What Would It Take to Say We Found Life? We Asked a NASA Expert: Episode 63

What would we need to say that we have found life?

We call this the podium test. What would you need for you personally to stand with confidence in front of an international audience and make this assertion? When you put it this way, I think that for many scientists, the bar is really high.

So, of course, there would be obvious things, you know, a very clear signature of technology or a skeleton or something like that. But we think that a lot of evidence that we could meet first will be much more subtle. For example, chemical signs of life that should be detected above an abiotic chemistry. And really, what we see could depend a lot on where we look.

On Mars, for example, the long history of exploration gives us a lot of context for what we could find. But we are potentially talking about samples that have billions of years in these cases, and on earth, these kinds of samples, the evidence of life is often degraded and difficult to detect.

On the ocean worlds of our external solar system, therefore places like the moon of Jupiter Europa and the moon of Saturn Enladus, there is the enticing possibility of existing life, which means life that is always alive. But potentially, we are talking about extremely low quantities of samples that should be analyzed with a relatively limited amount of instrumentation which can be transported from billions of miles of land.

And then for exoplanets, they are planets beyond our own solar system. Really, what we are looking for, there are very great signs of life of life that can be detectable through a telescope from many light years. Thus, changes such as oxygenation of the earth’s atmosphere or surface color changes.

Thus, one of these things, if they suspected of being proof of life, would be very strongly examined in a very specific and personalized way to this particular observation. But I think there are also general principles that we can follow. And the first is right: are we sure we see what we think see? Many of these environments are not very well known to us, and we must therefore convince ourselves that we really see a clear signal which represents what we think it represents.

Carl Sagan said one day: “Life is the hypothesis of the last appeal”, which means that we have to work hard for such a claim to exclude other possibilities. So what are these possibilities? One is contamination. The spacecraft and the instruments we use to search for life -by -life are built in an environment, the earth, which is full of life. And we must therefore convince ourselves that what we see is not proof of our own life, but proofs of Aboriginal life.

If this is the case, we should ask, the life of the type we see is there? And finally, we must ask, is there another way than life to do this thing, one of the possible abiotic processes that we know and even those that we do not know? And as you can imagine, it will be a challenge.

Once we have evidence in hand that we really think represent proofs of life, we can now start to develop hypotheses. For example, do we have distinct independent evidence that corroborates what we have seen and increase our confidence in life?

In the end, all of this must be looked at harshly by the whole scientific community, and in this sense, I think that the word really operational in our question is us. What does it take to say that we have found proof of life? Because really, the answer, I think, depends on the part of the complete scientific community examining and skepticizing this observation to finally say that we, scientists, we as a community and us, as a humanity, have found life.

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