The Color of an Exoplanet

Artist’s concept of exoplanet HAT-P-7b. Image Credit: NASA

The search for extrasolar planets has already detected rocky planets and interesting planetary candidates in the Habitable Zone of their host stars. Astrobiologists are pioneering new ways of imaging and examining these worlds, including how to assess their habitability.

A new NAI-funded paper in the journal Astrobiology explores how a visible light filter photometry reading of an exoplanet might look if that planet had life on it.

Such a reading of Earth, the pale blue dot, shows a “red edge” caused by green plants as they absorb light in the red part of the visible spectrum. But the characteristics of vegetation (or any organism with chlorophyll) on an exoplanet could vary depending on its host star.

The signature of chlorophyll near a hot star could have a blue, rather than red, edge to protect a plant’s leaves from overheating. Or on a planet that orbits a cool, dim star chlorophyll may appear black as it tries to absorb as much light as possible across the whole range of the visible spectrum.