Martian Cloud May Form Ice Without Dust Seeds
A new study combining Mars Express observations with modeling suggests the Arsia Mons Elongated Cloud may form ice without dust particles. The cloud appears each morning during southern spring and summer, can stretch about 1,800 kilometers, and then evaporates. Simulations indicate that rapid lifting and cooling create conditions for water vapor to turn directly into ice, a process not previously seen in a planetary atmosphere.
Mars Express has followed the Arsia Mons Elongated Cloud since 2018, using three instruments: the Visual Monitoring Camera, High-Resolution Stereo Camera, and OMEGA. With ESA’s ExoMars Trace Gas Orbiter, it can view Mars in the morning, when the cloud is present.
The cloud reappears every morning during the southern hemisphere’s spring and summer, a dust-rich period, reaching roughly 1,800 kilometers before disappearing. Simulations indicate Arsia Mons creates a strong wave that raises humid air several kilometers within minutes; it cools by 30 degrees in ten minutes. This can push relative humidity to extreme levels, allowing homogeneous nucleation—a process proposed for the high atmospheres of Earth and Venus but not previously observed.
This finding could interest planetary scientists and climate modelers by challenging assumptions about cloud formation beyond Earth. It may improve simulations of Mars’s atmosphere, which could eventually aid mission planning and weather forecasting. For the public, it may deepen appreciation of how alien environments can produce phenomena not