Mars is dry, not water-free. Its thin atmosphere holds a small amount of water vapor, and when local air becomes cold enough, that vapor can form ice clouds. Some Martian clouds are made of frozen carbon dioxide instead. The cloud’s ingredients and location depend on temperature, altitude, season, and airborne particles.
How can a dry atmosphere make clouds?
“Dry” describes how little water vapor the atmosphere contains; it does not mean there is none. NASA/JPL says the Martian atmosphere contains less than a tenth of the amount of water vapor found in Earth’s atmosphere, in the context of explaining why clouds are rare. That small supply can still form clouds when local conditions allow vapor to freeze.
On Earth, clouds can consist of liquid droplets or ice crystals. Mars’s low temperatures and pressures instead favor ice clouds: water ice or carbon-dioxide ice. Present-day surface conditions do not allow liquid water to persist for long, so a bright cloud should not be assumed to contain ordinary liquid droplets or to bring rain. NASA Science’s overview of Martian clouds and its Mars facts page describe this contrast.
What are Martian clouds made of?
| Cloud type | Material | Conditions and settings | Identification |
|---|---|---|---|
| Water-ice cloud | Frozen H2O formed from atmospheric water vapor | Forms when temperatures and vapor conditions favor freezing, with airborne particles providing surfaces for ice to nucleate. Seasonal activity is reported in some low-latitude regions. | Appearance alone does not establish composition; altitude, temperature, or other evidence may be needed. |
| Carbon-dioxide-ice cloud | Frozen CO2, also called dry ice | Requires sufficiently cold conditions; NASA describes likely examples at high altitude and clouds in polar winter. | Some observed high clouds are identified as likely CO2 ice, rather than definitively so from an image alone. |
Carbon dioxide is not a trace ingredient on Mars: NASA reports that it makes up more than 95% of the atmosphere. Because both water and carbon dioxide can freeze there, a cloud’s Earth-like white appearance is not enough to tell what it contains. See NASA’s reports on colorful clouds photographed by Curiosity and shining clouds over Mars.
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Why do particles matter for water-ice clouds?
Water vapor needs suitable conditions and a surface on which ice can begin to form. NASA describes Martian water-ice cloud formation as favored when dust is present and cloud nucleation and condensation are thermodynamically possible. Dust can provide nuclei for ice growth.
At high altitudes, meteoric smoke—tiny particles left when micrometeoroids ablate in the atmosphere—has been proposed as another source of ice nuclei. A NASA-hosted study discusses this mechanism through model simulations; it does not establish that every observed high cloud has been directly traced to meteoric smoke. NASA’s water-cycle explanation and its discussion of meteoric smoke as a possible source of high-altitude ice nuclei describe these processes.
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Where and when do clouds appear?
Martian clouds are not distributed evenly across the planet or throughout the year. NASA reports substantial cloud activity for a few months around northern summer solstice in a belt extending roughly from 10° south to 30° north. Curiosity has also photographed twilight clouds in Gale Crater.
Altitude and season shape the type of cloud observed. NASA says high clouds are likely to be dry-ice clouds because the upper atmosphere is very cold, while polar-winter CO2 clouds are another reported setting. Individual images can be difficult to identify conclusively without additional analysis.
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A NASA Technical Reports Server-hosted study inferred that particular cirrus-like clouds were about 50–80 km high and probably made of carbon-dioxide ice; it also described lower, wave-like layers as potentially water ice. That range applies to those reported observations, not to all Martian clouds. The study is available as Water and carbon dioxide each form mesospheric clouds on Mars.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Do Martian clouds affect the climate?
Clouds can influence how the atmosphere heats and cools. NASA notes that their role may have been more important in Mars’s past, but the available evidence here does not establish a single, universal numerical climate effect or show that clouds alone warmed ancient Mars enough to sustain surface water.
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