Dione

Dione, satellite of Saturn

Dione was discovered in 1672 by Giovanni Domenico Cassini.
Dione mainly consists of water in the form of ice; but, in view of its density higher than that of the other moons of Saturn (except Titan, whose density is increased by the gravitational compression), it contains probably a rather important quantity of denser matter, such as rocks of silicates.
The sights taken in 500 kilometers of distance, allow to confirm that the observed white volutes are gigantic cliffs of ice which covering Dione.
Dione is in synchronous rotation with Saturn, it makes a revolution on herself for a rotation around Saturn.

Image: Dione, one of sixty moons of Saturn

Dione	Characteristics

Discovered date	March,21 1684
Discovered by	Giovanni Domenico Cassini
Mean radius	561.4 km
Mass	1.096 x 10²¹ kg
Mean density	1 478 g/m³
Semi-major axis	377 396 km
Eccentricity	0.0022
Average orbital speed	10.027 km/s
Escape velocity	0.51 m/s
Orbital period	2.736915 d
Inclination (Saturn's equator)	0.019°
Temperature	≈87 K
Rotation period	Synchronous

The surface of Dione

The surface of Dione was modeled by it a cryovolcanic intense activity as its sister Enceladus, the other satellite of Saturn. Enceladus is younger than Dione, and its activity is thus more recent, more intense. This tectonic activity is certainly the reason for which seem these today streak whites.
The surface of Dione certainly knew too the same scars, but the strong activity meteoritic to which one it was subjected erased tracks.
The peculiarity of Dione is that its two faces are dissimilar, as Rhea. In the past, it is nevertheless the face defers, with regard to its movement on the orbit, which knows impacts bigger than those of the face before (100 km in diameter, against 30 km for the face before). This oddity can be of for a violent impact which would have knocked down Dione on its orbit.

The simulations showed, considering the size and considering the mass of the satellite, that an impact 35 km in diameter would have been able to be sufficient to make this reversal. Dione possesses several bigger impacts than it, it was able to be so knocked down several times. The current state of the surface shows us that Dione did not change position on its orbit since several billion years. The albedo of Dione decreases as we move of before in front of the back face.
It is probably of in a more important layer of deposits meteoritic, what confirms the theory according to which Dione is blocked in synchronous rotation since billions of years.

Image: The surface of Dione was modeled by it a cryovolcanic intense activity.