Hubble allows close look at planetary weather shifts

March 22, 1995|By Frank D. Roylance | Frank D. Roylance,Sun Staff Writer

Here's the latest from the Hubble Space Telescope "weather center":

The higher temperatures and global dust storms on Mars in the 1970s have ended. The skies are now clear and 36 degrees colder, on average, with morning haze and lingering clouds near the volcanoes.

Closer to the sun, meanwhile, the sulfuric acid showers that made things miserable on Venus two decades ago continue to diminish. Skies there remain cloudy, however, with temperatures in the 800s.

These kinds of weather observations, announced yesterday at NASA headquarters in Washington, are a first for scientists, who hope to use them to see how planetary climates work and to plan for future landings by robotic or manned spacecraft.

Weather changes on Earth are a daily affair, and long-term climatological data have been systematically gathered, studied and debated for more than a century. But only since the Hubble telescope made almost continual observations possible have scientists begun to get regular reports from other planets. And the picture has surprised them.

For example, "our early assumptions about the Martian climate were wrong," said Dr. Philip James of the University of Toledo in Ohio.

The global dust storms and relatively mild climate noted on Mars when the Viking robot landers visited in 1976 turned out to be a temporary feature of a far more complex climate, he said.

"We just happened to visit Mars when it was dusty, and now the dust has settled out," he said.

Four years of photographs and spectrographic analyses by Hubble instruments now show that the Martian skies have cleared and the climate has cooled dramatically since the 1970s.

"It's 36 degrees Fahrenheit colder on a global average," said Dr. Steven Lee, a planetary scientist at the University of Colorado. By comparison, climatologists are debating whether industrial activity on Earth has raised temperatures by a degree or two in the past century. Some say a change of four or five degrees would be catastrophic for agriculture.

Planetary scientists believe the end of the Martian dust storms has produced the cooling, because it was the fine dust particles -- as fine as smoke -- that absorbed the solar energy and produced the warming.

Temperatures on Mars can drop 100 degrees at night. They can range from as high as 32 degrees Fahrenheit to nearly 200 degrees below zero.

While skies have generally cleared, Hubble photos show that clouds of water ice continue to cling to the slopes of the planet's giant volcanoes as warm afternoon air is pushed to the top, forming ice crystals.

Scientists are also watching for changes in the planet's color patterns that indicate where seasonal winds have blown fine red dust across darker regions of coarse sand.

Hubble observations of Venus show that the amount of sulfur dioxide in the planet's upper atmosphere has dropped to one-tenth the concentrations found by the Venus Pioneer spacecraft in 1978.

Scientists now suspect the higher readings were the result of earlier, undetected volcanic eruptions that have since ended, allowing the sulfur dioxide to fall from the upper atmosphere in showers of 80 percent sulfuric acid rain.

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