Saturn: the "Ringed Beauty" and His Moons
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Hyperion-anagliph-PIA06244.jpgStereo-Hyperion! (from about 176.000 Km)67 visiteCaption NASA originale:"Saturn's moon Hyperion pops into view in this stereo anaglyph (or 3D view) created from Cassini images. Images taken from slightly different viewing angles allow construction of such stereo views, which are helpful in interpreting the moon's irregular shape.
Hyperion's unusual dimensions are 164 by 130 by 107 Km (such as 102 by 81 by 66 miles).
Craters are visible on the moon's surface down to the limit of resolution in this image, about 1 Km (0,6 mile) per pixel. The fresh appearance of most of these craters, combined with their high spatial density, makes Hyperion look something like a sponge. The moon's spongy-looking exterior is an interesting coincidence, as Hyperion's density seems to indicate that it is porous and much of its interior is filled with voids.
Dark material is concentrated in the bottoms of many craters visible here, perhaps resulting from the down slope movement of material, combined with sublimation of brighter ice".
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Hyperion.jpgHyperion: the "sponge-like" moon80 visiteDa "NASA - Picture of the Day" del 26 Luglio 2005:"Recent HR images from the Cassini spacecraft orbiting Saturn show Hyperion to be an even stranger place than thought before. Previously, it was known that the length of a day on Hyperion is unpredictable. The moon's highly elliptical orbit around Saturn, its highly non-spherical shape and its locked 4:3 orbital resonance with Titan torque Hyperion around so much it is hard to predict when the Sun will rise next. The newly imaged craters on the unusually coarse surface are surely the result of impacts, but for some reason have dark centers. The low density of Hyperion indicates it might even be a spelunker's paradise, riddled with tremendous caverns".
Nota: la prima volta che la NASA dice espressamente che i crateri visibili sono "surely the result of impacts". A parte l'ovvia assurdit di una simile certezza (irraggiungibile per definizione), molti Ricercatori credono che gli impatti ebbero un ruolo MARGINALE nella definizione di questo ed altri mondi...
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INORBIT-61686main_soi2-516.jpgOrbital Insertion Complete - In orbit around Saturn (1)82 visitenessun commento
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INORBIT2-61690main_soi4-516.jpgOrbital Insertion Complete - In orbit around Saturn (2)84 visitenessun commento
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INORBIT3-61692main_soi5-516.jpgOrbital Insertion Complete - In orbit around Saturn (3)70 visitenessun commento
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INORBIT4-61694main_soi6-516.jpgOrbital Insertion Complete - In orbit around Saturn (4)69 visitenessun commento
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Iapetus from Voyager 2.jpgJapetus from Voyager 270 visitenessun commento
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JAPETUS from 3.000.000 Km.jpgJapetus from Cassini-Huygens - approx. 3.000.000 Km away69 visiteIapetus Data and Statistics
Discovered by = Giovanni Domenico Cassini
Date of discovery = 1671
Mass (kg) = 1.88e+21
Mass (Earth = 1) = 3.1459e-04
Equatorial radius = 730 Km
Equatorial radius (Earth = 1) = 1.1446e-01
Mean density (gm/cm^3) = 1.21
Mean distance from Saturn = 3.561.300 Km
Rotational period (days) = 79.33018
Orbital period (days) = 79,33018
Mean orbital velocity (km/sec) = 3,27
Orbital inclination (degrees) = 14,72
Escape velocity (km/sec) = 0,586
Visual geometric albedo = 0,2
Magnitude (Vo) = 10,2-11,9
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Janus and Enceladus-PIA08207.jpgJanus and Enceladus65 visiteCaption originale:"Wrinkled and cracked Enceladus hangs in the distance as the pitted ring moon Janus, at right, rounds the outer edge of the F-Ring. Enceladus is remarkable for its actively venting South Polar Region, while Janus is known for its orbital swap with the moon Epimetheus. The bright core of the F-Ring is perhaps 50 Km wide and contains numerous clumps and kinks.
Dimmer, flanking ringlets on either side of the core wind into a tight spiral structure, discovered in Cassini images.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 21, 2006, at a distance of approx. 565.000 Km (such as about 351.000 miles) from Janus; 702.000 Km (about 436.000 miles) from Enceladus and 530.000 Km (approx. 329.000 miles) from Saturn.
Image scale is roughly 3 Km (about 2 miles) per pixel on Janus and approx. 4 Km (a little more than 2 miles) per pixel on Enceladus".
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Janus and Epimetheus-PIA08170.jpgJanus, Epimetheus and the "Orbital Switch"76 visiteCaption NASA originale:"In their orbital ballet, Janus and Epimetheus swap positions every four years - one moon moving closer to Saturn, the other moving farther away. The two recently changed positions (the swap occurring on January 21, 2006), and Janus will remain the innermost of the pair until 2010, when they will switch positions again.
Although the moons appear to be close in the image, they are not. Janus is about 40.000 Km (appx. 25.000 miles) farther away from Cassini than Epimetheus (at left) in this view. In fact, even when they are at their closest, tugging at each other and swapping orbital positions, they are never closer than about 15.000 Km (about 9.000 miles).
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 20, 2006 at a distance of approx. 452.000 Km(about 281.000 miles) from Epimetheus and 492.000 Km (about 306,000 miles) from Janus. The image scale is about 3 Km (appx. 2 miles) per pixel on both moons".
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Janus from Voyager 2.jpgJanus from Voyager 282 visiteGiano, un'altra (fra le tante...) Lune Minori di Saturno.
Ma Voi sapevate chi era Giano, nella Mitologia Romana? Era - ovviamente - una Divinit il cui compito (decisamente delicato) era quello di vegliare sulle "Porte del Paradiso".
Il "Guardiano della Dimora degli Dei", insomma.
Da non dimenticare, infine, il fatto che Gennaio proprio il mese dell'anno che deve a Giano (Janus) il suo nome.
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Janus&Epimetheus-PIA07699.jpgHigh-Phase in the Darkness: Janus and Epimetheus64 visiteThis close pairing of Janus and Epimetheus shows the 2 moons at "high phase," meaning that only a thin sliver of sunlit terrain is visible on each moon. Portions of each are also lit feebly by reflected light from Saturn.
Janus (181 Km, or about 113 miles across) is at top and Epimetheus (116 Km, or about 72 miles across) is below.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 25, 2005, at a distance of approx. 479.000 Km(roughly 298.000 miles) from Janus and about 455,000 Km (roughly 283.000 miles) from Epimetheus. The image scale is about 3 Km (approx 2 miles) per pixel on both moons.
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