It is not common to see cloudy days on Mars, which has a thin and dry atmosphere. Clouds are normally seen at the planet’s equator at the coldest time of the year, when Mars is farthest from the Sun during its oval orbit.
However, scientists behind the Curiosity rover , the longest-lived robot on the red planet – studying its characteristics since 2012 – have captured unusual images: clouds over Curiosity in an unexpected area, and at a much earlier time than expected.
This is detailed by NASA in a statement, published at the end of May. These are “wispy puffs filled with ice crystals that scattered the light of the setting or twilight sun, some of them glittering and colorful.”
There is no doubt that the images are spectacular; However, what is remarkable about these images is that they could help scientists understand how clouds form on Mars and why they are different.
In fact, the Curiosity team has already made a new discovery: clouds that appear earlier than expected in the Martian year are also found at higher altitudes than usual.
Most Martian clouds float no more than 60 kilometers in the sky and are made up of water ice. But the clouds that Curiosity has captured are higher altitudes, where it is much colder, indicating that they are likely made of frozen carbon dioxide or dry ice.
The thin, wavy structures of these clouds are easier to see with images from Curiosity’s black-and-white navigational cameras. But it’s the color images from the rover’s Mast Camera, or Mastcam, show how these clouds literally ‘glow’.
Detected just after sunset, their ice crystals catch the light gradually fading, making them appear to glow in an increasingly darker sky. These twilight clouds, also known as ‘noctilucent’ clouds (from Latin, ‘night glow’), become brighter as they fill with crystals; then they darken as the Sun descends in the sky.
Even more impressive are the iridescent or ‘mother of pearl’ clouds, which are a set of shimmering pastel colors. This characteristic color is because the cloud particles are nearly identical in size, according to Mark Lemmon, an atmospheric scientist at the Institute for Space Sciences in Boulder, Colorado: “That usually happens right after the clouds have all formed and grown. At the same rhythm”.
