Stunning Nasa images capture hints of Saturn moon's underground ocean

Extract from The Guardian

Cassini spacecraft images as it flew by Enceladus capture the grooved and cratered surface of the moon, and the bright streaks of vapor plumes

This image shows Saturn’s moon Enceladus as the Cassini spacecraft made a close flyby of the icy moon. Photograph: AP

Alan Yuhas in New York

@alanyuhas

Saturday 31 October 2015 05.08 AEDT 

A Nasa spacecraft that dived through a geyser plume on one of Saturn’s moons, closer to the surface than ever before, has delivered the first images and data from its “taste” of an underground ocean.

The Cassini spacecraft made its lowest pass over Enceladus on Wednesday, flying only 30 miles above the moon’s south pole and through jets of freezing water vapour and other molecules erupting from below ground.

Last year researchers discovered a deep saltwater ocean inside Enceladus, after seeing hints of it in the jets of vapor first photographed in 2005. Cassini’s lowest flyby should help them solve some of the moon’s mysteries, including whether undersea vents heat the ocean – and whether that ocean could support life a billion kilometres from Earth.

Images taken by Cassini as it swept past Enceladus captured the pale, grooved and cratered surface of the moon, and the bright streaks of vapor plumes erupting from its south pole.

This image shows Saturn’s moon Enceladus, center, as the Cassini spacecraft prepared to make a close flyby of the icy moon. A portion of the planet’s ring is at left. Photograph: AP“We know all of the data from the Enceladus flyby has been successfully transmitted to the ground and teams are now looking at that,” said Linda Spilker, Cassini project scientist at Nasa’s Jet Propulsion Lab in Pasadena, California. The probe’s measurements of the chemical makeup of the plume are likely to take weeks to complete, she added.

“There’s quite a variety of smoking guns we’re looking for here,” said Paul Helfenstein, a mission scientist and research associate at Cornell Center for Astrophysics and Planetary Science.

A sensor on board the spacecraft has “tasted the eruptions of vapor and ice materials” and will identify any of the basic ingredients of life, he said. After past, higher-altitude journeys through the plume, Cassini has detected water vapor, methane, nitrogen, ammonia and other molecules associated with life. But Wednesday’s pass was the lowest ever, through a range more likely to hold heavier, more complex organic molecules.

“Enceladus is not just an ocean world, it’s a world that might provide a habitable environment for life as we know it,” program scientist Curt Niebur told reporters on Monday.

Helfenstein and his cohorts are hunting in particular for hydrogen gas, which would be an indirect measure of the reactions where Enceladus’ ocean and rocky core meet. Hydrogen would indicate hot vents at the bottom of the ocean, of the same kind as vents that also appear in Earth’s oceans and have habitable conditions for simple life. The prospect of hydrothermal activity on Enceladus has made the tiny world one of scientists’ best hopes for finding life elsewhere.

Cassini will also search for any hint of salt in the spray, a key clue to both chemical reactions in the depths and how the ocean stays liquid so far from the sun.

“For the chemistry of life you’d need a source of heat that’s capable of driving the chemical reactions,” Helfenstein said, as well as the right temperature conditions and contact between the moon’s ocean and rocky core.

Geysers and fissures cover Enceladus in patterns called “tiger stripes”, and Cassini has passed through a plume over the “Damascus” stripe on Wednesday. There is evidence for more than 100 discrete geysers, and the moon’s chemical plumes appear to spew from both individual jets and curtain-like eruptions.

Scientists believe an underground ocean of liquid water is the source of the shooting jet stream. Photograph: AP“The spacing of the geysers on the tiger stripes isn’t random,” Helfenstein said, and probably determined by the force of Saturn’s gravity on the moon. The gravity has a kneading effect, he said, pushing and pulling on the moon with enough power to apparently generate heat and create the regular geological patterns.Although Enceladus is tiny compared to Earth – it could fit within Arizona’s borders – its liquid ocean has made it a prime suspect for the search for life, according to Nasa’s mantra: “follow the water”. That imperative has guided researchers to liquid water on Mars, an underground ocean on Jupiter’s moon Europa, and methane lakes on Titan, another of Saturn’s moons.In December Cassini will measure the temperature of Enceladus in a final flight past the moon, more than 18 years after it launched from Earth and more than a decade after it first entered orbit around Saturn.