I will believe in life on Mars when I see it hopping by. But in the meantime: Dark streaks on Mars may be a sign of flowing streams of salty water. (NASA/JPL/University of Arizona via AP)

Is there life beyond Earth? I assume so, though there’s no solid data for it. What happened on Earth could happen elsewhere, one would think. NASA and most astrobiologists have been water chauvinists and carbon chauvinists, because, as I wrote yesterday on the SOS blog, water is so handy for biochemistry and carbon is terrific for constructing complex molecules that are stable at varying temperatures (or so I’m told by actual astrobiologists). The new evidence for liquid water on the surface of Mars is potentially a big deal. Life might find a foothold in ephemeral pools at the base of one of those Martian hills. Or it could hunker down in an aquifer.

But there’s another possibility worth pondering: That a planet typically will not have just a tiny bit of life.

[Invasive interstitial link for those who are already losing interest: Do we really want to know if we’re not alone in the universe?]

Life on Earth is incredibly rambunctious, invasive, promiscuous, adaptive — pick your adjective. So one might infer that this is a general property of biospheres. Life finds a way. It doesn’t hunker down in a tiny little pool somewhere. It should be everywhere. Planetary scientist David Grinspoon promotes this conjecture, which is something of a cousin to the Gaia hypothesis. We had an e-mail exchange about it this week:


I am personally very skeptical about the chances of finding living Martians today.

This is because I think that Mars lacks the qualities of a living world. The only planet we know of with life has been drastically altered by that life over billions of years, and I suspect this is a quality of planets with robust biospheres.  I don’t think a planet can be a little bit alive.  I’ve developed this in books and a few articles, and I refer to it as the Living Worlds Hypothesis.  Obviously closely related to the Gaia hypothesis.

I think that if there were bugs in the aquifer related to these briny seeps they would be leaving very obvious chemical signatures in the surface and atmosphere.  And I think that a planet may need to be more “alive” in the geological sense, to be alive biologically.

However, this is a hypothesis about the character of life and its relationship with planets.  I would love nothing more than to learn I was wrong about this.


My follow-up question: Is there a way to test the hypothesis?


It’s not a very easy idea to devise a simple test for, as it’s half science, half natural philosophy. Very much like the Gaia hypothesis, which is also famously hard to test, it’s an idea about the character of life and its relationship to planets.

But I would say that Mars is shaping up to be an excellent test of the idea.

If a planet can be a little bit alive, and life needs only local environs with the right conditions, and does not depend upon planetary qualities of the kind I’ve described, then Mars should have life in the pockets of water we know are there.  Not necessarily these extremely briny seeps, but certainly in the buried aquifers that must exist at some depth.

If there is life on Mars in isolated oases, then the idea is wrong.

There’s one way to find out: Go look. Read my NASA story today that includes John Grunsfeld’s suggestion for a life-detection experiment on Mars that wouldn’t violate planetary protection rules.

Further reading:

Rachel Feltman’s review of ‘The Martian’

Did Andy Weir and ‘The Martian’ just save the space program?

Yet another buzzkill story about NASA’s human spaceflight program

Mars is hard

Geoff Marcy asks, ‘Where are they?’