Black Trees Under Two Suns

Gliese 667 is one of two multiple star systems (the other being 55 CnC) known to host planets below 10 Earth masses. Image Credit: ESO/L. Calçada

A sky with two suns is a favorite image for science fiction films, but how would a binary star system affect life evolving on an orbiting planet?

Jack O’Malley-James of the University of St. Andrews has studied what plants might be like on an Earth-like planet with two or three suns and found that they may appear black or grey. He presented results at the RAS National Astronomy Meeting in Llandudnoon Tuesday 19th April.

Photosynthesis — converting sunlight into energy — is the basis for the majority of life on Earth. It is the energy source for plants and, hence, animals higher up the food chain. With multiple light sources, life may have adapted to use all suns, or different forms may develop that choose to use one specific sun. This may be the more likely option for planets on which parts of the surface are illuminated by only one sun for long periods of time.

“If a planet were found in a system with two or more stars, there would potentially be multiple sources of energy available to drive photosynthesis. The temperature of a star determines its color and, hence, the color of light used for photosynthesis. Depending on the colors of their star-light, plants would evolve very differently,”said O’Malley-James.

O’Malley-James is working on a PhD, supervised by Dr. Jane Greaves at the University of St. Andrews, Prof. John Raven of the University of Dundee and Prof. Charles Cockell of The Open University, to assess the potential for photosynthetic life in multi-star systems with different combinations of Sun-like stars and red dwarfs.

Black plants on a world with two suns. Credit: University of Saint Andrews

Sun-like stars are known to host exoplanets and red dwarfs are the most common type of star in our Galaxy, often found in multi-star systems, and old and stable enough for life to have evolved. Over 25% of Sun-like stars and 50% of red dwarfs are found in multi-star systems. In the team’s simulations, the Earth-like planets either orbit two stars close together or orbit one of two widely separated stars. The team has also looked at combinations of these scenarios, with two close stars and one more distant star.
