If any habitable alien planets are orbiting two or more stars, they’ve probably evolved trees that would look black to human eyes, a new simulation suggests. Such shadowy plants may even move or secrete sunscreen to shield themselves from deadly star flares, the research leader speculates.
Sunlight fuels life on Earth by powering photosynthesis, a process that converts solar radiation and carbon into sugars. Our sun’s color, temperature, and distance from Earth have coaxed photosynthetic plants to absorb most wavelengths of light except for infrared and green, which these plants instead strongly reflect.
But most stars in the nearby universe aren’t like the sun. About 80 percent of the Milky Way’s stars are dim red dwarfs. As a result, astrobiologists have suggested that photosynthetic plants on worlds orbiting lone red dwarfs could take on hues of red, blue, yellow, purple, or even grayish-black to best absorb the starlight. A third of all star systems, meanwhile, contain two or more stars, and it’s not known how plants might evolve under mixed light sources.
“Rather than plants using light from, say, both a sunlike star and a red dwarf, we think you’d see them evolve a diversity of colors and use [the two types of starlight] preferentially,” said simulation leader Jack O’Malley-James, an astrobiologist at the University of St. Andrews in the U.K. “On a world orbiting two red dwarf stars, you’d essentially get one color, and you’d probably see them as black.”
O’Malley-James and colleagues simulated an Earthlike world orbiting a variety of double- and triple-star systems. Some models contained only red dwarf stars, while others used one red dwarf and one sunlike star, or even two sunlike stars.