Gale Crater Clouds, variant by Stuart Rankin
Via Flickr:
Clouds that wouldn't be out of place over Death Valley, but seen by Curiosity over Gale Crater. Color/processing variant. Image source: www.jpl.nasa.gov/news/nasas-curiosity-rover-captures-shin... Original caption: The science team is studying the clouds, which arrived earlier and formed higher than expected, to learn more about the Red Planet. Cloudy days are rare in the thin, dry atmosphere of Mars. Clouds are typically found at the planetâs equator in the coldest time of year, when Mars is the farthest from the Sun in its oval-shaped orbit. But one full Martian year ago â two Earth years â scientists noticed clouds forming over NASAâs Curiosity rover earlier than expected. This year, they were ready to start documenting these âearlyâ clouds from the moment they first appeared in late January. What resulted are images of wispy puffs filled with ice crystals that scattered light from the setting Sun, some of them shimmering with color. More than just spectacular displays, such images help scientists understand how clouds form on Mars and why these recent ones are different. In fact, Curiosityâs team has already made one new discovery: The early-arrival clouds are actually at higher altitudes than is typical. Most Martian clouds hover no more than about 37 miles (60 kilometers) in the sky and are composed of water ice. But the clouds Curiosity has imaged are at a higher altitude, where itâs very cold, indicating that they are likely made of frozen carbon dioxide, or dry ice. Scientists look for subtle clues to establish a cloudâs altitude, and it will take more analysis to say for sure which of Curiosityâs recent images show water-ice clouds and which show dry-ice ones. The fine, rippling structures of these clouds are easier to see with images from Curiosityâs black-and-white navigation cameras. But itâs the color images from the roverâs Mast Camera, or Mastcam, that really shine â literally. Viewed just after sunset, their ice crystals catch the fading light, causing them to appear to glow against the darkening sky. These twilight clouds, also known as ânoctilucentâ (Latin for ânight shiningâ) clouds, grow brighter as they fill with crystals, then darken after the Sunâs position in the sky drops below their altitude. This is just one useful clue scientists use to determine how high they are. Even more stunning are iridescent, or âmother of pearlâ clouds. âIf you see a cloud with a shimmery pastel set of colors in it, thatâs because the cloud particles are all nearly identical in size,â said Mark Lemmon, an atmospheric scientist with the Space Science Institute in Boulder, Colorado. âThatâs usually happening just after the clouds have formed and have all grown at the same rate.â These clouds are among the more colorful things on the Red Planet, he added. If you were skygazing next to Curiosity, you could see the colors with the naked eye, although theyâd be faint. âI always marvel at the colors that show up: reds and greens and blues and purples,â Lemmon said. âItâs really cool to see something shining with lots of color on Mars.â
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