Mars’s long cloud may form without dust, simulation suggests

Researchers have reproduced Mars’s Arsia Mons Elongated Cloud in a meteorological model after allowing ice particles to form directly from water vapour, the European Space Agency says. The proposed process, called homogeneous nucleation, would let the cloud form without dust or other particles acting as seeds for the ice. The study by Jorge Hernández-Bernal and colleagues was published in Nature Geoscience. [1]

The team used data from three Mars Express cameras: the Visual Monitoring Camera, High Resolution Stereo Camera and OMEGA. In ESA’s account of the proposed mechanism, winds passing the 20-kilometre-high Arsia Mons volcano lift moist air and cool it rapidly, creating conditions in which water vapour can freeze into cloud particles. [1]

The water-ice cloud appears downwind of the volcano during southern Martian spring and summer. It forms and fades daily and can stretch up to 1,800 kilometres. Researchers had already identified it as an orographic cloud, formed as wind flows past high ground; the new model addresses how its ice particles might form. [1]