For a planet to support life, it has been traditionally thought that it must orbit its parent star at a distance where the temperature is right so that liquid water can exist on the planet's surface, like Earth does. This is called the star's 'habitable zone'. This idea has already been challenged in the past by suggestions that moons orbiting Jupiter, Saturn, and Neptune - which are far outside the Sun's habitable zone - may harbor life, and the Sun's habitable zone has even been conservatively expanded to include the orbit of Mars.
A new study by researchers at the University of Aberdeen suggests that more planets may support life than we previously thought.
"There is a significant habitat for microorganisms below the surface of the Earth, extending down several kilometres. And some workers believe that the bulk of life on Earth could even reside in this deep biosphere." said Professor John Parnell from the University of Aberdeen, while addressing an audience at last week's British Science Festival.
Sean McMahon, a PhD student working with Parnell added: "If you take into account the possibility of deep biospheres, then you have a problem reconciling that with the idea of a narrow habitable zone defined only by conditions at the surface."
Parnell and McMahon are using this idea of deep biospheres to develop a model that will help planet-hunting astronomers pick out more planets from their surveys that may support life.
NASA's Kepler mission is the current leader in the search for extrasolar planets, having discovered over 2,300 potential candidates, and 74 confirmed planets. COROT, a joint mission between the French and European Space Agencies, has found 23 confirmed planets since 2007, with another 2 potentials awaiting confirmation.
Canada is making its own contributions to the search. It was three Canadian astronomers that came up with the method currently used to find extrasolar planets, although they missed their chance at glory. The MOST space telescope, run by the Canadian Space Agency, the Space Flight Laboratory at the University of Toronto Institute for Aerospace Studies and the University of British Columbia, has made several key discoveries since its launch, including several confirmed planets. Another project currently being developed is the Dunlap Institute Arctic Telescope, by astronomers at the University of Toronto, which will scan the long arctic nights for more exoplanets, looking for worlds that may support life.