| Piú viste - Titan: The "Foggy" Moon |
Titan-Lakes-South_Polar_Lake-00-PIA06240.jpgOntario Lacus and the South Polar Regions of Titan58 visiteThis view of Titan's South Polar Region reveals an intriguing dark feature that may be the site of a past or present lake of liquid hydrocarbons.
The true nature of this feature, seen here at left of center, is not yet known, but the shore-like smoothness of its perimeter and its presence in an area where frequent convective storm clouds have been observed by Cassini and Earth-based astronomers make it the best candidate thus far for an open body of liquid on Titan.
If this interpretation is correct, then other very dark but smaller features seen in the South Polar Region, some of which are captured in this image, may also be the sites of liquid hydrocarbon reservoirs.
In addition to the notion that the dark feature is or was a lake filled with liquid hydrocarbons, scientists have speculated about other possibilities. For instance, it is plausible that the lake is simply a broad depression filled by dark, solid hydrocarbons falling from the atmosphere onto Titan's surface. In this case, the smoothed outline might be the result of a process unrelated to rainfall, such as a sinkhole or a volcanic caldera.
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Titan-Lakes-South_Polar_Lake-01-PIA06241-PCF-LXTT-IPF-000.jpgOntario Lacus and the South Polar Regions of Titan58 visiteCaption NASA originale:"Although it is far too cold for blossoming flowers, summer does bring storm clouds and presumably rain to Titan's south polar region.
The observed persistence of convective storm activity in the region during the Southern Titan Summer has led scientists to speculate that the dark, footprint-shaped feature near the upper left could be a past or present reservoir for Titan's methane rains".
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Titan-Regions-Fensal_and_Aztlan_Region-PIA07732.jpgFensal and Aztlan Region on Titan58 visiteDuring its Sept. 7, 2005, flyby of Titan, Cassini acquired images of territory on the moon's Saturn-facing hemisphere that were assembled to create this mosaic. Once known only as "The H" because the Region looks something like the letter on its side, features in this Region now possess provisional names. The Northern Branch of the H is now called Fensal, while the Southern Branch is known as Aztlan.
Fensal is littered with small "islands" ranging in size from 5 to 40 Km across. These landforms currently are thought to be water ice upland areas, surrounded by shallower terrain that is filled-in with dark particulate material from the atmosphere. A few larger islands are also seen, like Bazaruto Facula (near right, containing a dark crater) and several islands in Western Fensal. When viewed in images of Shangri-La (on the other side of Titan), island-like landforms of this size tend to occur in clusters with apparent preferred orientations. The small islands in Fensal appear much more scattered (and most appear roughly circular), although a few islands do have an east-west orientation to their long axis.
Aztlan, on the other hand, appears comparatively devoid of small islands, with three large islands in its western reaches, plus only a few smaller islands. The largest of these islands is called "Sotra Facula" (just right of center in the bottom left mosaic frame), and measures 240 by 120 kilometers (149 to 75 miles) across.
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Titan-Surface-33-PIA06440.jpgThe surface of Titan (again)58 visiteOriginal caption:"Images from the European Space Agency's Huygens probe descent imager/spectral radiometer side-looking imager and from the medium resolution imager, acquired after landing, were merged to produce this image.
The horizon's position implies a pitch of the imager/spectral radiometer, nose-upward, by 1 to 2° with no measurable roll. The "stones" (?) in the foreground are 4 to 6" (10 to 15 cm) in size, presumably made of water ice and these lie on a darker, finer-grained substrate.
A region with a relatively low number of rocks lies between clusters of rocks in the foreground and the background and matches the general orientation of channel-like features in the panorama of PIA06439.
The scene evokes the possibility of a dry lakebed".
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Titan-N00055566.jpgWhat's happening on Titan? (3)58 visiteCaption NASA:"N00055566.jpg was taken on March 20, 2006 and received on Earth March 20, 2006. The camera was pointing toward Titan that, at the time, was approximately 972.794 Km away.
The image was taken using the P0 and UV3 filters".
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Titan-Rivers-Unnamed_Rivers_and_Channels-PIA08428-0.jpgThe rivers of Titan...58 visiteThis image from the Synthetic Aperture Radar instrument on the Cassini spacecraft shows the radar-bright western margin of Xanadu, one of the most prominent features on Titan.
In radar images, bright regions indicate a rough or scattering material, while a dark region might be smoother or more absorbing. This image was taken during a flyby of Titan on April 30, 2006.
Narrow, sinuous, radar-bright channels, meandering like a maze, are seen on the right-hand-side of the image. These may be river networks that might have flowed onto the dark areas on the left of the image. Vast, dark areas covered by dunes are seen on the equatorial regions of Titan (see PIA03567) and have been referred to as Titan's "sand seas". Near the middle of the image is a radar-bright area that has a boundary with the dark sand seas. Because the radar illumination is coming from the top, this indicates that the bright region, Xanadu, is topographically higher than the sand seas.
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Titan-Rivers-Unnamed_Rivers_and_Channels-PIA08604-0.jpgCold Rivers58 visiteCaption NASA originale:"A network of river channels is located atop Xanadu, the continent-sized Region on Saturn's moon Titan.
This radar image was captured by the Cassini Radar Mapper on April 30, 2006.
These winding, meandering river channels start from the top of the image and run like a fork in the road, splitting to the right and left of the image. At Titan's chilly conditions, streams of methane and/or ethane might flow across parts of the Region.
The picture is roughly 230 Km (about 143 miles) wide by 340 Km (such as approx. 211 miles) long, and shows features as small as about 500 mt (approx. 1640 feet)".
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Titan-Lakes-Unnamed_North_Polar_Lakes-01-PIA08630-2.jpgTitanian Northern Lakes (2)58 visiteCaption NASA originale:"For all these reasons, scientists interpret the dark areas as lakes of liquid methane or ethane, making Titan the only body in the Solar System besides Earth known to possess lakes. Because such lakes may wax and wane over time, and winds may alter the roughness of their surfaces. Repeat coverage of these areas should test whether indeed these are bodies of liquid.
These two radar images were acquired by the Cassini radar instrument in synthetic aperture mode on July 21, 2006.
The image (1) is centered near 80° North Lat. and 92° West Long.; it measures about 380x120 Km.
The image (2) is centered near 78° North Lat. and 18° West Long.; it measures about 425x120 Km.
Smallest details in this image are about 500 mt (roughly 1640 feet) across".
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Titan-N00067442.jpgShort "light-streak" in the space of Titan58 visiteCaption NASA:"N00067442.jpg was taken on October 10, 2006 and received on Earth on the same day. The camera was pointing toward Titan that, at the time, was approximately 168.568 Km away.
This image was taken using the CL1 and CB3 filters and it has not been validated or calibrated".
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Titan-PIA06107-00.jpgThe "True Colors" of Titan, according to Lunexit58 visiteLa NASA, allorchè si tratta di colorizzare Titano, oscilla fra il giallo/arancio (come ben si vede nei frames Voyager), il giallo "canarino", con bordi bluastri (si vedano i primi frames Cassini, tipo PIA06089) ed una colorazione ambigua che potremmo definire giallo/salmonato, con bordi verde chiaro (ultimi frames Cassini, tipo PIA08351). Ma la NASA ha le idee chiare in tema di colori? Diremmo proprio di no, ed a nulla valgono le precisazioni che vengono fatte allorchè la NASA stessa precisa le diverse lunghezze d'onda impiegate per le colorizzazioni (jargon&tecnochiacchiere, nulla di più).
E allora?
E allora subentra - ancora una volta - il buon senso e l'osservazione telescopica (sia da Terra, sia HST). Risultato: Titano è (globalmente) color giallo-pallido, con toni più chiari ed accesi nelle sue Regioni Nord Polari e più sbiaditi in quelle Equatoriali.
Ed i bordi blu e verdi? Ed i bianchi accesi? E gli arancioni? Beh, se la NASA "li vede", vuol dire che ci saranno; ma noi non li "vediamo", neppure filtrando banda-per-banda i loro stessi color-frames e quindi...Questo è Titano, secondo noi, in "colori naturali" (ossìa come li vedremmo se ci trovassimo nei suoi pressi).
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Titan-Craters-Unnamed_Crater-PIA09175.jpgFresh Crater on Titan?58 visiteCaption NASA:"This radar image of Titan shows a semi-circular feature that may be part of an impact crater. Very few impact craters have been seen on Titan so far, implying that the surface is young. Each new crater identified on Titan helps scientists to constrain the age of the surface.
Taken by Cassini's radar mapper on Jan. 13, 2007, during a flyby of Titan, the image swath revealed what appeared to be the northernmost half of an impact crater. This crater is roughly 180 Km (about 110 miles) wide. Only three impact craters have been identified on Titan and several others, like this one, are likely to also have been caused by impact. The bright material is interpreted to be part of the crater's ejecta blanket, and is likely topographically higher than the surrounding plains. The inner part of the crater is dark, and may represent smooth deposits that have covered the inside of the crater.
This image was taken in synthetic aperture mode and has a resolution of approx. 350 mt (1150 feet). North is toward the top left corner of the image, which is approx. 240 Km (about 150 miles) wide by 140 Km (90 miles) high. The image is centered at about 26,5° North and 9° West".
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Titan-Regions-Sinlap_Region-LS28_PSS_LASoderblom_VIMSRADAR20070323.jpgSinlap Region and Guabonito Crater58 visiteIn this composite image, Titan’s surface areas are correlated.
The top pair is composed by Cassini’s radar images, while the bottom pair shows Cassini’s VIMS images. Each of the four panels corresponds to an area about 200 Km wide.
The left views show the Sinlap Crater; the brown features in the bottom panel correspond to the large dune fields visible in the top panel.
The right views show the Guabonito Region situated at about 150 Km East of the Huygens Landing Site. MareKromium
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