The unknown 99%

The Viking landers touched down on Mars back in 1975. I was nine. You couldn’t follow events as they happened back then the way you can these days via the internet. But when the daily paper had pictures and accounts of what was taking place on the surface of our sibling planet I was fascinated by the coverage and wanted more. 

Part of the mission of the landers was to test Martian soil for life. But how does one go about designing a test to determine whether there is life in a handful of dust? NASA tried to figure it out. With at least one of the experiments on Viking it was hoped by inundating a soil sample with tasty wet nutrients, microbes would happily start eating and excreting and growing in a way that the Earth-sent instruments could detect. It makes sense, doesn’t it? Do that to any random scoop of Earth soil and sensitive instruments will readily detect life-specific activity. Why shouldn’t it work elsewhere?

Some surprising activity took place, all right. But it wasn’t a life-like response. It was more like an instantaneous chemical reaction. The eventual conclusion was that the inundated soil reacted more like an Alka-seltzer tablet than cellular life — and for similar reasons. Did that mean the soil was sterile? Considering that the soil was continuously exposed to harsh radiation that would kill Earth life and that the soil was extremely dry, it didn’t seem likely that the rapid response to the water had anything to do with life. 

But when you are designing experiments you don’t always know what your test will be overlooking. Most Earth life wouldn’t have responded to that yummy wet food either, according to Sarah Johnson in her book about seeking life on Mars:

When the Viking payload was being designed, no one realized that the vast majority of microbes wouldn’t grow in a nutrient-rich broth — in other words, that they couldn’t be cultured. It wasn’t until we started identifying life by its genes — not waiting for cells to grow in a petri dish but instead breaking them open within a pinch of dirt or a drop of ocean — that we came to understand that less than 1 percent of the life on Earth could be grown in a lab or, by extension, a lab on a spacecraft on Mars.

The 1% of the life that will culture in any given pinch of soil blinds us to the 99% that won’t. Perhaps there was life in that Martian soil sample that the experiment wasn’t designed to find. The situation it would have survive in is so hostile it’s hard to imagine a successful adaptation, but who knows? It might be easier to imagine microbial life under the Martian surface where there really are stores of liquid water and volcanic activity may provide sufficient energy for life to feed on. In other words, we’re still looking.

source: 

The Sirens of Mars: searching for life on another world

by Sarah Stewart Johnson

2020. Crown, New York