NASA’s Curiosity rover has captured images of clouds on Mars. As noted by the researchers, they are like “swirling fluff filled with ice crystals that scatter light.”

Clouds are rarely found in Mars’ atmosphere, but they usually form at its equator during the coldest time of the year, according to NASA. The scientists noticed that in the past year, two years ago, Earth time, the clouds started to form earlier than expected, so they can be observed with fewer problems.

These images allowed NASA’s Curiosity team to gain new insights into the planet. The early clouds are at a higher height than the rest of the clouds, which usually hang about 60 km above the planet’s surface and are composed of water ice. Clouds at high altitudes are likely composed of frozen carbon dioxide, NASA notes. Curiosity provided both black and white and color images – more detail is seen more clearly in black and white photos.

The researchers noted that when viewed just after sunset, the ice crystals catch the dying light, so they appear to glow against a dark sky. These crepuscular clouds, also called “noctyl”, become brighter as they fill up with crystals and then darken as the sun becomes lower. This is just one useful feature for researchers by which scientists determine how high they are.

Curiosity also captured images of iridescent “pearlescent” clouds in pastel colors. Mark Lemmon, an atmospheric scientist at the Space Science Institute in Boulder, Colorado, says in a NASA report that these colors are caused by cloud particles that are nearly the same size. “This usually happens immediately after the formation of clouds, which grow at the same rate,” the scientists noted.