R EMOTE DETECTION OF BIOLOGICAL PIGMENTS BY SPECTRO - POLARIMETRY Svetlana BERDYUGINA 1,2, Tina ŠANTL-TEMKIV 3, Kai FINSTER 3,4, Jefferey R. KUHN 2, Dave HARRINGTON 2 1 Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany 2 University of Hawaii, Makawao, USA 3 Aarhus University, Stellar Astrophysics Centre, Aarhus, Denmark, 4 Aarhus University, Department of Bioscience, Microbiology Section, Aarhus, Denmark Correspondence to: (S. Berdyugina) R ESULTS & DISCUSSION On Earth, the biosphere is an important part of both the planetary surface and the atmosphere, which is used as a major dispersal route by many organisms. The surface biosphere emits a substantial amount of bioaerosols to the atmosphere, where they on average comprise 25% of total airborne particles larger than 0.2 μm [3]. Both surface biosphere and bioaerosols are directly in contact with Sun’s radiation, which on the one hand serves as a source of energy to some organisms but on the other hand poses a substantial threat via UV radiation and production of reactive oxygen species. Many of these organisms evolved a potential to produce pigments, i.e., molecules that selectively absorb certain wavelengths of light, in order to harvest energy or protect the organisms. These biopigments may serve as a novel biosignatures on Earth-like planets. I NTRODUCTION R EFERENCES [1] S. V. Berdyugina, A.V. Berdyugin, D.M. Fluri, and V. Piirola, Astrophysical Journal Letters 673 (2008) [2] S. V. Berdyugina, A.V. Berdyugin, D.M. Fluri, and V. Piirola, Astrophysical Journal Letters 728 (2011) [3] R. Jaenicke, S. Metthias-Maser and S. Gruber, Environmental Chemistry 4 (2007) AIM We carried out a laboratory spectro-polarimetric study of light reflected by various pigmented bacterial types and terrestrial plants as well as non-biological samples (e.g., sands). Fig. 1. The experimental setup is shown. Samples were illuminated by an unpolarized light source at different light incident angles . The reflectance angle  was varied by rotating the sample holder. The reflected light was modulated by a quarter-wave-plate (QWP) and linear polarizer (LP) to obtain measurements of four Stokes parameters: intensity I, linear polarization Q and U, and circular polarization V. Measured reflection spectra were used to synthesize polarized spectra of Earth-like planets with various contributions from land, photosynthetic organisms, ocean, atmosphere, and clouds. M ETHODS  The presence of chlorophyll and other biopigments is revealed by both absorption and polarization.  Different parts of plants and bacterial cells showed similar spectra for the same color, which implies that the observed color was caused by the same type of biopigments.  Maximum polarization is associated with maximum absorption, i.e., scattered photons that escaped the absorption are highly polarized.  The so-called “red edge” is visible for most samples.  Absorption features correspond to the color of the sand.  Polarization is significantly less prominent. Gypsum, White Sands Sand, Western Australia Sand, Central Australia Sand, central Sahara Fig 3: Reflectance and polarized spectra of various sands. Fig 2: Reflectance and polarized spectra of red leaves, flower petals (left) and the pink pigmented microbe Methylobacterium sp. (right). Fig 1: Reflectance and polarized spectra of green leaves (left) and the cyanobacterium Synechococcus sp (right). Fig 4: Modeled reflectance and polarized spectra for planets with Earth-like atmosphere 100% of biopigment surface coverage 100% of desert coverage  A high linear polarization degree clearly indicates the presence of various biopigments (bottom left).  Inorganic sands show less linear polaization (bottom right). C ONCLUSIONS 1.Characteristic signatures of biopigments are very different from inorganic pigments found in sands and rocks, especially when albedo is combined with polarimetric signals. 2.The high polarization associated with absorption features of biopigments can serve as a strong biosignature for remote detection of life. Inspired by the recent demonstration of polarized reflected light being detectable from exoplanetary atmospheres [1,2], we aim at identifying spectro-polarimetric biosignatures that were resulting from biological polarization, e.g., selective light absorption or scattering by biogenic molecules.