Enceladus (Saturn II)
Enceladus ("en SEL a dus") is the eighth of Saturn's known satellites.
orbit:238,020 km from Saturn
Discovered in:1789 by Herschel.
Enceladus has the highest albedo (>0.9) of any body in the solar system. Its surface is dominated by fresh, clean ice.
At least five different types of terrain have been identified on Enceladus. In addition to craters there are smooth plains and extensive linear cracks and ridges. At least some of the surface is relatively young, probably less than 100 million years.
This means that Enceladus must have been active until very recently (and perhaps is still active today). Perhaps some sort of "water volcanism" is at work.
Enceladus is much too small to be heated by the decay of radioactive material in its interior at present (the heat would have all dissipated long ago).
Enceladus is locked in a 1:2 resonance with Dione (similar to the situation between Io and Europa). This may provide a heating mechanism but it is probably insufficient to melt water ice. Enceladus may therefore be composed of some low-melting point material rather than pure water.
Enceladus may be the source of the material in Saturn's tenuous E ring. And since the material cannot persist in the ring for more than a few thousand years, it may be due to very recent activity on Enceladus. Another possibility, though, is that the rings are maintained by high-velocity collisions between dust particles and the various moons.
Tethys (Saturn III)
Tethys ( "TEE this" ) is the ninth of Saturn's known satellites.
orbit:294,660 km from Saturn
Discovered by:Cassini in 1684.
Tethys' low density indicates that it is almost completely composed of water ice, similar to Dione and Rhea.
The western hemisphere is dominated by a huge impact crater, called Odysseus, whose 400 km diameter is nearly 2/5 of that of Tethys itself. That such an impact didn't shatter Tethys completely indicates that it may have been liquid or at least not very solid at the time. The crater is now quite flat (or more precisely, it conforms to Tethys' spherical shape), like the craters on Callisto, without the high ring mountains and central peaks commonly seen on the Moon and Mercury
The second major feature seen on Tethys is a huge valley (called Ithaca Chasma) 100 km wide and 3 to 5 km deep which runs 2000 km or 3/4 of the way around Tethys' circumference.
Clearly then, Tethys has not always been frozen solid. At some point in its past it was probably liquid. The impact craters from that era have been smoothed out. As it froze and expanded, the surface must have cracked to accommodate the extra volume producing Ithaca Chasma. The smaller impact craters we see today are more recent.
There are no albedo features on Tethys as there are on Rhea and Dione.
Telesto and Calypso orbit in Tethys' Lagrange points (60 degrees ahead and behind Tethys in the same orbit).
Telesto (Saturn XIII)
Telesto ("tah LESS toh") is the tenth of Saturn's known satellites.
orbit: 294,660 km from Saturn
diameter:29 km (34 x 28 x 36)
Discovered by:Smith, Reitsema, Larson and Fountain in 1980 from ground-based observations.
Telesto is in Tethys' leading Lagrange point.
Calypso (Saturn XIV)
Calypso ("ka LIP so") is the eleventh of Saturn's known satellites.
orbit:294,660 km from Saturn
diameter:26 km (34 x 22 x 22)
Discovered by:Pascu, Seidelmann, Baum and Currie in 1980 from ground-based observations with prototype cameras destined for the HST.
Calypso is in Tethys' trailing Lagrange point.
Calypso and Telesto are among the smallest moons in the solar system.
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Last Modified : 5 Sep. 2001
Created By#C0115361 Team