Circular polarization in scattered light as a possible biomarker

Abstract

Original article can be found at : http://www.sciencedirect.com/ Copyright ElsevierBiological molecules exhibit homochirality and are optically active. Therefore, it is possible that the scattering of light by biological molecules might result in a macroscopic signature in the form of circular polarization. If this is the case, then circular polarization spectroscopy, which may be utilized in remote sensing, can offer a powerful indicator of the presence of a universal biosignature, namely homochirality. Here, we describe laboratory experiments designed to investigate this idea. We focus on photosynthetic microorganisms, and also show results from macroscopic vegetation and control minerals. In the microorganisms, we find unambiguous circular polarization associated with electronic absorption bands of the photosynthetic apparatus. Macroscopic vegetation yields a stronger and more complex signature while the control minerals produce low-levels of circular polarization unrelated to their spectra. We propose a heuristic explanation of our results, which is that the polarization is produced by circular dichroism in the material after the light has undergone its last scattering event. The results are encouraging for the use of circular polarization spectroscopy in remote sensing of a generic biomarker from space or the ground

Innovative technology for optical and infrared astronomy

“…Homochirality should be detectable via circular polarisation (Sparks et al 19 ), but the signal from a planet covered with primitive life is likely (at least) an order of magnitude smaller than the degree of linear polarisation from atmospheric scattering. Even larger telescopes (with a very good control of polarization cross-talk) will therefore be required to answer the biggest question of all: 'Is there other life out there?'…”

Remote sensing of life: polarimetric signatures of photosynthetic pigments as sensitive biomarkers

“…Early studies of Pospergelis (1969) followed by Wolstencroft (1974) and others presented measurements of full Stokes and circular polarization of leaves and mineral samples. Sparks et al (2009) continued this investigation with microbes. It was found that a unique circular polarization signature associated with homohirality in living organisms is extremely weak (5 × 10 -4 at most under laboratory conditions) which would require unrealistic exposure time with a gigantic space telescope to be detected on distant planets, but it can perhaps be searched for in the Solar system objects.…”

Triple Wollaston-prism complete-Stokes imaging polarimeter

“…In addition, all known biological systems have evolved to prefer a particular chirality (or handedness) of organic molecules. This asymmetry in the occurrence of stereoisomers can lead to a unique polarization signal through circular dichroism or optical activity [7,10]. In order to exploit these phenomena one needs to build a polarimeter that can measure both linear and circular polarization, using a robust design that is suitable for a moving platform.…”

“…However, polarization has not been as extensively investigated for imaging applications, although some exciting applications are starting to be explored. [6], and the search for biological activity on other planets [7]. There are even some animals, such as the mantis shrimp, that have evolved sophisticated polarimetric visual systems to obtain valuable information from their environment, and are sensitive to all the polarization components of light [8].…”

“…However, polarization has not been as extensively investigated for imaging applications, although some exciting applications are starting to be explored. Polarimeters can be used in such diverse areas as passive remote sensing [1] for the detection of improvised explosive devices [2], characterization of aerosol particles in the Earth atmosphere [3], extra-solar planet detection [4], remote mapping of planetary magnetospheres [5], quality control for welding [6], and the search for biological activity on other planets [7]. There are even some animals, such as the mantis shrimp, that have evolved sophisticated polarimetric visual systems to obtain valuable information from their environment, and are sensitive to all the polarization components of light [8].…”