But the really amazing data came from the LIDAR instrument, which was able to track the formation of the clouds at the atmosphere's boundary layer. Cloud formation became more pronounced as the summer gradually faded and the atmosphere cooled at night, and the scientists were eventually able to detect cirrus-like clouds as they dropped "tilted vertical sheets" of ice particles back to the surface of the planet. In short, they watched it snow.

For more, check out this Ars Technica story.