MISSION to MARS.

Scientists hunt for clues to the mysterious history of water on Mars 

At 12:01 P.M. Pacific Standard Time on December 3, 1999, the Mars Polar Lander spacecraft beamed one last "okay-to-go" signal to Earth before descending into the dusty Martin atmosphere. Its mission: to probe and analyze soil on the Red Planet's southern pole. From that moment on, scientists and engineers at NASA's Jet Propulsion Lab in Pasadena, California, could do nothing but hold their breath.

Millions of TV viewers around the world witnessed a tense control room as NASA awaited news of Polar Lander, which had traveled 127 million kilometers (79 million miles) to reach Mars' rocky surface. The spacecraft was scheduled to "phone home" with another "okay" signal 30 minutes after landing. But that signal never came. Polar Lander simply vanished.

Scientists still don't have a clue what happened. "The answer may have something to do with the Martian surface itself," says Stephen Clifford, a planetary scientist at the Lunar and Planetary Institute in Houston, Texas "At this point, any hypothesis is pure speculation," Three possible scenarios; Polar Lander may have sunk into Martian dust, landed on the side of a canyon and toppled over, or crashed due to a design flaw.

For NASA, the loss was a devastating blow. Polar Lander's disappearance was NASA's second major failure in three months. In September 1999, the space agency lost contact with the Mars Climate Orbiter satellite, which was about to launch a detailed study of the Martian atmosphere (see SW 11/1/99, p.7).

But rather than hang their heads, scientists view the losses as a challenge to forge ahead in the ongoing exploration of Mars. In fact, just one week after Polar Lander' s disappearance, the journal Science reported an amazing new find: evidence of an ancient Martian ocean! The report has spawned newfound excitement about the Red Planet and revives an age-old question: Is there life on Mars?

QUEST FOR WATER

Polar Lander's objective was to teach scientists about possible water ice (mixed with soil) and other volatiles (chemically reactive substances) at Mars' southern pole. Since most organisms on Earth need water to survive, researchers think studying water on Mars could lead to the discovery of life. "The more water-rich a planet is, the greater the likelihood that life can evolve there," Clifford says.

For years, close-up pictures of the Red Planet have revealed a Martian surface riddled with river like channels resembling those on Earth (see pictures, above right). Many scientists wonder whether the same dynamics that formed rivers and oceans on our planet are responsible for what they see on Mars. But with frigid average surface temperatures of -53 [degrees] C (-63 [degrees] F), Mars' current climate is too cold for liquid water to be stable on the rocky red crust. Yet most experts agree that Mars may have been hospitable to liquid water in the distant past.

"There is ample evidence that a fluid with properties very much like water once flowed on Mars," says Michael Malin, lead investigator for imaging systems aboard the Mars Global Surveyor (MGS) satellite, currently in orbit around the Red Planet. High-resolution MGS photos support the theory that billions of years ago the Martian surface underwent Earth-like erosion (wearing away) when Mars' atmosphere was much warmer--and wetter.

Yet scientists remain at odds about how water could have flowed on Mars' surface long enough to carve out the planet's present features. And researchers can only speculate as to where such vast amounts of water disappeared to, if indeed water did stretch across the planet sometime during its 4-billion-year history.

NEW FIND

Planetary scientists are moving closer to an understanding of Martian water thanks to the Mars Orbiter laser altimeter. The altimeter, an instrument on the Global Surveyor satellite, helps scientists map the topography (physical features) of Mars' surface by measuring the altitude (height) of landforms (see SW 9/20/99, p. 6).

To gauge the height of a Martian volcano, for example, the altimeter shoots a beam of concentrated light to the volcano top. The beam rebounds back to Global Surveyor, and the altimeter measures the elapsed round-trip time and estimates the elevation. The quicker it takes a light beam to strike Mars and bounce back, the higher the landform.

"The laser altimeter is extremely important to our understanding of the geological and physical processes on Mars," says James Head, a planetary geologist at Brown University in Providence, R.I. Head is a member of Mars' laser altimeter research team--the same team that used altimeter data to analyze what some scientists are calling a "shoreline" from an ancient Martian ocean (see map, p. 12).

Today, craters--circular depressions caused by crashed meteors--blanket most of Mars' surface. But Head and his team found that a large region of Mars' northern hemisphere has few well-defined craters. Could a vast ocean have once covered the area and eroded the craters' sharp features? "Below the proposed shoreline, there's a lot of smooth land," Head says. "This supports the idea that there was water below the line at one point."

But even with such tantalizing evidence, scientists are a long way from proving that water indeed carved out Mars' Earth-like features. That's because physical evidence of past bodies of water has yet to be found. "All direct evidence of large-scale water flows on Mars has been destroyed over billions of years," Malin explains.

LIFE ON MARS?

Perhaps more than anything else, scientists are eager to find out if Martian life existed in the past--or still exists. Ever since telescopes first zoomed in on Mars in the 17th century, people have conjured up a wild variety of images of what Martians might look like. But space probes like the 1997 Sojourner land rover have yielded no evidence of such alien beings.

Most experts agree that if life did at one time evolve on Mars, finding evidence of that life--which would likely take the form of tiny organisms--won't be easy. Still, many scientists are optimistic. "We've got organisms on Earth that adapted to life deep below the surface in underground water wells," says Stephen Clifford. "If life like that evolved on Mars four billion years ago, there's no reason why it wouldn't exist today."

Despite last year's disappointing losses, the future of Martian exploration looks promising. This year, two major films about fictitious Mars missions--Red Planet and Mission to Mars--are certain to heighten interest in our planetary neighbor. More important, plans for new sets of NASA orbiters and landers--one to launch in 2001, the other in 2003--are already in the works. Without a doubt, each new mission will inch scientists closer to understanding the mysteries of planet Mars. Stay tuned!

RELATED ARTICLE: Magnetic Mars

Last year, the Mars Global Surveyor satellite detected a curious pattern of magnetic stripes in the Martian crust. Planetary scientists say the stripes suggest that Martian crust may have formed like Earth's crust: from lava welling up through large fractures (cracks) in low-lying crustal regions (see diagram).

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When Earthly lava seeps up through a fracture, it adds itself as new matter to existing tectonic plates, huge slabs of rock that slide atop Earth's churning liquid layers. As the lava cools and hardens, minerals in the lava act like magnets, orienting themselves to face north or south. This depends on the direction of Earth's magnetic field, lines of force that surround the planet. Every 10 or 20 thousand years, Earth's magnetic field reverses--the magnetic North Pole becomes the South Pole and vice versa. When that happens, minerals in Earth's crust also flip-flop, creating a new "stripe" in the crust.

Surveyor data shows that minerals in the Martian crust might have done the same. Though scientists say Martian crust is now hard and unchanging, the fantastic find goes to show that the Red Planet may have once been geologically active--and possibly hospitable to life!