ASTRONOMERS PLAN TO CHASE DOWN A COMET

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From:AOLNewsProfiles@aol.net
Title:ASTRONOMERS PLAN TO CHASE DOWN A COMET
Source:Reuter
Date:April 09, 1996


By Maggie Fox

LIVERPOOL, England (Reuter) - Astronomers tired of trying to

get a quick and unfulfilling peek at comets when they make their

rare visits to Earth's neighborhood revealed plans Tuesday to

chase one down and take closer look.

A team of international scientists told the National

Astronomy Meeting in Liverpool Tuesday they hope to learn more

about why comets form their dramatic tails when they near the

sun on their rare visits to the neighborhood of Earth.

But the rendezvous of spacecraft and comet will not take

place until the year 2012.

The astronomers have named their mission Rosetta, after the

stone with a multi-lingual inscription that helped experts

decipher ancient Egyptian hieroglyphics.

The comet that Rosetta will chase is a frequent visitor

called Wirtanen.

While last month's Comet Hyakutake, one of the brightest

this century, is thought to pass near the Earth once every

20,000 years, the less spectacular Wirtanen appears every five

years.

Astronomers are keen to study comets because they are a

physical link to the beginnings of the universe and can tell a

lot about how it evolved.

``Comets are in fact the most primitive matter that we can

analyze in the solar system,'' said Colin Pillinger of the Open

University in Milton Keynes, England, who is helping to design

some of the instruments aboard the landers.

``If you get the cometary matter, you get the most primitive

matter ... in the chain of evolutionary links to interstellar

material,'' said Gerhard Schwehm, coordinator of the mission.

Astronomers already know a lot about Wirtanen and think they

can chase it down.

``What we want to do is actually go into orbit around the

comet,'' Schwehm, who works at the Dutch space agency ESTEC,

said. Even an object as small as a comet has enough gravity to

do this, he said.

Rosetta will stay with the comet as it approaches the sun

and warms up, its ice turning directly into gas in a process

that creates a comet's long, brilliant tail.

But because so little is known about comets, the landers and

instruments must be carefully designed. Comets are believed to

be balls of ice and dust -- but no one even knows how solid they

are.

``Some people say you will sink in because it is like loose

snow,'' Schwehm said. ``Others say it has a crust. You have to

design a lander that can cope with a soft surface or hard.''

And then there is the small size of the lander. ``It is only

one metre (three feet) across,'' Schwehm said. ``If you land in

a crack ...''

Astronomers will also have to be patient. Rosetta will be

not be launched until 2003 and will orbit the sun twice, getting

``gravity boosts'' from the Earth and Mars before heading across

the asteroid belt to meet Wirtanen. It will not come close to

the comet until 2012 -- nine years later.

Schwehm is philosophical about having to wait more than 15

years to learn Wirtanen's secrets. ``It's the only chance we

have to get data from the comet,'' he said. ``There have been

other missions where you had to wait a long time.''

He said scientists applying to take part in the $1 billion

project were being asked to give details about who will take

over from them. ``This goes up to the retirement age of most of

us,'' he smiled.

Rosetta will be launched as part of the U.S. space agency

NASA's Cassini mission, which will orbit Saturn for four years