The water geysers of Enceladus spew the most material when the small moon ventures farthest from Saturn, planetary scientists in the US have found. This discovery confirms a prediction of a theory that says the geysers' strength depends on Saturn's tide.
Discovered by the German-born English astronomer William Herschel in 1789, eight years after he spotted the planet Uranus, Enceladus is the sixth largest of Saturn's 62 known satellites. The small moon is 238,000 km from Saturn's centre, about two-thirds of the distance from the Earth to the Moon. Because Saturn is so massive, though, its gravity forces Enceladus to circle it every 1.37 days.
With a diameter of just 500 km, Enceladus is only one-seventh the size of the Earth's Moon and it lacks the radioactive elements that heat the Earth's core. This makes it an unlikely world for geysers or any other geological activity.
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