Because Mars’ atmosphere is 96% carbon dioxide, thick clouds like Earth rarely form. On Mars, clouds are usually visible near the equator during the coldest time of the year. However, on Mars a year ago, or on Earth’s time axis, two years ago, scientists discovered that clouds were forming in the sky faster than expected through NASA’s Curiosity probe.
Judging by the same time this year, the Curiosity team has been waiting for the clouds to form. The images taken this time are not only fantastic to look at, but also provide new insights. These early clouds appear at higher elevations than the regular clouds on Mars. Usually, Martian clouds are 60 km high and consist mainly of water ice. But I think this cloud is probably frozen carbon dioxide, or dry ice particles.
The research team released two types of images: a black-and-white photograph and a color composite image. In black and white, the clouds floating in the sky have regular shapes like scaly clouds seen from the Earth’s sky. On the other hand, the color image looks like a thin, brightly shaded cloud covering the faint sky before the storm.
The clouds in this color image, taken after sunset, are the Latin word for noctilucent, which brightens as crystals fill. It gets dark when sunlight stops shining on the clouds by sunset. Cloud light conditions after sunset are clues to determine cloud heights.
NASA has also photographed the mother of pearls, which appear as brightly iridescent as pearls on the back of an oyster. The most spectacular scenery seen on Mars, it seems that all the cloud particles have grown at the same size and at the same rate. Related information can be found here.