FAITH Magazine March – April 2011
It is hardly unknown for scientists to hold opposing views. But when two prominent institutions almost simultaneously publish contradictory reports on a hotly disputed topic, we can look forward to an interesting debate. One such topic is the existence of extra-terrestrial life, and the two institutions in question are Harvard University and the Carnegie Institution of Washington.
In September 2010, Dr Paul Butler, an astrophysicist at the Carnegie Institution, and Professor Stephen Vogt of the Lick Observatory, University of California, published a paper in The Astrophysical Journal reporting the detection of an "exoplanet" (a planet orbiting a star outside the solar system) that they believe may have just the right conditions to support life.
Known as Gliese 581 g, the planet orbits a star named Gliese 581, which is about 20 light years away (the nearest star to the Sun is 4.3 light years away). It is one of six planets discovered around this star, all of which have near-circular orbits. Calculations indicate that in several ways it is quite an Earth-like planet: its radius is 1.2 to 2.5 times that of Earth; its mass is 3.1 to 4.3 times greater; and, crucially, its orbit lies within its star's "Goldilocks zone", which means its surface temperature is neither too hot nor too cold for liquid water - and therefore potentially life - to exist on its surface.
Unlike Earth, Gliese 581 g is "tidally locked". This means that, like the planet Mercury and our own moon, one side constantly faces its star while the other side is constantly in the dark. As a result the surface is much hotter on the near side than on the far side, and the most habitable zone would be the intermediate area between the light and dark sides of the planet. Yet we know that life on Earth can thrive in extreme conditions: from the Antarctic (where temperatures can drop to almost -90°C) to hydrothermal vents on the ocean floor (where temperatures can exceed 460°C). So there is no reason why life should not exist on another planet where temperatures vary greatly.
Gliese 581 is a red dwarf star, which means its expected lifetime is far longer than our Sun's: it could well last hundreds of billions of years, which is much longer than the present age of the universe. Red dwarfs (or M dwarfs as they are also known) are by far the most common stars around, comprising some 70 per cent of all the stars in our galaxy. They are much smaller, dimmer and cooler than stars like our Sun, and for a long time scientists searching for life on other worlds paid little attention to them; the general feeling was that they gave out so little heat and light, compared with the Sun, that they were unlikely to host habitable planets.
That consensus has changed in the last few years, and astronomers are now focusing their efforts on these diminutive stars. Because red dwarfs have such long lifetimes, there's far more time for the chemicals and reactions necessary to support life to develop on one of their planets. The Carnegie website (www.carnegiescience.edu) has the text of the research team's announcement; it also has a link to a "video press release" which gives a clear visual impression of the findings. The authors are convinced that given enough time we will discover life elsewhere in the universe.
In January of this year, however, a different research group, led by Harvard astrophysicist Dr Howard Smith, reached quite the opposite conclusion. His analysis of some 500 exoplanets led him to believe that none of these planets had the right conditions for life, and he plays down the chances of finding any extra-terrestrial life. Of course, 500 exoplanets are barely a drop in the ocean compared with all the planets thought likely to exist even in our own galaxy, let alone in the universe, so Dr Smith's conclusion could be deemed premature and statistically irrelevant. Yet he has at least reminded us just how remarkable our own planet really is.
So, who do we believe - Dr Smith, who thinks all the exoplanets discovered so far are "very hostile to life as we know it", or the Carnegie team, for whom the chances of aliens existing on an Earth-like planet are "100 per cent"? As a comment on The Daily Telegraph website (24 January 2011) put it: "It is hard to tell which of these two categoric declarations is the more worrying."
Of course, plenty of other scientists are in the hunt for life-supporting worlds outside our solar system. In March 2009 Nasa launched its Kepler Space Telescope, which was specifically designed, as its mission statement says, to "search for habitable planets". Its website (www.kepler.nasa.gov) provides the latest updates on this programme. So far Nasa has detected nine confirmed exoplanets, though none that would be in their star's habitable zone. The programme's latest confirmed planetary find is Kepler-10b, whose discovery was announced on 10 January this year; the planet is rocky and similar in size to Earth, but its orbit is too close to its star for it to be able to support life.
And what if astronomers did eventually discover intelligent life? What would be the theological implications? Would those alien creatures need baptism? Fr Stephen Wang raises the question here: http://bridgesandtangents.wordpress.com/2010/04/11/the-search-for-extra-terrestrial-intelligence/. Answers on a postcard.
The Carnegie Institution of Washington has recently created a website detailing a 400-year history of cosmology from Galileo (c. 1610) to the present day (http://cosmology.carnegiescience.edu). The site analyses the achievements of 20 scientists, or collaborations of scientists, over the past four centuries, and has a timeline that is well worth seeing.