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Enceladus satellite of Saturn, discovered by William Herschel. It has a diameter of 500 km, a mass of ~ 1020 kg and a density of ~ 1.2 g / cm3. The semi-major axis measuring 238,000 km, the orbital period of 1.37 days. Its surface, reflecting nearly 100% of the incident sunlight, is the ‘white’ from those of all the planets and the solar system satellites. Until the passage of the two Voyager spacecraft in the early 1980s, the characteristics of this celestial body were little known, apart from the identification of water ice on the surface. Voyager 1 has uncovered that Enceladus orbits in the densest region of East ring of Saturn, while Voyager 2 revealed that despite its small size the satellite has regions that vary from ancient surfaces with many impact craters in newer areas dated about 100 million years.

The Cassini spacecraft in the mid-2000s has acquired additional data that have answered many of the questions opened by the Voyager probes have posed new.

Cassini has made several close flybys in 2005, revealing details of the surface and the environment. In particular, the probe discovered a water-rich plume that rises in the south polar region. This finding, together with the presence of internal heat leakage and few impact craters in the south polar, shows that Enceladus is geologically active today. The moons of the gas giants systems are often trapped in orbital resonances involving the forced libration or orbital eccentricity; the proximity to the mother planet can also induce the satellite heating generated by tidal forces. Enceladus is one of three celestial bodies in the outer solar system (along with Jupiter‘s moon Io and Neptune’s moon Triton) where active eruptions have been observed.

The analysis of the emitted gases suggests that they have been generated from the liquid water beneath the surface. Together with the chemical analysis of the plume, these discoveries have fueled speculation that Enceladus is an important topic of study in the field of astrobiology. It has also been suggested that Enceladus is the source of the East Ring materials.

Enceladus satellite of Saturn, discovered by William Herschel.

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Enceladus satellite of Saturn, discovered by William Herschel.