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A rover got a new view of some peculiar extraterrestrial clouds, flecked in rainbow colors and moving across the Martian sky.
Curiosity, a set of NASA‘s robotic “eyes” on the Red Planet, recorded 16 minutes of so-called noctilucent clouds flying overhead on Jan. 17. These clouds, sometimes referred to as twilight clouds because they’re too faint to see in daylight, appear iridescent by scattering light from the setting sun.
Scientists have released a video of the clouds, below in an X post, sped up about 480 times and repeated four times. Amid the flowing clouds are red and green hues.
Though these high fliers also can be observed at the edge of space above Earth, there are distinct differences between Mars’ mother-of-pearl clouds and those of our home planet: Mars’ are made of dry ice — a type of cloud that doesn’t exist in Earth’s atmosphere — while Earth’s are composed of water ice. Mars simply doesn’t have enough water vapor at the highest altitudes necessary for those clouds to form and reflect sunlight after sundown, said Mark Lemmon, an atmospheric scientist with the Space Science Institute in Colorado.
“I think Earth has pretty noctilucent clouds more often, if you live in the right place,” he told Mashable. “The best from each planet is pretty spectacular.”
In the video, noctilucent clouds can be seen drifting near the top of the frame, at an altitude between 37 and 50 miles. These views were captured with Curiosity‘s left Mastcam as the rover continues a journey toward the boxwork region below Mount Sharp.
Though the images may look like they’re being recorded from the perspective of space, as if gazing at a curved right side of the Red Planet, this is, in fact, a skyward view from the Martian ground. Three corners of the images are missing — giving a similar appearance as the hemisphere of a planet — because the rover’s camera happens to have a stuck color filter wheel.
At least as far back as the 19th century, astronomers have gazed up at Earth’s sky and wondered about this kind of cloud, the highest in the atmosphere. Rain clouds tend to form no more than 10 miles up, but the noctilucent clouds, composed of water-ice, hover some 50 miles above the planet’s surface in a layer of the atmosphere known as the mesosphere.
They were still largely a mystery to scientists until about 20 years ago, when NASA’s Aeronomy of Ice in the Mesosphere mission studied them. Researchers learned that the clouds form when ice crystals condense on meteor smoke — tiny particles from shooting stars that burn up in the atmosphere. Perhaps even more surprising was that the ice within the mesosphere formed a single continuous layer.
At summertime, these iridescent clouds shimmer at dusk and dawn near Earth’s North and South Poles. Astronaut Matthew Dominick shared a spectacular photo he took on the Fourth of July from the International Space Station.
Credit: Matthew Dominick / Earth Science and Remote Sensing Unit / NASA Johnson Space Center
“We have had so many great sunrises lately with amazing noctilucent clouds,” Dominick said on X in July 2024. “Probably taken a 1,000 images or so in the past week of them.”
Iridescent clouds were first seen on Mars by NASA’s Pathfinder mission in 1997. Curiosity didn’t observe them until two decades later in 2019. Though this is the fourth such year the rover has spotted them in the early fall, a looming question is why these mother-of-pearl carbon dioxide clouds haven’t been spotted elsewhere on the Red Planet. NASA’s Perseverance rover, located in the northern hemisphere’s Jezero Crater, hasn’t seen any.
Scientists think certain Martian regions might be more inclined to form them. One possibility is that gravity waves, which can cool the air, might be causing carbon dioxide to condense into ice in the southern latitudes.
Lemmon led a paper on Curiosity’s first two seasons of twilight cloud observations. The study was published late last year in Geophysical Research Letters. He recalls that the first time he ever saw them, he actually thought it was a mistake — some kind of color artifact appearing in the images. Now scientists can predict and plan for them.
“Their beauty surprises me every time I see a new example,” he said.
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NASA’s Curiosity rover has captured images of rainbow-colored noctilucent clouds in Mars’ atmosphere. Made of dry ice, these aren’t like Earth’s clouds.
