Saturn moon could harbour alien life

 The European Space Agency (Esa) is planning a mission to hunt for alien life on the surface of one of Saturn’s moons.

Scientists want to send a probe to the icy world of Enceladus, which contains a warm saltwater ocean beneath a thick frozen crust, and could harbour tiny organisms living in volcanic vents.

Enceladus – the sixth largest of Saturn’s 274 moons – has been a target in the search for extra-terrestrial life since Nasa’s Cassini spacecraft flew over it in 2005 and spotted geyser-like jets shooting water vapour and ice particles into space.

The water plumes are coming from cracks in the icy crust which reach down to the ocean, and offer a tantalising glimpse of what is underneath. They revealed the ocean was rich in organics, salts, and essential elements for life.

A recent review of the Cassini data found that the sprays contain complex organic molecules, suggesting chemical reactions are happening deep below the ice, increasing hope that the moon is habitable.

The new mission, which is scheduled for launch in 2042 or 2043, would see a spacecraft make a soft landing on Enceladus and take samples of water raining down on to the surface from the plumes.

Dr Joern Helbert, the head of the solar system science directorate at Esa, said: “In Enceladus, we have a very special case because ocean water is being expelled, so you can sample it.

“It makes a super fascinating target because you have heat, you have liquid water, you have organics, so you basically have everything you would need naturally to form life.

“I think there is agreement in the science communities that Enceladus is a potentially habitable world.”

The team will be hunting for biosignatures – chemical fingerprints or structures that are exclusively produced by life.

For example, on Earth, amino acids and other molecules can exist in two mirror-image forms, like a pair of gloves that reflect each other’s shape, rather than copying it.

But amino acids that are used to build proteins are only “left-handed”. They have no mirror image. Similarly, all DNA and RNA – structures which help build proteins – are made of “right-handed” sugars.

The concept is known as chirality, and if it were seen on Enceladus, it would hint that biological life is present.

Clusters of life could be breakthrough

Life also tends to cluster together, so if biosignatures are found in high quantities in certain areas, it could suggest living organisms are grouping together in hospitable locations.

The team has also not ruled out that life itself may get inadvertently sucked up through the ice cracks and ejected on to the surface, but say it is not as likely as finding biosignatures.

“It’s a very strong speculation, and I would never say no (to finding organisms) but what we are looking for is things like complex amino acids,” said Dr Helbert.

“I mean, if under the microscope we see something moving, then yeah, but we would not build the mission on the assumption that we need to see something moving under our microscope.”

If life does exist on Encedalus, scientists think it could be similar to the extremophile microorganisms which live in the hydrothermal vents known as “black smokers” where superheated, mineral-rich water emerges from the ocean floor, forming chimneys.

Black smokers are swarming with life; from microbes which use chemicals like hydrogen sulphide instead of sunlight for energy, to giant tubeworms, clams, and scale worms that have symbiotic relationships with chemosynthetic bacteria.

“If you’ve ever seen the black smokers in the depths of the ocean on Earth, they are teeming with life, and there are extremophiles that don’t depend on sunlight,” said Dr Helbert.

“It might not look like life on Earth, but life tends to cluster, and even if you don’t know what life it is, if we see there’s this clustering pattern, instead of just a distribution, that would again, be a very strong hint that there is life activity.”

The mission will take around eight years to reach Saturn’s system, and then will make fly-bys of Titan, Saturn’s largest moon, using it for a gravity-assist to help the spacecraft drop into the orbit of Enceladus around 2055.

Enceladus is not well mapped, and it is currently unknown if the surface is hard ice or soft snow.

The mission will spend one to two months mapping the moon’s South Pole, where the ice is the thinnest, to find a suitable landing spot and avoid hazards before releasing the lander.

If hints of life are found, then there would be follow-up missions which would seek to go beneath the surface, into the ocean itself.

Nasa is currently developing a shoal of dozens of tiny swimming robots which could explore the oceans on moons, looking for chemical and temperature signals.

The plan is to send the robots inside a nuclear-powered thermal drill which would melt the miles-thick ice, creating a tunnel so that the robot swim team can reach the liquid ocean beneath.

Previously, scientists have tended to look for life on rocky planets like Earth, which fall in the Goldilocks Zone, where conditions are neither too hot, nor too cold for liquid water.

But if life is found on Enceladus it would open up the possibility that life could be present on trillions of icy worlds.

“It would really redefine our definition of the habitable zone,” added Dr Helbert.

The mission was funded by European science ministers at an Esa conference in November.

Dr Joseph Aschbacher, the head of Esa, said: “When we talk about this we all get very excited because astrobiology is saying, if you are looking for places of life somewhere in the Solar System, outside planet Earth, this is the place you would look.

“We know from planet Earth that life is possible in darkness, without oxygen, without light.

“Just imagine for a moment what this means to go there to search, possibly find traces of life. I think this is just too amazing.”