page_title: Cirrus cloud
section_title: Extraterrestrial
hierarchical_section_title: Cirrus cloud / Extraterrestrial
caption_attribution_description: English: Clouds add drama to the sky above "Endurance Crater" in this mosaic of frames taken by the navigation camera on NASA's Mars Exploration Rover Opportunity at about 9:30 a.m. on the rover's 290th sol (Nov. 16, 2004). The view spans an arc from east on the left to the southwest on the right. These clouds are part of a band that forms near the equator when Mars is near the part of its orbit that is farthest from the Sun. For Opportunity (and Spirit and the rest of the southern hemisphere), this occurs in late fall and early winter. During this period, atmospheric temperatures and the amount of water vapor combine to form large-scale clouds. These clouds look like Earth's cirrus clouds and share other similarities with cirrus clouds in that they are believed to be composed entirely of water-ice particles with sizes on the order of several micrometers (a few ten-thousandths of an inch). The images that are combined to produce this view have been processed to remove geometrical distortion associated with the camera's 45-degree field of view. In addition, special image processing has been applied to enhance the clouds and make them visible across the entire mosaic. The rim of Endurance was processed using the same technique, illustrating how much enhancement was done. Glare from the Sun washed out the clouds on the left in the original images; this glare was removed.
context_page_description: Cirrus is a genus of atmospheric cloud generally characterized by thin, wispy strands, giving the type its name from the Latin word cirrus, meaning a ringlet or curling lock of hair. This cloud can form at any altitude between 5,000 and 13,700 m above sea level. The strands of cloud sometimes appear in tufts of a distinctive form referred to by the common name of "mares' tails".
  From the surface of Earth, cirrus typically appears white, or a light
  grey in color. It forms when water vapor undergoes deposition at altitudes above 5,500 m in temperate regions and above 6,400 m in tropical regions. It also forms from the outflow of tropical cyclones or the anvils of cumulonimbus clouds. Since cirrus clouds arrive in advance of the frontal system or tropical cyclone, it indicates that weather conditions may soon deteriorate. While it indicates the arrival of precipitation, cirrus clouds only produce fall streaks.
  Jet stream-powered cirrus can grow long enough to stretch across continents while remaining only a few kilometers deep. When visible light interacts with the ice crystals in cirrus cloud, it produces optical phenomena such as sun dogs and halos.
context_section_description: Cirrus clouds have been observed on several other planets. On 18 September 2008, the Martian Lander Phoenix took a time-lapse photograph of a group of cirrus clouds moving across the Martian sky using LiDAR. Near the end of its mission, the Phoenix Lander detected more thin clouds close to the north pole of Mars. Over the course of several days, they thickened, lowered, and eventually began snowing. The total precipitation was only a few thousandths of a millimeter. James Whiteway from York University concluded that "precipitation is a component of the [Martian] hydrologic cycle." These clouds formed during the Martian night in two layers, one around 4,000 m (13,000 ft) above ground and the other at surface level. They lasted through early morning before being burned away by the sun. The crystals in these clouds were formed at a temperature of −65 °C (−85 °F), and they were shaped roughly like ellipsoids 0.127 millimeters long and 0.042 millimeters wide.
  On Jupiter, cirrus clouds are composed of ammonia. When Jupiter's South Equatorial Belt disappeared, one hypothesis put forward by Glenn Orten was that a large quantity of ammonia cirrus clouds had formed above it, hiding it from view. NASA's Cassini probe detected these clouds on Saturn and thin water-ice cirrus on Saturn's moon Titan. Cirrus clouds composed of methane ice exist on Uranus. On Neptune, thin wispy clouds which could possibly be cirrus have been detected over the Great Dark Spot. As on Uranus, these are probably methane crystals.
  Interstellar cirrus clouds are composed of tiny dust grains smaller than a micrometer and are therefore not true clouds of this genus which are composed of ice crystals or other frozen liquids. They range from a few light years to dozens of light years across. While they are not technically cirrus clouds, the dust clouds are referred to as "cirrus" because of their similarity to the clouds on Earth. They also emit infrared radiation, similar to the way cirrus clouds on Earth reflect heat being radiated out into space.
caption: Cirrus clouds on Mars
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