Worlds living under two suns might be covered in forests and glens of gray or black, according to a Royal Astronomical Society presentation reported by ScienceNow. With disparate wavelengths to harness at once, plants might deploy densely packed pigments of different hues. To our eyes, such broad spectrum absorption would make the leaves look black.
Red dwarf stars are the most common in the Milky Way and could frequently pair up with large companions here and in other galaxies. Astronomers have detected three planetary systems shone on by binary stars, but in each case the planets orbited only the primary star and the smaller companion was distant. In many cases the violence of two stars’ gravitational fields would simply hurl worlds out into the void. Red dwarfs themselves might pose hazards to life, lashing out with enormous flares.
Our green planet isn’t so unlike these imagined graylings swimming through space. Chlorophyll, which comes in three forms, is helped in its light-to-sugar alchemy by handmaiden pigments like carotenoids, anthocyanins, and betalains. These other yellow, orange, red, blue, and purple pigments are nearly ever-present but are more easily observed in autumn foliage and ripening fruit when chlorophyll drains away (or in some species, like members of the rose family, in young leaves before chlorophyll fills in), or by turning over forest understory leaves. These pigments absorb wavelengths that chlorophyll fails to catch for energy or protection against damage, or reflect light back into the chlorophyll before it can exit the leaf. One point of curiosity is that science has yet to identify a plant in which anthocyanins and betalains coexist.
If our sun were to capture a stray red dwarf, might evolution favor plants best able to boost and adapt use of their complementary pigments?
An absolutely wonderful way to enjoy stars and leaves in one setting is to hike up Inwood Hill for a picnic before sharing the splendor of the heavens with the Inwood Astronomy Project.
Eerie gray planets aside, it’s beautiful to imagine worlds of myriad hues. I’m with Robert Frost, however, on the point that there’s one color no living world can maintain:
Nature’s first green is gold,
Her hardest hue to hold.
Her early leaf’s a flower;
But only so an hour.
Then leaf subsides to leaf.
So Eden sank to grief,
So dawn goes down to day.
Nothing gold can stay.