Wednesday, April 29, 2009

Potential Universal Biosphere Signal: Homochirality

Detection of circular polarization in light scattered from photosynthetic microbes

1. William B. Sparksa,1,
2. James Houghb,
3. Thomas A. Germerc,
4. Feng Chend,
5. Shiladitya DasSarmad,
6. Priya DasSarmad,
7. Frank T. Robbd,
8. Nadine Mansete,
9. Ludmilla Kolokolovaf,
10. Neill Reida,
11. F. Duccio Macchettoa and
12. William Martinb

-Author Affiliations

aSpace Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218;
bCenter for Astrophysics Research, University of Hertfordshire, Hatfield AL10 9AB, United Kingdom;
cNational Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899;
dCenter of Marine Biotechnology, University of Maryland Biotechnology Institute, 701 East Pratt Street, Suite 236, Baltimore, MD 21202;
eCanada-France-Hawaii Telescope, 65-1238 Mamalahoa Highway, Kamuela, HI 96743; and
fDepartment of Astronomy, University of Maryland, College Park, MD 20742


Edited by Rita R. Colwell, University of Maryland, College Park, MD, and approved March 24, 2009 (received for review October 10, 2008)


The identification of a universal biosignature that could be sensed remotely is critical to the prospects for success in the search for life elsewhere in the universe. A candidate universal biosignature is homochirality, which is likely to be a generic property of all biochemical life. Because of the optical activity of chiral molecules, it has been hypothesized that this unique characteristic may provide a suitable remote sensing probe using circular polarization spectroscopy. Here, we report the detection of circular polarization in light scattered by photosynthetic microbes. We show that the circular polarization appears to arise from circular dichroism of the strong electronic transitions of photosynthetic absorption bands. We conclude that circular polarization spectroscopy could provide a powerful remote sensing technique for generic life searches.

* homochirality
* life detection
* remote sensing


* 1To whom correspondence should be addressed. E-mail:

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