| Distance to Saturn | 294 660 km |
| Period of revolution | 1.89 terrestrial days |
| Diameter | 1060 km |
| Mass (Earth=1) | 0.0001041 |
| Density (water =1) | 1 |
| Composition | icy water predominantly and rock |
| Albedo | 0,80 |
| Temperature on the surface | -188 °C |
|
- The falts :
The Ithaca Chasma structure takes about 5 to 10 % of Tethys' surface area. It's a system of Canyons of about 100 km wide
by 4 km deep at some points and that travels more than 1000 km from the North to the South.
These canyons are nearly concentric around the Odyssey crater. The edges of these canyons have been heavily damaged
by more recent impacts than the ones that have created the cratered areas. The canyons are therefore very old but younger
than the heavily cratered zones. A big crater, Telemachus, even covers this same canyon. This crater is therefore relatively recent.
(view images 1,5 and 7)
|
Other smaller faults are also more visible on more or less the whole surface.
To explain the presence of this flaw, we have two possibilities: either they are the consequence
of the Odyssey impact, or they have appeared during an expansion of the whole satellite
due to the cooling that has followed its creation.
- The plains :
They actually aren't really plains but regions, less cratered, located at the antipodes of Odyssey
(view image 5). These regions should show the trail of
the seismic activity following to the impact in the form of a mountain range and fractures
(like the region located at the antipodes of the Caloris basin on Mercury). But it is
possible that this region has been through a renewal of its surface that would have cleared the trails.
A flow of material in direction of the surface would have been possible by a weakening of the surface layer because of the impact.
Other important craters are also noticeable on
Cassini's images
: The Penelope and Melanthius craters
(view image 6).
This one does not have a central peak but a small mountain range
(view image 5).
Changing the images like we have done with
Mimas
has permitted us to obtain the images in artificial colours that show that the materials at the surface
are slightly different in composition and texture. This difference on the images 3 and 4 in artificial colours
coincide with the variations in
albedo that we can observe on image 1.
Internal structure and composition:
Tethys' shape has been determined with the help of photographs from the probes
Voyager 1 and 2.
The shape of the satellite is represented at best by a tri-axial ellipsoid. The average diameter is then of 1060 km and
the difference between the biggest and the smallest axis is of about 10 km. This difference allows us to establish whether a body is differentiated or not,
in comparison with theoretical values. In Tethys' case, this would indicate a concentration of mass in the centre, in the core of rock.
But since Tethys' density is close by to the one of icy water, this core must be small (10 % of the total mass if
we consider that Tethys doesn't present any porosity). The core is covered by a mantle of icy water.
Figures 1 to 7(credit: JPL/NASA)
2)Odyssey crater (at the top) Melanthius crater (at the bottom)
3) Odyssey crater
4) black and white images and in artificial colours of the satellites face turned toward Saturn
Penelope crater on the left, Melanthius crater at the top
and flattening of the limb at the top right
5) black and white and in artificial colours images:
Ithaca Chasma and Telemachus crater at the top, Penelope crater and plains at the bottom
6)Melanthius crater
7) Ithaca Chasma: details
