The moon is covered in snaking ridges, chasms and scratches, which probably means that the moon has been repeatedly squeezed and stretched.
Cassini passed within 1200 kilometres of Enceladus on Thursday, taking detailed pictures of its surface, resolving details as tiny as 60 metres across. The landscape revealed is remarkably complicated for such a small moon – only 500 kilometres across.
“Enceladus is a geologist’s paradise,” says William McKinnon of Washington University in St. Louis, US. “It has endless sets of closely-spaced fractures and faults.” He adds there are also blocks of high terrain and a variety of rifts.
This is all evidence of a tumultuous past, according to Paul Schenk of the Lunar and Planetary Institute in Houston, US. “It has been pulled, stretched and compressed in multiple episodes of deformation and relaxation.” The gravity of Saturn and another moon, Dione, are probably combining to disturb the interior of Enceladus, causing these upheavals, he says.
The same processes may be destroying old craters, heating the surface so that it slowly slumps – even causing floods of icy lava. “I’m betting that liquid ammonia-water is involved,” says McKinnon. He also points out what seem to be volcanic ice ridges.
And Enceladus’s bright surface suggests there may be even more energetic volcanism at work. It is the brightest body in the solar system, so close to pure white that it must be covered in fresh ice – or snow – fired out of ice geysers. These geysers might blast some of that snow into orbit around Saturn, forming the planet’s tenuous E ring, suggest scientists. They are looking out for volcanic plumes on the moon’s horizon, where they would be easiest to spot against the inky blackness of space.