Tethys
Saturn III
Tethys Facts
- Tethys is the ninth of Saturn's known satellites:
- distance from Saturn: 294,660 km
- diameter: 1060 km
- mass: 7.55e20 kg
- Pronounced "TEE this"
- In Greek mythology Tethys was a Titaness
and sea goddess who was both sister and wife of Oceanus.
- Discovered by Cassini in 1684.
- Tethys's 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
(picture 2). 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's 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's circumference
(picture 1, above).
- 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's
Lagrange points
(60 degrees ahead and behind Tethys in the same orbit).
Pictures
- (above) Tethys
250k gif;
33k gif;
212k gif;
18k jpg
Tethys, moon of Saturn, showing large impact crater
144k gif
- Color image of Tethys (showing little color)
45k jpg
- Another color composite of Tethys
101k gif
More about Tethys
Telesto
- Telesto (Saturn XIII) is the tenth of Saturn's known satellites:
- distance from Saturn: 294,660 km
- diameter: 29 km (34 x 28 x 36)
a.k.a. 1980 S 13
- Pronounced "tah LESS toh".
- In Greek mythology Telesto was a daughter of Oceanus and Tethys.
- Discovered by Smith, Reitsema, Larson and Fountain in 1980
from ground-based observations.
- Telesto is in Tethys's leading
Lagrange point.
Calypso
- Calypso (Saturn XIV) is the eleventh of Saturn's known satellites:
- distance from Saturn: 294,660 km
- diameter: 26 km (34 x 22 x 22)
a.k.a. 1980 S 25
- Pronounced "ka LIP so".
- In Greek mythology Calypso was a sea nymph who delayed
Odysseus on her island for seven years.
- Discovered by Pascu, Smith and others in 1980
from ground-based observations with prototype cameras
destined for the HST.
- Calypso is in Tethys's trailing
Lagrange point.
- Calypso and Telesto are among the
smallest moons in the solar system.
Pictures
- Note: the pictures of Calypso on the Voyager CD-ROMs are
mislabeled; they're really
pictures of Prometheus.
Similarly, the pictures labeled Telesto are really
pictures of Pandora.
The only real pictures of Calypso and Telesto are the ones above.
- montage of Helene, Epimetheus, Calypso, Janus, Telesto, Pandora and Prometheus
15k jpg
More about Telesto and Calypso
Open Issues
- How did Telesto and Calypso end up in the Lagrange points? Are they
remnants of a collision?
... Saturn
... Enceladus
... Tethys / Telesto / Calypso
... Dione
...
Bill Arnett; last updated:
1995 February 16