Monday, February 04, 2008

Habitable Zones More Extensive

via Astrobiology, a new look at both our own world and exoplanets like those found in the Gliese system have caused researchers to expand the habitable zone found around distant stars. In effect, previous searches for planets with liquid water ignored the latitudinal variation that effects temperature so much here on Earth. Adding in effects like hydrothermal vents, volcanic activity and tidal forces, and the distance in which liquid water could range on a distant world could more than double.

"In old models of planetary conditions, average global temperatures provided approximate figures. For example, the Earth is said to have a mean global temperature of 15°C. This simplification is useful for mathematical modelling but doesn’t reflect reality. We know that some places on the Earth are much hotter and others colder. There’s also great variability in temperatures during different seasons. The latitude of continents dramatically influences temperature as well. Consider that Africa is hotter than Antarctica, even though they’re on the same planet. Professor Siegfried Franck of the Potsdam Institute realised that such variations on a planet could change our views on habitable zones.

Franck and his team devised equations to take into account temperature variations caused by the latitude of continents. They found that areas of frozen worlds could be habitable even though they are far from their parent stars. “Our result was that if we investigate this latitudinal dependence, the outer edge of the habitable zone can be extended a remarkable amount,” says Franck."

To use our own system as an example, liquid water could exist under the right conditions on a planet up to twice as distant as the Earth is from the Sun. Therefore, hardy types of biological organisms (such as extremophiles found in the Artic and Antarctic regions on Earth) could exist on frozen worlds far from their parent stars, such as the Gliese system, where a pair of large "super Earths" exist just inside the habitable zone of their star. Such organisms might hibernate for long periods until temperatures raise for brief periods in the planet's orbit or local conditions activate the creatures.

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