Alex McColgan

to be signs of life, based on a set of criteria.

It has 7 levels, ranging from we found something that could be caused by life, all the way to multiple teams have independently confirmed life more than once.

NASA hasn't stated where the discovery in the Jezero crater falls, but I'd guess probably somewhere between levels 3 and 4.

If the samples come back, and independent labs around the world all confirm that what we are seeing really did come from a biological origin, that would push us up to a level 6.

Level 7 might even require going back to Mars and finding the same evidence in a completely different location.

So, when NASA says this discovery could be the clearest sign of life we've ever found on Mars, they don't mean to say it is clearly life.

But the Mars sample return mission could finally reveal whether we've always been alone in the universe, or did we once have a cosmic neighbour?

Even if our sample turns out to not be life, it's still an extraordinary discovery that will help us understand our own origins even better.

See, we think Mars is like a time capsule of an early Earth.

Unlike Earth, Mars doesn't have any continental drift or an active plate tectonic system.

Its crust has been frozen in place for billions of years, preserved in a way Earth's crust could never be.

The ancient landscapes on our planet have been erased through tectonics, erosion, oceans and volcanism.

So when we study Mars, we're not just asking whether it once carried life, we're also peering into a record of planetary conditions that resemble Earth at the dawn of biology.

In that sense, Mars is a window into our own origins, offering clues to what Earth might have looked and felt like before life left its mark.

But let's dream for a moment, shall we?

What if the sample does turn out to be life?

Well, most immediately, it would indicate that Mars was habitable far longer than we imagined, since the sample comes from relatively young sediment.

But more importantly, we'd finally answer the question,

Can life exist on other planets?

And in the same breath, open a Pandora's box of follow-ups.