...And snow
The snow didn't come until close to the end of the mission. It too is similar to the snow that falls to the ground at Earth's poles, sometimes called "diamond dust." Whiteway describes it as "ice crystals sparkling in the air."

The observations show that "precipitation is a component of the hydrologic cycle" on Mars, which was not suspected before the Phoenix mission, Whiteway said.

How the finding might impact our understanding of the global Mars water cycle — both now and in the distant past, when the planet is suspected to have been warmer and wetter — is not yet known.

The new information can be used to modify Martian climate models, which currently don't feature these newly discovered clouds and precipitation, "and then we'll see what the implications are," Whiteway said.