[Rand]

Riguardo a Phoebe su Wikipedia c'è scritto che grazie ai nuovi dati forniti da Cassini:

However, images from the Cassini-Huygens space probe indicate that Phoebe's craters show a considerable variation in brightness, which indicate the presence of large quantities of ice below a relatively thin blanket of dark surface deposits some 300 to 500 metres (980 to 1,600 feet) thick. In addition, quantities of carbon dioxide have been detected on the surface, a finding which has never been replicated on an asteroid. It is estimated that Phoebe is about 50% rock, as opposed to the 35% or so that typifies Saturn's inner moons. For these reasons, scientists are coming to believe that Phoebe is in fact a captured Centaur, one of a number of icy planetoids from the Kuiper belt that orbit the Sun between Jupiter and Neptune[11][12]. Phoebe is the first such object to be imaged as anything other than a dot.

gli scienziati credono che sia un asteroide proveniente dalla fascia di Kuiper catturato da Saturno. Questa è una delle foto fatte:



un miglioramento notevole rispetto a quelle di Voyager 2:



Riguardo a Giapeto e ai suoi due colori:

NASA scientists now believe that the dark material may be lag (residue) from the sublimation (evaporation) of water ice on the surface of Iapetus,[13] possibly darkened further upon exposure to sunlight. Because of its slow rotation of 79 days (equal to its revolution and the longest in the Saturnian system), Iapetus likely had the warmest daytime surface temperature and coldest nighttime temperature in the Saturnian system even before the development of the color contrast; near the equator, heat absorption by the dark material results in a daytime temperatures of 128 K in the dark Cassini Regio compared to 113 K in the bright Roncevaux Terra.[14] The difference in temperature means that ice preferentially sublimates from Cassini, and precipitates in Roncevaux and especially at the even colder poles. Over geologic time scales, this would further darken Cassini and brighten Roncevaux and the poles, with all exposed ice being lost from Cassini, creating a thermal positive feedback for ever greater contrast in albedo. It is estimated that, at current temperatures, over one thousand million years Cassini would lose about 20 meters of ice to sublimation, while Roncevaux would lose only 10 centimeters, not considering the ice transferred from the dark regions.[14] This model explains the distribution of light and dark areas, the absence of shades of grey, and the thinness of the dark material covering Cassini.

(Preso tutto da Wikipedia seguendo i link da questo articolo)