Colours of exoplanets could reveal signs of life

One way to find whether exoplanets would contain life forms would be by looking at their distinctive colours, say scientists.

When seen from space, Earth gives off a large amount of near-infrared light, which is reflecting off the chlorophyll in plants.

It is possible that we might see a similar "red edge" on distant exoplanets if they also host green vegetation.

But Siddharth Hegde and Lisa Kaltenegger of the Max Planck Institute for Astronomy in Heidelberg, Germany, think that many rocky worlds will possibly have extreme heat, dryness or acidity, and that hardier life forms will dominate their surfaces, according to the New Scientist.

To find out what would these organisms look like from a distance, the pair looked at 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.

They calculated that seen from afar each type of organism would create a unique colour pattern. Lichens, for instance, appear more yellow than the algae or bacteria.

Finding these patterns could help narrow down exoplanets for more detailed searches, the scientists said.

It''s an attractive idea, said Nicolas Cowan of Northwestern University in Evanston, Illinois.

But he noted that the work has its limits.

For instance, he said that atmospheres on other planets may be very different from our own and could scatter light in ways we wouldn''t expect.

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