In a Mars exploration milestone, a laser remote sensing instrument on the Phoenix Mars lander has detected snow falling on the red planet. Data from the light detection and ranging (lidar) instrument—designed to gather information about interactions between the Martian atmosphere and ground surface—showed the snow falling from clouds about 4 kilometers (2.5 miles) above the spacecraft’s landing site.

“Nothing like this view has ever been seen on Mars,” said Jim Whiteway, a space engineering professor at York University, Toronto, and lead scientist for the Canadian-designed laser on Phoenix. “We’ll be looking for signs that the snow may even reach the ground.”

Currently data show the snow vaporizing before it reached the ground, but the finding is significant, as it shows that the Martian atmosphere is a transport mechanism for water-ice and vapor, according to the mission’s principal investigator Peter Smith of the University of Arizona.

In addition, Martian soil samples taken during recent Phoenix experiments show the presence of calcium carbonate (the main ingredient of chalk), and particles that could be clay. On Earth, most carbonates and clays form only in the presence of liquid water. The samples were taken from trenches dug by the lander’s robotic arm and were analyzed by two laboratory instruments—the Thermal and Evolved Gas Analyzer (TEGA) and the wet chemistry laboratory of the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA).

After a nine-month cruise from Earth, the Phoenix mission executed a near-perfect landing on the surface of Mars on May 25, 2008. Just weeks later, the mission confirmed the presence of water ice in a subsurface layer near its landing site in Mars’s northern arctic plains. Determining whether that ice ever thaws could help answer the question of whether the environment there has ever been favorable for life.

Originally planned as a three-month mission, Phoenix is now in its fifth month. But with Martian winter approaching, it now faces a decline in solar energy that will bring the lander’s activities to a halt before the end of the year. “For nearly three months after landing, the sun never went below the horizon at our landing site,” said Barry Goldstein, Phoenix project manager at NASA’s Jet Propulsion Laboratory (JPL). “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.”

[Via Phoenix Mission news release]