Why study Enceladus?

The activity of Saturn's icy satellite Enceladus was one of the big surprises of the Cassini mission to Saturn. The south pole of the 500km diameter moon is unusually hot and a plume of water vapor and tiny ice grains extends to space. Scientists believe that there is liquid water below the icy surface, with chemical conditions favorable for the formation of precursors of live. Enceladus is one of the three bodies in the solar system where water is expected, together with Mars and Jupiter's satellite Europa.

	The ice grains, also called dust, are only 1/1000 of a millimeter in size. They are directly visible as a fine spray in Cassini images, when lit by the sun from behind, ejected as jets from the south polar region of Enceladus.
	The sources of the plume are located on the `Tiger Stripes', four aligned cracks in the ice shell of Enceladus, visible in bluer color in the lower part of the image. The moon itself was discovered by the German/British astronomer Wilhelm Herschel in 1789.
	He could not have picked a better name, since ancient Greeks attributed earth quakes and volcanism to action of the giant Enceladus. In Greek mythology Athena defeated Enceladus in a fight, smashing the island of Sicily on the Giant. There he now lies half buried below the mountain of Aethna as in the scene pictured here in the park of Versailles. He is unable to escape, yet his struggle to do so was believed to shake the earth (Vergil, 3rd book of the Aeneid), thereby explaining the activity of the volcano to ancient Greeks and Romans.
	Those grains that escaped from Enceladus over thousands of years form Saturn's E ring, a huge dust ring that extends outside Saturn's main ring system from about three Saturnian radii (about 60,000 km) out to at least eight Saturnian radii, and probably much further out. Naturally, the E ring is densest near Enceladus. In the this image we see this part of the ring with Enceladus in the center. But the dust grains born at Enceladus slowly migrate outward, away from the moon, due to the action of charged atoms and molecules (the plasma in the Saturnian system) and Saturn's magnetic field, and so they gradually formed the less dense parts of the E ring.
	This is how the artist and scientist Bill Hartmann paints the view from Enceladus over its south polar terrain, with a jet of ejected ice particles and vapor. From the Cassini images obtained over the last two years it became clear that at least the largest jets remain permanently active over this time span, although their strength may be subject to variation, in contrast to the Yellowstone geysers with their short eruptions after longer periods of quiescence.