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IMPACT! Scientists blast
projectile into comet
July 4, 2005
Special to World Science
Scientists shot a washing machine-sized projectile into a comet,
eight times faster than a rifle bullet. The impact created an enormous blast
visible on images sent back to Earth, and whose size surprised even some mission
scientists.
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This image from NASA TV is a view from Deep Impact's flyby showing the impactor colliding with comet Tempel
1. (NASA)
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This image of Tempel 1 was taken from the side of the comet opposite the
impact, by the high-resolution camera on the flyby spacecraft after the
collision. (NASA/JPL)
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Comet Tempel 1 six minutes before it hit NASA's Deep Impact probe. The picture was taken by the probe's impactor targeting sensor.
(NASA/JPL- Caltech/UMD)
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One of the last images of Comet Tempel 1 sent back by the flyby
spacecraft before the collision. (NASA)
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A diagram of the Deep Impact spacecraft, and below it, the projectile.
(NASA)
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NASA researchers confirmed
the impact at 1:57 a.m. Eastern U.S. time, in a project designed to better
understand what comets are made of.
| Update: 12 hours later
A bright spray of gaseous material from
Comet Tempel 1 was continuing in the aftermath of the explosion, and its
force would make scientists have to revise their understanding of comet
structure, researchers said at a press conference 12 hours after the
impact.
“It’s going to take some time and some real
debate” to understand why the blast was so bright, said
co-investigator Pete Schultz at the conference, held at 2 p.m. Eastern
U.S. time at the NASA Jet Propulsion Laboratory in Pasadena, Calif.
Preliminary indications were that the
projectile initially went through some dusty, soft surface, explaining
an initial brightening that preceded the full burst, Schultz said.
Moments later, it appears to have hit some harder, icier material
inside.
Researchers said the spray was
probably a result of volatile, or quickly vaporizing gasses inside the
comet. The spray could go on for several weeks if these gases are
plentiful, said Michael A’Hearn,
mission principal investigator.
Also on Monday, the European Space
Agency announced confirmation that Tempel 1 contains water, based on
measurements of the emissions taken by its spaceborne XMM-Newton
Observatory.
It will take around a week before
scientists figure out the size of the crater left by the collision, A’Hearn
said at the conference. But “I don’t think it’s
house-sized; I think it’s bigger than that,” he added.
Another puzzle is that the comet’s
surface looks much different from those of the other two comets
scientists have gotten close looks at in recent years, comets Wild2 and
Borelli, A’Hearn added. “We don’t understand what this means yet.” |
A sequence of images sent
back by cameras on the projectile revealed growing amounts of detail on the
rocky-looking comet as a huge crater came to view. Later, images showed a bright
blast showering off the speeding, potato-shaped object.
Now, the task of analyzing
the images and other data from the mission begins.
Some scientists predict the blast will reveal organic material in the comet—the types of molecules that characterize life. Others say the mission could provide information on how comets could serve as water-supply and fueling stations for future space travelers.
“We want to find out what are the guts of a comet,” said mission principal investigator and University of Maryland astronomer Michael A’Hearn.
The impact is supposed to eject ice, dust and gas from the crater and reveal the pristine material beneath. This is believed to be material left over from the Solar System’s formation 4½ billion years ago.
The nature of the blast could reveal how soft or hard the comet is, said Don Yeomans, a member of the Deep Impact science team.
Comets are generally believed to be something like dirty snowballs, but no one
is sure.
“If the comet is solid like a block of ice, the crater will be relatively small,” he
explained before the impact. But if it’s softer or more loosely packed, “like a soufflé,” he added, “we’re expecting a much larger crater,” possibly the size of an American football field. “Either way we’re going to know how a comet is put
together.”
Comets could also provide water and rocket fuel for future space travelers, he added. “Comets may well be watering holes and fueling stations for interplanetary travel,” he said.
The $330 million NASA mission took off with the Jan. 12 launch of a spacecraft the size of a subcompact car, carrying a copper projectile the size of a washing machine.
Twenty-four hours before the planned July 4 impact, the spacecraft shot out its projectile. The comet and projectile were to come together at 37,000 kilometers (23,000 miles) per hour, well over eight times faster than a speeding rifle bullet.
The flyby craft was designed to send back pictures of the event, and data from spectrometers—instruments that analyze light to provide information on the types of molecules in the comet.
Space-borne observatories were also watching, including include NASA’s Hubble and Spitzer space telescopes and the Chandra X-ray Observatory, as were observatories on Earth. The impact was visible from Earth telescopes between Arizona and New Zealand, scientists said.
The projectile will be far too small to appreciably change the comet’s trajectory, they added, comparing the impact to a pebble hitting a truck. The comet is believed to be about half the size of Manhattan.
The flyby craft was to release its projectile when it and the comet were about 83 million miles (134 million km) from Earth, a distance slightly less than that between the Sun and the Earth.
Researchers with Cardiff University in Cardiff, U.K., predicted that the impact results will bear out their theory that comets contain organic matter. Some scientists believe organic material deposited by a comet could have produced life on Earth and other planets.
“The outer crust of the comet will consist of asphalt-like material with permafrost beneath. The small icy fragments blasted out by the impact will include organic matter,” the Cardiff researchers said in a statement last week.
The blast experiment “will show, we believe, that a comet is not a rubble pile, nor a conglomerate of ices, but a porous mass of organics and ice under the black asphalt
crust,” said Cardiff Professor Chandra Wickramasinghe.
He added that the comet may contain biological material similar to some that’s
found in the Arctic.
Although scientists want to learn about the comet’s interior, they also want to better understand the evolutionary changes in its mantle, or upper crust.
This is one reason they picked Tempel 1. Discovered in 1867 by Ernst Tempel, it has made many passages through the inner solar system, orbiting the Sun every 5.5 years. This makes Tempel 1, otherwise a fairly typical comet, a good target to study evolutionary change in the mantle, researchers said.
Astronomers believe Tempel 1 comes from the Kuiper belt, a disc-shaped region of comets and asteroids that lies beyond Neptune’s orbit and extends out for several hundred times the Earth-Sun distance.
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