Study links Mars cloud to rare ice-forming process

A study published in Nature Geoscience proposes that a rare ice-forming process helps explain the long cloud that regularly appears near Arsia Mons on Mars. Simulations that included ice forming directly from water vapor reproduced the cloud more closely than models relying on the usual dust-seeded process, researchers reported. The Arsia Mons Elongated Cloud forms during spring and summer in Mars’s southern hemisphere, appearing in the morning and dissipating later in the day. It can extend about 1,800 kilometers downwind of Arsia Mons, a volcano roughly 20 kilometers high. The cycle repeats over several months. Clouds commonly form when water vapor condenses or freezes around particles such as dust. The study’s researchers say that process alone did not recreate the cloud’s observed behavior in their simulations. Their model fit improved when it incorporated homogeneous nucleation, in which water vapor forms ice particles without first attaching to a dust particle or other surface. The proposed explanation depends on a rapid change in atmospheric conditions as winds pass the volcano. In the simulations, rising moist air cools by about 30 degrees Celsius in roughly 10 minutes.