3 Mar. 2011

 

Habitable zones at risk from tides

 

A cold shower awaits those that saw rocky planets located in the so-called "habitable zone" around red dwarfs as one of the most likely places to find life. The habitable zone is the range of distances from the central star within which a planet similar to the Earth can retain liquid water, something thought to be fundamental for the appearance and development of life.
In recent years, largely because of the relative ease of detection, several, probably rocky, planets (with atmospheres) have been discovered within the habitable zone of red dwarfs. It was therefore thought that this kind of system was the ideal place to search for extraterrestrial life.
But a team of astronomers, led by René Heller of the Astrophysical Institute Potsdam, have studied the effects of the tides exerted by these small stars on their nearby planets, obtaining very discouraging results. In only a few million years, tidal forces act to bring the spin axis of the planet so that it is perpendicular to the orbital plane, causing large differences in the temperature at the poles and the equator. This is expected to create very violent storms and an eventual evaporation of the atmosphere.
Apart from this, Heller's team predicts that the internal friction caused by tidal forces on the planet would also result in an extremely active, global vulcanism. As if this weren't enough, sooner or later the orbital period and spin period would become synchronised, so that one hemisphere was permanently irradiated by the star while the other was in a deep freeze.
Applying their model to the promising exoplanet, Gliese 581g, Heller and colleagues concluded that the presence of liquid water on the surface could be excluded. It would appear that if we want to find a second Earth we need to look for it around a second Sun.

 

by Michele Ferrara & Marcel Clemens

credit: Astrophysical Institute Potsdam, ESO/L. Calcada (image)