The development of means of direct detection of exoplanets is in full swing, and it sets the researchers question: how the received image exoplanets and aktolun you can use to determine their habitability? Astronomers from Germany and the USA after the simulation of different options of such "color", came to the conclusion that it really is possible to judge about the presence and even to some extent on the composition of the biosphere.

As it looks from space the Earth, is known: in 1990, at the request of Carl Sagan Voyager-1" photographed the planet with the removal of 6 billion km, the Result was predictable: 0,12 pixel, or "pale blue dot" Pale Blue Dot).

The Siddhartha Hedge of the astronomy Institute of max Plank Society (Germany) and Lisa Kaltenegger of the Harvard-Smithsonian center for astrophysics (USA) note: this color is 100% due to the habitability of the Earth, mainly water, covering 70% of its surface. In addition, a significant contribution give vegetation (which covered 60% of the solid surface), snow, desert, etc.

However, this planet looked not always, and it is very likely that such a color not available to many of potentially habitable planets outside our Solar system.

Moreover, the hypothetical observer (with equipment appropriate level) from another star system will see not only this blue color. It is well known that when the daily rotation of the Earth absorption of red light will periodically to fall sharply ("red edge") - as from the oceanic expanses of alien telescope will go on lush (reflecting light in the red spectral range) area of the land. Albedo plants on the average will grow from 680 to 730 nm, from 5 to 50%, which can not be overlooked. However, the scientists, the life will provide indicators of this kind only if certain conditions. Around stars other than the Sun, spectral class of possible "blue edge"when (avoid overheating shorter-wavelength radiation) albedo plants will be to increase dramatically, not in the red and infrared parts of the spectrum, and in ultra-violet and purple.

On the other hand, the researchers note, color analysis can help identify a less developed life - for example, extremophilic. Lichens, biofilms, bacterial mats effectively detected by specific colors, and their dominance, undoubtedly, will give the surface of the planet their shades.

In General, the authors when selecting objects is recommended to give preference to the planets of the blue part of the spectrum before reddish type of Mars. Among other things this color indicates significant presence of liquid water, which increases the chances of detecting life.

At the same time remain ways that are not detectable in the mentioned way. Soil extremophiles for protection from ultraviolet radiation and other threats may disappear altogether from the surface, and then their influence on the color of exoplanets will be minimal. It is very difficult to observe the planet with serious cloudy...

And one more thing. Modern scientific world is not quite firmly believes in the uniqueness of the current shades of solid earth. As in other geological epochs color might be different from today, right? For example, the hypothesis of "purple Earth" implies that at the time when the life of the planet could not look green and red-purple. In the process of photosynthesis ancient autotrophs could use chlorophyll and different substance, bakteriokhlorofill. It and today employs a group of photosynthetic proteobakterii living in the water. They contain red pigments: bacteriochlorophylls a and b and carotinoids, giving them a purple color. Such pigments allow to use effectively (absorb) light green part of the spectrum. Now, if you believe the "purple Earth", except bakteriokhlorofill, first autotrophs could use for photosynthesis aldehyde vitamin a, which also had to give them specific red color.

By the way, it is assumed that the green clariilovee organisms acquired by chance in competition with purple. After ousting those primary autotrophs green entrenched as a common feature of photosynthetic organisms. In short, if the hypothesis is correct, then green even in the conditions of life under the sun-like star random, and therefore cannot be considered as reliable evidence of highly developed life.

With a Preprint of the relevant survey can be found here.

Prepared based on materials Technology Review.