Martian sunsets are uniquely moody, but NASA’s Curiosity rover captured one last month that stands out. As the sun set over the horizon on February 2, rays of light illuminated a bank of clouds. These “sunrays” are also known as crepuscular rays, from the Latin word for “twilight”. It was the first time the sun’s rays have been seen so clearly on Mars.
Curiosity captured the scene during the rover’s latest twilight cloud survey, which builds on its 2021 observations of nocturnal or nocturnal clouds. While most Martian clouds do not hover more than 60 kilometers above the ground and are composed of water ice, the clouds in the latest images appear to be at a higher altitude, where it is particularly cold. This suggests that these clouds are made of carbon dioxide ice or dry ice.
As on Earth, clouds provide scientists with complex but crucial information for understanding the weather. By looking at when and where clouds form, scientists can learn more about the composition and temperatures of the Martian atmosphere and its winds.
The 2021 cloud survey included more imaging from Curiosity’s black-and-white navigation cameras, providing a detailed look at a cloud’s structure as it moves. But the recent study, which began in January and will conclude in mid-March, relies more often on the rover’s color Mast Camera, or Mastcam, which helps scientists see how cloud particles grow over time.
In addition to the image of sun rays, Curiosity captured a set of colorful clouds shaped like a feather on January 27. When illuminated by sunlight, certain types of clouds can create a rainbow-like display called an iris.
“Where we see iridescence, it means that a cloud’s particle sizes are identical to their neighbors in every part of the cloud,” said Mark Lemmon, an atmospheric scientist at the Space Science Institute in Boulder, Colorado. “By looking at color gradients, we see the particle size change across the cloud. This tells us about the way the cloud evolves and how its particles change size over time.”
Curiosity captured both the sun’s rays and iridescent clouds as panoramas, each pieced together from 28 images sent to Earth. The images have been processed to emphasize the highlights.