Monday, November 18, 2013

Are we poised for a jaw dropping discovery?

In my bones I feel that searching for extra-terrestrial intelligence is slightly loopy. Yet many leading scientists, especially at the SETI Institute, engage in the search and sustain their hopes that a sign of intelligent life will one day manifest itself. Radio signals are the usual target, but the lights of alien cities have also been canvassed.

The foregoing is only a digression, since I really wanted to talk about the prospects of finding any sort of life in the universe. An editorial in last week’s New Scientist suggested that if life is common in the universe, we will have found signs of it by the middle of the next decade, “a truly jaw-dropping discovery”.

This prediction of finding signs of life within 12 years or so is based on the NASA Kepler spacecraft’s hunt for habitable exoplanets. These are defined as rocky planets, roughly Earth-sized, orbiting other stars in the habitable zone where water is likely to be liquid.  For three years (finishing last May when the camera malfunctioned) Kepler surveyed a tiny patch of the Milky Way. Even though using an inefficient detection method, it found over two thousand planets, a handful of which seem Earth-like. 

Optimists, extrapolating these results to the whole sky, say it looks certain that our galaxy is home to billions of Earthlike planets.  There are pessimists though. One posted a comment to the New Scientist website claiming Kepler has not found a single earth size planet in the habitable zone.

Paul Davies: life on earth
may have been a fluke
Kepler's successor, the Transiting Exoplanet Survey Satellite, is due to launch in 2017. It's being designed to search for the most promising exoplanet targets for next-generation studies. Restricting its search to nearby stars, it will scour the sky for small rocky worlds, and is expected to find hundreds. Future instruments such as the James Webb Space Telescope and the proposed StarShade mission will follow up these discoveries, probing the planets' atmospheres for signs of life. For example, to an alien astronomer, the oxygen, ozone and methane in Earth’s atmosphere would be a giveaway, because these gases are unstable, so their abundance here would indicate their being continually replenished by life.  So these gases, if present in an exoplanet’s atmosphere, would be an indicator of life as we know it; whilst certain other unstable gases could, by the same logic, be evidence of weird life.

A few comments about New Scientist’s expectation of a truly jaw-dropping discovery. First, notice their caveat “if life is common in the universe”. Many argue that life is probably very rare in the universe. If so, most (perhaps all) of those billions of Earthlike planets could be completely sterile.

Paul Davies (a guru of mine) is fond of saying that fifty years ago scientists used to say life was very unlikely; and now the fashion is to say it's very likely … yet nothing has changed: we're just as ignorant now about what causes life to arise as ever we were.  Here's a review of his 2010 book The Eerie Silence.

Next, if scientists succeed in analyzing a planet’s atmosphere and conclude “wow, life!” they won't, from that data alone, be able to tell intelligent life from microbes. But no matter, to me that would be jaw dropping enough.  Of course you can be sure that the SETI radio antennae will immediately be trained on any such planet. That may be loopy but it has to be done.