As the Curiosity rover explores its way around Mars, it isn’t only looking down at the martian rocks and regolith — it is also looking up at the martian sky. Like Earth, Mars has its own seasonal weather patterns, but with its different atmosphere that weather can include some unusual phenomena, such as striking colorful clouds.
A recent video created from images captured by Curiosity shows clouds tinted red and green flowing though the sky over Mars. Captured using the rover’s Mastcam instrument on January 17, 2025, the video shows the clouds during twilight on the red planet.
Credit: NASA/JPL-Caltech/MSSS/SSI
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These clouds have been observed before, as Mars sometimes sees iridescent ‘mother of pearl’ clouds due to the way light from the sun is scattered. Though Mars has a very thin atmosphere, at just 1% of the density of Earth’s atmosphere, it can still have clouds made of water ice or carbon dioxide ice. It is these carbon dioxide clouds, which form at high altitudes, that show the coloful effects.
“I’ll always remember the first time I saw those iridescent clouds and was sure at first it was some color artifact,” said researcher Mark Lemmon of 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.”
The shimmering clouds can be spotted in Mars’s southern hemisphere, where Curiosity is located, during the early fall period. Observations each year have helped researchers to learn more about them, but it’s still not clear why these clouds form over the Gale Crater, where Curiosity is, and not in other locations. The Perseverance rover, for example, is exploring in the Jezero Crater in the planet’s northern hemisphere but has never seen any carbon dioxide clouds.
The researchers suspect that certain regions of the planet may form these clouds more easily due to gravity waves affecting 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,” Lemmon said. “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.”