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No “typical” comets, astronomers suggest based on comet-shoot study
Sept. 6, 2005
Special to World Science
After two months of studying data from an experiment that involved shooting a projectile at a comet, astronomers are
unveiling new findings about what the test revealed.
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A composite of images taken by the impactor targeting sensor on the spacecraft that collided with comet Tempel 1. The arrows point out two areas where the surface is smooth instead of spotted with depressions.
(Ó
Science)
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Among the more important of these revelations: there may be no such thing as a “typical” comet, 35 astronomers said in a paper published in the upcoming Sept. 9 edition of the research journal
Science.
The astronomers noted that the comet is very different from two other closely-studied comets believed to come from the same area of space. This “raises the question of whether any comet is typical when looked at closely,” the researchers, led by Michael A’Hearn of the University of Maryland in College Park, Md., wrote.
Tempel 1, the comet in the projectile experiment, “is the first comet to show evidence for
impact craters,” and the elongated shape of its core is also different, they added.
Tempel 1 also seems to have a fine powder covering its surface to a depth of tens of meters, the researchers
added. The dust periodically bursts out as a result of warming from the Sun.
Ices probably lie slightly below this surface,
the researchers added, and the comet seems to contain many organic molecules—chemical
ingredients of life. Many scientists have speculated that comets could have
jump-started life on Earth by bringing such substances here.
Overall, Tempel 1 has a very fluffy structure that
is weaker than a bank of powder snow, A’Hearn said at a press conference
Monday. The dust is held together by gravity. However, that gravity is so weak, if you could stand on the bank and jump, you would
launch yourself into space.
The conclusion that so much dust covered the
surface was based on the huge amount of dust kicked up after the projectile
struck. Astronomers could also draw conclusions about the types of substances in
the comet based on characteristics of the light from the blast.
Researchers wanted to study a typical comet when they chose Tempel 1 as the target of a projectile size of a washing
machine. The copper impactor struck on July 4, with a burst whose size surprised
the scientists conducting the mission.
The purpose of the experiment was to watch the explosion resulting from the blast, and see
what it could reveal about the comet’s structure.
Tempel 1 is about half the size of Manhattan and is thought to come 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.
It was hoped that the impact would eject material from the surface of the comet and reveal the pristine material beneath. This is believed to be material left over from the Solar System’s formation 4˝ billion years ago.
Researchers have said from the beginning of the
mission that the impactor would be far too small to noticeably change the comet’s
path, which is not headed toward Earth. One researcher compared the mission to
throwing a pebble at a speeding truck.
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