The discovery could imply a modification in the estimations of the number of planets potentially harboring
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 fulfill 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.
In the middle between these extremes lies the so called "radiative habitable zone" also nicknamed the
"Goldilocks Zone" with a dense and wet atmosphere
where heat could be trapped and water could condense at the surface.
This new idea means that these systems can be even more hospitable to habitable planets than single
stars and it has been presented by 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.
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 break 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.
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.
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
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.
Scientists have applied these ideas to evaluate the case of all the binary systems with known planets discovered
by Kepler space telescope. In total six binary systems with circumbinary planets (planets orbiting the two stars)
have been discovered so far:
Kepler 16, Kepler 34, Kepler 35, Kepler 38, Kepler 47, and Kepler 64.
They found that at least three systems - Kepler 34, Kepler 47, and Kepler 64 -- could be very
hospitable to planets because one or both the components are tidally synchronized and hence its activity
has been reduced below the level of single stars of the same age.
Kepler 34 - formed by two almost identical stars with a similar size as the Sun - could even harbor
more than one habitable planet inside its Goldilocks Zone.
The stars in the Kepler 34 system have the right stellar separation and orbital eccentricity to have almost
all its radiative habitable zone free of damaging X-ray and EUV radiation almost from the very beginning.