Rhea:
| Distance to Saturn | 527 040 km |
| Period of revolution | 4.52 terrestrial days |
| Diameter | 1530 km |
| Mass (Earth=1) | 0.0004168 |
| Density (water =1) | 1.33 |
| Composition | Icy water and silicates |
| Albedo | 0.60 |
| Temperature of surface | -200 °C |
|
Rhea is Saturn's second largest satellite and its fifth furthest away.
Its surface has common with
Dione.
's.
Rheas surface has several characteristics that will tell us its age.
The biggest crater is named Tarawa and has a diameter of 360km.
Tarawa is a very old crater since it has smaller ones inside it.
Another big crater is distinguishable by its shiny mark in a star shape
that comes from the impact of materials that were ejected.
These materials are still shiny, it is a more recent crater than the others.
(view images 1)
|
The
Cassini probe
has permitted the photographing in detail of its surface, and to obtain images in artificial colours
that clearly show the difference between some regions of the surface. (view page on
Mimas for the explanation
on the images in fake colour).
image 2 shows us a difference between
the Northern and the Southern hemisphere while
image 3 permits to point out the shiny trails on the surface.
These trails would be the proof of the existence of tectonics in the past.
Internal structure and composition:
The low density of Rhea tells us that this satellite's mass is composed 75 %
of ice water and 25 % of rocks. Iron could also be present but then in very small quantity.
Knowing this information, it very unlikely that the structure is separated in a metallic core, a mantle of rock
and an external layer of ice since the quantity of iron is small.
It is more logical to consider a core of rock with an icy mantle or a non-differentiated structure.
Indeed the measure of the moment of inertia (0.391) indicates us that the body is
only a bit differentiated or even homogeneous.
Figures 1 to 3(credit: JPL/NASA)
1) Tarawa crater (diameter of 360 km)
and shiny trails due to a crater
2) Contrast North - South in the image in fake colours
3) The shiny furrows are put in evidence in the image in fake colours
