Mars Craft Detects Falling Snow

Soil Tests Also Hint at Past Presence of Liquid Groundwater

Icy snow falls from high in Mars's atmosphere and may even reach the planet's surface, scientists working with NASA's Phoenix lander reported yesterday.

Laser instruments aboard the lander detected the snow in clouds about 2 1/2 miles above the surface and followed the precipitation as it fell more than a mile. But because of limitations with the technology, it was unclear whether any of the powdery stuff made it all the way to the surface.

"Nothing like this view has ever been seen on Mars," said Jim Whiteway of York University in Toronto, lead scientist for the Canadian-supplied Meteorological Station on Phoenix. "We'll be looking for signs that the snow may even reach the ground."

In addition to finding snow, the Phoenix team reported discovering material in the Martian soil that had once been dissolved in water -- clays and calcium carbonate (limestone) that could have formed only in the presence of liquid water. Although the lander's instruments earlier found water ice below Mars's polar surface and had photographed surface fog and clouds, it has found nothing like liquid water on the surface.

The presence of nutrients and other material that once dissolved in water, however, plus the continuing presence of water as snow, vapor and ice, is leading researchers to conclude that Mars's polar regions might have supported life in the past -- when the region was much warmer. Because Mars wobbles on its axis far more than Earth does -- in some very long-term cycles, the poles face the sun -- the northern region where Phoenix landed has, in the past, been warm.

"Is this a habitable zone on Mars? I think we are approaching this hypothesis," said principal investigator Peter Smith of the University of Arizona.

In addition, Michael Hecht of NASA's Jet Propulsion Laboratory said that further analysis of the Martian dust by the lander's onboard laboratory has determined that it is as alkaline as ocean water, with a pH of 8.3. He said this finding also suggests that life could have existed on Mars.

Whiteway said the snow, along with frost and fog, began to appear about a month ago, as temperatures cooled on Mars. "This is now occurring every night," he said.

In an interview after the teleconference, Whiteway likened the snow to "diamond dust" that falls in the Arctic and Antarctica.

"What this is telling us is that water does rise from the ground to the atmosphere and then precipitates down," he said. "So there is a hydrological cycle on Mars, and now other experts will study the data and try to determine what it all means."

Although the Phoenix instruments could not determine whether the snow hit the ground, Whiteway said there are some indications that it does. Images of the thin but distinct Martian clouds can be seen on the NASA Web site at http://www.nasa.gov/phoenix.

With daylight quickly diminishing as the Martian winter starts, the Phoenix is not expected to continue operating for many more weeks. The spacecraft has a "Lazarus" feature that could return it to operation when the sun returns, but the brutally cold temperatures during the winter are expected to freeze and crack parts essential to its operation.