Find a purple planet, and you may have spotted alien life. Some of the first Earthlings were purple bacteria that ruled the planet about 3 billion years ago. If any Earth-like exoplanets host similar microbes, their distinctive hue will be visible from space.
But we are more likely to find microbial aliens than other kinds, because these life forms thrived on Earth for aeons before larger life forms evolved, and they will survive long after complex life dies out. Esther Sanromá at the Institute of Astrophysics of the Canary Islands and her colleagues wondered if the types of microbes that existed in our planet’s past would give off a unique signature when seen from afar. If so, perhaps we could detect signs of similar microbes living on distant worlds.
They created a model of an exoplanet similar to very early Earth and then considered several scenarios, such as the distribution of continents, cloud cover and whether microbial life thrives on land or at sea. They found that if the purple microbes flourish on land or along nutrient-rich coastlines, they produce a telltale signal in the total light reflected by the planet. If they live only in oceans, the colour is harder to see.
“A world overrun by purple bacteria could show us a very interesting spectral fingerprint,” says Lisa Kaltenegger of the Max Planck Institute for Astronomy in Heidelberg, Germany, who was not part of the research team.
The James Webb Space Telescope, due to launch in 2018, could measure such a signal, as long as the purple planet’s star system is not too far away. That star will also have to be small enough that it doesn’t outshine its orbiting planet, otherwise we will have to wait for the next generation of telescopes, which will be more sensitive and may be able to filter out the glare from brighter stars.
Plated Lumberer - Dorky temporary name. A beast of burden native to the Bex homeworld, used for meat, labor, hides and especially for the thick armor plating that covers its dorsal region. The plating is tough but flexible and is used for an almost countless array of things from shelters to jewelry and apparel.