Saturn: the "Ringed Beauty" and His Moons
|
|
|
Japetus-Orbit-00.jpgSide view of Japetus's orbit68 visiteThe orbit of Japetus is somewhat unusual. Although it is Saturn's third-largest moon, it orbits much farther from Saturn than the next closest major moon, Titan. It has also the most inclined Orbital Plane of the regular satellites; only the irregular outer satellites like Phoebe have more inclined orbits. The cause of this is unknown.
Because of this distant, inclined orbit, Japetus is the only large moon from which the Rings of Saturn would be clearly visible; from the other inner moons, the Rings would be edge-on and difficult to see.MareKromium
|
|
Japetus-Orbit-01.jpgPolar view of Japetus's orbit53 visitenessun commentoMareKromium
|
|
Japetus-PIA06145_modest.jpgSharp views of Japetus53 visiteIn sequenza, alcune delle migliori immagini di Giapeto ottenute da Cassini e superiori, per qualità e dettaglio, a quelle ottenute dalla Sonda Voyager 2 qualche anno fa. Le immagini a colori visibili sulla Sn dell'Osservatore ed al centro sono state ottenute usando (e combinando) i filtri per l'ultravioletto (a 338 Nnmts), il verde (a 568 Nnmts) e l'infrarosso (a 930 Nnmts); l'immagine a Dx è stata ottenuta riprendendo nel cosiddetto "spettro visibile". Le immagini sono state riprese da una distanza oscillante fra gli 1,1 e gli 1,3 MKMs; Giapeto si caratterizza sia per il gigantesco cratere da impatto visibile nell'emisfero sud (400 Km di diametro), sia per alcune notevoli differenze di albedo fra diverse zone della sua superficie (il che ci fa supporre che esistano aree ricoperte, probabilmente, da vasti depositi di polveri - che sono causa di una bassa riflessione della luce ergo di una bassa albedo - ed altre aree che, forse, sono costituite da rocce o addirittura da depositi di ghiaccio).
|
|
Japetus-PIA06167_modest.jpgJapetus in "near-true" color54 visiteCaption NASA originale:"This near-true color view from Cassini reveals the colorful and intriguing surface of Saturn's moon Iapetus in unrivaled clarity. The images taken with different spectral filters and used for this composite were taken at the same time as the clear frames used in PIA06166. The use of color on Iapetus is particularly helpful for discriminating between shadows (which appear black) and the intrinsically dark terrain (which appears brownish). This image shows the northern part of the dark Cassini Regio and the transition zone to a brighter surface at high northern latitudes. Within the transition zone, the surface is stained by roughly north-south trending wispy streaks of dark material. The absence of an atmosphere on Iapetus means that the material was deposited by some means other than precipitation, such as ballistic placement from impacts occurring elsewhere on Japetus, or was captured from elsewhere in the Saturn system".
|
|
Japetus-PIA06168_modest.jpgJapetus53 visiteCaption NASA originale:"This image reveals a heavily cratered surface and shows the boundary between Iapetus' bright trailing hemisphere and Cassini Regio - a large, dark region that covers the leading hemisphere of the moon's surface. Some of the dark material appears to have collected inside the rim of a large impact structure about 250 Km across that lies just beyond the edge of the dark region (seen here near the right of the image). NASA's Voyager images (see PIA02268) this feature appeared as a dark 'moat' and had been hypothesized to be an impact structure. The recent images from Cassini confirm an impact origin for this feature.
|
|
Japetus-PIA06170_modest.jpgJapetus in HR53 visiteCaption NASA originale:"This oblique view of Saturn's moon Japetus from high latitude shows how the dark, heavily cratered terrain of Cassini Regio transitions to a bright, icy terrain at high latitudes. In this mosaic of 2 HR images taken during Cassini's New Year's Eve 2004 flyby of Japetus, the direction toward the north pole is approximately 15° below the horizontal on the right. At the equator terrains are uniformly covered with a dark mantle of material that has a reflectivity of about 4%. At latitudes toward the pole of about 40°, the dark deposits become patchy and diffuse as the surface transitions to a much brighter, icy terrain near the pole. The brightest icy materials exhibit visual reflectivity over 60%. Superimposed on the bright terrain is a subtle, ghostly pattern of crudely parallel, north-south trending wispy streaks. The streaks, which were discovered during this flyby of Iapetus, are typically a few kilometers wide and sometimes tens of kilometers long. Their appearance and orientation may be connected with the emplacement of dark materials that cover Cassini Regio. The dark materials might represent the gradual accumulation of dark debris falling from space, or alternatively, may represent fallout from plume-style eruptions that may have accompanied the formation of Iapetus's enigmatic equatorial ridge (see PIA 06166)".
|
|
Japetus-PIA06171_modest.jpgLandslide on Japetus53 visiteCaption NASA originale:"A spectacular landslide within the low-brightness region of Japetus's surface known as Cassini Regio. The landslide material appears to have collapsed from a scarp 15 Km high that forms the rim of an ancient 600 Km impact basin. Unconsolidated rubble from the landslide extends halfway across a conspicuous, 120-Km diameter flat-floored impact crater that lies just inside the basin scarp. Landslides are common geological phenomena on many planetary bodies, including Earth and Mars. The appearance of this landslide on an icy satellite with low-brightness cratered terrain is reminiscent of landslide features that were observed during NASA's Galileo mission on the Jovian satellite Callisto. The fact that the Japetus landslide traveled many kilometers from the basin scarp could indicate that the surface material is very fine-grained and perhaps was fluffed by mechanical forces that allowed the landslide debris to flow extended distances".
|
|
Japetus-PIA06521_modest.jpgThe "dark side" of Japetus61 visiteCaption NASA originale: "This image shows the dark, leading hemisphere of the mysterious moon Iapetus. The dark area is the Cassini region, named for Giovanni Cassini, who discovered the moon in 1672. The diameter of Iapetus is of approx. 1,436 Km (892 miles).
Cassini noted that he was able to see the moon on one side of its orbit around Saturn, but not on the other side. From this, he correctly deduced that one hemisphere must be dark while the other is much brighter".
|
|
Japetus-PIA06646.jpgJapetus: a clear view in the darkness53 visiteNon è certo un frame di qualità eccezionale, ma - finalmente! - si torna a vedere Giapeto, la "Luna Bifronte" (ossìa per metà chiara e luminosa e per metà nera come la pece).
Questo il commento NASA originale:"This view shows one of the huge impact basins on the terminator of Saturn's moon Iapetus and a smaller, but still fairly large, crater near the southern bright-dark boundary. Just visible near the western limb, in the dark territory of Cassini Regio, is the moon's mysterious equatorial ridge. The ridge was discovered in Cassini images and reaches 20 Km (approx. 12 miles) high in places. This view shows principally the leading hemisphere on Iapetus. North is up and tilted 15 degrees to the right. The image was taken with the Cassini spacecraft narrow-angle camera on March 19, 2005, through spectral filters sensitive to wavelengths of infrared light centered at 752 nnmts. The view was acquired at a distance of approximately 1,4 MKM from Iapetus and at a phase angle of 70°. Resolution is 8 Km/pixel".
|
|
Japetus-PIA07000_modest.jpgJapetus' surface composition (organic material?!?)53 visiteCaption NASA originale:"These two color composite images of Saturn's moon Japetus from Cassini's visual and infrared mapping spectrometer were obtained on Dec. 31, 2004, an hour and a half before the New Year, at a distance of 121.000 Km (75.186 miles), with a spatial resolution of about 60 Km (37 miles).
The three colors used in the left mosaic correspond to 1.01, 1.51, and 2 microns, while the right mosaic is comprised of images at 3.0, 3.21, and 4.60 microns. The two images show the vast difference in the composition of the bright and dark regions of Japetus. As one moves from the near infrared 1 to 2 micron spectral region (left image) to the 3 to 5 micron spectral region (right image) the bright, ice-rich region on Japetus turns dark and the dark region rich in organics turns bright".
|
|
Japetus-PIA07002_modest.jpgJapetus' surface composition (organic material?!?)53 visiteCaption NASA originale:"The three colors used in the mosaic correspond to 1.01, 3.21, and 3.80 microns. The different colors represent vastly different surface compositions. The upper bright blue region is rich in water ice, while the lower, dark brown region is composed mainly of a substance rich in organic material. The yellow region consists of a mixture of ice and organics, suggesting a gradual change in composition on the surface. This pattern suggests Iapetus swept up the dark material, which may have come from debris created from meteoritic impacts onto the small, outer satellites of Saturn".
|
|
Japetus-PIA07003_modest.jpgJapetus' surface composition (organic material?!?)62 visiteCaption NASA originale:"The polar water ice is relatively dark at this wavelength, so the ice cap is not seen. The next frame shows carbon dioxide on the surface. The carbon dioxide peaks at mid latitudes and shows less strength at the pole and along the equator (the dark band curving near the left edge of the image). The third frame shows the strength of water absorption on Japetus. The brightest regions are due to water ice near the pole. The grayer areas indicate water bound to minerals on the surface. The color composite shows water as blue, carbon dioxide as green, and non-ice minerals as red".
|
|
| 2245 immagini su 188 pagina(e) |
 |
|
|
|
|
72 | |
|
|
|
|
