(CNN) – The Curiosity rover has witnessed a colorful wonder on Mars: bright clouds.
The color is rare in this frozen desert, apart from the predominant red. But in the skies over Curiosity, the clouds seem to almost glow with color.
Unlike Earth, Mars doesn’t have many cloudy days. The red planet has a thin, dry atmosphere, so clouds tend to appear in the skies above the Martian equator when the planet is cold and furthest from the sun in its oval-shaped orbit every two Earth years.
That changed two Earth years ago, or one Martian year, when Curiosity detected clouds that arrived earlier and formed higher than expected in the atmosphere.
Preparing for this event should it happen again, the Curiosity team on Earth sent instructions to the rover to search for the first clouds in late January.
Curiosity’s camera captured the wispy clouds, which are filled with ice crystals. These ice crystals appear to glow because they scatter sunlight. In addition to being a dazzling sight, these images are helping scientists understand more about Martian cloud formation.
These early-arriving clouds form at a higher and cooler altitude, so they are essentially made of dry ice (frozen carbon dioxide). Scientists are still studying them to find out why this happens.
Images taken in March by the rover’s navigation cameras, which capture black-and-white photos, show ripples in the clouds. But color images taken by the camera on the rover’s mast after sunset reveal bright, glowing clouds.
Why do you see incandescent colored clouds on Mars?
As the sun sets, these tall clouds become almost incandescent, filling with ice crystals and reflecting the fading sunlight. They then darken as the sunlight fades.
“If you see a cloud with a glittering set of pastel colors, it’s because the particles in the cloud are nearly identical in size,” said Mark Lemmon, an atmospheric scientist at the Institute for Space Sciences in Boulder, Colorado, in a statement.
“That usually happens right after the clouds have formed and all grew at the same rate,” he added.
“I always marvel at the colors that appear: reds, greens, blues, and purples,” Lemmon said. “It’s really cool to see something glowing with a lot of color on Mars.”