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Steven A. Benner, Allen Lane

Fifty years ago last month, a life-detection test developed by Gil Levin, a NASA investigator and an engineer schooled in sensing dangerous microbial colonies in sewage, landed on Mars. It was on board Viking 1, the first of two life-seeking landers.

Amazingly, both of the landers succeeded straight away. Levin鈥檚 test, alongside two others, quickly gave what planetary scientists call strong 鈥渓ife affirmative鈥� results.

This should have been a triumph for Levin and NASA鈥檚 Viking team. Unfortunately, a consensus developed within the Mars-exploration community, making it fearful of anything so bold as to claim the discovery of alien life so soon. A negative interpretation of the results prevailed, which pulled the rug from under Viking鈥檚 finding that, on the balance of evidence (and within the experiment鈥檚 definition of life), there is life on Mars.

Worse, this propagated down the decades to influence Mars-exploration policy even today, despite the fact that findings by the Curiosity rover (which landed in 2012) should have corrected it. The result: since Viking, space agencies have run timid missions in search of signs of ancient life, past habitability and water, rather than bold missions to find existing life.

This is the core argument of Meet The Neighbors: Life on Mars and how to find it, a captivating tale of misunderstood (if not actually gamed) planetary biochemistry, and its impact. Its author is Steven Benner, an astrobiologist, organic biochemist and synthetic biologist, whose team at Harvard University was the first to synthesise a working, protein-encoding artificial gene.

The error influenced Mars exploration policy even today, despite findings by the Curiosity rover

Benner reveals what the Viking tests found, and why they were so vulnerable to dismissal by naysayers, by undertaking a fresh analysis of the raw data and the research published on the results at the time. Then, pleasingly, he demolishes those arguments.

It all seemed so cut and dried at first, with Robert Jastrow, then director of NASA鈥檚 Goddard Institute for Space Studies, quoted in magazine as saying: 鈥淪hort of seeing something wiggling on the end of a pin, the case for life on Mars is now as complete as the Viking experiments could make it.鈥�

Benner goes into detail on the three life-detection experiments, including the controls run to rule out chemical, rather than biological, action. Levin鈥檚 鈥渓abelled release鈥� experiment fed radiocarbon-tagged nutrients like formic acid, glycine and lactic acid to a sample of Martian soil, which then released radioactive carbon dioxide, 鈥渋ndicating the presence of respiring microbial life鈥�, he writes.

A second test found that the carbon from radiolabelled carbon monoxide and CO₂ could be 鈥渇ixed鈥� into the molecules of the organic materials in the Martian soil. This was deemed analogous to how plants on Earth fix CO₂ in photosynthesis and thus 鈥渆vidence of an active Martian biosphere鈥�. In the third test, water was added to Martian soil, producing a significant amount of oxygen and an 鈥渆xchange of CO₂ with the soil鈥�, supporting the existence of bioactive soil on Mars.

But all three 鈥渓ife-positive鈥� results fell after the gas chromatography-mass spectrometer (GC-MS) on the landers found no evidence of any organic content in the Martian soil where Viking 1 touched down, at Chryse Planitia, or on soil where Viking 2 landed, at Utopia Planitia, 6460 kilometres away. As a result, an unknown oxidising surface chemical, rather than a microbial life form, was put forward as the explanation and accepted by the Mars-exploration community as the source of life-positive results.

It was all tosh, says Benner. First, it turned out the GC-MS was nowhere near sensitive enough to pick up organics. NASA鈥檚 Curiosity rover discovered the Martian surface is full of organics 鈥� notably perchlorates 鈥� so the GC-MS results could be discarded. Mars, says Benner, is alive again, a bold claim well supported by this absorbing, convincing book.

Space agencies should now harness the economics of reusable rocketry to mount searches for existing life on Mars, says Benner. He argues they should focus on microbes that might have RNA-based building blocks 鈥� a theory he has honed with his research on artificial genes and the fact that ribose has been found in samples from the asteroid Bennu.

Viking鈥檚 resurrection would have pleased the late Levin and his late NASA collaborator Patricia Straat for another reason. Both founded a pressure group . As China plans to deliver Mars samples to Earth in 2031, Meet the Neighbors brings that issue into sharp relief.

Paul Marks writes about technology, aviation and space. He is based in London

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