US:ICY SNOW falls from high in the Martian atmosphere and may even reach the planet's surface, scientists working with Nasa's Phoenix Mars lander have reported.
Laser instruments aboard the lander detected the snow in clouds about 2½ miles above the surface and followed the precipitation as it fell more than a mile toward the ground.
Because of limitations with the technology, though, it was unclear whether any of the powdery stuff made it all the way to the Martian 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.
In addition to finding snow, the Phoenix team reported that it had discovered material in the Martian soil that had once been dissolved in water - clays and calcium carbonate (limestone) that could only have formed in the presence of liquid water.
While the lander's instruments had 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, vapour and ice, is leading researchers to the conclusion 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 - in some very long-term cycles the poles actually 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 Peter Smith of the University of Arizona, the lander's principal investigator.
Images of the thin but distinct Martian clouds can be seen at the Nasa website, www.nasa.gov/phoenix. Scientists have previously theorised that snow falls on Mars, but they had never before seen it in real time.
- (Los Angeles Times-Washington Post service)