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Titan-PIA08246.jpgTitan54 visiteCaption NASA:"This remarkably clear view from that flyby shows the moon's characteristically dark Mid-Latitudes, and more Southern Terrain than the Cassini spacecraft has usually been able to glimpse. This was the first in a series of "illuminated outbound flybys" of Titan where the illuminated Hemisphere was visible following the closest approach. Cassini's flyby of Titan on July 22, 2006 sent the spacecraft into a more inclined orbit about Saturn.
The image was taken in polarized infrared light with the Cassini spacecraft wide-angle camera on July 22, 2006 at a distance of approx. 148.000 Km (about 92.000 miles) from Titan.
Image scale is roughly 9 Km (about 5 miles) per pixel".
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Titan-PIA08351.jpgClose "Friends"...54 visiteCaption NASA originale:"Cassini peers around the hazy limb of Titan to spy the sunlit South Pole of Saturn in the distance beyond.
The thick, smog-like atmosphere of frigid Titan is a major source of interest for the Cassini mission. The moon is 5.150 Km (about 3.200 miles) across.
Images taken using red, green and blue spectral filters were combined to create this natural-color view. The image was taken with the Cassini spacecraft narrow-angle camera on Dec. 26, 2005, at a distance of approx. 26.000 Km (about 16.000 miles) from Titan. Image scale is roughly 1 Km (4.643 feet) per pixel".
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Titan-PIA08391.jpgHiding behind the Rings55 visiteCassini delivers this stunning vista showing small, battered Epimetheus and smog-enshrouded Titan, with Saturn's A and F-Rings stretching across the scene.
The color information in the colorized view is completely artificial: it is derived from red, green and blue images taken at nearly the same time and phase angle as the clear filter image. This color information was overlaid onto the previously released clear filter view in order to approximate the scene as it might appear to human eyes.
The prominent dark region visible in the A-Ring is the Encke Gap (about 325 Km, or 200 miles wide), in which the moon Pan and several narrow ringlets reside. Moon-driven features which score the A-Ring can easily be seen to the left and right of the Encke Gap.
A couple of bright clumps can be seen in the F-Ring.
Epimetheus is 116 Km (72 miles) across and giant Titan is 5.150 kilometers (3.200 miles) across.
The view was acquired with the Cassini spacecraft narrow-angle camera on April 28, 2006, at a distance of approx. 667.000 Km (about 415.000 miles) from Epimetheus and 1,8 MKM (about 1,1 MMs) from Titan. The image captures the illuminated side of the Rings. The image scale is roughly 4 Km (about 2 miles) per pixel on Epimetheus and about 11 Km (approx. 7 miles) per pixel on Titan.MareKromium
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Titan-PIA08733.jpgCrescent Titan (HR)68 visiteCaption NASA originale:"This composite image, composed of two images taken with Cassini's Visual and Infrared Mapping Spectrometer (VIMS), shows a crescent view of Saturn's moon Titan.
The data were obtained during a flyby on July 22, 2006, at a distance of 15.700 Km (about 9.700 miles) from Titan. The image was constructed from images taken at wavelengths of 1,26 microns (blue), 2 microns (green) and 5 microns (red)".
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Titan-PIA08868.jpgTitanian "Bands"54 visiteCaption NASA:"Titan bears a distinct East-West banded pattern in this Cassini spacecraft image taken in the ultraviolet.
The ultraviolet wavelength allows Cassini to see Titan's stratosphere, where superrotation -- in which the atmosphere moves around the moon faster than Titan rotates -- is strong. The recent appearance of this feature may be a harbinger of seasonal change on Titan.
The moon's halo -- its detached, high-altitude global haze layer -- is visible here as well, and is often its most prominent feature in such ultraviolet views. North on Titan is up and rotated 6° to the right in this image.
The view was obtained by the Cassini spacecraft narrow-angle camera using a spectral filter sensitive to wavelengths of polarized ultraviolet light.
The view was acquired on Dec. 25, 2006 at a distance of approx. 1,3 MKM (about 800.000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 123°.
Image scale is roughly 8 Km per pixel".
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Titan-PIA08879.jpgTitan (true colors - elab. NASA)54 visiteCaption NASA:"Looking toward high Northern Latitudes on Titan, the Cassini spacecraft spies a banded pattern encircling the Pole.
This sort of feature is what scientists expect to see in the Stratosphere of Titan, where the Atmosphere is superrotating, or moving around the moon faster than the moon itself rotates.
Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were taken by the Cassini spacecraft wide-angle camera on Jan. 28, 2007 at a distance of approx. 196.000 Km (about 122.000 miles) from Titan. Image scale is 12 Km (approx. 7 miles) per pixel".
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Titan-PIA08943.jpgAn "Orthographic View" of Titan54 visiteCaption NASA:"Cassini acquired this view of Titan on April 13, 2007, following a flyby of the Mercury-sized moon. Titan's equatorial Dark Regions are visible in this view, along with faint, dark lineaments (linear features) in the otherwise bland-looking terrain of the North. Near the Terminator are the dark, lake-like features identified in Cassini flybys early in 2007.
To the east of the lake-like features is a bright patch of clouds that likely consist of a mixture of Methane and Ethane.
This view of Titan is an orthographic reprojection centered on 27,4° North Latitude. An orthographic view is most like the view seen by a distant observer looking through a telescope.
The view was obtained using a filter sensitive to near-infrared light centered at 939 nanometers, allowing for observations of Titan's Surface and Lower Atmosphere, added together. An image taken using a filter sensitive to visible light centered at 619 nanometers was then subtracted from the product, effectively removing the lower atmosphere contribution to the brightness values in the image, increasing image contrast and improving the visibility of surface features.
The Cassini spacecraft acquired this view with its narrow-angle camera at a distance of approx. 1,2 MKM (about 800.000 miles) from Titan. Image scale is roughly 7 Km (such as about 5 miles) per pixel".
MareKromium
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Titan-PIA08945.jpgA new "Ortographic View" of Titan66 visiteBright and dark terrains on Titan's Trailing Hemisphere are revealed by Cassini's Imaging Science Subsystem in this mosaic of images taken during the T28 flyby in April 2007. The Region shown in this image, centered on the northern part of Titan's Trailing Hemisphere (near 31,2° North and 220,7° West), had only been seen at very low resolution until February 2007, when Cassini flew over this area for the first time. This mosaic consists of images taken during one of a series of flybys in early 2007 designed to study this long unavailable part of Titan.
Several intriguing surface features can be seen in this mosaic that warrant further study. Along the top of the mosaic is a series of dark lineaments, or linear features, that stand out against the blandness of the Northern, Mid-Latitude Terrain.
These features were also observed by the RADAR instrument in December 2006 and represent an area of potential future co-analysis for the RADAR and camera teams. Another such region is the large bright area known as Adiri at bottom center, also imaged by RADAR in October 2005.
The mosaic shows a number of dark areas within Adiri Regio that line up with small dune fields observed by RADAR. A portion of the dark terrain surrounding Adiri was also observed in 2005 by RADAR, and likewise was found to consist of large stretches of longitudinal dune fields - further supporting the correlation between equatorial dark regions and dune "seas".
To the East of Adiri is a dark spot surrounded by a ring of bright material, which may be associated with an impact crater similar to Sinlap, discovered earlier in the Cassini mission (see PIA6222).
This mosaic consists of 29 separate frames using a total of 116 images.
Each frame consists of three images, taken using a filter sensitive to near-infrared light centered at 938 nanometers, allowing for observations of Titan's surface and lower atmosphere, added together. An image taken using a filter sensitive to visible light centered at 619 nanometers was then subtracted from the product, effectively removing the lower atmosphere contribution to the brightness values in the image, increasing image contrast and improving the visibility of surface features.
This process is also intended to reduce noise, but some camera artifacts still remain, such as a dark ring caused by dust in the camera system near the bottom right of each frame.
The images used for this mosaic were taken on April 11, 2007 from distances ranging from approx. 106.000 to 180.000 Km (such as from about 66.000 to 112.000 miles).
This mosaic is in an orthographic view of Titan (an orthographic view is most like the view seen by a distant observer looking through a telescope).
MareKromium
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Titan-PIA09007.jpg...Ring of Fire... (natural colors; elab. Lunexit)54 visiteCaption NASA:"This celestial circle of light is produced by the glow of Sunlight scattered through the periphery of Titan's atmosphere as the Sun is occulted by Titan. It is the sum of all the sunsets and sunrises taking place on Titan at once.
The intriguing structure of Titan's North Polar "hood" can be seen at upper left.
A thin, detached, high-altitude global haze layer encircles the moon.
North on Titan is up and rotated 23° to the left.
The image was taken in visible blue light with the Cassini spacecraft wide-angle camera on June 29, 2007. The view was obtained at a distance of approx. 210.000 Km (about 131.000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 167°.
Image scale is roughly 12 Km (about 8 miles) per pixel".MareKromium
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Titan-PIA09032.jpgTitanian "Sierras"54 visiteCaption NASA originale"This composite image shows a massive mountain range running just south of Titan's Equator. Near the center of the image, the mountain range runs from South-East to North-West. It is about 150 Km long (approx. 93 miles) and 30 Km (about 19 miles) wide and approx. 1,5 Km (nearly a mile) high.
This range and smaller ranges to the West and East of the main range, probably results from material welling up below as the crust of Titan is pulled apart by tectonic forces.
This image was obtained during an Oct. 25 flyby designed to obtain the highest resolution infrared views of Titan yet. Cassini's VIMS resolved surface features as small as 400 meters (1,300 feet).
This composite image was taken at a distance of about 12.000 Km (7.200 miles) from Titan. This image was constructed from images taken at wavelengths of 1,3 microns shown in blue, 2 microns shown in green and 5 microns shown in red".MareKromium
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Titan-PIA09034.jpgCloudless Titan...54 visiteCaption NASA originale:"This image is a composite of several images taken during two separate Titan flybys on Oct. 9 (T19) and Oct. 25 (T20), 2006.
The large circular feature near the center of Titan's disk may be the remnant of a very old impact basin. The mountain ranges to the South-East of the circular feature and the long dark, linear feature to the North-West of the old impact scar may have resulted from tectonic activity on Titan caused by the energy released when the impact occurred.
The Oct. 9 images form the background globe for context and the most recent images from the Oct. 25 flyby are overlaid. The Oct. 9 images were taken at an average distance of about 30,000 Km (approx. 18.000 miles). The Oct. 25 images were taken at a distance of 12.000 Km (about 7.200 miles). The images were taken at wavelengths of 1,3 microns shown in blue, 2 microns shown in green and 5 microns shown in red".MareKromium
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Titan-PIA09034_H-1.jpgCrescent Titan71 visiteHuygens scored a first in 2005 by measuring the electrical conductivity of Titan’s atmosphere. The results hint at a new way to investigate the subsurface layers of Titan and could provide insight into whether or not Titan has a subsurface ocean.
The Permittivity, Waves and Altimetry (PWA) sensor on the Huygens Atmosphere Structure Instrument (HASI) detected an extremely low frequency (ELF) radio wave during the descent. It was oscillating very slowly for a radio wave, just 36 times a second, and increased slightly in frequency as the probe reached lower altitudes.
If the PWA team confirms that the signal is a natural phenomenon and not an artefact of the way the instrument worked, they will have discovered a powerful new way to probe not just the atmosphere of Titan but its subsurface as well.
The only other world on which ELF waves were detected before was Earth. They are reflected by both the surface of the Earth and its ionosphere, the rarefied region of the atmosphere where most particles are electrically charged. This turns the atmosphere into a giant ‘sound box’ where certain frequencies of ELF waves resonate and are reinforced, whilst other die away.
On Titan, however, the surface is a poor reflector because of its low conductivity and so these waves penetrate the interior. “The wave could have been reflected by the liquid-ice boundary of a subsurface ocean of water and ammonia predicted by theoretical models,” says Fernando Simões, CETP/IPSL-CNRS, France, and a member of the PWA team.
If Simões is right, successful modelling of how ELF waves resonate on Titan could lend support to the ocean’s existence and tell scientists about the depth at which it sits. Understanding the resonance however, is difficult.
Above about 100 kilometres altitude on Earth, the ionosphere provides the upper reflecting layer of the resonating cavity. At Titan, PWA revealed that things are more complicated. Apart from the ionosphere, at a much higher altitude of about 1200 kilometres, Huygens found a layer of ionized particles consisting of electrons, at 63 kilometres. “This does not match any previous prediction for Titan,” says Simões. To some extent, it splits Titan’s atmosphere into two resonating chambers.
With so much at stake, the PWA team are checking to make sure the detection is real and not an artefact generated by the spacecraft. They have already ruled out electrical interference from the instrument itself.
Two small arms, one on either side of Huygens, create an antenna and the team’s next goal is to investigate whether the arms could have oscillated during the descent. Simões and colleagues are building a special chamber to hold a replica of the instrument at the low temperature of Titan’s atmosphere, between 100-200 degrees Kelvin (about -173 to -73 °C), in order to check whether the antenna resonates at 36 hertz. If it does, it probably means that the signal is an artefact. If it does not, confidence in the signal’s reality will increase and the investigation of the atmosphere and subsurface can begin.
But perhaps the biggest mystery is what generated the ELF wave in the first place. On Earth, they are initiated by lightning strikes that make electrons in the atmosphere oscillate, releasing the ELF waves.
The PWA was designed to search for ELF waves on Titan while a microphone on Huygens kept an ear out for thunder – a sure sign of lightning. Cassini has also been watching for lightning using its cameras.
However, Huygens suggests that there is no lightning, or very little. “If there is lightning on Titan, it is significantly less than the amount of lightning that Earth experiences,” says Simões. So what generated Titan’s ELF? No one is quite sure yet. “It might be generated by an interaction with Saturn’s magnetosphere or related to Titan’s intrinsic fields,” suggests Simões. “Titan is proving to be an intriguing environment.”
One thing is certain: there is plenty to investigate. “The measurement of atmospheric electricity is something really new and exciting,” says Jean-Pierre Lebreton, ESA Huygens Project Scientist. “We could send similar instruments to study atmospheric electricity on other celestial bodies, in particular Venus, Mars, and the giant planets,” adds Simões.
The PWA team expect to release more definitive results when their investigation is complete.
MareKromium
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