The light signatures of lichens and algae reflected in a distant planet's distinctive coloring could be evidence of alien life, German researchers say.

Seen from space, Earth gives off a large amount of near-infrared light reflected off the chlorophyll in plants, and similar light wavelength might be seen on distant exoplanets if they also host green vegetation, they said.

However, Siddharth Hegde and Lisa Kaltenegger of the Max Planck Institute for Astronomy in Heidelberg, Germany, said they think many rocky exoplanets will have extreme heat, dryness or acidity, and that hardier life forms -- like lichens and algae -- will dominate their surfaces.

To discover what such organisms would look like from a distance, the researchers analyzed the light reflected by some of Earth's more extreme life forms: lichens in arid regions, bacterial mats in very hot water and red algae in acid mine drainage, NewScientist.com reported.

Seen from across space, each type of organism would create a unique color pattern, they said; lichens, for instance, would appear more yellow than the algae or bacteria.

While such color patterns wouldn't necessarily mean life is present, Hegde and Kaltennegger said, it could be a step toward narrowing down exoplanets for more detailed searches.