASA probe collides with comet Tempel 1 in this image taken by the
impactor's mother ship, capturing the climax to the Deep Impact mission.
[Agencies]
| The first images returned from
the Deep Impact fly-by spacecraft showed a small fireball followed by a much
larger, incandescent flash that engulfed one end of the comet Tempel 1 as the
impactor smashed into its surface at 1:52 a.m. EDT (0552 GMT) on Monday.
The impactor was vaporized upon slamming into the comet at 23,000 mph (37,000
kph) -- the speed it would take to fly from New York to Los Angeles in about six
minutes.
The collision, which occurred 83 million miles from Earth, marks the first
time a spacecraft has come in contact with a comet.
Observatories on the ground reported that the explosion brightened the comet
by a factor of 5 within 15 minutes of impact, scientists at NASA's Jet
Propulsion Laboratory in Pasadena said.
Scientists could not immediately determine the size of the crater produced by
the impact because of the large plume of ice, dust and gases streaming out and
obscuring one end of the comet, which is half the size of Manhattan.
"We are waiting for the outgassing to stop. It's clear it's was still coming
out for several hours ... and could go on for weeks," principal scientist Mike
A'Hearn told reporters at a Monday news conference.
The Deep Impact team had estimated the washing machine-sized impactor would
punch a hole anywhere from the size of a house to a football stadium, depending
on the composition of the comet's surface.
"We know that we created quite a crater. We believe it penetrated quite
deeply so we know we'll get a good look at the interior," Project Manager Rick
Grammier said on Monday. "We just have a wealth of scientific information to go
through in the next few months."
'BIG CHANGES'
The impact sent up twin plumes of debris, the first appearing as a narrow
column that cast a long shadow across the comet. Another plume appeared seconds
later on the heels of a brighter explosion, then fanned out in a star shape.
Scientists said the plumes stretched for "at least thousands of kilometers" into
space.
Co-investigator Pete Schultz said the twin flashes showed that the impactor
encountered softer, layered material on the comet's surface then hit a thick,
hard crust.
A spectrometer aboard the fly-by spacecraft captured "big changes" in the
spectra of debris flying up from the crater, indicating a variety of materials
were freed by the impact, A'Hearn said.
Comets are made of gas, dust, organic material and ice from the solar
system's farthest regions. Because they were not heated by the Sun during the
formation of the solar system, comets retain the original chemical mixture from
which the planets formed 4.6 billion years ago.
Scientists think comets may be responsible for first bringing water and
organic material to Earth by crashing into its surface during a period of heavy
comet activity 3.9 billion years ago -- around the same time as the first signs
of life.
Tempel 1's rough surface, closely revealed for the first time in images
snapped by the impactor up to 3 seconds before impact, differed markedly from
the two other comets scientists have been able to observe up close, A'Hearn
said.
The surface showed what appeared to be layering, craters, small bright
features and smooth areas that defy physics by stretching around two sides of
the comet, he said.
"There is something more going on here than we understand," he said.
A'Hearn also said the Deep Impact team has been forced to reevaluate its
ideas about Tempel 1's shape, which is more like a muffin or a loaf of bread
than a pickle.
The $333-million Deep Impact mission is the eighth in NASA's Discovery
Program to produce relatively cheap missions, such as the 1997 Mars Pathfinder,
to explore the solar system.
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