Closing in on alien life

NASA’s Cassini spacecraft has detected hydrogen in a plume of gas and icy particles spraying from Saturn’s moon Enceladus, prompting the question could it be a suitable energy source for microbes to exist in its sub-surface oceans.

Forty years ago, scientists on Earth found an astonishing oasis of life clustered around vents at the bottom of the ocean. Despite being thousands of metres under the sea and therefore far away from sunlight, life was being sustained via the energy produced from hydrothermal activity released from the vents.

This discovery changed how we thought about how life can cope on our planet and elsewhere in the Solar System. Now, this new detection along with a further revelation that Hubble has also just found additional evidence of plumes erupting from Jupiter’s moon Europa, these results are tantalising close to answering whether we are indeed alone in the Universe or not.

“This is the closest we’ve come, so far, to identifying a place with some of the ingredients needed for a habitable environment,” says Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate.

The detection of hydrogen gas in the plumes of Enceladus is suggestive that like on Earth, hydrogen is pouring into the moon’s subsurface ocean from hydrothermal activity on the seafloor. If that is the case, then it is also reasonable to think that microbe life – if it exists – could be flourishing due to a process known as ‘methanogenesis’. This reaction involves combining hydrogen with carbon dioxide dissolved in water to produce methane.

The production of methane is an important and widespread form of microbial metabolism and a source of energy for metabolism is one of the three primary ingredients for life as we know it to exist. The other two necessary ingredients are liquid water and the right chemical ingredients – primarily carbon, hydrogen, oxygen, nitrogen, phosphorus and sulphur.

From these current observations researchers have determined that nearly 98 percent of the gas in the plume is water, about 1 percent is hydrogen and the rest is a mixture of other molecules including carbon dioxide, methane and ammonia. And although Cassini has not yet shown that phosphorus and sulphur are present in Enceladus’s ocean, it is possible that they are present as the rocky core of this icy world is thought to be chemically similar to meteorites that contain these two elements.

The plumes on Enceladus are also associated with hotter regions on the moon. It had already been suggested from previous results in 2015 that hot water on the moon was interacting with rock beneath the sea. This new finding is therefore an independent line of evidence supporting the theory of hydrothermal activity taking place in the ocean of Enceladus.

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