While NASA's Perseverance rover has been getting a lot of attention following its arrival on Mars in February, the Curiosity rover is still working on the Martian surface, where it's been since August 2012. Curiosity continues to make important discoveries on the Red Planet. Last week, NASA's Jet Propulsion Laboratory announced that Curiosity had captured images of shining clouds on Mars.

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Clouds don't often form in the thin and dry atmosphere of Mars. NASA writes that 'Clouds are typically found at the planet's equator in the coldest time of year, when Mars is the farthest from the Sun in its oval-shaped orbit.' However, a Martian year ago – two Earth years – scientists observed that clouds formed over the Curiosity rover earlier than expected.

Armed with that observation, the Curiosity team was ready to document 'early' clouds this year. They first appeared in late January as wispy puffs. These clouds were filled with ice crystals, which scattered light at sunset. This scattering of light resulted in a colorful, spectacular display and a rare one on Mars.

Caption for the above GIF: 'This GIF shows clouds drifting over Mount Sharp on Mars, as viewed by NASA's Curiosity rover on March 19, 2021, the 3,063rd Martian day, or sol, of the mission. Each frame of the scene was stitched together from six individual images.' Credit: NASA/JPL-Caltech/MSSS

The clouds are more than just nice to look at. They're also important pieces of the puzzle when trying to understand how clouds form on Mars. The Curiosity team discovered that the early-arrival clouds formed at higher than typical altitudes. 'Most Martian clouds hover no more than about 60 km (30 mi) in the sky and are composed of water ice. But the clouds Curiosity has imaged are at a higher altitude, where it's very cold, indicating that they are likely made of frozen carbon dioxide, or dry ice.' Scientists must look very carefully at data and images to determine if the images Curiosity recently captured show water-ice clouds or dry-ice clouds. The analysis is ongoing.

The clouds above were viewed just after sunset when the ice crystals catch the fading light, which makes them appear to glow against the darkening sky. The clouds, also known as 'noctilucent' clouds, glow brighter as they accumulate more ice crystals and 'then darken when the Sun's position in the sky drops below their altitude.' This is one way that scientists can try to determine the altitude of the observed clouds.

'NASA’s Curiosity Mars rover spotted these iridescent, or 'mother of pearl,' clouds on March 5, 2021, the 3,048th Martian day, or sol, of the mission. Seen here are five frames stitched together from a much wider panorama taken by the rover’s Mast Camera, or Mastcam.' Credit: NASA/JPL-Caltech/MSSS

The iridescent clouds seen above, also known as 'mother of pearl' clouds, are caused by the cloud particles being all nearly identical in size. Mark Lemmon, an atmospheric scientist with the Space Science Institute in Boulder, CO, said, 'That's usually happening just after the clouds have formed and have all grown at the same rate.' Lemmon adds, 'I always marvel at the colors that show up: reds and greens and blues and purples. It's really cool to see something shining with lots of color on Mars.' If you were on Mars, standing next to the rover, you'd be able to see the colors with the naked eye, although they'd appear fainter than in the image above.

Caption for above GIF: ‘Using the navigation cameras on its mast, NASA's Curiosity Mars rover took these images of clouds just after sunset on March 31, 2021, the 3,075th sol, or Martian day, of the mission.' Credit: NASA/JPL-Caltech

If you'd like to learn more about the Curiosity Mars rover, visit NASA's dedicated Curiosity website. You can also read about the selfie Curiosity sent back to Earth this spring by clicking here. To read about the Mars Exploration Program, visit NASA.