NASA scientists are now saying that Martian clouds may retain less water than expected. Planetary scientist Tony Colaprete reports that the clouds they are studying form at much colder temperatures than the ones here on Earth. It turns out that it's harder to start the cloud formation process at these temperatures—the cloud particles become larger and drop out of the sky more quickly, resulting in a drier atmosphere. Understanding its clouds, which play a key role in carrying water away from the ice cap at the north pole, helps scientists like Colaprete make sense of the larger water cycle on Mars and, in turn, its overall climate.—Gregory Mone