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Raumfahrt - Titan im Focus von Cassini

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Candle in the Dark
Saturn's rings cut across an eerie scene that is ruled by Titan's luminous crescent and globe-encircling haze, broken by the small moon Enceladus, whose icy jets are dimly visible at its south pole. North is up. 
The scattered light around planet-sized Titan (5,150 kilometers, or 3,200 miles across) makes the moon's solid surface visible in silhouette. Enceladus (505 kilometers, or 314 miles across) enjoys far clearer skies than its giant sibling moon. 
This view shows the unlit side of Saturn's rings. 
The image was taken in visible red light with the Cassini spacecraft narrow-angle camera on June 10, 2006 at a distance of approximately 3.9 million kilometers (2.4 million miles) from Enceladus and 5.3 million kilometers (3.3 million miles) from Titan. The view was obtained at a Sun-moon-spacecraft, or phase, angle of about 160 degrees relative to both moons. Image scale is 23 kilometers (15 miles) per pixel on Enceladus and 32 kilometers (20 miles) on Titan. 
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A Tale of Two Moons
Many denizens of the Saturn system wear a uniformly gray mantle of darkened ice, but not these two moons. The brightest body in the solar system, Enceladus, is contrasted here against Titan's smoggy, golden murk. 
Ironically, what these two moons hold in common gives rise to their stark contrasting colors. Both bodies are, to varying degrees, geologically active. For Enceladus, its southern polar vents emit a spray of icy particles that coats the small moon, giving it a clean, white veneer. On Titan, yet undefined processes are supplying the atmosphere with methane and other chemicals that are broken down by sunlight. These chemicals are creating the thick yellow-orange haze that is spread through the atmosphere and, over geologic time, falls and coats the surface. 
The thin, bluish haze along Titan's limb is caused when sunlight is scattered by haze particles roughly the same size as the wavelength of blue light, or around 400 nanometers. 
Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained on Feb. 5, 2006, using the Cassini spacecraft narrow-angle camera at a distance of 4.1 million kilometers (2.5 million miles) from Enceladus and 5.3 million kilometers (3.3 miles) from Titan. Resolution in the original images was 25 kilometers (16 miles) per pixel on Enceladus and 32 kilometers (20 miles) per pixel on Titan. The view has been magnified by a factor of two. 
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Hovering Over Titan
A mosaic of nine processed images recently acquired during Cassini's first very close flyby of Saturn's moon Titan on Oct. 26, 2004, constitutes the most detailed full-disc view of the mysterious moon. 
The view is centered on 15 degrees South latitude, and 156 degrees West longitude. Brightness variations across the surface and bright clouds near the south pole are easily seen. 
The images that comprise the mosaic have been processed to reduce the effects of the atmosphere and to sharpen surface features. The mosaic has been trimmed to show only the illuminated surface and not the atmosphere above the edge of the moon. The Sun was behind Cassini so nearly the full disc is illuminated. Pixels scales of the composite images vary from 2 to 4 kilometers per pixel (1.2 to 2.5 miles per pixel). 
Surface features are best seen near the center of the disc, where the spacecraft is looking directly downwards; the contrast becomes progressively lower and surface features become fuzzier towards the outside, where the spacecraft is peering through haze, a circumstance that washes out surface features. 
The brighter region on the right side and equatorial region is named Xanadu Regio. Scientists are actively debating what processes may have created the bizarre surface brightness patterns seen here. The images hint at a young surface with, no obvious craters. However, the exact nature of that activity, whether tectonic, wind-blown, fluvial, marine, or volcanic is still to be determined. 
The images comprising this mosaic were acquired from distances ranging from 650,000 kilometers (400,000 miles) to 300,000 kilometers (200,000 miles). 
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Composite of Titan's Surface Seen During Descent
This composite was produced from images returned yesterday, January 14, 2005, by the European Space Agency's Huygens probe during its successful descent to land on Titan. It shows a full 360-degree view around Huygens. The left-hand side, behind Huygens, shows a boundary between light and dark areas. The white streaks seen near this boundary could be ground 'fog,' as they were not immediately visible from higher altitudes. 
As the probe descended, it drifted over a plateau (center of image) and was heading towards its landing site in a dark area (right). From the drift of the probe, the wind speed has been estimated at around 6-7 kilometers (about 4 miles) per hour. 
These images were taken from an altitude of about 8 kilometers (about 5 miles) with aresolution of about 20 meters (about 65 feet) per pixel. The images were taken by the Descent Imager/Spectral Radiometer, one of two NASA instruments on the probe. 
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Titan Descent
This picture is a composite of 30 images from ESA's Huygens probe. They were taken from an altitude varying from 13 kilometers down to 8 kilometers when the probe was descending towards its landing site. 
The images have a resolution of about 20 meters per pixel and cover an area extending out to 30 kilometers. 
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Liquid Lakes on Titan
The existence of oceans or lakes of liquid methane on Saturn's moon Titan was predicted more than 20 years ago. But with a dense haze preventing a closer look it has not been possible to confirm their presence. Until the Cassini flyby of July 22, 2006, that is. 
Radar imaging data from the flyby, published this week in the journal Nature, provide convincing evidence for large bodies of liquid. This image, used on the journal's cover, gives a taste of what Cassini saw. Intensity in this colorized image is proportional to how much radar brightness is returned, or more specifically, the logarithm of the radar backscatter cross-section. The colors are not a representation of what the human eye would see. 
The lakes, darker than the surrounding terrain, are emphasized here by tinting regions of low backscatter in blue. Radar-brighter regions are shown in tan. The strip of radar imagery is foreshortened to simulate an oblique view of the highest latitude region, seen from a point to its west. 
This radar image was acquired by the Cassini radar instrument in synthetic aperture mode on July 22, 2006. The image is centered near 80 degrees north, 35 degrees west and is about 140 kilometers (84 miles) across. Smallest details in this image are about 500 meters (1,640 feet) across. 
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Mapping Titan's Changes
The three mosaics shown here were composed with data from Cassini's visual and infrared mapping spectrometer taken during the last three Titan flybys, on Oct. 28, 2005 (left image), Dec. 26, 2005 (middle image), and Jan. 15, 2006 (right image). 
These false-color images were constructed from images taken at the following wavelengths: 1.6 microns (blue), 2.01 (green), and 5 microns (red). 
The viewing geometry of the December flyby is roughly on Titan's opposite hemisphere from the flybys in October and January. There are several important features to note in the images. The first is that the south polar cloud system was very bright during the December flyby, while during the October and January flybys, it is barely visible, indicating that the atmosphere over Titan's south pole is very dynamic. 
In the December (middle) mosaic, a north polar hood that is bright at 5 microns is visible. Its composition is unknown. The north polar hood is barely seen in the October (left image) and January (right image) data. Visible in the October and January images just south of the equator is Tui Reggio, a region nicknamed the "chevron." This region is very bright at 5 microns and is among the brightest features on Titan at that wavelength. Tui Reggio is thought to be a surface deposit, probably of volcanic origin, and may be water and/or carbon dioxide frozen from the vapor. The January flyby data show that the western margins of Tui Reggio have a complex flow-like character consistent with eruptive phenomena.
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First Color View of Titan's Surface
This image was returned yesterday, January 14, 2005, by the European Space Agency's Huygens probe during its successful descent to land on Titan. This is the colored view, following processing to add reflection spectra data, and gives a better indication of the actual color of the surface. 
Initially thought to be rocks or ice blocks, they are more pebble-sized. The two rock-like objects just below the middle of the image are about 15 centimeters (about 6 inches) (left) and 4 centimeters (about 1.5 inches) (center) across respectively, at a distance of about 85 centimeters (about 33 inches) from Huygens. The surface is darker than originally expected, consisting of a mixture of water and hydrocarbon ice. There is also evidence of erosion at the base of these objects, indicating possible fluvial activity. 
The image was taken with the Descent Imager/Spectral Radiometer, one of two NASA instruments on the probe. 
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Flyover of Sotra Facula, Titan
This image is based on data from NASA's Cassini spacecraft and shows a flyover of an area of Saturn's moon Titan known as Sotra Facula. Scientists believe Sotra is the best case for an ice volcano -- or cryovolcano -- region on Titan. The flyover shows two peaks more than 1,000 meters (3,000 feet) tall and multiple craters as deep as 1,500 meters (5,000 feet). It also shows finger-like flows. All of these are land features that indicate cryovolcanism. The 3-D topography comes from Cassini's radar instrument. Topography has been vertically exaggerated by a factor of 10. The false color in the initial frames shows different compositions of surface material as detected by Cassini's visual and infrared mapping spectrometer. In this color scheme, dunes tend to look relatively brown-blue. Blue suggests the presence of some exposed ice. Scientists think the bright areas have an organic coating that hides the ice and is different and lighter than the dunes. The finger-like flows appear bright yellowish-white, like the mountain and caldera. The second set of colors shows elevation, with blue being lowest and yellow and white being the highest. Dunes here appear blue because they tend to occupy low areas. The finger-like flows are harder to see in the elevation data, indicating that they are thin, maybe less than about 100 meters (300 feet) thick. 
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Clouds Clearing around Titan's North Pole
This pair of false-color images, made from data obtained by NASA's Cassini spacecraft, shows clouds covering parts of Saturn's moon Titan in yellow. Based on the way near-infrared channels of light were color-coded, cloud cover appears yellow, while Titan's hazy atmosphere appears magenta. The images show cloud cover dissolving from Titan's north polar region between May 12, 2008 (left), and Dec. 12, 2009 (right). The clouds in the second image appear around 40 degrees south latitude, still active late after Titan's equinox. 
Cassini's first observations of clouds near this latitude occurred during summer in the southern hemisphere. Equinox, when the sun shone directly over the equator, occurred in August 2009. It brought a changing of the seasons, as Titan moved out of southern summer into northern spring. 
For the past six years, Cassini has observed clouds clustered in three distinct latitude regions of Titan: large clouds at the north pole, patchy cloud at the south pole and a narrow belt around 40 degrees south. Now scientists are seeing evidence of seasonal circulation turnover at Titan. Clouds at the south pole disappeared just before equinox and the clouds in the north are thinning out. This activity agrees with models that predict cloud activity reversing from one hemisphere to another. 
During winter in the northern hemisphere, northern polar clouds of ethane formed in Titan's troposphere, the lowest part of the atmosphere, from a constant influx of ethane and aerosols from a higher part of the atmosphere known as the stratosphere. In the southern hemisphere, atmospheric gases enriched with methane welled up from the surface to produce mid- and high-latitude clouds. 
The data for the images was detected by Cassini's visual and infrared mapping spectrometer in near-infrared wavelengths. Scientists focused on three wavelengths of infrared radiation that were particularly good for observing cloud signatures and assigned them red, green and blue channels. Emissions in the 2 micron wavelength of light, colored red, detect the Titan surface. Emissions in the 2.11 micron wavelength, colored green, detect the lowest part of the Titan atmosphere, or troposphere. Emissions at the 2.21 micron wavelength, colored blue, detect the hazy stratosphere, a higher part of the atmosphere. The clouds appear yellowish because they lit up the channels designated red and green, but not the blue channel. 
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'Black Cat' on Titan
This radar image of the surface of Saturn's moon Titan was acquired on October 26, 2004, when the Cassini spacecraft flew approximately 1,600 kilometers (994 miles) above the surface and acquired radar data for the first time. 
Brighter areas may correspond to rougher terrains and darker areas are thought to be smoother. This image highlights some of the darker terrain, which the Cassiniteam has dubbed "Si-Si the Cat." This nickname was chosen after a team member'sdaughter, Si-Si, pointed out that the dark terrain has a cat-like appearance. Theinterconnected dark spots are consistent with a very smooth or highly absorbingsolid, or could conceivably be liquid. 
The image is about 250 kilometers (155 miles) wide by 478 kilometers (297 miles) long, and is centered at 50 N, 54 W in the northern hemisphere of Titan, over a region that has not yet been imaged optically. The smallest details seen on the image vary from about 300 meters (984 feet) to 1 kilometer (.62 mile). 
The data were acquired in the synthetic aperture radar mode of Cassini's radar instrument. In this mode, radio signals are bounced off the surface of Titan. 
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Neutral Gas Cloud Around Titan
Images from the magnetospheric imaging instrument and the ion and neutral camera onboard the Cassini spacecraft reveal aspects of the interactions between Saturn's dynamic population of hot energetic ions and the clouds of cold neutral atoms. Future observations may further explain the relationships between these interactions. 
The most recent image of Titan reveals the emission of high-speed neutral atoms from a globular region approximately 70,000 kilometers (43,496 miles) in diameter, clearly centered on Titan. It is only 1/25 as bright as the region seen toward dawn during Saturn orbit insertion, even though Cassini is now closer to Titan. There is an extended emission region around the Titan cloud, but it is much dimmer than the Titan cloud itself and even dimmer compared to the emission seen in the dawn direction at orbit insertion. In this image, the X marks the direction toward the Sun; the Y marks the direction toward Saturn's dawn; and the Z marks Saturn's rotation axis. The dot in the center marks Titan. 
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Titan's North Polar Region
This Cassini false-color mosaic shows all synthetic-aperture radar images to date of Titan's north polar region. Approximately 60 percent of Titan's north polar region, above 60 degrees north latitude, is now mapped with radar. About 14 percent of the mapped region is covered by what is interpreted as liquid hydrocarbon lakes. 
Features thought to be liquid are shown in blue and black, and the areas likely to be solid surface are tinted brown. The terrain in the upper left of this mosaic is imaged at lower resolution than the remainder of the image 
Most of the many lakes and seas seen so far are contained in this image, including the largest known body of liquid on Titan. These seas are most likely filled with liquid ethane, methane and dissolved nitrogen. 
Many bays, islands and presumed tributary networks are associated with the seas. The large feature in the upper right center of this image is at least 100,000 square kilometers (40,000 square miles) in area, greater in extent than Lake Superior (82,000 square kilometers or 32,000 square miles), one of Earth's largest lakes. This Titan feature covers a greater fraction of the surface, at least 0.12 percent, than the Black Sea, Earth's largest terrestrial inland sea, at 0.085 percent. Larger seas may exist, as it is probable that some of these bodies are connected, either in areas unmapped by radar or under the surface (see PIA08365). 
Of the 400 observed lakes and seas, 70 percent of their area is taken up by large "seas" greater than 26,000 square kilometers (10,000 square miles). 
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Exploring the Wetlands of Titan
Cassini peers through the murky orange haze of Titan to spy what are believed to be bodies of liquid hydrocarbons, two of them as large as seas on Earth, near the moon's north pole. 
This movie blends a near natural-color view and an infrared glimpse of Titan's surface obtained by the visual cameras, followed by a transition to imagery collected by the radar instrument aboard Cassini, for a dramatic reveal of the north pole of Saturn's largest moon. As the movie zooms in on the north pole, the most readily visible bodies are outlined in blue. The largest of these, on the left, is as big as the Caspian Sea on Earth; the next largest, on the right, is about the size of Lake Superior. When compared to the surface area of Titan however (which is six times smaller than Earth's), these bodies are equivalent in size to the Bay of Bengal and Timor Sea, respectively. Geographically speaking, they are more like seas.
The movie continues with a gradual transition to a polar map of the radar imagery taken so far by Cassini of the north polar region. It is clear that one of the radar swaths has intersected a small upper bay of the largest sea, and has almost entirely imaged the second one. 
The extreme darkness of these regions in the radar data argues strongly for the presence of liquid hydrocarbons, such as methane and ethane, which remain liquid at Titan's frigid temperature of minus 180 degrees Celsius (minus 288 degrees Fahrenheit). 
The movie continues with a pan across the pole and the radar imagery that has uncovered a multitude of much smaller lakes. 
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Mercator Projection of Huygens's View at Different Altitudes
This poster shows a flattened (Mercator) projection of the view from the descent imager/spectral radiometer on the European Space Agency's Huygens probe at four different altitudes. The images were taken on Jan. 14, 2005. 
The Huygens probe was delivered to Saturn's moon Titan by the Cassini spacecraft, which is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif. NASA supplied two instruments on the probe, the descent imager/spectral radiometer and the gas chromatograph mass spectrometer.
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Mosaic of River Channel and Ridge Area on Titan
This mosaic of three frames from the Huygens Descent Imager/ Spectral Radiometer (DISR) instrument provides unprecedented detail of the high ridge area including the flow down into a major river channel from different sources. 
The Descent Imager/Spectral Radiometer is one of two NASA instruments on the probe. 
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Purple Haze
Encircled in purple stratospheric haze, Titan appears as a softly glowing sphere in this colorized image taken one day after Cassini’s first flyby of the moon on July 2, 2004. 
This image shows a thin, detached haze layer that appears to float above the main atmospheric haze. Because of its thinness, the high haze layer is best seen at the moon’s limb. NASA's Voyager spacecraft detected such detached haze layers on Titan during their flybys in the early 1980s. 
The image, which shows Titan's southern polar region, was taken using a spectral filter sensitive to wavelengths of ultraviolet light centered at 338 nanometers. The image has been false-colored to approximate what the human eye might see were our vision able to extend into the ultraviolet: The globe of Titan retains the pale orange hue our eyes usually see, and both the main atmospheric haze and the thin detached layer have been given their natural purple color. The haze layers have been brightened for visibility. 
The best possible observations of the detached layer are made in ultraviolet light because the small haze particles which populate this part of Titan's upper atmosphere scatter short wavelengths more efficiently than longer visible or infrared wavelengths. This accounts for the bluish-purple color. 
Images like this one reveal some of the key steps in the formation and evolution of Titan's haze. The process begins in the high atmosphere (at altitudes higher than 600 kilometers or 370 miles), where solar ultraviolet light breaks down methane and nitrogen molecules. The products react to form more complex organic molecules containing carbon, hydrogen and nitrogen, and these in turn combine to form the very small particles seen as high hazes. The small particles stick upon collision with one another, forming larger particles which fall deeper into the atmosphere to maintain the lower main haze layer which is thick enough to obscure the surface at visible wavelengths. The altitude of the detached haze layer observed by Cassini (near 500 kilometers or 310 miles) is significantly higher than the detached haze seen by Voyager (at 300 to 350 kilometers or 185 to 215 miles). The upward shift in haze altitude from Voyager to Cassini suggests the possibility of seasonality in haze production or atmospheric circulation strength. The image was taken with the Cassini spacecraft narrow-angle camera on July 3, 2004, at a distance of about 789,000 kilometers (491,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 114 degrees. The image scale is 4.7 kilometers (2.9 miles) per pixel. 
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Crescent Titan
NASA's Cassini spacecraft took this raw image of Saturn's moon Titan on Oct. 14, 2010, kicking off an action-packed long weekend that took the spacecraft by eight other moons. The camera was pointing toward Titan at approximately 207,643 kilometers (129,023 miles) away. This image has not been validated or calibrated. 
Image credit: NASA/JPL/SSI
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Titan and Tethys
NASA's Cassini spacecraft obtained this raw image of Saturn's moons Titan and Tethys on Oct. 18, 2010. Titan, Saturn's largest moon, is the larger, hazy moon in the background. Tethys is the bright icy moon in the foreground. The rings of Saturn faintly etch the top of this image. The image has not been validated or calibrated. 
Image credit: NASA/JPL/SSI
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Bright streaks of clouds on Titan
NASA's Cassini spacecraft obtained this raw image of Saturn's moon Titan on Oct. 18, 2010. Bright clouds streak the moon's midsection, likely an indication of changing seasons and the arrival of spring in the northern hemisphere. Cassini's imaging camera was about 2.5 million kilometers (1.5 million miles) away from Titan. The rings of Saturn faintly etch the top of this image. The image has not been validated or calibrated. 
Image credit: NASA/JPL/SSI
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Titan's Arrow-Shaped Storm
A huge arrow-shaped storm blows across the equatorial region of Titan in this image from NASA's Cassini spacecraft, chronicling the seasonal weather changes on Saturn's largest moon. 
This storm created large effects in the form of dark -- likely wet -- areas on the surface of the moon, visible in later images. After this storm dissipated, Cassini observed significant changes on Titan's surface at the southern boundary of the dune field named Belet. Those changes covered an area of 500,000 square kilometers (193,000 square miles), or roughly the combined area of Arizona and Utah in the United States. See PIA12818 to learn more.
The part of the storm that is visible here measures 1,200 kilometers (750 miles) in length east-to-west. The wings of the storm that trail off to the northwest and southwest from the easternmost point of the storm are each 1,500 kilometers (930 miles) long. 
Titan's weather has been changing since the August 2009 equinox, when the sun lay directly over the equators of Saturn and its moons, and storms at low latitudes are now more common. See PIA11667 to learn how the sun's illumination of the Saturnian system changed during the equinox transition to spring in the northern hemispheres and to fall in the southern hemispheres of the planet and its moons. See PIA12813 to learn more about Titan's changing weather. 
This image is a mosaic of two Cassini images. Most of this view is from an image of the storm captured on Sept. 27, 2010. However, because that image's framing cut off the south polar region of the moon, a second image taken on July 9, 2010, was used to fill in that portion of the moon. This second image was re-projected to the same viewing geometry as the first. 
Lit terrain seen here is in the area between the trailing hemisphere, which is the side of Titan that faces backward in its orbit around Saturn, and the side of Titan that always faces away from Saturn. North on Titan (5,150 kilometers or 3,200 miles across) is up. The images were taken with the Cassini spacecraft narrow-angle camera using a spectral filter of near-infrared light centered at 938 nanometers. The view was acquired at a distance of approximately 1.3 million kilometers (808,000 miles) from Titan and at a sun-Titan-spacecraft, or phase, angle of 44 degrees. Image scale is 8 kilometers (5 miles) per pixel. 
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Equatorial Titan Clouds
NASA's Cassini spacecraft chronicles the change of seasons as it captures clouds concentrated near the equator of Saturn's largest moon, Titan. 
Methane clouds in the troposphere, the lowest part of the atmosphere, appear white here and are mostly near Titan's equator. The darkest areas are surface features that have a low albedo, meaning they do not reflect much light. Cassini observations of clouds like these provide evidence of a seasonal shift of Titan's weather systems to low latitudes following the August 2009 equinox in the Saturnian system. (During equinox, the sun lies directly over the equator. See PIA11667 to learn how the sun's illumination of the Saturnian system changed during the equinox transition to spring in the northern hemispheres and to fall in the southern hemispheres of the planet and its moons.) 
In 2004, during Titan's late southern summer, extensive cloud systems were common in Titan's south polar region (see PIA06110, PIA06124 and PIA06241). Since 2005, southern polar systems have been observed infrequently, and one year after the equinox, extensive near-equatorial clouds have been seen. This image was taken on Oct. 18, 2010, a little more than one Earth year after the Saturnian equinox, which happens once in roughly 15 Earth years. 
The cloud patterns observed from late southern summer to early southern fall on Titan suggest that Titan's global atmospheric circulation is influenced by both the atmosphere and the surface. The temperature of the surface responds more rapidly to changes in illumination than does the thick atmosphere. Outbreaks such as the clouds seen here may be the Titan equivalent of what creates the Earth's tropical rainforest climates, even though the delayed reaction to the change of seasons and the apparently sudden shift is more reminiscent of the behavior over Earth's tropical oceans than over tropical land areas. 
A few clouds can be seen in Titan's southern latitudes here. See PIA12813 for a movie of clouds moving through the middle southern latitudes of Titan. 
Some clouds are also visible in the high northern latitudes here. See PIA12811 and PIA12812 for movies showing clouds near the moon's north pole. 
This view looks toward the Saturn-facing side of Titan (5,150 kilometers or 3,200 miles across). North is up. The image appears slightly grainy because it was re-projected to a scale of 6 kilometers (4 miles) per pixel. Scale in the original image was 15 kilometers (9 miles) per pixel. 
This view consists of an average of three images taken using a filter sensitive to near-infrared light centered at 938 nanometers, which allows for detection of Titan's surface and lower atmosphere, plus an image taken using a filter sensitive to visible light centered at 619 nanometers. 
The images were taken with the Cassini spacecraft's narrow-angle camera at a distance of approximately 2.5 million kilometers (1.6 million miles) from Titan and at a sun-Titan-spacecraft, or phase, angle of 56 degrees. 
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Tortula Facula
These side-by-side images obtained by NASA's Cassini spacecraft show the feature named Tortola Facula on Saturn's moon Titan. The left image was obtained by the visual and infrared mapping spectrometer data on Oct. 26, 2004, at a resolution of 2 kilometers (1 mile) per pixel This mosaic focuses on an area around 9 degrees north latitude and 145 degrees west longitude. In 2005, scientists interpreted Tortola Facula as an ice volcano. 
The right image shows the same feature, as seen by Cassini's radar instrument on May 12, 2008, at a much higher resolution of 300 meters per pixel. Scientists now think that this feature is a nondescript obstacle surrounded by obvious wind-blown sand dunes, similar to those commonly found in this region of Titan. In radar images, objects appear bright when they are tilted toward the spacecraft or have rough surfaces. 
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Titan and Callisto
These images compare surface features observed by NASA's Cassini spacecraft at the Xanadu region on Saturn's moon Titan (left), and features observed by NASA's Galileo spacecraft on Jupiter's cratered moon Callisto (right). The Cassini radar image, obtained on a Titan flyby April 30, 2006, is centered on 10 degrees south latitude and 85 degrees west longitude. The Galileo camera image, obtained on June 25, 1997, is centered on 6 degrees south latitude and 7 degrees west longitude. Titan may originally have had a cratered landscape similar to Callisto that has since been eroded by rainfall and runoff. There are many large circular features in Titan's Xanadu region that have some of the characteristics of impact craters - such as central peaks and inward-facing circular cliffs - which make scientists think they are, in fact, eroded impact craters. The surface of Callisto also has a substantially eroded cratered landscape. Instead of erosion by weather, scientists theorize the erosion on Callisto was caused by ground ice evaporating away. 
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Moons Small to Large
The Cassini spacecraft views Saturn with a selection of its moons in varying sizes. 
Saturn's largest moon, Titan, is in the center of the image. Titan is 5,150 kilometers, or 3,200 miles, across. The smaller moon Enceladus (504 kilometers, or 313 miles across) is on the far right, appearing just below the rings. The tiny moon Pandora (81 kilometers, or 50 miles across) is barely detectable as a speck on the far left, beyond the thin F ring. To enhance visibility, 
Pandora has been brightened by a factor of two relative to the rest of the image. 
This view looks toward anti-Saturn side of Titan and toward the northern, sunlit side of the rings from just above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on Jan. 15, 2011 using a combination of polarized and spectral filters sensitive to wavelengths of near-infrared light centered at 752 nanometers. The view was acquired at a distance of approximately 844,000 kilometers (524,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 78 degrees. Image scale is 50 kilometers (31 miles) per pixel.
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Slicing Before Titan
Saturn's rings cut across this view of the planet's largest moon, Titan. 
Dark albedo features on Titan (5,150 kilometers, or 3,200 miles across) and the moon's north polar hood are visible here. See PIA08137 and PIA09739 to learn more. 
This view looks toward the southern, unilluminated side of the rings from just below the ringplane and toward the Saturn-facing side of Titan. North on Titan is up. The image was taken with the Cassini spacecraft narrow-angle camera on May 12, 2011 using a spectral filter sensitive to wavelengths of near-infrared light centered at 938 nanometers. The view was acquired at a distance of approximately 2.3 million kilometers (1.4 million miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 11 degrees. Image scale is 14 kilometers (9 miles) per pixel.
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Craters Before Haze
The Cassini spacecraft views the cratered surface of Saturn's moon Tethys in front of the hazy orb of the planet's largest moon, Titan.Tethys (1,062 kilometers, or 660 miles across) is much closer than Titan (5,150 kilometers, or 3,200 miles across) to Cassini. This view looks toward the Saturn-facing side of Titan and toward the area between the trailing hemisphere and anti-Saturn side of Tethys. Saturn is out of the frame, far to the left. The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on July 14, 2011. The view was acquired at a distance of approximately 3.2 million kilometers (2 million miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 18 degrees. Image scale is 19 kilometers (12 miles) per pixel on Titan. The view was acquired at a distance of approximately 1.9 million kilometers (1.2 million miles) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 18 degrees. Image scale is 11 kilometers (7 miles) per pixel on Tethys.
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East of Huygens
Saturn's rings lie in the distance as the Cassini spacecraft looks toward Titan and its dark region called Shangri-La, east of the landing site of the Huygens Probe. 
The moon's north polar hood is also visible here. See PIA09739 and PIA08137 to learn more about Titan's atmosphere. 
This view looks toward the anti-Saturn side of Titan (5,150 kilometers, or 3,200 miles across). North on Titan is up. This view looks toward the northern, sunlit side of the rings from just above the ringplane. 
The image was taken with the Cassini spacecraft narrow-angle camera on Aug. 9, 2011 using a spectral filter sensitive to wavelengths of near-infrared light centered at 938 nanometers. The view was acquired at a distance of approximately 1.4 million kilometers (870,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 35 degrees. Image scale is 8 kilometers (5 miles) per pixel. 
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Titan's Kraken Mare
The Cassini spacecraft looks toward Saturn's largest moon, Titan, and spies the huge Kraken Mare in the moon's north. 
Kraken Mare, a large sea of liquid hydrocarbons, is visible as a dark area near the top of the image. See PIA12811 and PIA11626 to learn more. 
This view looks toward the Saturn-facing side of Titan (3,200 miles across, or 5,150 kilometers,). North on Titan is up and rotated 29 degrees to the left. 
The image was taken with the Cassini spacecraft narrow-angle camera on Sept. 14, 2011 using a spectral filter sensitive to wavelengths of near-infrared light centered at 938 nanometers. The view was acquired at a distance of approximately 1.2 million miles (1.9 million kilometers) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 26 degrees. Image scale is 7 miles (12 kilometers) per pixel. 
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Orange and Blue Hazes
These views from Cassini look toward the south polar region of Saturn's largest moon, Titan, and show a depression within the moon's orange and blue haze layers near the south pole. 
The close-up view was captured with the narrow-angle camera. Another view taken a second later with the wide-angle camera is also included here for context. 
The moon's high altitude haze layer appears blue here whereas the main atmospheric haze is orange. The difference in color could be due to particle size of the haze. The blue haze likely consists of smaller particles than the orange haze. 
The depressed or attenuated layer appears in the transition area between the orange and blue hazes about a third of the way in from the left edge of the narrow-angle image. The moon's south pole is in the upper right of this image. This view suggests Titan's north polar vortex, or hood, is beginning to flip from north to south. SeePIA11603 and PIA11667. 
The southern pole of Titan is going into darkness with the sun advancing towards the north with each passing day. The upper layer of Titan's hazes is still illuminated by sunlight. 
Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained on Sept. 11, 2011 at a distance of approximately 83,000 miles (134,000 kilometers) from Titan. Image scale is 2,581 feet (787 meters) per pixel. 
Image credit: NASA/JPL-Caltech/Space Science Institute
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True Colors, Deceptive Sizes
Saturn's largest moon, Titan, appears deceptively small paired here with Dione, Saturn's third-largest moon, in this view from Cassini. 
Titan (3200 miles, 5150 kilometers across) is much farther from the spacecraft than Dione (698 miles, 1123 kilometers across) is in this view. The view was captured at a distance of approximately 684,000 miles (1.1 million kilometers) from Titan but only about 85,000 miles (136,000 kilometers) from Dione. 
Titan appears in true color but has been brightened by a factor of about 1.6 relative to Dione. This view looks toward the Saturn-facing side of Titan and the area between the Saturn-facing side and leading hemisphere of Dione. North is up on the moons. 
Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained with the Cassini spacecraft wide-angle camera on Nov. 6, 2011. Scale in the original image was 5 miles (8 kilometers) per pixel on Dione and 41 miles (66 kilometers) per pixel on Titan. The image has been magnified by a factor of 1.5 and contrast-enhanced to aid visibility. 
Image credit: NASA/JPL-Caltech/Space Science Institute
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Titan Upfront
The colorful globe of Saturn's largest moon, Titan, passes in front of the planet and its rings in this true color snapshot from NASA's Cassini spacecraft. 
The north polar hood can be seen on Titan (3200 miles, 5150 kilometers across) and appears as a detached layer at the top of the moon here. See PIA08137 and PIA09739 to learn more about Titan's atmosphere and the north polar hood. 
This view looks toward the northern, sunlit side of the rings from just above the ring plane. 
Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained with the Cassini spacecraft narrow-angle camera on May 21, 2011 at a distance of approximately 1.4 million miles (2.3 million kilometers) from Titan. Image scale is 9 miles (14 kilometers) per pixel on Titan. 
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Titan and Dione
Saturn's third-largest moon Dione can be seen through the haze of its largest moon, Titan, in this view of the two posing before the planet and its rings from NASA's Cassini spacecraft. 
The north polar hood can be seen on Titan appearing as a detached layer at the top of the moon here. See PIA08137 and PIA09739 to learn more about Titan's atmosphere and the north polar hood. 
See PIA10560 and PIA07638 to learn more about and see a closer view of the wisps on Dione's trailing hemisphere, which appear as bright streaks here. 
This view looks toward the anti-Saturn side of Titan (3200 miles, 5150 kilometers across) and Dione (698 miles, 1123 kilometers across). North is up on the moons. This view looks toward the northern, sunlit side of the rings from just above the ring plane. 
Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained with the Cassini spacecraft narrow-angle camera on May 21, 2011 at a distance of approximately 1.4 million miles (2.3 million kilometers) from Titan 2 million miles (3.2 million kilometers) from Dione. Image scale is 9 miles (14 kilometers) per pixel on Titan and 12 miles (19 kilometers) on Dione. 
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Haze Before Ice
Saturn's moon Tethys, with its stark white icy surface, peeps out from behind the larger, hazy, colorful Titan in this Cassini view of the two moons. Saturn's rings lie between the two. 
The north polar hood can be seen on Titan appearing as a detached layer at the top of the moon here. See PIA08137 and PIA09739 to learn more about Titan's atmosphere and the north polar hood. 
Ithaca Chasma, a long series of scarps or cliffs on Tethys, faintly can be seen running north-south on that moon. See PIA10460 to learn more. 
This view looks toward the anti-Saturn side of Titan (3200 miles, 5150 kilometers across) and the Saturn-facing side of Tethys (660 miles, 1062 kilometers across). This view looks toward the northern, sunlit side of the rings from just above the ring plane. 
Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were acquired with the Cassini spacecraft narrow-angle camera on May 21, 2011 at a distance of approximately 1.4 million miles (2.3 million kilometers) from Titan and 2.4 million miles (3.8 million kilometers) from Tethys. Image scale is 9 miles (14 kilometers) per pixel on Titan and 18 miles (27 kilometers) per pixel on Tethys. 
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Welcome Disruption
Rhea Before Titan
Craters appear well defined on icy Rhea in front of the hazy orb of the much larger moon Titan in this Cassini spacecraft view of these two Saturn moons. 
See PIA08137 and PIA14913 to learn more about the hazy atmosphere on Titan (3,200 miles, or5,150 kilometers across). See PIA07763 and PIA11465 for closer views of craters on Rhea (949 miles, or 1,528 kilometers across). 
Lit terrain seen here is on the leading hemispheres of Rhea and Titan. North on the moons is up and rotated 13 degrees to the left. The limb, or edge of the visible disk, of Rhea is slightly overexposed in this view. 
The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Dec. 10, 2011. The view was acquired at a distance of approximately 1.2 million miles (2 million kilometers) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 109 degrees. The view was acquired at a distance of approximately 810,000 miles (1.3 million kilometers) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 109 degrees. Image scale is 8 miles (12 kilometers) per pixel on Titan and 5 miles (8 kilometers) per pixel on Rhea. 
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Fotos; NASA
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