| Piú viste - Saturn: the "Ringed Beauty" and His Moons |
Dione-N00028850.jpgDione and Rhea (4)57 visitenessun commento
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Rhea-N00028939.jpgRhea (from approx. 2,5 MKM) and Tethys57 visiteUn'altra immagine del "Carosello Planetario" costituito dalle Lune di Saturno che si inseguono e si incrociano, davanti agli occhi di Cassini. Forse ci sbagliamo, perchè - in fondo - viviamo in un mondo cui le "cose che interessano" sono altre... Tuttavia noi crediamo che un simile spettacolo riuscirebbe ad interessare ed affascinare chiunque!
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Mimas-PIA06591.jpg"Phase-locked" Mimas!57 visiteCaption NASA originale:"Cassini's ability to remain precisely and steadily pointed at targets, such as Saturn's moon Mimas (seen here) yields sharp images despite the relatively high speed at which the spacecraft moves.
Cassini was traveling at more than 13 Km per second when it acquired this view, which shows crisp detail on Mimas against the backdrop of Saturn's Northern Hemisphere. Shadows of the icy rings stretch across the atmosphere and appear to be blurred because of the spacecraft motion.
The part of Mimas visible here always faces away from Saturn as the moon orbits the Gas Giant. In scientific language (jargon...), Mimas is said to be "phase-locked".
The image has been rotated so that North on Mimas (and Saturn) is up. This view was obtained with the Cassini spacecraft narrow angle camera on Jan. 18, 2005, at a distance of approx. 1,25 MKM from Mimas and at a phase angle of 114°. The image was taken using filters sensitive to wavelengths of infrared and polarized light. Res. is 7 Km/pixel".
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Japetus-A-The-Wall-Mosaic-l.jpgThe "Wall" of Japetus57 visiteEffettivamente la configurazione esteriore della superficie di Giapeto non ci è proprio possibile definirla "convenzionale": in questa immagine ripresa dalla Sonda Cassini possiamo vedere un interessante rilievo superficiale che il Prof. Hoagland ha, secondo noi correttamente, definito "Wall": un muro.
Ora andiamo a vedere - con il prossimo frame - un detail mgnf di questo "muro"...
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Epimetheus-N00028963.jpgEpimetheus and a 'string of ring'57 visiteUn piccolo calambour per celebrare questa immagine, certo non perfetta, ma comunque molto suggestiva, della shepherd-moon Epimetheus che brilla accanto alla porzione più esterna degli Anelli di Saturno, visti esattamente di profilo. Notate in particolare come i "nodi" degli Anelli (ossìa quelle loro irregolarità che alla NASA sono chiamate "clumps"--->lett. blocchi/gruppi) in frames come questo si possono vedere molto bene: guardate in alto, in prossimità della fine della 'striscia di luce'.
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Phoebe-2-PIA06117.jpgPhoebe: names, features and details57 visitevedi il commento al frame che precede
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Saturn-PIA06196.jpgGravitational Anomalies and Interferences57 visiteIn fondo, per quanto ne sappiamo, i Fenomeni Transitori non sono una prerogativa unica della superficie dei pianeti e non si manifestano solamente attraverso 'outgassing', 'annebbiamenti' e/o fenomeni luminosi! Anche i fenomeni gravitazionali possono essere transitori, allorchè ci si trovi in un ambiente - per così dire - "affollato" da corpi celesti, quale può essere un'area di confine di uno degli Anelli di Saturno. Comunque eccoVi una parte della Caption NASA originale al riguardo:"Images taken of Saturn's rings by Cassini immediately after it entered orbit around Saturn have turned up circumstantial evidence that an unseen moon may be orbiting dead center in the narrow Keeler Gap in Saturn's outer A-Ring. Several faint discontinuities, or spikes, in the outer gap edge have been found in 2 narrow-angle camera images of the illuminated side of the Rings. These features are similar to the spikes protruding inward from the core of the F-Ring during Prometheus's passages and it is likely that the features are caused by the passages of a yet-unseen moonlet on an eccentric orbit within the Keeler gap".
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Enceladus-PIA06597.jpgEnceladus and Tethys57 visiteCaption NASA originale:"In this unusual view, Cassini captured two icy moons of Saturn, Tethys and Enceladus, in a single narrow-angle frame. Little detail is visible on the surface of bright Enceladus, but battered Tethys shows many craters and the huge canyon system, Ithaca Chasma. Tethys has a diameter of 1.071 Km (approx. 665 miles) across, while Enceladus is 505 Km (approx. 314 miles) across.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 29, 2005, at a distance of approx. 3,7 MKM (approx. 2,3 MMs) from Tethys and 3,5 MKM (approx. 2,2 MMs) from Enceladus. Resolution in the original image was 22 Km (approx. 14 miles) per pixel on Tethys and 21 Km (approx. 13 miles) per pixel on Enceladus. The image has been contrast-enhanced and magnified by a factor of two to aid visibility".
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Dione-PIA06199.jpgDione and Rhea: full sequence of their "dance"57 visiteCaption NASA originale:"Rhea (1.528 Km across) is larger than Dione (1.118 Km), but also is farther away as seen here, which explains why the two moons appear to be roughly the same angular size.
The view shows principally the anti-Saturn side of Dione, and the Saturn-facing side of far-off Rhea.
The images in this mosaic were taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 20, 2005, at a distance of approximately 1,5 MKM (approx. 900.000 miles) from Dione and about 2,3 MKM (approx. 1,4 MMs) from Rhea.
The image scale is approximately 9 Km per pixel on Dione and 14 Km per pixel on Rhea".
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Enceladus-N00030097.jpgEnceladus, from approx. 12.000 Km57 visiteAncora un grande e tortuoso crack della superficie di questa luna che, non più nè meno di Giapeto o Mimas, ci mostra, a mano a mano che ci avviciniamo, un volto capace di suscitare dei grandi interessi e che fa nascere infinite curiosità.
Perchè Encelado è così luminosa?
Che cosa è successo alla superficie di Encelado, e quando?
Proveremo un landing anche su Encelado, in futuro?!?...
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Enceladus-N00030103.jpgEnceladus, from approx. 6.000 Km57 visitenessun commento
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Enceladus-PIA06206_modest.jpgEnceladus (close-up)57 visiteCaption NASA originale:"Fractures are nearly ubiquitous in this terrain, cutting across each other and across impact craters. Scientists can use the relationships between different features to determine the order in which they formed, thereby unraveling the moon's past. For example, almost all the craters in this mosaic have fractures running through their rims and floors, indicating that the craters formed first. This means that Enceladus has been geologically active relatively recently, especially compared to some of its neighbors in the Saturn system. There is an impressive variety of fractures visible here--from the wide east-west rifts near the upper left of the mosaic to the very fine north-south fractures in the center (which are approximately 100 to 400 meters). Due to the complexity of this terrain, the task of unraveling Enceladus' history promises to be a worthy challenge for planetary scientists".
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