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J.B. Dalton (NASA Ames Research Center, National Research Council Resident Associate)
Infrared spectral measurements on the sulfur-metabolizing bacteria Sulfolobus shibatae, the radiation-resistant Deinococcus radiodurans and common Escherichia coli have been performed under pressure and temperature conditions appropriate to Europa. Initial results indicate distinct correlations with infrared spectra of Europa measured by telescopic and spacecraft instruments.
Several explanations have been proposed for the distorted water absorption features in the Europan spectrum, including the presence of water in a bound state (e.g. hydrates) which prevents certain allowed vibrational transitions. Living cells contain water in many bound forms, including hydrates. Additionally, the red to brown coloration of the bacteria studied appear consistent with the colors observed by Galileo SSI. Room temperature measurements of primitive biological samples reveal spectral structure strikingly similar to that of Europa, though the band positions are not correct because the cellular water is liquid.
For this experiment, samples were measured under nitrogen at room temperature and every ten degrees down to 100 K. At cryogenic temperatures the chamber was evacuated to 0.01 mbar. The primary water absorption bands at 1.0, 1.25, 1.5, and 2.0 microns in the samples shifted to the positions observed in the Europa spectra. The distorted and asymmetric features of the 1.5 and 2.0 micron bands were reproduced in detail.
Two extraneous bands due to amide bonds in the cells' protein coatings were observed at 2.05 and 2.17 microns. The protein amide bonds are the weakest bonds in the cellular structure and would be among the first to disintegrate upon exposure to particle bombardment at the Europan surface. Experiments involving radiation processing of frozen materials must be conducted before it will be possible to determine whether the results of this study could indeed be evidence for life on Europa.
The author(s) of this abstract have provided an email address for comments about the abstract: dalton@mail.arc.nasa.gov