[Prev][Next][Index][Thread]

(meteorobs) Satellites May Be Shattered By Invisible Meteors



New Scientist

UK Contact:
Claire Bowles, claire.bowles@rbi.codot uk, 44 171 331 2751

US Contact:
Barbara Thurlow, newscidc@idtdot net, (202) 452-1178

EMBARGOED FOR RELEASE: 30 SEPTEMBER 1998 at 2:00 p.m. EDT

Satellites May Be Shattered By Invisible Meteors

THE Leonid meteor storm that may light up the sky in Asia when it strikes
the Earth next month could pose a bigger threat to satellites than
astronomers had feared.

Every year, around mid-November, the Earth crosses the orbit of a comet called
Tempel-Tuttle and passes through debris the comet has shed. This burns up in
the upper atmosphere as a meteor shower. Every 32 to 33 years, the Earth runs
into an especially dense cloud of debris, turning the shower into a storm. At
the peak of the last storm, in 1966, the skies above North America were lit
up by 5000 meteors in just 20 minutes.

Astronomers are now bracing themselves for the next Leonid storm, predicted
to reach a peak around 17 November. Communications and other satellites could
be threatened by the bombardment -- and both NASA and the Russian Space Agency
have postponed launches until the danger has passed.

No one knows just how bad the damage will be. For example, astronomers can't
predict with certainty exactly where the densest part of the debris cloud is.
Now Duncan Steel, an astronomer with Spaceguard Australia in Adelaide, has
thrown another variable into the equation. If his model of the chemical
composition of the Leonid meteors is correct, attempts to observe the
approaching meteors may detect only a few per cent of them.

Steel says that data gathered during the recent visits by comets Hale-Bopp
and Hyakutake reveal that the dust these comets gave off was rich in volatile
organic compounds. If the same is true of the cometary debris that forms the
Leonids, most of the meteors may be invisible. This is because if they are
made of highly volatile material, many will burn up at relatively low
temperatures -- too low to leave behind glowing trails detectable from the
ground. Cool-burning meteors will also emit relatively few electrons, and
that will make them invisible to ground-based radars, which can only spot
electron-dense trails.

"If small meteoroids in storms are largely composed of organics, then none
of the data collected to date gives a realistic assessment of the hazard
level," says Steel, whose conclusions are published this week in the journal
Astronomy and Geophysics (vol 39, p 24).

Current estimates put the risk of a serious impact between a meteor and a
large satellite at about one in a thousand. Steel says his study suggests
that this "seriously underestimates" the hazard. "If I am right, the economic
loss caused by the Leonids may be immense," he says.

Other astronomers agree that the reliability of the storm predictions depends
crucially on the composition of the meteors. "Steel's paper is very
interesting -- though whether it is actually correct is another matter," says
Iwan Williams of Queen Mary and Westfield College, London. "We may know after
the Leonids next month."

Steel's advice is not to rely too heavily on satellite communication and
navigation systems in the coming month. "I would not depend for my life on
the Global Positioning System being fully functional on 18 November," he
says.

Author: Robert Matthews
New Scientist issue 3rd October 1998

PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS ARTICLE - THANK YOU