Snow falling from the Martian clouds have been detected by NASA's Phoenix Mars Lander, with possibilities of it even reaching the planet's surface.
Laser instruments on the lander have detected the snow clouds about 2.5 miles above the spacecraft's landing site and also followed its precipitation.
"We'll be looking for signs that the snow may even reach the ground," said Jim Whiteway, of York University, Toronto, lead scientist for the Canadian-supplied Meteorological Station on Phoenix.
Soil test experiments have also provided evidence of past interaction between minerals and liquid water, processes that occur on earth, NASA has said.
"Nothing like this view has ever been seen on Mars," Whiteway said.
The Phoenix experiments also yielded clues pointing to calcium carbonate, the main composition of chalk, and particles that could be clay. Most carbonates and clays on earth form only in the presence of liquid water.
Since it landed on May 25, Phoenix has already confirmed that a hard subsurface layer at its far-northern site contains water-ice.
"We are still collecting data and have lots of analysis ahead, but we are making good progress on the big questions we set out for ourselves," said Phoenix Principal Investigator Peter Smith of the University of Arizona, Tucson.
The Phoenix mission's main aim is to determine whether ice ever thaws on Mars. This would help answer whether the environment there has been favourable for life.
The evidence for calcium carbonate in soil samples comes from trenches dug by the Phoenix robotic arm. There are two laboratory instruments --Thermal and Evolved Gas Analyzer and Microscopy, Electrochemistry and Conductivity Analyzer -- involved.
"We have found carbonate. This points toward episodes of interaction with water in the past," said William Boynton of the University of Arizona, lead scientist for the TEGA.
The TEGA evidence for calcium carbonate came from a high-temperature release of carbon dioxide from soil samples.
The MECA evidence came from a buffering effect characteristic of calcium carbonate assessed in wet chemistry analysis of the soil.
Both TEGA, and the microscopy part of MECA have turned up hints of a clay-like substance.
"We are seeing smooth-surfaced, platy particles with the atomic-force microscope, not inconsistent with the appearance of clay particles," said Michael Hecht, MECA lead scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.
The Phoenix mission, originally planned for three months on Mars, now is in its fifth month. However, it faces a decline in solar energy that is expected to curtail and then end the lander's activities before the end of the year.
Before power ceases, the Phoenix team will attempt to activate a microphone on the lander to possibly capture sounds on Mars.
"For nearly three months after landing, the sun never went below the horizon at our landing site," said Barry Goldstein, JPL Phoenix project manager.
"Now it is gone for more than four hours each night, and the output from our solar panels is dropping each week. Before the end of October, there won't be enough energy to keep using the robotic arm," Goldstein added.