Astrobiological musings

March 27, 2007

I was fairly astounded to find that astrobiology – the study of whether life exists elsewhere in the universe – is actually a respected field of study in academia. At its heart astrobiology is quite speculative, since we only have one notable data point of evidence that life occurs at all in the universe, namely good ol’ Mama Earth. There is however, a useful rule of thumb often attributed to Richard Feynman (who is incidentally also credited with a good portion of modern physics), that whatever is not forbidden in nature is mandatory. That is to say, if nature allows for the existence of self-replicating molecular systems on one rock around a fairly average star, then its not unreasonable to think life might exist elsewhere. The case for the commonality of life is strengthened further by the relatively recent discovery of so-called “extremophiles” thriving in the least likely of places on Earth: boiling water surrounding hydrothermal vents, underneath permafrost, and inside rocks to name just a few. Here’s an example of a particular extremophile.

A Pompeii worm colony near a hydrothermal vent.

This is a Pompeii worm colony near a hydrothermal vent. Needless to say, the existence of such extreme forms of life greatly reduces the number of necessary environmental criteria for life. Thus microbial life at least might very well be quite common in the universe.

In fact we might not need to look beyond our own solar system for other forms of life. Our very own Europa (one of Jupiter’s 63 moons!) might not only have liquid water beneath its icy surface but also have a significant heat source. That whole source of heat thing is not irrelevant when you consider that at Jupiter’s orbital distance the luminosity of the Sun isn’t that much greater than the background stars. The source of heat is unknown at the moment, but an intriguing possibility is the strong gravitational tidal flexing Jupiter’s large mass provides. There are actually two interesting bits of evidence for liquid water under the icy shell of Europa: 1) cracks in the ice crust appear to heal with time, and 2) the magnetic field around Europa is significantly smaller than would be expected since Jupiter has a substantial magnetic field. This happens near highly conductive bodies, such as a salty ocean perhaps.

The “heat plus water” equation seems to be more than enough for some of Earth’s extremophilic organisms, which bodes quite well for possible Europan biology. Given all of this it’s quite unfortunate that NASA somehow finds it more useful to waste oodles on a boondoggle to send humans to Mars rather than sending a much cheaper unmanned mission to Europa on a well-motivated search for extraterrestrial life. This despite the fact that we already have two wonderfully adept geologists on Mars right now living off of sunlight alone: the Mars Exploration Rovers Spirit and Opportunity. Here’s an example of two competing ideas regarding the Europan interior.

Alternative theories on the Europan interior.

Of course none of this says anything about the possibilities of complex or intelligent life. For that you probably need to satisfy much more stringent criteria such as the veritable Goldilock’s condition: a habitable planet must not be so far from its parent star that it gets too little light but also not so close that everything boils away. Getting the distance from the star just right is probably the most significant impediment to the development of intelligent life. Read more about the unfolding saga that is astrobiology here and here.

This might all be pure speculation since any would-be astrobiologist is forced to confront Fermi’s paradox regarding extraterrestrial life: if intelligent life is common why hasn’t it called us up yet? Or would it be too convenient for us to assume that another civilization would choose to communicate with us using radio-waves? Perhaps they’re so advanced that we can’t possibly hope to receive their communications given our limited technological capabilities? While although possible that’s not a falsifiable hypothesis and thus outside the bounds of science, but that won’t stop us from fun pontifications.

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