Planets with two parent stars face a double whammy of radiation, a situation that would seemingly make them far less suitable for life than single-star systems.
But appearances can be deceiving.
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New research suggests that the gravitational arm-wrestling by a pair of suitably positioned parent stars should carve out a magnetically protected habitable zone for an orbiting brood.
"We need to be more open-minded when thinking about habitability of a significant fraction of the stars in the galaxy that are in binary systems that could provide enhanced habitability conditions," astronomer Jorge Zuluaga with the Institute of Physics at the University of Antioquia in Colombia, told Discovery News.
Zuluaga and colleagues focused on the impact a pair of orbiting stars would have on each others' rates of rotation, which in turn affects how magnetically active they are. The specifics depend on how big and how far apart the two stars are, but generally computer simulations showed there could be magnetically quiet regions around binary stars, a finding that greatly expands their so-called "habitable zones" -- orbits where water could exist on a planet's surface.
Water is believed to be necessary for life, but it's not the only factor. For example, in our solar system Venus and Mars, though situated in the sun's habitable zone, presently do not have life-friendly atmospheres.
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Increased solar activity from a very young sun may be partly or wholly to blame for why Venus and Mars evolved so differently from Earth. The new research suggests that if the sun had a suitably positioned partner star, its early, violent outbursts may have been tempered.
"Habitability is not just a matter of being inside a star's habitable zone. You need to consider other factors. For example, the magnetic activity of the star, the magnetic protection of the planets and the emission of a higher level of radiation at the beginning of the stellar life," Zuluaga said.
To illustrate, scientists took a closer look at six binary systems with orbiting planets found by NASA's Kepler space telescope. Taking into account the stars' gravitational interactions, the researchers found three of the systems were well-suited to have planets in habitable zones. The study showed the habitable zone of one system, known as Kepler 34, was nearly free of damaging X-ray and extreme ultraviolet radiation.
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"This paper really represents a new idea. If there are two stars in a binary system you have gravitational tidal forces, like how the moon pulls on Earth and causes the oceans' tides. That causes the stars to slow down their spins over time," said astronomer Paul Mason with the University of Texas at El Paso.
"It's like a marriage almost. Because they are bound together, they pre-maturely slow each other down, which is really good for the planets that are out there orbiting around. It helps them hold on to their water," Mason told Discovery News.
The research is appears online at arXiv.org and will be published in an upcoming edition of Astrophysical Journal Letters.