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How's the weather on Mars? Probes: In launches tomorrow and Jan. 3, NASA hopes to send two research craft to study the planet's climate and seek water.

THE BALTIMORE SUN

Barely 17 months after NASA's little Sojourner robot began creeping around a martian plain sniffing at rocks, the space agency is about to launch the second wave of its scientific invasion of the red planet.

In a pair of launches set for tomorrow and Jan. 3, NASA hopes to hurl a new climate-research satellite into orbit over Mars' north and south poles, and another to a soft landing in the martian antarctic.

And just before the new Mars lander sets down next Dec. 3, it will fling two softball-sized "lawn darts" into the martian soil at 400 mph to search for buried water and carbon dioxide ices.

Scientists are hoping the $190 million venture will gather a wealth of pictures, climate and geophysical data from Mars, and even radio back the first ambient sounds from another world.

"This really is a mission of exploration, in a place [the martian antarctic] where we've never been," said Bruce Jakosky, a planetary scientist at the University of Colorado.

It will focus on "understanding the present-day climate of Mars, the seasonal cycle, what controls the atmosphere, the behavior of water, carbon dioxide and the polar caps."

The two spacecraft won't search for life. But their findings will guide planning for missions to return soil samples to Earth in the next decade, and later to land human explorers. Both efforts will seek clues to whether life could have evolved on Mars.

Getting to Mars is still risky business. Of 27 attempts since 1960 by the United States, the Soviet Union and Russia, 17 were total failures.

Of the six Mars missions launched in the past 20 years, the only successes have been the National Aeronautics and Space Administration's Pathfinder lander with its Sojourner rover, and the Mars Global Surveyor orbital mission, both launched in 1996.

Pathfinder landed on July 4, 1997, and beamed back pictures of distant hills and a rock-strewn outwash plain. Its Sojourner rover analyzed the chemistry of nearby rocks, delighting the public and scientists for two months and 23 days before contact was lost.

Global Surveyor continues to send back data and pictures with unprecedented detail. A study published Sunday in the journal Science said the spacecraft has discovered that Mars' north pole sits in a depression, so that any liquid ground water would flow toward the pole rather than away from it, as had been assumed.

During the next decade, NASA plans to launch pairs of orbiters and landers every 26 months -- each time Earth and Mars are aligned for such a mission.

Previous Mars missions have revealed water-carved channels and dry lakeshores, but any liquid water -- and any life it might have nurtured -- have disappeared. With its next two missions, NASA wants to map and measure any water stored in frozen ground water reserves and study Mars' atmosphere and climate mechanisms for clues to past conditions.

Launch of the Mars Climate Orbiter is set for tomorrow afternoon at the Cape Canaveral Air Station in Florida. The spacecraft will need 10 1/2 months to make the journey. On Jan. 3, 1999, a second Delta rocket carrying the Mars Polar Lander is scheduled for launch on an 11-month voyage.

The Climate Orbiter should arrive at Mars on Oct. 23, 1999. It will enter a circular orbit 262 miles above the martian poles and wait there to serve as a radio relay station for the Mars Polar Lander.

When the lander arrives on Dec. 3, it will head straight for the surface. Slowed by a parachute and landing thrusters -- and snapping pictures on the way down -- it will land at a spot roughly equivalent in latitude to McMurdo Sound, on Earth's Antarctica.

From orbit, it appears to be an oddly layered terrain, perhaps the result of alternating deposits of water ice and dust. If so, it may contain a record of 100,000 years of Martian climate change.

If that layering is also present on a very small scale, scientists may get their first look when the lander's 6 1/2 -foot robot arm digs a trench. The scoop will drop dirt into an oven at 1,880 degrees Fahrenheit, where instruments will measure any water vapor driven from the soil by the heat.

The 639-pound lander also carries a stereo camera to photograph the landing site; a weather tower to measure wind, temperature, air pressure and water vapor; a laser ranging device to measure the height of overhead clouds; and a hearing-aid microphone to capture the sounds of martian winds and the mechanical noises of the spacecraft itself.

"It is a remarkable achievement in terms of packaging," said Carl Pilcher, director of NASA's solar system explorations.

The lander is expected to survive for 60 to 90 days, until the dark antarctic winter arrives and freezes its batteries.

The Polar Lander carries no rover. But it will not be alone on the surface. Ten minutes before it touches down, it is to release twin instrument packages dubbed "Deep Space 2." The size of basketballs, they will plummet directly to the planet's surface.

"It's actually not a landing," said Deep Space 2 project manager Sarah Gavit. "We're crashing on Mars." The "microprobes" and their tiny soil labs will have to survive impacts up to 60,000 times the force of gravity -- like a computer hit by a truck at 400 mph.

Made of super-stiff materials assembled with epoxy glues, the microprobes look like smoke detectors fitted with car-phone antennas. They should stop at the surface, but the impact will drive a tethered dart the size of a salt shaker two or three feet farther into the dirt.

Hitting on solid rock would splatter the devices, and anything fluffier than a sand dune would probably swallow them up, leaving them too deep and too cold to function.

Geologists, however, suspect the region's soil has little rock. It's "kind of like tundra, frozen soil," Gavit said. If so, the probes will likely survive and in a few hours would begin drilling sideways, pulling bits of soil into tiny ovens. Any gases boiled off would be searched for traces of water and carbon dioxide, and the results would be relayed back to Earth via the Climate Orbiter.

After three to six days, the landers will fall silent, and the orbiter would begin its main mission -- a two-year study of the martian surface and atmosphere.

Scientists hope to get back daily weather photos and color maps with details as small as a baseball infield. They expect to measure and track dust, water vapor and clouds moving through the martian atmosphere.

The data should help them understand how those elements combine to steer the martian climate. And "by understanding climate change at work today," Zurek said, "we can extrapolate to the past."

Pub Date: 12/09/98

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