Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsMars can form clouds because “dry” means it has very little water vapor, not none—and clouds do not have to be made of liquid water. In Mars’s cold, thin atmosphere, water vapor can freeze into ice, while carbon dioxide can also freeze into dry-ice clouds. Where and when clouds form depends on the available vapor, temperature, altitude, season, and particles that help ice begin to form.
What “dry” means on Mars
Mars has far less atmospheric water vapor than Earth, but its atmosphere is not water-free. NASA/JPL described the amount as less than a tenth of the water vapor in Earth’s atmosphere in its 2010 explanation of Martian clouds. That comparison explains why water clouds are relatively rare; it does not mean the atmosphere lacks enough water for clouds to form under the right local conditions.
A cloud can form when air becomes cold enough for its vapor to condense or deposit as ice. Even a small supply of vapor can reach the conditions needed for ice formation in a particular place. Mars’s low pressure and cold temperatures also mean that its clouds should not be pictured as ordinary clouds of liquid droplets: NASA notes that water-ice and carbon-dioxide-ice clouds form under Martian conditions.
What Martian clouds are made of
| Cloud material | How it forms | Where it is observed or expected |
|---|---|---|
| Water ice (H2O) | Water vapor freezes or deposits as ice when temperature and other conditions favor cloud formation. Suspended particles can provide surfaces where ice nucleates. | NASA reports seasonal cloud activity in a low-latitude belt, and water-ice clouds have been associated with lower wave-like layers in specific observations. |
| Carbon-dioxide ice (CO2, or dry ice) | Carbon dioxide freezes when the atmosphere is sufficiently cold. | NASA describes high-altitude clouds as likely dry-ice clouds; polar-winter clouds are also described. Individual images may need further analysis to establish composition. |
Carbon dioxide is not a trace ingredient on Mars: NASA says the atmosphere is more than 95% CO2 in its Curiosity cloud report. That makes CO2 another possible cloud-forming material, but it does not mean every cloud is dry ice. A cloud’s appearance alone is not enough to identify what it contains.
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How water-ice clouds get started
Cooling helps water vapor turn into ice, but tiny airborne particles can also matter. Dust can provide nuclei—surfaces on which ice begins to form—when the air is otherwise favorable for nucleation and condensation. NASA’s overview of the Martian water cycle describes this relationship between dust and water-ice cloud formation.
At high altitudes, meteoric smoke—the fine material left as micrometeoroids ablate in the atmosphere—is another proposed source of ice nuclei. A NASA-hosted study summary discusses model simulations in which meteoric smoke could supply abundant nuclei. This is a proposed mechanism supported by modeling, not evidence that every observed high cloud has been directly traced to meteoric smoke.
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Where and when clouds appear
Martian clouds are not evenly distributed across the planet or throughout the year. NASA reports substantial orbital observations of cloud activity for a few months around northern summer solstice, roughly between 10° south and 30° north latitude, in its cloud-season overview. Curiosity has also photographed twilight clouds from Gale Crater, as described in NASA’s report on shining clouds.
High-altitude clouds are especially cold, making carbon-dioxide ice a likely explanation for some observations. In a study hosted by NASA’s Technical Reports Server, researchers inferred that particular cirrus-like clouds lay about 50–80 km high and were probably CO2 ice; lower wave-like layers in those observations may have been water ice. That height range applies to those reported clouds, not to all Martian clouds. Composition can remain uncertain when an image does not establish the cloud’s altitude, temperature, or spectral signature.
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Why Martian clouds are not like Earth’s rain clouds
Earth’s clouds can contain liquid-water droplets or ice crystals. Mars’s low atmospheric pressure and cold conditions instead favor ice clouds. NASA’s Mars facts overview explains why present-day surface liquid water cannot persist for long under typical Martian surface conditions. So a bright or wispy feature in a Mars image should not be taken as evidence of liquid droplets or impending rain; it may be water ice or frozen carbon dioxide.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why the clouds matter to Mars’s climate
Clouds interact with sunlight and heat emitted by the surface and atmosphere, so they can affect atmospheric heating and cooling. NASA notes that clouds may have played a more important role in Mars’s past climate. The available evidence does not establish one universal numerical climate effect, or show that clouds alone warmed ancient Mars enough to sustain surface water.
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