Two sun system 'better suited for life'

FACom researchers and astronomers of the University of Texas (El Paso) and New Mexico State University have discovered a physical mechanism that could make binary stars more hospitable to habitable planets than single stars.

The discovery could imply a modification in the estimations of the number of planets potentially harbouring life in the galaxy and in the future selection of targets for the search of life elsewhere.

Habitability is the term astronomers use for referring to the general condition a planet must fulfil in order to be suitable for life.

It has been customary to think that habitability is determined mainly by the amount of light a planet receives from its host star.

If the planet receives too much light it is too hot and water will be boiling in its atmosphere (if it has one).

On the other hand, if the planet is too far and light from the star shines weakly, the surface is too cold and water becomes frozen.

Habitability of planets around binary stars (systems formed by two stars orbiting a common center of mass) are subject to similar conditions as described before in the case of single stars.

However, a new mechanism may exist among binary stars, not present in single stars, enhancing (or reducing) the conditions for habitability in this type of stellar environment.

Prof. Jorge Zuluaga and Pablo Cuartas, researchers of FACom and faculty members of the Institute of Physics at the University of Antioquia, together with astronomers Paul A. Mason and Joni Clark of the University of Texas at El Paso (UTEP) and New Mexico State University, released a paper explaining the mechanism that could make some binary systems, ideal places for the search of habitable planets.

In essence the mechanism discovered by Mason et al. is relatively simple.

Binary stars attract each other to their center of gravity but also deform mutually due to the action of the so-called tidal forces.

It is well known that tidal forces could also brake the rotation of the bodies involved. The best documented case is that of our Moon, which has reduced its rotation rate due to tidal forces from Earth to the point that it spins as slowly as it revolves around the Earth (approx. 27 days).

This is why the Moon always shows the same face to the Earth. This phenomenon is called tidal synchronization and is a common feature among moons, close-in exoplanets, and of-course binary star systems.

If the stars in a binary system are synchronized from the very beginning and at the same period of translation in their orbits (of the order of 15 to 30 days), activity of young stars in those systems could be substantially reduced.

In other words, very young stellar components of tidally synchronized binaries could look like grown-up quiet stars, at least in terms of rotation and hence magnetic activity.

This effect has been called by the researchers "rotational aging."

The benefits of an early rotational aging are evident: planets could receive much less high energy radiation at the beginning of their evolution, probably preserving their gaseous envelopes and/or their inventory of water.

If this would have happened in the solar system, Venus probably and perhaps also Mars would be presently habitable.