Yes. Some clouds high above Mars contain frozen carbon dioxide, often called dry ice. Mars also has water-ice clouds, but at especially cold heights, carbon dioxide gas can form tiny ice crystals. Those high clouds may glow after sunset because they remain in sunlight while the rover and ground beneath them have already entered shadow.
What did Curiosity see above Mars in 2025?
On January 17, 2025, NASA’s Curiosity rover recorded an extraordinary sequence of twilight clouds with its Mast Camera. According to NASA’s interpretation, the bright plumes near the top of the image are carbon dioxide ice clouds around 37 to 50 miles (60 to 80 kilometers) above the surface. Fainter lower clouds are made of water ice. The released image has been brightened and color-enhanced to reveal structures that would otherwise be difficult to see.
Why can carbon dioxide turn into cloud ice?
A cloud needs particles: drops or crystals suspended in the atmosphere. Most clouds familiar to people on Earth form from water. Mars’s thin atmosphere is instead composed mainly of carbon dioxide. In its very cold upper atmosphere, some of that gas can deposit into tiny solid crystals. At lower, warmer levels, any falling dry-ice crystals may sublimate—change directly from solid to gas—before they reach the ground.
What makes a twilight cloud glow?
The geometry is similar to the way an airplane high in the sky can still catch sunlight after sunset at ground level. From the rover’s position, the Sun is below the local horizon, but sunlight still strikes cloud layers high in the atmosphere. Their particles reflect and scatter it, giving a bright appearance against a darkening sky. Scientists call such high clouds noctilucent—night-shining. The clouds do not generate their own light.
Are these clouds the same as frost on the ground?
Some Martian surface frost is also frozen carbon dioxide, especially in the polar regions, but a high cloud and a surface coating are different physical settings. Cloud crystals are suspended in air, while frost forms on cold solid surfaces. Both can disappear through sublimation as their environment warms. For that comparison, see why Mars’s morning frost can disappear after sunrise.
Can high dry-ice clouds make snow?
Carbon dioxide snowfall can occur on Mars under some circumstances, particularly in polar winter. But it would be a mistake to assume the specific high-altitude clouds pictured above are snowing onto the ground. NASA reports that some of their falling ice crystals likely enter warmer air and evaporate before they could arrive at the surface. Observation of a cloud is not automatically observation of surface precipitation.
Why do researchers study the cloud colors?
Cloud brightness, shape and motion can help scientists investigate atmospheric conditions, particle size and altitude. Rover observations repeated across different Martian seasons can reveal changing patterns. But image processing is important: NASA notes that the 2025 view has been enhanced, so it should not be described as a completely unprocessed photograph of what a human eye would see.
Frequently asked questions
Does Mars have ordinary water clouds, too?
Yes. Water-ice clouds have been photographed over Mars, including in the lower part of Curiosity’s 2025 twilight image.
Does “dry ice” mean the clouds are artificial?
No. Dry ice is simply solid carbon dioxide, a naturally occurring material in the Martian environment.
Can the clouds shine when the Sun is completely gone?
The bright twilight effect depends on sunlight still reaching their high altitude, even after it disappears below the rover’s horizon. The clouds are not self-luminous.
Source: NASA, Curiosity Views Twilight Clouds, including the video and original scientific caption.
Leave a Reply