Cassini spacecraft finds possibility of alien life, then runs out of fuel. Could there be life in our own solar system?
This is the question posed by the discovery of hydrogen gas erupting in plumes from Saturn’s moon Enceladus, indicating the likely existence of an energy supply for microbial life.
The presence of hydrogen, detected by the Cassini spacecraft and announced by Nasa, is seen as tantalising evidence that in the ocean beneath the moon’s icy surface chemical reactions are taking place that are strikingly similar to those that occur at hydrothermal vents on the Earth’s ocean floors.
Until 11 years ago, Saturn’s tiny moon, with a diameter about the length of England, was regarded as an unremarkable object. But then Cassini discovered plumes coming from its south pole, indicating the presence of liquid water, often the first item on the checklist when seeking out the places in the universe that might host life.
Since then, scientists have ticked off some of the other chemical elements thought to be required – carbon, nitrogen, oxygen, and now hydrogen (the other two, phosphorus and sulphur, have yet to be detected but are almost certainly present).
Prof Andrew Coates, a Cassini scientist based at University College London’s Mullard Space Science Laboratory, said: “There are four things you need for life: liquid water, the right chemistry, a source of energy, and enough time for life to develop. This gives that chemical imbalance, that gives you a source of energy.”
As Saturn moves in its orbit, the plumes have been observed to vary in intensity and it is not known whether conditions would have been stable enough for a chain of reactions leading to the emergence of life to occur uninterrupted. On Earth, it took millions of years after favourable conditions appeared for life to spark into existence. “We don’t know if there has been enough time or not on Enceladus,” said Coates.
The great mystery of whether humans are alone in the universe and what other lifeforms might look like – from basic microbes to advanced civilisations – remains out of reach for now. But Cassini’s findings add to scientists’ growing confidence that there are places beyond Earth where life might find a viable home – and that some of them are probably within reach of a spacecraft.