Satellite reveals 'whole new Mars'

Recently published map of Martian surface provides insights into how

Scientists studying Mars say they are seeing "a new planet." Mars itself hasn't changed. But data pouring in from the Mars Global Surveyor spacecraft are changing scientists' perspective.

A new topographical map compiled using information from the surveyor satellite has charted every wrinkle, rumple, and contour of the planet's rough-hewn face to an accuracy of at least 42 feet. As a result, researchers are gaining insights into how the planet evolved and where water - the building block of life as we know it - may have once flowed.

Moreover, the chart is so comprehensive that it represents the best global topographic map of any object in the universe. "We now know the topography of Mars better than many continental regions on Earth," says Carl Pilcher, NASA's science director for solar-system exploration.

Published May 28 in the journal Science, the map was presented to scientists at a meeting of the American Geophysical Union in Boston this week. While it includes some data taken last summer, most measurements were made this spring. A precision map showing how gravity varies over Mars' surface is to be published next month, and magnetic charts will follow.

"We're very satisfied that, once we put the whole thing together, we're going to have a whole new Mars," says Mario Acuna from NASA's Goddard Space Flight Center in Greenbelt, Md.

It's taken a while to even get this far. The spacecraft settled into its close-in circular mapping orbit in March, but it should have arrived a year earlier.

Structural weakness in one of two solar panels caused delays as controllers gradually eased the craft into the desired orbit. Now it is sending back hundreds of thousands of high-precision measurements every day of topography, magnetism in the crust, and gravity.

Earth looks unimpressive

The topographical map is based on height measurements taken by the spacecraft's infrared laser altimeter. Over large parts of the relatively flat northern hemisphere, the accuracy is better than six feet. And across the planet, it is charting topographic extremes that make Earth's mountains, canyons, and troughs look decidedly unimpressive. The map, for example, shows that the tallest Martian peak stretches 19 miles above its lowest point. That's 1-1/2 times larger than the range of elevations on Earth.

What mapping-team leader David Smith from the Goddard center calls the map's "most curious feature" shows the rugged southern hemisphere standing higher than the smoother northern region. This means that, generally, water would drain from south to north.

Yet topographic team member Maria Zuber from the Massachusetts Institute of Technology in Cambridge notes that the southern region shows basins where water could also accumulate.

Big divot

Near the south pole, the crater Hellas also surprised scientists. They knew the 1,300-mile-wide feature existed. They didn't know it is nearly six miles deep. It could easily swallow Mt. Everest.

An asteroid impact probably blasted out the crater, throwing out enough dust and rock to spread a two-mile-thick blanket over the United States. This surrounds the Hellas basin with debris that rises 1-1/4 miles above its surroundings and extends 2,500 miles from Hellas's center.

Dr. Zuber explains that such accurate topographic detail supplies a missing key ingredient for computer programs that simulate how the Martian atmosphere circulates over the planet. Also, when combined with gravity data showing how mass is distributed beneath the surface, the map will give new insight into the planet's structure.

Dr. Acuna says scientists now have new puzzles to solve in trying to understand how Mars became the way it is today. Previous theories don't fit the precision data now being gathered.

Among other things, magnetic data show that iron has accumulated in the Martian crust. It did not sink into the planet's core as it did on Earth.

Scientists don't understand how this happened.

Summing up the situation during a press conference, Acuna remarked that Mars is showing "it's just like any other planet [in that] they all have their own personality."

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