Rocky grains stir theories of life on Saturn moon

Grains of rock spewed into deep space suggest a small moon of Saturn has hydrothermal vents, boosting theories that it may harbour microbial life, scientists said on March 11.

Reporting in the journal Nature , astrophysicists in the United States offered a solution to a decade-old mystery over dust streaming from Saturn’s rings.

The grains are disgorged from a mineral-rich balmy sea beneath the planet’s ice-crusted moon Enceladus, they suggested.

It is the first indication of ongoing hydrothermal activity beyond Earth, a possible clue to the existence of warm, water-rich conditions conducive to life beyond our planet.

“It is 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,” said Sean Hsu of the University of Colorado at Boulder, who led the four-year probe.

Enceladus looks like a ball of ice, 500 kilometres in diameter, its mostly smooth exterior marked by a few shallow, wavy ridges and small pockmarks from space impacts.

At its south pole, Enceladus disgorges fountains of ice crystals from what is thought to be a sub-surface ocean about 10 km (six miles) deep — about the size of Lake Superior, the second largest freshwater body on Earth.

One theory is that the water can exist in liquid form, despite the deep chill of the outer Solar System, thanks to a phenomenon called tidal heating. The guts of Enceladus are squeezed and released by the gravitational pull of Saturn, causing friction and thus warmth.

But the wonders of Enceladus do not appear to end there.

The unmanned U.S. probe Cassini found nano-sized (billionths of a metre) grains streaming out of Saturn’s so-called “E” ring, which is believed to comprise Enceladus crystals.

For years, scientists have been trying to figure what these specks are and how they got there.

Based on measurements from Cassini’s onboard instruments of the grains’ chemical signature, Hsu’s team concluded they were likely grains of silica — the mineral found on Earth in quartz and sand — from the Enceladus sea.

They then used computer simulations and lab tests to calculate how this could happen.

Very hot water, at least 90 degrees Celsius, that is slightly alkaline and super-saturated with silica, must be shooting upwards from the moon’s spongy rocks, before coming into contact with cooler water at the ocean floor. The big drop in temperature causes the grains to form, which are eventually spouted from the south pole with water, which instantly freezes on contact with space.The grains’ tiny size suggests the process is fast— a 50-km (30-mile) trip from their hydrothermal origins to outer space that would take only a few years; otherwise the specks would be much bigger.

“Ten years ago, it was a big mystery why the nano-grains were made of silica rather than water ice,” said co-author Sascha Kempf. “Now we know the observations were correct. We know where the silica particles are coming from, and why we are seeing them. We learned something very unexpected.” — AFP

Recommended for you