10 September 2012 Last updated at 15:40 GMT

More planets could harbour life

New computer models suggest there could be many more habitable planets out there than previously thought.

Scientists have developed models to help them identify planets in far-away solar systems that are capable of supporting life.

Estimates of habitable planet numbers have been based on the likelihood of them having surface water.

But a new model allows scientists to identify planets with underground water kept liquid by planetary heat.

The research was presented at the British Science Festival in Aberdeen.

Water is fundamental for life as we know it.

Planets too close to their sun lose surface water to the atmosphere through evaporation.

Surface water on planets located in the more frigid distant reaches from their sun is locked away as ice.

The dogma was, for water to exist in its life-giving liquid form, a planet had to be the right distance from its sun - in the habitablezone.

As Sean McMahon, the PhD student from Aberdeen University who is carrying out the work explained: "It's the idea of a range ofdistances from a star within which the surface of an Earth-like planet is not too hot or too cold for water to be liquid.

"So traditionally people have said that if a planet is in this Goldilocks zone - not too hot and not too cold - then it can have liquidwater on its surface and be a habitable planet"

But researchers are starting to think that the Goldilocks theory is far too simple.

Planets can receive two sources of heat - heat direct from the star and heat generated deep inside the planet.

As you descend through the crust of the Earth, the temperature gets higher and higher. Even when the surface is frozen, water canexist below ground.

Immense quantities of water in fact - teaming with primitive life.

As Prof John Parnell, also from Aberdeen University, who is leading the study, said: "There is a significant habitat formicroorganisms below the surface of the Earth, extending down several kilometres.

By Jonathan BallBBC News

BBC News - More planets could harbour life http://www.bbc.co.uk/news/science-environment-19545186

1 of 2 9/10/2012 7:27 PM

"And some workers believe that the bulk of life on Earth could even reside in this deep biosphere."

So the Aberdeen team are developing models to predict which far-flung planets might harbour underground reservoirs of liquidwater with the possibility of alien life.

Explaining their rationale, Mr McMahon said: "If you take into account the possibility of deep biospheres, then you have a problemreconciling that with the idea of a narrow habitable zone defined only by conditions at the surface."

As you move away from the star the amount of heat a planet receives from the star decreases and the surface water freezes - butany water held deep inside will stay liquid if the internal heat is high enough - and that water could support life.

Even a planet so far from the star that it receives almost no solar heat could still maintain underground liquid water.

According to Mr McMahon, "There will be several times more [habitable] planets".

More Science & Environment stories

Lava study backs dry early Mars[/news/science-environment-19525421]A study of rocks at an old French A-bomb test site in the Pacific has led a team of scientists to conclude that early Mars was not so warm and wet, as many argue.Smart sharks pass on feeding tips[/nature/19484530]UK to fight energy product ruling[/news/science-environment-19545185]

BBC © 2012 The BBC is not responsible for the contentof external sites. Read more.

BBC News - More planets could harbour life http://www.bbc.co.uk/news/science-environment-19545186

2 of 2 9/10/2012 7:27 PM