Earth-like planets could grow black trees

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

In a new study, researchers have assessed the potential for photosynthetic life in multi-star systems with different combinations of sunlike stars and red dwarfs to figure out what plants might be like. The team has speculated that on an Earth-like planet with two or three suns, the vegetation may appear black or grey.

"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," said PhD student Jack O'Malley-James from the University of St. Andrews in Scotland.

"The temperature of a star determines its colour and, hence, the colour of light used for photosynthesis. Depending on the colours of their star-light, plants would evolve very differently."

Adapting to multiple suns

Photosynthesis - converting sunlight into energy - is the basis for the majority of life on Earth. It is the energy source for plants and, accordingly, 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.

Assessing a combination of scenarios

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.