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Thursday, May 28, 1998 Published at 20:53 GMT 21:53 UK


Cosmic clouds threaten Earth

The Horsehead Nebula is a huge cosmic gas cloud (photo credit: NASA)

Hollywood's latest disaster movie fixation, the Earth threatened by the impact of giant comets or asteroids, could be dangerously out of date according to scientists in the US.

They believe life on Earth is more likely to be wiped out by an impact with a cosmic cloud.

The predictions by Gary Zank, from the Bartol Research Institute at the University of Delaware, have been presented to the American Geophysical Union's spring meeting in Boston, Massachusetts.

[ image: The Cygnus Loop, a Supernova blastwave meets a cosmic gas cloud (NASA)]
The Cygnus Loop, a Supernova blastwave meets a cosmic gas cloud (NASA)
His research shows that if the Solar System hits even a small gas cloud in space, the "bubble" surrounding it which protects life on our planet could burst.

"The protective solar wind would be extinguished, and cosmic radiation might lead to gene mutations," he said.

"Hydrogen would bombard the Earth, producing increased cloud cover, leading perhaps to global warming, or extreme amounts of precipitation and ice ages."

He based his prediction on computer simulations of what might happen to the "cocoon" created by the solar wind, charged particles flowing out from the sun.

"We're surrounded by hot gas. As our sun moves through extremely `empty' or low-density interstellar space, the solar wind produces a protective bubble, the heliosphere around our Solar System, which allows life to flourish on Earth.

[ image: Eta Carinae, prior to explosion, giving out vast clouds of gas (NASA)]
Eta Carinae, prior to explosion, giving out vast clouds of gas (NASA)
"Unfortunately, we could bump into a small cloud at any time, and we probably won't see it coming. Without the heliosphere, neutral hydrogen would interact with our atmosphere, possibly producing catastrophic climate changes, while our exposure to deadly cosmic radiation in the form of very high-energy cosmic rays would increase.

"We won't know that our heliosphere is collapsing until we see highly elevated levels of neutral hydrogen and cosmic rays," said Professor Zank.

Although there is no need to panic right now, our descendants in 50,000 years should be alarmed.

Pushed by galactic wind, a particularly troublesome cloud zone located in a star-forming region near the Aquila Rift, about 815 light years away, is "clearly headed our way" according to Professor Zank.

He is also warning that small knots of gas called the "Local Fluff" could be encountered far sooner.

Mankind has been lucky so far, Professor Zank believes, as over the past five million years "we've had incredibly smooth sailing" because the sun has been coasting through calm interstellar waters that are virtually empty, containing on average less than one atom per cubic inch of space.

Although the solar system is in a region of space containing between three and four atoms per cubic inch, the weather in space could change because the universe is "full of clouds".

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