Mars Weather: It's Stranger Than You Thought

posted: 04:29 pm EST
23 February 2000

WASHINGTON – Signs of martian snowfall, avalanches, "dust devils"
and evidence for ancient oceans from the Mars Global Surveyor are
profoundly changing how scientists perceive the Red Planet.

It's a far cry from the dry and dead world imagined by previous

"The Mars we thought we knew was not the real Mars," says Ken
Edgett, a geologist with Malin Space Science Systems of San
Diego, California, which built the orbiter's cameras. "I'm
personally surprised."

Next month, scientists like Edgett will compare notes at the
annual Lunar and Planetary Institute conference in Houston.

"We have craters the size of the L.A. basin which were filled up
and then possibly exhumed."
Ken Edgett, Geologist with Malin Space Science Systems

But first they offered a tantalizing hint of their findings at a
session on Mars exploration at the American Association for the
Advancement of Science's (AAAS) annual meeting February 18 in

Edgett, for example, has discovered the mystery behind curious
dark bands that crisscross the martian surface.

When he first saw them in 1998, he dubbed them "SUV tracks,"
since they resembled the trail left by sport utility vehicles on

Now he has found the real culprit -- dust devils, swirling clouds
of dust and wind that leave behind a dark streak. The dust
devils, which first were seen on Mars in the early 1970s on the
Viking mission, apparently pick up lighter dust and deposit a
darker material underneath.

"It's pretty neat," Edgett said. "We caught it in action."

These dark trails across a Martian plain -- spotted by NASA's
Mars Global Surveyor and dubbed SUV tracks -- puzzled researchers
until recently, when geologist Ken Edgett discovered that they
mark the path of dust devils.

The orbiter also sent back dramatic pictures of the rock and soil
layers of Mars' geology and photos of apparent avalanches on
crater lips that have occurred in the past two years. As well as
evidence of massive craters that seemed to have undergone
profound changes.

"We have craters the size of the L.A. basin which were filled up
and then possibly exhumed," he said.

How this happened is still a mystery.

"This is not a Mars we can address with a camera. We're going to
have to send people," to understand the complex landscape, he

David Smith, a researcher at NASA's Goddard Space Flight Center
in Greenbelt, Maryland, laid out a series of surprises for the

His team, led by Massachusetts Institute of Technology geologist
Maria Zuber, measured the plains of northern Mars and found them
to be extraordinarily flat.

"It's as if from L.A. to Washington it is so flat that there is
only a deviation of 10 meters (32.8 feet)," he said. "That is
about as flat as can be."

Such data could provide important evidence that the northern
plains in at least some part of Mars' past were in fact oceans.
The ocean theory remains controversial, given that water on the
surface of Mars today would dissipate immediately into the thin

Smith’s team also found vivid detail of the strangely contoured
quality of the martian surface, with its highlands in the south
sloping dramatically to the plains below.

He noted that the Utopia basin in the northern plains -- barely
visible to scientists until recently -- reveals strange cracks
that could be due to faulting, but also resemble fissures found
on Jupiter's frozen moon Europa.

Based on gravity data, the martian basin likely was once an
astonishing 7.45 miles (12 kilometers) deep, but was somehow
filled in over the centuries.

Data from the poles, meanwhile, confirms that the ice is
primarily water, but it is unclear how long it has existed there.

Three views of the layered terrain near the martian south pole
taken between August 1999 and February 2000. The wavey, almost
parallel lines in the upper half of each picture are exposed
layers of the south polar "layered terrain". As the terrain began
to defrost in early August 1999, dark spots appeared. Wind
occasionally picks up some of the dark material and blows it
across the landscape, creating dark streaks. By late September,
much of the scene is covered with these dark spots and narrow,
dark wind streaks. By February, all of the frost and dark spots
were gone, revealing the underlying layered terrain surface.

The receding ice caps on Mars hint at a climatic warming trend.
If the caps melted, Smith said, they would cover the planet to a
depth of 29.5 feet (9 meters). If concentrated in one place like
the northern plains, "that would make a modest-sized ocean."

Another mystery is why the south polar cap, with its thin layers
of water ice, is slightly offset from the pole itself.

"It's something we don't understand," Smith said.

What is clear is that clouds hover over the caps as the weather
starts to warm in the martian spring in the northern and southern

Orbiter data shows that those thin clouds vanish as the sun
rises, and that the material falls back to Mars as frost or snow.

"This is clearly evidence that it snows on Mars," Smith said.