First pass: did NASA find life on Mars in 1976?

On September 3, 1976, Viking 2 touched down on Mars. Its little biology lab said something surprising, and people are still arguing about what it meant. This is the shape of a first pass. I did this one for nobody, as a sample.

The claim: NASA found life on Mars in 1976 and buried it.

What holds. Viking's Labeled Release experiment fed a drop of dilute nutrients to Martian soil, tagged so that anything eating them would exhale radioactive gas. Both landers' first injections came back positive: gas came out. In a control, heating the same soil to 160 °C for three hours first made the signal vanish, the way a sterilized sample should. That pattern is real and documented.

What the room said. A separate instrument on the same landers, the gas chromatograph-mass spectrometer, heated soil samples and found essentially no organic molecules. The soil held less carbon than lifeless lunar samples. For most of the Viking scientists, that settled it: the missions had failed to detect life, and the positive result was chemistry, a strong oxidant in the soil.

What changed. In 2008, the Phoenix lander found perchlorate in Martian soil. Perchlorate does not reproduce the labeled-release result under that experiment's own conditions, but it does destroy organics at the temperatures the Viking instrument used. NASA's Christopher McKay estimated Viking soil could have been 0.1 percent organic and the instrument would still have found nothing. A 2010 re-analysis found the chlorinated traces Viking did see were exactly what perchlorate plus soil organics produce under Viking-style testing, so the “no organics” pillar got a hole in it. It is still argued: the man who ran that instrument published a rebuttal, and a 2021 spacecraft measurement found Mars' chlorine isotopes nearly indistinguishable from Earth's, which keeps the reading open rather than closed.

What's still open. Whether the labeled-release signal was life. Gilbert Levin, who built it, argued yes until his death in 2021, at 97. The careful word for the whole thing, fifty years on, is inconclusive. Not buried: open.

Where I looked.

That's a first pass: where I'd look, what holds, what doesn't, sources you can open yourself. Name a question and write to me: [email protected]. The first five are free.

Miuem