How long can a scientific field like astrobiology thrive without succeeding in identifying its actual object of study – life elsewhere in the universe beyond Earth?

That was the question reflected upon by Kai Finster, Professor of Astrobiology at Aarhus University, in the previous issue of Aktuel Naturvidenskab.

Shortly after that issue was published, NASA and DTU released a new study in the scientific journal Nature, presenting the strongest evidence to date that there was life on Mars approximately 3.5 billion years ago.

NASA’s rover Perseverance, which is exploring Mars using advanced cameras, has observed so-called “leopard-spotted” deposits in fossilised mud on the planet.

These spots contain sulphur- and phosphate-bearing iron minerals as well as organic carbon in close proximity – and sulphate has also been found immediately surrounding the spots. On Earth, such elements would be interpreted as signs of the past presence of microorganisms.

“We know that there are bacteria here on Earth that use sulphate instead of oxygen. When they do, the sulphate is converted into sulphide, which can bind with iron to form iron–sulphur minerals – including greigite, traces of which have in fact been found,” Kai Finster explains.

And so the question arises: Where does the sulphide found in the spots come from? Was it formed through geochemical processes, or by microbial activity?

The Strongest Evidence Yet – But…

The authors of the article did not explicitly state that they had found life on Mars. Instead, they proposed several hypotheses based on the assumption that there could be a chemical explanation for what they observed.

From there, they proceeded systematically, testing each hypothesis one by one.

“It is a very sober and methodical way of reasoning and engaging with data,” says Kai Finster, explaining further:

Sulphate can indeed be converted into sulphide through chemical processes. However, this only occurs at very high temperatures, and the researchers’ analyses show that this was not the case here.

According to them, conversion at low temperatures can only occur through biological pathways.

“So, for some of the hypotheses there is a known chemical explanation. But these chemical explanations fall short when it comes to identifying the source of the sulphide, for instance,” explains Kai Finster.

In any case, the chemistry we know today cannot confirm the hypothesis – whereas known biology actually can.

“We have therefore never been closer to proving that there was once life on Mars. But it is by no means certain that we will ever be able to confirm it,” says the professor.

An Unrealistic Space Mission

Even though this represents a major step towards proof, we are still far from it, Kai Finster assesses.

“To prove that there has been life on Mars, we would need to collect samples and bring them back to Earth for detailed examination in a specialised laboratory,” he explains.

The researchers behind the study reach the same conclusion. But such a mission is not imminent – and is unlikely to happen in the near future, Kai Finster states.

“It probably won’t happen in my lifetime. Perhaps never at all. Right now, it looks highly unrealistic,” he says.

That is partly because it takes many years to plan and carry out such a mission. In the case of the new discoveries of the leopard-spotted deposits, 14 years passed from the time the investigations were planned until the results were published.

It also requires an enormous amount of funding to reach that point – and that funding simply does not exist at present.

NASA, moreover, is facing major cuts under Donald Trump’s austerity measures. As things stand, the space agency will have to cut 24 per cent of its budget next year, with research taking the hardest hit, Kai Finster concludes.

The EU and Denmark Must Unite

NASA and the European Space Agency (ESA) have already proposed and partially planned such a mission – Mars Sample Return. However, the US President has announced that he intends to cancel it.

“A mission like this is extremely expensive. Therefore, it may never become a reality unless funding can be secured, either through the federal budget or from foundations,” says Kai Finster.

NASA estimates that bringing the samples back to Earth will cost 11 billion US dollars – equivalent to around 77 billion Danish kroner – and could be completed by 2040.

“But it would be worth every penny, because it could provide an answer to the question of how widespread life is in the universe – and I think that’s incredibly exciting,” says Kai Finster.

The space agency also notes that Mars Sample Return would be one of the most complex missions ever undertaken:

“Landing safely, collecting the samples, launching a rocket with them from another planet – which has never been done before – and transporting the samples safely over more than 53 million kilometres back to Earth is no small task,” NASA states.

That, however, is the price and the process required today if we want to prove that there has been life on Mars. Still, that does not mean we should give up hope of retrieving the samples, Kai Finster believes.

“In the past, we’ve tended to leave such endeavours to the Americans, but in the current situation, the EU and Denmark must step up. I hope that our politicians and major funding bodies can recognise the value of this kind of mission,” he says, adding:

“There are wealthy individuals in Europe who could easily donate substantial sums to such a mission. Perhaps one could appeal to their spirit of discovery – not the kind that sends them into space to admire Earth from above, but the kind that benefits us all and deepens our understanding of the world.”

Reaching Out to Other Scientists

The researchers behind the study conclude by encouraging others to investigate whether unknown chemical processes might explain how the spots on Mars were formed.

“In doing so, they ensure transparency and invite others to test and offer alternative explanations – which is central to research, where we can never be 100 per cent certain,” says Kai Finster.

Yet regardless of what new explanations may emerge, it cannot be stated with certainty that there was once life on Mars unless the samples can be brought back to Earth, the professor emphasises.

“Whether or not biology is involved, the achievement of the group of researchers behind the article is truly impressive,” he says.

“If life does exist on Mars, it would mean that life is far more common than we have so far believed. And even though we still don’t know how life began here on Earth, a discovery on Mars would suggest that life emerges spontaneously when the right ingredients and conditions are present.”

All in all, astrobiology has strengthened its case since the previous issue – even if definitive proof of life elsewhere in the universe may still lie far in the future.