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Year in Review: 1997

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Re-rank the list of top news stories of 1997

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Princess Diana's death stuns the world

Weld steps out -
Cellucci steps forward

Mother Teresa is laid
to rest at age 87

Chinese rule returns
to Hong Kong

Supreme Court strikes
down 'Net decency act

UPS strike disrupts thousands of firms

Heaven's Gate cult commits mass suicide

Mars Pathfinder explores Red Planet

Ellen comes out, marking a first in TV

For the first time, a mammal is cloned


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Clouds, wild temperatures mark Mars

By David L. Chandler, Globe Staff, 8/01/97

An August sunset on Mars.<br> (NASA Photo)
A summer sunset on the Martian surface. (NASA Photo)

CAMBRIDGE - The salmon-colored skies of Mars have been decked with an unexpected expanse of mackerel clouds just before sunrise the last few mornings, and the sunsets have been bright white with just the faintest tinge of blue.

During the day, the clouds burn off and the skies turn a solid pink, but the Mars Pathfinder's weather station has revealed astonishing jumps in temperature that scientists had never imagined: Changes of 30 to 40 degrees Fahrenheit within a few seconds. And the stormy fall season is still at least a month away.

''The atmospheric things we're seeing are beyond anything we'd hoped to see, prior to getting down on the surface,'' said Pathfinder chief scientist Matthew Golombek at a national meeting here of the American Astronomical Society's Division of Planetary Sciences.

The abrupt temperature changes recorded by sensors on a 3-foot mast on Pathfinder's stationary lander, called the Sagan Station, are apparently caused by sudden gusts of wind that stir up warmer air from near the ground, said Robert Haberle of the Pathfinder weather team. Even between the three sensors on the mast, the lowest of which is about a foot high, there can be a 20 to 30 degree difference in temperature, he said.

''All it takes is a gusty wind, and you can get great variations in temperature,'' he said. At times, right at ground level it may be ''warm enough to go barefooted, if you were brave enough,'' but just 3 feet above ground the temperature could be only 10 to 15 degrees.

But the most exciting weather observations so far, the scientists said, are the cloudy skies above the landing site in Mars' tropics. Displaying an image taken just before sunrise on Pathfinder's 16th Martian day (called a sol), Mark Lemmon of the imaging team said it was ''the first picture ever taken from another planet showing an overcast sky . . . We were hoping to see clouds like these'' -- something the Viking landers never were able to see.

''We're going to learn a lot about the atmosphere of Mars by looking at these pictures,'' Lemmon said.

But despite the clouds of water-ice crystals that Pathfinder's camera has seen before dawn, there's one thing the Mars forecasters are sure of: ''It definitely will not rain on Mars,'' Haberle said, because water cannot exist in liquid form in the thin, cold air.

The Viking landers in 1976 did, however, occasionally see frost on the ground in early morning, and as the seasons change Pathfinder may see frost as well.

The barometer readings show that the atmospheric pressure has passed through its annual minimum, meaning summer is nearing its end and the turbulent fall may begin in about a month, Haberle said.

''We're going to start to see weather systems similar to those we see on Earth,'' with fronts passing through from west to east, Haberle said. ''Beyond that, we might actually see some dust storms begin to form. We expect fairly spectacular storms will begin to develop.''

But one thing Pathfinder's cameras will never see is an Earth-like blue sky, the scientists said -- contrary to some earlier predictions that Mars might have the opposite pattern from Earth: pink skies during the day and bright blue sunsets.

''You're never going to see a blue sky on Mars,'' said Haberle, because the planet's thin atmosphere contains ''not enough molecules to scatter the light'' as Earth's does to give the sky its blue appearance.

Meanwhile, the Sojourner rover is continuing to roam around the landscape, measuring the chemical composition of rocks and soil. Today. it is expected to visit a sand bar called Mermaid Dune, where it will study the composition of what appears to be a type of soil different from those previously tested.


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