| Piú viste - Saturn: the "Ringed Beauty" and His Moons |
Rhea-N00029812.jpgRhea and the Rings, from about 2MKM56 visitenessun commento
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Enceladus-N00030034.jpgEnceladus, from approx. 51.000 Km56 visiteUna sequenza di frames che ci mostrano il rapido passaggio ravvicinato (---> fly-by) della Sonda Cassini accanto al corpo celeste più luminoso dell'intero Sistema Solare. Molto suggestive sono queste prime immagini del bordo (---> limb) di Encelado, ma estremamente interessanti, non solo dal punto di vista scientifico, sono i frames che ci mostrano la superficie di questa gelida luna Saturniana.
Ma andiamo con calma...
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Enceladus-N00030040.jpgEnceladus, from approx. 46.000 Km56 visiteGli immensi crepacci e le striature (la cui origine è ancora ben lungi dall'essere anche solo immaginata) che caratterizzano tutta la superficie di Encelado sono molto ben definiti in questa veduta della "luna di neve", ripresa da una distanza di circa 46.000 Km.
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Enceladus-N00030047.jpgEnceladus, from approx. 43.000 Km56 visitenessun commento
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Enceladus-N00030055.jpgEnceladus, from approx. 28.000 Km56 visiteAncora un'immagine del bordo di Encelado la quale ci consente di apprezzare, attraverso le ombre che definiscono i rilievi più significativi, una fittissima rete di canyons ed un quantitativo di crateri da impatto non particolarmente elevato (un chiaro segno, quest'ultimo, di una recente - in senso geologico... - ancorchè parziale 'ridefinizione' della superficie di questo corpo celeste).
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Enceladus-N00030060.jpgEnceladus, from approx. 26.000 Km56 visitenessun commento
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Enceladus-N00030108.jpgEnceladus, from approx. 5.000 Km56 visitenessun commento
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Tethys-N00030191.jpgTethys from approx. 197.000 Km56 visiteDa una luna all'altra, viaggiando sulle "autostrade" che vengono disegnate dalle orbite della Sonda Cassini intorno a Saturno, così come si passa da una città all'altra, sulle autostrade del nostro Pianeta. Dopo Encelado, avvicinata, sfiorata e superata, adesso è la volta di Teti, le cui caratteristiche superficiali - come già potete vedere molto bene in questo frame - sono decisamente diverse: non vediamo canyons, gole e canali, infatti, ma solo un terreno butterato da migliaia e migliaia di crateri da impatto. Un mondo lontano ma, in fondo, piuttosto simile alla nostra Luna e, da questo punto di vista, forse, un mondo molto più familiare...
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Enceladus-PIA06207.jpgEnceladus' "crispy & fractured" surface56 visite(...) The rims and interiors of many craters seem to be sliced by a pervasive system of narrow, parallel grooves into slabs or lanes that typically are about 1 Km in width. The widely varied appearances of fractures in this region attest to the fact that the surface of Enceladus has been shaped by a long history of intense tectonic activity. The oldest fractures are characterized by a soft, muted appearance and are overprinted by numerous, superimposed impact craters. More recent fractures exhibit topographic relief that is relatively "crisp" in appearance, and they appear to slice through pre-existing impact craters and older fractures. On the right side of the image is a conspicuous and twisted network of ridges and troughs forming a distinct tectonic region on Enceladus. The paucity of craters and the sharp appearance of the topography in this area indicate that this is a relatively young terrain on Enceladus. One possibility is that the walls of the fractures expose outcrops of solid ice, or ice with different grain-sizes compared to powdery surface materials that blanket flat-lying surfaces. It is also possible that the color identifies some compositional difference between buried ice and ice at the surface. The distinct coloration of "youthful" fracture walls are nearly absent in the oldest fractures. This is consistent with the possibility that the older fractures are covered with a drape of particulate material which mantles nearly all the oldest features on the satellite.
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Dione-N00030564.jpgA "hat-trick" of Moons!56 visiteAncora un'immagine spettacolare che ci mostra, questa volta, addirittura una "tripletta" di lune Saturniane. Le caratteristiche superficiali ci aiutano a riconoscerne almeno due, cioè quelle più grandi ed - apparentemente - più vicine (diremmo che si tratti di Dione e Rhea). Sapreste individuare la terza?
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Tethys in natural colors-V2.jpgTethys in natural colors56 visiteCaption NASA originale:"Voyager 2 obtained this image of Tethys on Aug. 25, when the spacecraft was 594.000 Km from this moon of Saturn. This photograph was compiled from images taken through the violet, clear and green filters of Voyager's narrow-angle camera. Tethys shows two distinct types of terrain - bright, densely cratered regions and relatively dark, lightly cratered planes that extend in a broad belt across the satellite. The densely cratered terrain is believed to be part of the ancient crust of the satellite; the lightly cratered planes are thought to have been formed later by internal processes. Also clearly seen is a trough that runs parallel to the terminator (the day-night boundary, seen at right). This trough is an extension of the huge canyon system that also Voyager 1 saw and photographed . This system extends nearly 2/3rds the distance around Tethys".
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Dione-PIA06611.jpgStreaks on Dione56 visiteCaption NASA originale:"Wispy streaks curl over the horizon on Saturn's moon Dione, caught here in a distant view from Cassini. The streaks were first revealed by NASA's Voyager spacecraft and subsequently were shown by Cassini to be an immense system of linear fractures in the moon's surface. The image was taken with the Cassini spacecraft narrow-angle camera using a filter sensitive to wavelengths of ultraviolet light centered at 338 nnmts. The image was acquired on Feb. 18, 2005, at a distance of approximately 1,3 MKM from Dione and at a phase angle of 118°. The image scale is 8 Km per pixel".
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