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In a NASA-modeled northern-summer example near Mars’s equator, water-ice clouds build slowly overnight, are thickest shortly before sunrise, and disperse as daytime warming changes the conditions that let them grow. They begin to form again around dusk. That is one modeled pattern—not a schedule followed by every Martian cloud.
How Mars clouds form overnight
Mars has an active water cycle: water moves from the surface into the atmosphere, travels with atmospheric circulation, and can return as frost or snow. NASA identifies the north residual water-ice cap as the main current source of atmospheric water described in its water-cycle overview. In northern summer, seasonal carbon-dioxide ice retreats, exposing water ice that can sublimate into vapor. Other sources, including the regolith, may also contribute.
Clouds form when water vapor condenses onto ice nuclei under suitable temperature and pressure conditions. Dust in the atmosphere can provide nuclei, but condensation and cloud growth must also be thermodynamically favored, as NASA’s Mars cloud-formation modeling overview explains. Overnight cooling can create conditions that allow ice crystals to grow when vapor and nuclei are present.
In NASA’s 2019 supercomputer simulation, the clouds form gradually overnight near the equator, reach their greatest thickness just before sunrise, and disperse quickly as the day warms. They start to reform around dusk. Several peaks in the Tharsis Montes volcano chain project above the modeled cloud layer.
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Why they disperse after sunrise—and why timing varies
In that modeled case, daylight warming is followed by rapid cloud dispersal. The source describes a northern-summer scenario near the equator, not a universal rule that all clouds vanish at sunrise. Cloud activity varies with season and location.
NASA reports strong orbital-observation cloud activity in a band from about 10° south to 30° north latitude for a few months around northern summer solstice. Perseverance’s location in Jezero crater, at about 18° north, is well placed to observe that seasonal activity. These observations are a seasonal and geographic pattern, not evidence that cloud timing is identical everywhere throughout the Martian year. See NASA’s overview of Martian cloud activity.
Not all Martian clouds are the same
Modern Mars clouds can be made of water ice or carbon-dioxide ice. NASA says carbon-dioxide clouds form at higher altitudes and lower temperatures than water-ice clouds. Their composition, local time, season, latitude, and height all matter when comparing one cloud observation with another.
A different example comes from Curiosity’s observations in early southern fall: high-altitude carbon-dioxide twilight clouds appeared alongside lower water-ice clouds. In those images, NASA reports carbon-dioxide clouds around 60–80 kilometers (37–50 miles) above the surface and water-ice clouds around 50 kilometers (31 miles). Those heights describe that observation, not every cloud on Mars. NASA notes that the reason carbon-dioxide twilight clouds have not been seen at other rover locations remains unknown; gravity-wave cooling is one possible explanation, not a settled answer. Read NASA’s report on Curiosity’s colorful clouds.
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How Martian clouds affect the atmosphere and surface
Though present-day Martian clouds are thin compared with many Earth clouds because atmospheric water is scarce, they can still influence temperatures and circulation. Their radiative effects—how they absorb, emit, and scatter energy—depend on altitude, location, and optical properties. NASA modeling indicates those effects can substantially alter atmospheric thermal structure and global-scale winds, affecting how water moves around the planet.
Clouds may also help explain an unusual twice-daily temperature rhythm in Mars’s atmosphere, called a semi-diurnal atmospheric tide. In 2013, NASA’s Mars Climate Sounder observations reported temperature swings as large as 58 degrees Fahrenheit (32 kelvins) in this pattern. Researchers found that adding water-ice-cloud radiative effects to climate models reproduced aspects of the observed rhythm. The observations also identified equatorial water-ice clouds at 10–30 kilometers (6–19 miles) altitude in the context of that analysis. Armin Kleinboehl, the study’s lead author and a NASA Jet Propulsion Laboratory researcher, described the pattern: “We see a temperature maximum in the middle of the day, but we also see a temperature maximum a little after midnight.” See JPL’s account of the temperature rhythm.
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Closer to the ground, NASA’s Perseverance science team notes that clouds around sunset emit thermal radiation downward. As a result, the surface cools more slowly after sunset than it would under clear skies.
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