Planet Mars: Iridescent Clouds after Sunset | NASA's Curiosity Rover
NASA’s Curiosity Mars rover captured this feather-shaped iridescent cloud just after sunset on Jan. 27, 2023.
NASA’s Curiosity Mars rover captured these drifting noctilucent, or twilight, clouds on Jan. 17, 2025, the 4,426th Martian day, or sol, of Curiosity’s mission.
NASA’s Curiosity Mars rover captured these feather-shaped and wispy iridescent clouds just after sunset on January 2023 and January 2025. Studying the colors in iridescent clouds tells scientists something about particle size within the clouds and how they grow over time. These clouds were captured as part of a seasonal imaging campaign to study noctilucent, or “night-shining” clouds. While the Martian clouds may look like the kind seen in Earth’s skies, they include frozen carbon dioxide, or dry ice. Sometimes these clouds even create a rainbow of colors, producing iridescent, or “mother-of-pearl” clouds. Too faint to be seen in daylight, they are only visible when the clouds are especially high and evening has fallen.
Martian clouds are made of either water ice or, at higher altitudes and lower temperatures, carbon dioxide ice. Mars’ atmosphere is more than 95% carbon dioxide. The latter are the only kind of clouds observed at Mars producing iridescence, and they can be seen near the top of the new images at an altitude of around 37 to 50 miles (60 to 80 kilometers). They are also visible as white plumes falling through the atmosphere, traveling as low as 31 miles (50 kilometers) above the surface before evaporating because of rising temperatures.
Dawn of Twilight Clouds
Twilight clouds were first seen on Mars by NASA’s Pathfinder mission in 1997; Curiosity did not spot them until 2019, when it acquired its first-ever images of iridescence in the clouds. This is the fourth Mars year the rover has observed the phenomenon that occurs during early fall in the southern hemisphere.
Mark Lemmon, an atmospheric scientist with the Space Science Institute in Boulder, Colorado, led a paper summarizing Curiosity’s first two seasons of twilight cloud observations, which published late last year in Geophysical Research Letters. “I’ll always remember the first time I saw those iridescent clouds and was sure at first it was some color artifact,” he said. “Now it’s become so predictable that we can plan our shots in advance; the clouds show up at exactly the same time of year.”
Each sighting is an opportunity to learn more about the particle size and growth rate in Martian clouds. That, in turn, provides more information about the planet’s atmosphere.
Cloud Mystery
One major mystery is why twilight clouds made of carbon dioxide ice have not been spotted in other locations on Mars. Curiosity, which landed in 2012, is on Mount Sharp in Gale Crater, just south of the Martian equator. Pathfinder landed in Ares Vallis, north of the equator. NASA’s Perseverance rover, located in the northern hemisphere’s Jezero Crater, has not seen any carbon dioxide ice twilight clouds since its 2021 landing. Lemmon and others suspect that certain regions of Mars may be predisposed to forming them.
A possible source of the clouds could be gravity waves, he said, that can cool the atmosphere: “Carbon dioxide was not expected to be condensing into ice here, so something is cooling it to the point that it could happen. But Martian gravity waves are not fully understood and we’re not entirely sure what is causing twilight clouds to form in one place but not another.”
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Curiosity was built by NASA's Jet Propulsion Laboratory (JPL). It is managed by Caltech in Pasadena, California. JPL leads the mission on behalf of NASA's Science Mission Directorate in Washington. Malin Space Science Systems in San Diego built and operates Mastcam.
Image Credit: NASA/JPL-Caltech/MSSS
Release Dates: Feb. 11-12, 2025
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