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The spacecraft Galileo, hopscotching through the solar system, flashed reports of a cosmic phenomenon that may be destroying the ozone layer on Earth, scientists say.

Scientists at the Jet Propulsion Laboratory in Pasadena, Calif., told reporters Wednesday Galileo had sent back valuable data over the seven days it was in the vicinity of Earth.

Dr. Bob Carlson, one of the Galileo scientists, said the data showed a cloud in the stratosphere almost 10 miles above Antarctica. Such clouds are known to form in the southern hemisphere winter, in September and October, Carlson said. They collect molecules of such chemicals as chlorine and bromine, and as the sun comes up during spring these chemicals react with sunlight and cause depletion of the ozone layer -- the protective barrier that shields the Earth from the sun's deadly ultra-violet rays.

"What is surprising here is that these clouds are hardly ever seen this late" in the year, Carlson said, suggesting the formation of a vicious circle. "It may be that there is a feedback effect that goes on because as these things destroy ozone, there is less ozone in the stratosphere. Ozone heats up the stratosphere; with less ozone there is less heating.

"It gets colder, and as it gets colder more clouds form, destroying more ozone and the cycle goes on," he said.

Scientists said Galileo's findings warranted further investigation of the phenomenon over the Antarctic.

All the photographs Galileo took of Earth damage
cloud bank were of the planet's southern hemisphere -- mainly Antarctica, Australia and South America -- because the northern hemisphere was in the dark as it passed by.

Galileo also took never-before-seen pictures of the moon, including several showing an impact basin 1,200 miles in diameter that, on Earth, would stretch from Mexico to Canada and from Los Angeles to Kansas City in the Midwest, Dr. James Head said. The largest known crater before the latest pictures was 800 miles in diameter.

Galileo, launched from the now-grounded space shuttle Atlantis in October 1989, is the first to return to Earth's vicinity after visiting another planet, Venus.

It will receive another Earth-boost next December to send it on its way to its eventual destination, Jupiter, which it is expected to reach in 1995.

But Galileo's next celestial encounter will be with the asteroid Gaspar in October. It will fly within 1,000 miles of the mile-square object in the first meeting between a man-made space probe and an asteroid.

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