Evidence of geological activity involving water and hot rock suggests that Saturn’s moon Enceladus might be a suitable home for life.

Scientists analysing data from the Cassini spacecraft, which has been exploring Saturn and its moons since 2004, have found microscopic grains of rock bearing the hallmarks of hydrothermal activity.

The silica grains are thought to have originated in plumes from geysers observed on Enceladus, whose icy surface is believed to cover a watery ocean.

They are the first clear indication of hydrothermal activity, which involves seawater infiltrating and reacting with rock to emerge as a heated, mineral-laden solution. On Earth, such activity in the deep oceans generates nutrient chemicals that harbour life.

We methodically searched for alternate explanations for the nanosilica grains, but every new result pointed to a single, most likely origin

Lead researcher Sean Hsu, from the University of Colorado at Boulder, said: “It’s very exciting that we can use these tiny grains of rock, spewed into space by geysers, to tell us about conditions on − and beneath − the ocean floor of an icy moon.”

The size of the grains, between six and nine nanometres across, provided the vital clue to their origins.

On Earth, the most common way to form silica grains of this size is through hydrothermal activity involving a specific range of conditions. Cassini scientist Frank Postberg, from Heidelberg University in Germany, co-author of the research published in the journal Nature, said: “We methodically searched for alternate explanations for the nanosilica grains, but every new result pointed to a single, most likely origin.”

The geysers erupting from the south polar of Enceladus vent from fractures in the moon’s wrinkled surface.

Gravity measurements suggest that a 10-kilometre deep ocean exists beneath an ice shell 30 to 40 kilometres thick.