September 29, 2010 | David F. Coppedge

Probability Life Not Found on Exoplanet: 100%

Headlines are screaming that an earthlike planet in its star’s habitable zone has been found.  Many sources, though, are claiming that life must certainly exist on this planet.  Their hubris stems from the words of Steve Vogt, an astronomy professor at UC Santa Cruz.  “Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say, my own personal feeling is that the chances of life on this planet are 100 percent,” he said at a press briefing today.  “I have almost no doubt about it.
    That’s all the headline writers needed: “Planet’s Life Odds ‘100 Percent,’ Astronomer Says,” Jeanna Bryner wrote for Live Science – an article echoed on  “Life Likely on Newfound Earth-Size World” announced another Live Science headline.  Some sources were a little more tentative.  David Shiga wrote for New Scientist, “Found: first rocky exoplanet that could host life,” omitting the Vogt 100% number.  Science Daily wrote, “Newly Discovered Planet May Be First Truly Habitable Exoplanet.”  Another article explored the planetary system around Gliese 581, only stating that the discovery of its six planets is “further cementing its status as a top candidate to harbor extraterrestrial life.”
    One thing is 100% certain: no life has been found.  All that is known about this planet is that it is 3 to 4 times the size of our Earth, and it orbits a red dwarf star.  Those two factors reduce the probability of life (see the film The Privileged Planet on YouTube for explanation, esp. ch 4-5).  The only factor announced in the reports that could be favorable to life is that Gliese 581g, as it has been dubbed, orbits in the small star’s temperature habitable zone: the zone where liquid water could exist.  There are, however, requirements for a UV habitable zone (08/15/2006), a tidal habitable zone (06/11/2009 bullet 2), and a habitable zone immune from planetary migration (05/21/2009).  Many other factors that could affect habitability of this planet, like the presence of a large moon, plate tectonics, the right atmosphere, composition of the crust, and more, are unknown at this time, and probably will remain unknown for years.  The probability that life has not been found is certain – 100%, for now at least.
    Nevertheless, most of the articles cheerfully echoed Vogt’s confident 100% probability estimate, although some reported that co-discoverer Paul Butler (a planet-hunting pioneer), though optimistic, did not want to put a number on it.  None of the articles criticized Vogt for stating an evidence-free, and therefore unscientific, personal opinion.

Some day this exuberant, over-the-top headlining will backfire on the scientific community.  Is Gliese 581g an interesting place deserving of more study?  Certainly.  So is Titan, or Venus.  Given the track record of SETI, or of finding life right here in our own solar system, one would think scientists would have learned a little restraint.  Undoubtedly Dr. Vogt is assuming that if life had been found there, it would have evolved there by a long process of chemical and biological evolution.  Given the track record of explaining life right under their noses with that assumption, one would think scientists would have learned a little restraint.  In both cases, one would have thought incorrectly.  The chances of finding hubris in a naturalistic scientist’s brain, however, is 100%.  There’s almost no doubt about it.

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