NASA scientists believe an icy Saturn moon has all the ingredients needed for life

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The first living thing on Earth was likely born deep in our planet’s oceans. More precisely, life probably would have arisen in a hydrothermal vent, a crack through which Earth’s hot interior leaked energy and key chemicals creating the ingredients and conditions needed for genesis.

Using data from NASA’s Cassini mission, researchers have found nearly all these conditions and ingredients are likely present on Enceladus, the icy moon of Saturn. The discovery pushes Enceladus to the top of the list of places most worth searching for life beyond the Earth, and it’s likely to change the kind of instruments we will mount on future missions sent to ocean worlds in the solar system.

What makes this discovery more extraordinary is that the kit sent to Saturnian moons was not designed to find out this information. The Cassini spacecraft was designed to sniff the atmospheres of some of the celestial bodies it was going to visit. Instead it found a way to, in effect, taste the waters that sit underneath a 20-km thick layer of ice found on a moon of a planet that is 1.2 billion km from the Earth and found with great precision what chemicals they contain.

Composite map of the south pole of Saturnian moon Enceladus.
Composite map of the south pole of Saturnian moon Enceladus.
Image: NASA

The water tasting was made possible because of an unusual feature of Enceladus called “tiger stripes.” These four parallel depressions were likely created because of unusual heating in the moon’s core. The heating can, on occasion, be enough to crack open the thick, icy layer and spew vast amounts of water from the liquid ocean into space. In 2008 and 2015, the Cassini spacecraft made a flyby, coming within 50 km of the surface and passed through the ice-water plumes.

The data uncovered during the most recent dive has allowed a team of scientists, led by Hunter Waite at the Southwest Research Institute, to conclude that the Enceladus ocean contains hydrogen (up to 1.4% by volume) and carbon dioxide (0.8%). This is in addition carbon-containing compounds like methane, propane, acetylene, formaldehyde, and nitrogen-containing ammonia—all found previously.

Earlier Cassini flybys showed Enceladus has a solid, hot core, likely containing lots of iron. The heat is enough to maintain a liquid ocean underneath the thick ice layer. The core is also thought to be porous, which would allow some pockets of liquid ocean to heat up more than others while coming in contact with iron. These three things—heat, iron, and water—can create the “serpentinization reaction” where iron steals oxygen from water and release hydrogen in the process.

Icy plumes can be seen emanating from the “bottom” of Enceladus.
Icy plumes can be seen emanating from the “bottom” of Enceladus.
Image: NASA

Scientists believe six basic elements are necessary for life: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. There also needs to be a source of energy to get these elements to mix in the right way and create life. Cassini has shown that Enceladus has four of the six elements present (phosphorus and sulfur are missing), and it also has an energy source (some of which helps create hydrogen).

What makes this more exciting is that the serpentinization reaction also occurs in hydrothermal vents at the bottom of Earth’s oceans.  Though we don’t know with complete certainty, our best theories suggest that these are where life on Earth was first formed. The earliest Earth-creatures, called methanogens, ate hydrogen and carbon dioxide to create methane.

Can methanogens exist in the oceans of Enceladus? Yes. Do they exist? We can’t be sure just yet. The finding raises more questions than it answers, but it also creates the strongest case we have yet to send a space mission to find out. “All the conditions are right,” Waite said.

NASA is planning a mission to Europa, an icy moon of Jupiter, that is also thought to have a liquid ocean underneath. Though there isn’t yet a mission planned to Enceladus, it’s clear that we have the technology to probe ocean worlds to answer the question: is there life beyond Earth?

Whatever the space mission finds will be interesting. “If life does exist, it’s obvious we’ve found life somewhere else in the solar system,” Waite said. “If it doesn’t exist, and all the ingredients are there, why doesn’t it exist?”