This is the fourth largest moon of Saturn. In our entire solar system, in terms of size, it ranks 15th. Dione is a little smaller than her larger sister Rhea, whom I described to you some time ago. It is very similar to it in terms of construction and shape of the surface.

Approximately view of Dione taken by Cassini on June 7, 2005

By NASA / JPL / SSI / Gordan Ugarkovic link [Public domain]

This satellite was discovered by Giovanni Cassini in March 1684. Dione orbits Saturn in an orbit with a diameter of about 754,000 kilometers. The distance of the satellite from its planet is similar to that between Earth and the Moon. However, due to the much larger mass of Saturn and its enormous gravity, Dione circles its planet in 2 days and 18 hours. Thus, it moves much faster in its orbit than our Moon. This satellite is one of the few moons that share their orbit with others. In the case of Dione, these are two moons, called Trojans. They circulate before and behind Dione and are small objects with a small diameter. The larger one is the Helene moon with a diameter of 43 kilometers, and the smaller one is Polydeuces with a diameter of only 3.5 kilometers.

Dione, Earth & Moon size comparison

Earth image: By NASA, Lunar image: By Gregory H. Revera, Moon Dione image: By NASA/JPL/Space Science Institute link [Public domain images and CC BY-SA 3.0 license for moon image]

Comparison of Earth, our Moon and Dione. As you can see it is quite a small world. The moon, built of ice, has a diameter of 1122 kilometers, while its density is about 1.48 kg / dm3. Dione is therefore mainly made of water ice and partly of rock. The satellite kernel probably forms silicates. Scientists assume that the moon has a subsurface ocean of water, but this has not yet been confirmed. This satellite has a very rare atmosphere, built mainly of oxygen, coming from the reaction between the magnetosphere of Saturn and the shell of the satellite, made of ice. However, this atmosphere is millions of times rarer than our earthly one.

Dione - Evander basin

By NASA/Jet Propulsion Lab - Caltech/Space Science Institute link [Public domain]

The Dione area is mainly craters. They have similar shapes to other craters on typically ice moons. They are significantly different from those on our Moon and other rocky globes. The sizes of the largest ones on Dione exceed the diameter of 100 km. Most, however, are openings below 30 kilometers in diameter. The first photographs of Dione were made by the Voyager 1 spacecraft, but most of the information was provided by the Cassini spacecraft. The closest to the satellite flew in 2011, when it approached the surface of Dione at a distance of only 99 kilometers!

Greetings to lovers of Astronomy!

Sources:

Dione (moon)
Moons of Saturn
List of natural satellites
and my knowledge...

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