An international team of researchers has devised an unusual new way to search for life on other planets – searching for distinctive traces of biological photosynthetic pigments (biopigments) of plants in the light they reflect using polarization filters.
As Dr. Svetlana Berdyugina of the Institute of Physics of the University of Freiburg and the Freiburg Kiepenheuer Institute for Solar Physics and colleagues reported in the latest edition of the International Journal of Astrobiology, if these biopigments were present as a sign of life on another world, they would give off a detectable polarized signature in the reflected light.
Photosynthetic biopigments are plant substances which absorb and reflect particular wavelengths of visible light, thus making them appear in color in reflected wave ranges, the study authors said in a statement. They give plants (and other life forms) their colorful appearance, and the research team found unique traits in the part of the light spectrum they reflect.
Specifically, they found that the part of the spectrum reflected in colors given off by different types of plants oscillates in particular directions, which means that it becomes polarized. Each of these biopigments leave behind a colorful footprint in the polarized light, and the researchers can detect this signature with the help of polarization filters.
Discovery of habitable zone planets not a prerequisite
By using these polarization filters, which they explain work in much the same that that 3D movie glasses or polarized sunglasses do, the study authors can detect this unique signature in polarized light from plants that may exist on distant worlds. The high contrast of the biosignatures found in this light could help detect exoplanetary signals typically masked by stellar light.
“This technique could be instrumental in searching for life in Alpha Centauri, the planetary system closest to the Sun,” Dr. Berdyugina explained in a statement, noting that the nearby star Alpha Centauri B is ideal for conducting such searches due to its close proximity to Earth.
To date, no planet has been found in Alpha Centauri B’s habitable zone (the distance from a star at which a world is capable of maintaining liquid water on its surface). However, Dr. Berdyugina said that the newly-devised polarization technique could be used “to search for biosignatures that point to life” even now, before such a planet’s discovery.
Before more distant planetary systems can be explored using this method, however, larger telescopes will need to be built, she added. For now, though, Dr. Berdyugina and her colleagues from the University of Hawaii and the University of Aarhus in Denmark will have to be content to look for these biosignatures in the light emitted by the Alpha Centauri system.
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