New images, taken over 16 min on January 17, 2025 by the Mastcam instrument on NASA’s Curiosity rover, show noctilucent, or twilight clouds, in the atmosphere of Mars. Sometimes these clouds even create a rainbow of colors, producing iridescent, or mother-of-pearl clouds. Too faint to be seen in daylight, they’re 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.
The latter are the only kind of clouds observed at the Red Planet producing iridescence, and they can be seen near the top of the new images at an altitude of 60 to 80 km (37 to 50 miles).
They’re also visible as white plumes falling through the atmosphere, traveling as low as 50 km (31 miles) above the surface before evaporating because of rising temperatures.
Appearing briefly at the bottom of the images are water-ice clouds traveling in the opposite direction roughly 50 km above the Curiosity rover.
This Curiosity/Mastcam image shows noctilucent clouds in the Martian atmosphere. Image credit: NASA / JPL-Caltech / MSSS / SSI.
“I’ll always remember the first time I saw those iridescent clouds and was sure at first it was some color artifact,” said Dr. Mark Lemmon, an atmospheric scientist at the Space Science Institute.
“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.”
“A possible source of the clouds could be gravity waves, which 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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