2007 Annual Science Report
University of Hawaii, Manoa Reporting | JUL 2006 – JUN 2007
Induced Vibronic Circular Dichroism in Ice Bioclathrates as a Potential Remotely Observable Biosignature
Remote detection of extraterrestrial life is one of the most difficult and important challenges of Astrobiology. Perhaps the largest challenge here is to try to decide how to go about looking for life. As pointed out in a recent National Academies of Science report, the enormous variety of forms life could possibly take make it critical to avoid making too many assumptions about what to search for, otherwise we risk getting false negatives in our searches. To help meet this challenge, we have proposed a life search paradigm that is based only on the following two assumptions: that water is central to life and that life is comprised of chiral macromolecular elements that exist in enantiomeric excess. If these conditions are met, then it would be possible to use spectroscopic techniques to look for life using an approach known as Induced Vibronic Circular Dichroism (IVCD). This effect would be present for water intimately associated with chiral molecules, and would especially be present in bioclathrates. In the past year on this project, we have been developing a general equation that will allow us to predict the observability of IVCD in water ices of solar system bodies:
here, Fobs(λ) is the observed flux at wavelength λ, Fi(λ) is the incident flux at wavelength λ, aλ,T is the albedo of the object at the wavelength and temperature it is observed, Iw(λ,T) is the intensity of the water absorbance at the wavelength and temperature observed, and χwo is the amount of ordered water that is observed. Currently, we are working on establishing reliable estimates of the parameters that will influence these variables and will then use this equation to predict the ability to observe an IVCD signal in the ice on terrestrial bodies, with Europa being a major focus.