Hubble finds Mars' climate harsher than thought

[From USA TODAY, 05/20/97]
By Paul Hoversten, USA TODAY


WASHINGTON - Dramatic new images from the Hubble Space Telescope show that Mars is a psychedelic world.

Its skies turn from blue one week to pink the next. Bright white clouds of water ice form high in the frigid atmosphere, probably bending sunlight into rainbows and halos. Dust storms of 60 mph blow a thick haze of crimson smoke over a black sand surface.

But the Hubble images released Tuesday at NASA headquarters in Washington, D.C., also show that Mars' climate is much harsher than scientists had believed.

"We're finding a Mars that's colder, clearer, cloudier," says Todd Clancy of the Space Science Institute in Boulder, Colo. "The planet's weather apparently has a flip side to it."

Hubble's images, along with data from the National Radio Astronomy Observatory at Kitt Peak, Ariz., are the clearest pictures yet of Mars. The photos, taken barely three weeks apart on March 10 and March 30, are helping scientists develop the first weather map of Mars, before two U.S. robot probes arrive this year.

Scientists say Mars is anything but the monochromatic place seen by the Mariner and Viking spacecraft of the 1970s.

Mariner, which orbited Mars, and Viking, which landed, had the misfortune to encounter global reddish dust storms that spanned their mission lifetimes.

"The astonishing thing about the Hubble data is that Mars is really a dynamic planet, much more so than I was taught when I was in school 30 years ago," says Ed Weiler, the chief NASA scientist for Hubble.

The U.S. spacecraft heading for Mars - the Pathfinder, which lands July 4, and the Global Surveyor, which arrives Sept. 11 to map the planet from orbit - probably will have much cloudier and colder weather than the Vikings. They may well find blue skies.

Mars has two distinct climates that usually are associated with periods when it is nearest to the sun and when it is farthest. That happens every Martian year, which is equal to two Earth years.

When Mars is nearest to the sun, it gets 40% more sunlight than when it is farther away. The extra sunlight warms the average surface temperature by 80 degrees, to about zero, and stirs up continental-scale dust storms on the surface. The dust is swept high into the atmosphere, turning the sky pink and blanketing the planet.

When Mars is farthest from the sun, surface temperatures drop to 80 below zero or colder. Bright white clouds of water ice sweep away the reddish dust, making the sky appear blue. Mars' northern ice cap of frozen carbon dioxide expands as dry ice frosts most of the planet.

"At least for half a (Martian) year, you have skies that have some parallel to what you see on Earth," Clancy says. "A sky in the dust storm period is something like a very smoggy Los Angeles sky, perhaps beautiful in its own way."

The Hubble data shows that the Martian climate can change from week to week, from warm and dusty to cold and cloudy. Three contributing factors are Mars' elliptical orbit, its thin atmosphere and the interaction between dust and clouds.

The new images, Clancy says, "make it a much more beautiful planet, a much more Earth-like planet emotionally. And that makes it a more appealing planet."