Every night during Mars's winter, water-ice crystals fall from high, thin clouds over the north pole, new data from NASA's Mars Phoenix Lander have revealed.

The clouds resemble cirrus clouds on Earth, noted lead study author James Whiteway, an atmospheric physicist at York University in Toronto.

And the precipitation, he said, is similar to ice crystals that fall through the air in the Arctic in the middle of winter, called diamond dust.

"Mars is awfully dry. That's why it's surprising that you see snowfall."

The Phoenix lander arrived near Mars's north pole in May 2008 and collected data for five months before shutting down due to the extreme conditions of Martian winter.

Phoenix first spotted nightly clouds in early September, as winter began to set in, via an onboard weather instrument called LIDAR.