[This story ran on the AP news wire on May 20, 1997.]
WASHINGTON (AP) -- The Hubble Space Telescope, acting like an interplanetary weather satellite, has found that Mars is colder, cloudier and more unpleasant than astronomers once believed.
The weather changes rapidly on Mars, NASA scientists said [May 20], as they described the Hubble's role in preparing for the arrival on Mars of U.S. probes on July 4 and in September.
"If humans want to colonize another place in the solar system, Mars is the closest place to ours," said Ed Weiler, the Hubble program's chief scientist. "It's got clouds, it has an atmosphere, it has water. Temperature extremes are bad, but they are not that much worse than Antarctica. And people manage in Antarctica."
Twenty-one years ago, the Viking landers sent back images of a calm, dusty planet under a gray sky.
Instead, the Hubble shows the weather to be unpredictable. One week the sky is pink and cloudless, filled with the rust-colored dust raised from the Martian surface. The day would be warm, about 40 degrees below zero, Fahrenheit.
In just a few days, the dust is swept away, temperatures drop 40 degrees and brilliant water ice clouds appear against a dark blue sky.
Not just one region has those changes; they are planet-wide. The Hubble shows Mars is often more cloudy than dusty.
"The primary force changing Mars is moving dust," said Steven W. Lee, a planetary scientist as the university of Colorado. "Areas stable for 100 years have been changing."
The conditions on Mars will affect the operation of both the Mars Pathfinder, arriving on Mars on Independence Day, and the September 11 arrival of the Mars Global Surveyor, which will map the planet from orbit.
The Hubble will be used to make 11th-hour pictures of the red planet.
"If we see anything unusual with the Hubble, we can reprogram that day," said Matthew P. Golombek, a geologist at the Jet Propulsion Laboratory in California.
Pathfinder uses the atmosphere to slow for landing. Sunlight provides the power for both the lander and a small vehicle it will release to rove on the surface, investigating the materials it finds there.
The Global Surveyor is braked by friction as it enters the Martian atmosphere, whose density then becomes a key factor. The Hubble will track regional dust storms.
Hubble made color and black and white pictures of Mars just two weeks after Earth made its closest approach to the planet a few months ago -- 62 million miles away. Mars, at that time, was almost at its farthest point from the sun, and the faintness of sunlight chills the atmosphere and stimulates formation of water ice clouds.
Earth's orbit about the sun is circular, but Mars is not. The difference in average temperatures between the closest point and the farthest can be 80 degrees on Mars.
Original file name: CNI - Mars.Harsh Weather
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