Comet resembles asteroid
2008-01-28 11:31
Washington - Samples of rock dust
retrieved from a comet called Wild 2 are forcing scientists to
alter they way they think about these intriguing objects that
streak through our solar system.
A chemical analysis of the samples brought back to Earth by
Nasa's Stardust spacecraft showed that the comet is much more
like an asteroid than scientists had expected.
Comets are celestial bodies made of rock, dust and ice with
characteristic tails of gas and dust streams that are formed in
the solar system's distant, frigid reaches.
A long-standing
notion had been they were sort of a frozen time capsule of
material from when the solar system formed 4-1/2 billion years
ago, including stardust from other stars.
But this is not the case with Wild 2, scientists found.
A lot of the material detected in Wild 2's cometary dust
was formed very close to the sun in the early solar system and
was somehow later transported to the outer solar system, the
scientists said.
The rock dust closely resembles material from bodies called
chondritic meteorites from asteroids in the asteroid belt
between Mars and Jupiter, they reported in the journal Science.
Asteroids are fragments of ancient space rubble, made of rock
and metal, that commonly orbit the sun in that belt.
"Overall, this comet, Wild 2, is looking a lot more
asteroid-like than we had expected," Hope Ishii of the US
government's Lawrence Livermore National Laboratory, one of the
scientists, said.
"The material found in primitive objects just wasn't there
in the samples," another of the researchers, John Bradley of
the Lawrence Livermore National Laboratory, said. "I think this is science in action. It's really
exciting because it's just not what we expected."
Wild 2 is named for Swiss astronomer Paul Wild (pronounced
Vilt), who found it in 1978. Its diameter is five kilometres and
it orbits the sun every 6-1/2 years.
Stardust, launched in 1999, intercepted Wild 2 in 2004 in
the vicinity of the asteroid belt, collecting dust particles
from it.
The spacecraft returned to Earth in January 2006 with
a cargo of the tiny particles for scientists to study.