Like the rest of us, NASA's Curiosity Mars rover likes to watch the clouds roll by from time to time.
The car-size robot craned its neck skyward on May 7 and May 12, capturing gorgeous imagery of wispy clouds scudding through the Red Planet's atmosphere.
The clouds seem to lie about 19 miles (31 kilometers) up and are likely composed of water ice, NASA officials said. Cirrus clouds here on Earth are also made of water ice, but that doesn't mean the two planets' atmospheres are similar; Mars' air is 100 times thinner than that of Earth and is dominated by carbon dioxide, with just tiny traces of oxygen. (Earth's atmosphere is 78% nitrogen, 21% oxygen and trace amounts of various other substances.)
Related: Amazing Mars Photos by NASA's Curiosity Rover (Latest Images)
Curiosity wasn't just killing time or recharging its metaphorical batteries here. Mission scientists hope to learn a thing or two about Mars' atmospheric dynamics, especially after comparing Curiosity's observations with those gathered by NASA's InSight lander, which is camped out about 373 miles (600 kilometers) away.
"Capturing the same clouds from two vantage points can help scientists calculate their altitude," NASA officials wrote Wednesday (May 29) in a description of the newly released imagery.
Curiosity landed inside Mars' 96-mile-wide (154 km) Gale Crater in August 2012, tasked with determining if the area could ever have supported microbial life. The answer to that question is yes; Curiosity's work has shown that Gale hosted a potentially habitable lake-and-stream system for long stretches in the ancient past.
Since September 2014, Curiosity has been making its way up through the foothills of Mount Sharp, the 3.4-mile-high (5.5 km) mountain that rises from Gale's center. The goal is to climb high enough to learn about Mars' long-ago transition from a relatively warm and wet world to the cold desert planet we know today.
Curiosity has recently been exploring a region that mission team members call "the clay-bearing unit," because Mars orbiters have spotted evidence of clay minerals there. And the rover provided some definitive ground truth.
"Two samples the rover recently drilled at rock targets called 'Aberlady' and 'Kilmarie' have revealed the highest amounts of clay minerals ever found during the mission," NASA officials wrote in the photo description.
Clay minerals are associated with liquid water, so the new observations help flesh out the habitability history of Gale Crater.
"It's likely that the rocks in the area formed as layers of mud in ancient lakes — something Curiosity also found lower on Mount Sharp," NASA officials wrote. "Water interacted with sediment over time, leaving an abundance of clay in the rocks there."
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Mike Wall's book about the search for alien life, "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), is out now. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
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