麻豆传媒

Saturn鈥檚 small snow-white moon, Enceladus, has revealed a turbulent past, according to the latest images from NASA鈥檚 Cassini spacecraft.

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 鈥� only 500 kilometres across.

鈥淓nceladus is a geologist鈥檚 paradise,鈥� says William McKinnon of Washington University in St. Louis, US. 鈥淚t has endless sets of closely-spaced fractures and faults.鈥� He adds there are also blocks of high terrain and a variety of rifts.

Gravitational stresses

This is all evidence of a tumultuous past, according to Paul Schenk of the Lunar and Planetary Institute in Houston, US. 鈥淚t has been pulled, stretched and compressed in multiple episodes of deformation and relaxation.鈥� 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 鈥� even causing floods of icy lava. 鈥淚鈥檓 betting that liquid ammonia-water is involved,鈥� says McKinnon. He also points out what seem to be volcanic ice ridges.

And Enceladus鈥檚 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 鈥� or snow 鈥� fired out of ice geysers. These geysers might blast some of that snow into orbit around Saturn, forming the planet鈥檚 tenuous E ring, suggest scientists. They are looking out for volcanic plumes on the moon鈥檚 horizon, where they would be easiest to spot against the inky blackness of space.