Alex McColgan

Much more often, it's about proving a hypothesis false.

Over time and through a process of elimination, all roads seem to point to the same explanation.

And if that explanation holds up against enough skepticism, for long enough,

it eventually becomes an accepted theory, testable, reliable, and widely accepted by the scientific community.

In this paper, the Mars research team tried to prove that these minerals were not left behind by ancient alien life.

They started with a null hypothesis, and systematically investigated all the non-living explanations for what they found.

But after months of study, they concluded they just couldn't do it.

Now, saying we can't explain how this was done by something non-living is very different from saying this is a definitive sign of life.

For one thing, all our speculation and contained excitement is based on what we know about biochemistry on Earth.

And no matter how tempting it may be, we cannot allow ourselves to assume that just because something happens one way on Earth, it would happen the same way on Mars.

Maybe it has a totally different biochemistry we know nothing about.

NASA's being extra careful not to say too much too soon.

After all, we've been wrong about potential biosignatures on Mars before.

Back in 1976, the Viking lander tested Martian soil for life by squirting it with nutrients labelled with radioactive carbon-14.

If microbes were present, they'd metabolise the nutrients into radioactive carbon dioxide we could detect.

And to everyone's shock, that's exactly what happened.

Excited scientists thought they had proof of alien life.

But in 2008, NASA's Phoenix lander found Martian soil to be rich in perchlorate, a powerful oxidant that destroys organics and releases gas when heated.

What looked like a biological reason,

was really just chemistry, a false positive.