Nasa's Cassini probe is scheduled to make its lowest pass yet over Saturn's Enceladus moon on Wednesday (28 October), swooping through the moon's towering plume of ice and water vapour to provide new insights into how hospitable the ocean thought to cover Enceladus could be to life.
Earlier this year, Scientists found that Enceladus, a small moon orbiting the giant ringed planet, is likely to possess a liquid ocean under its icy crust, raising the prospects that it could host life. Cassini has been orbiting Saturn since 2004, and it quickly discovered that Enceladus has an icy plume shooting out from its south polar region.
"We'll fly by at roughly an altitude of thirty miles, which is approximately the distance between Washington DC and Baltimore. We go screaming by Enceladus at speeds in excess of 19,000mph. We're flying deep, the deepest we've ever been through this plume and these instruments will be sensing the gasses and will be looking at the particles that make up this plume," said the project's mission designer, Brent Buffington.
Nasa scientists are hopeful that the closest encounter yet with Enceladus will shed light on the possible hydrothermal activity taking place on the moon. The existence of liquid water could increase the chance of finding simple forms of life, Nasa says, though the latest mission is not designed to find life itself. Critically, Cassini will be trying to detect molecular hydrogen.
Cassini's Cosmic Dust Analyser helped the scientists find dust particles in one of Saturn's rings that came from plumes erupting from Enceladus. They contained silica nanoparticles probably formed in chemical reactions between the water and the ocean floor's rocky core. Life would be difficult to sustain on Enceladus without an internal heating system because the Saturnian moon is too far away from the Sun to receive its warmth.
Nasa Systems Engineer Morgan Cable says the evidence of the building blocks of life are encouraging so far: "Now Enceladus is a tiny moon but it's really intriguing. It's got this plume that is shooting out from its south pole.
"The plume's mostly comprised of water, water ice, that gets frozen when it's ejected out into space. Most of these particles are coming from these four major fractures that we call tiger stripes. Life needs three things, right? It needs water, it needs chemistry, and it needs energy. And right now some of these lines of evidence are telling us that Enceladus has these three things," she said.
Enceladus, which is only about 300 miles in diameter, is one of the few places beyond Earth likely to contain oceans, along with Saturn's large moon Titan and Jupiter's moons Europa and Ganymede. Only Enceladus and Europa, however, show evidence that their oceans are in contact with rock.