Biopigments can reveal life on other Earths

Examples of samples (plants and sands) with different pigments measured in the lab (top, left) and the polarized spectra of Earth-like planets with the visible surface completely covered by various biopigments and clear ocean (bottom, left). The instrument and laboratory setup are shown on the right.

Finding life on other planets is one of the ultimate goals of modern astrophysics. Prof. Dr. Svetlana Berdyugina and her team have proposed and developed a new approach for searching life on other planets. They have measured in the laboratory samples of terrestrial plants containing various biological photosynthetic pigments (biopigments, BP) and found that these biopigments modify reflected light in such a way that it becomes linearly polarized to a high degree. This means that the reflected electromagnetic wave oscillates preferably within one plane, and an external observer can see a very conspicuous signal of biopigments if the planet is observed in polarized light. The team has also measured non-biological samples like sand and rocks containing different mineral pigments. The measured data were used to model polarized and unpolarized spectra of Earth-like planets.

In contrast to biopigments, minerals do no show a very high polarization degree in the reflected light of planets and can be well distinguished from biopigments. This is an excellent news for future large telescopes and space missions which will search for life signatures on nearby Earth-like planets. A scientific paper with these results was submitted to the International Journal of Astrobiology and will be published in the fall 2014. An article in the University of Freiburg Magazine describing the research by Prof. Dr. Svetlana Berdyugina and her team can be found here.

The laboratory measurements were carried out with a prototype of the Innovative Polarimeter (InnoPol). InnoPol was built within an international cooperation between KIS, University of Hawaii (USA) and University of Turku (Finland) which was funded by the Leibniz Association. It is currently being commissioned at the 3.6m AEOS telescope of the Haleakala Observatory, Maui (USA). A copy of this prototype has been built at KIS and will be employed for further measurements of biological and non-biological samples in order to improve models of extrasolar Earths, their reflectance properties and atmospheres. This work is also supported by the ERC Advanced Grant HotMol.