The Icy Satellites

General Information

The ESPACE project

Jupiter's satellites

Saturne's satellites

Uranus's satellites

Neptune's satellites

Exploration missions

Work done at ROB

Contact, Info and Links

Saturn's satellites

 The icy satellites  Saturn's satellitesMimas

Mimas is the smallest spherical satellite in the solar system. Its principle characteristic is the Herschel crater, with a diameter of 130 km and that presents a central peak whose base is of about 25 km and that rises 6 km in altitude. Mimas must have nearly been destroyed by the impact.
1)Image of Cassini: Herschel crater(130 km wide)
Distance to Saturn185 520 km
Period of revolution0.94 terrestrial days
Diameter392 km
Mass (Earth=1)0.0000064
Density (water =1)1.20
Compositionice water and silicates
Temperature on the surface-200 °C
The rest of the surface is very cratered. The biggest craters (the ones that have a diameter greater than 15 km) are full of rough materials that probably come from the sliding of consecutive plains at others impact. The surface is so old that even these deposits have craters of impact. (view image 2)

The surface also has a couple a furrows, that are hard to detect with the craters. They could be the proof of an internal activity that goes way back or the consequence of the major impact that created the Herschel crater.
The Cassini probe is equipped of instruments that can take pictures at different wavelength intervals. (for example: in the red, the blue, the green, the U.V., infra-red, or in the visible field). In each of these intervals, the instrument measures the quantity of luminous energy received, that can be translated onto a dark pixel.

Image 1 was obtained in a visible wavelengths of the spectrum and is translated in pixel form that goes from white to black. This image therefore gives us information on the brightness of the surface, so that a human eye could directly see it, but doesn't give any indications on the real colours of the surface. It is a monochromatic image.

Frequent images in fake colours are made: Informations on the brightness of the surface in the blue, red, green channels are combined to obtain colours and add the monochromatic image so that the real brightness in the different zones are respected. It is also possible to combine the informations of tree different channels but to then represent them in the colours blue,red and green to give the human eye information more easily understandable. For example image 3 has been obtained with the canal U.V, green and infra-red.

This image in fake colours reveals the difference between certain zones of the surface. The same analyse has been done on Mimas' other face(image 4) and has also showed some differences. The origin of these differences is still unknown, there are small variations of composition or of texture of the materials of the surface. More particularly the zones around Herschel present a blue colour in the images in fake colours. It could have been non-uniformly ejected materials during the impact.

Internal structure
Mimas' shape has been determined first with the help of the photographs from the probes Voyager 1 et 2 and then with Cassini's. The shape of the satellite is represented by a triaxial ellipsoid. The average diameter is 392 km and the difference between the biggest and the smallest axis is of about 17 km. This difference permits us to establish if a body is differentiated or not, by comparing with theoretical values. In Mimas case, two models of internal structure are possible.
  • Differentiated internal structure : we have a core of rock and a mental of icy water.
  • Homogeneous internal structure: the satellite is composed of a homogeneous mix of icy water and of rock, but the surface could then be porous.
The value of the density permits us to deduce that Mimas contains little rock in comparison with Enceladus. If Mimas has a rock core, the radioactive heating will then be less important than in Enceladus' case. This could explain why Mimas isn't geologically active, even with the even more intense tide forces.
Figures 1 to 4 (credit: JPL/NASA)
2)Aged surface: craters in craters
3)Treatment in fake colours of image 1
4)Treatment of an image in fake colours

Valid XHTML 1.1