Curiosity Rover Spots First-Ever ‘Sun Rays’ on Mars

A murky vista starkly contrasts the shining rays of dying light; they spill over the horizon and illuminate the clouds. It could be an idyllic scene in many places on Earth, but it didn’t even happen on this planet. NASA has released new images from the aging but seemingly unstoppable Curiosity rover, captured during a recent cloud-imaging campaign. Among them is the first detection of sun rays on another world.

Most of the robotic exploration on Mars focuses on the surface and the search for evidence of life, but NASA has been looking skyward lately. Curiosity arrived on Mars in 2012 and began conducting a cloud survey in 2021 using its monochrome navigation cameras. These cameras are adept at following cloud structures as they drift across the horizon. More recently, NASA has tasked the color Mastcam with tracking clouds, which is ideal for analyzing particle size.

The image above shows rays of sunlight, also known as crepuscular rays, spreading through the wispy clouds. Mars’s atmosphere is just 1% as dense as Earth’s, but it still produces the occasional cloud. Most Martian clouds hover at an altitude of 37 miles (60 kilometers) or lower. The new images from the Mastcam appear to show cloud formations much higher. That suggests they are composed of carbon dioxide ice rather than water ice like the lower ones.

The second image shows a bright feather-like cloud. There are no visible crepuscular rays, but the fading sunlight has illuminated the cloud and been scattered into an iridescent rainbow. This is one reason NASA uses the Mastcam instead of the navigation cameras. Iridescence means the cloud’s particles are the same size in that part of the cloud. So, tracking the changing colors across the cloud can illustrate the changing particle sizes.

The Mastcam has a total resolution of under 2MP, but the cloud panoramas are much larger. NASA captured 28 frames for each panorama and then stitched them together to create the full-resolution image. The sunset happened on Feb. 2, 2023, the mission’s 3,730th Martian day (or Sol), and the feathery cloud appeared on Jan. 27 (Sol 3,724). NASA only designed Curiosity to last a few years, but there’s no end in sight for this intrepid robotic explorer.

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