EPSC Abstracts,
Vol. 3, EPSC2008-A-00388, 2008
European Planetary Science Congress, © Author(s) 2008
Targeting organic molecules in hydrothermal environments on Mars
J. Parnell (1), S. A. Bowden (1), P. Lindgren (2), R. Wilson (3) and J. M. Cooper (3)
(1) School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK, (2) Dept. of Geology and
Geochemistry, Stockholm University, Stockholm, Sweden, (3) Dept. of Electronics & Electrical Engineering,
University of Glasgow, UK ([email protected] / Fax: +44-1224-272785)
Hydrothermal deposits on Mars
Hydrothermal systems are proposed as environments
that could support organic synthesis, the evolution of
life or the maintenance of life [1,2,3]. They have
therefore been suggested as primary targets for
exploration on Mars [1,2,4,].There is now confidence
that hydrothermal deposits occur at the martian
surface. This is based on a range of criteria that could
point towards hydrothermal activity, including
volcanic activity, magmatic-driven tectonism, impact
cratering in icy terrains, hydrous alteration of minerals
and typical hydrothermal mineralogies [4]. The
proposals to search for evidence of life at martian
hydrothermal sites have been focussed on seeking
morphological evidence of microbial activity [5]. Here
we discuss the potential to seek a chemical signature
of organic matter in hydrothermal systems.
Organics in terrestrial hydrothermal systems
Terrestrial hydrothermal systems can have large
quantities of organic matter because they intersect
organic-rich sedimentary rocks or oil reservoirs. Thus
the signatures that they contain reflect some preexisting concentration of fossil organic compounds,
rather than life which was active in the hydrothermal
system. If any extant life was incorporated in these
hydrothermal systems, it is swamped by the fossil
molecules. Examples of environments where organic
materials may become entrained include subsurface
hydrothermal mineral deposits, generation of
hydrothermal systems by igneous intrusions, and hot
fluid venting at the seafloor. Nevertheless, there is
value in studying the interactions of hydrothermal
systems with fossil organic matter, for information
about the survivability of organic compounds, phase
relationships between carbonaceous and noncarbonaceous materials, and where in hydrothermal
deposits to find evidence of organic matter.
Microbial colonization of hot spring systems is
feasible at depth within the systems and at the surface
where the hydrothermal waters discharge. Discharging
fluids will also precipitate minerals due to drop in
temperature and pressure, and colonising organisms
are likely to become entrained by the minerals.
Attempts to find evidence of microbial activity related
to hydrothermal systems in the geological record have
therefore been focussed on hydrothermal mineral
precipitates. Organic matter is found in hydrothermal
precipitates back into the Precambrian [6].
Fig. 1 Settings for organic matter in hydrothermal systems. Surface
discharge could be in subaerial or subaqueous environment.
Application of SERS
Studies using conventional laser Raman instruments
have made a good case for application of this type of
spectroscopy to planetary exploration. The detection
of pigments sited in microbial matter in a range of
samples from extreme environments (e.g. [7]) has
supported development of the technique for space
exploration generally, and Mars exploration in
particular [8]. A major advantage of conventional
Raman spectroscopy is that it can be applied to
simultaneous characterization of bond types in both
organic and inorganic materials. Surface-Enhanced
Raman Spectroscopy (SERS) increases the sensitivity
by several orders of magnitude, and overcomes the
problems created by natural fluorescence [9]. SERS is
achieved by adsorbing the target analyte onto the
surface of a metal. We are combining the additional
sample processing necessary for SERS with sample
preparation in a microfluidic format (including
extraction and sample concentration). The final result
will be a very rapid assay, capable of detecting ppb
concentrations of certain organic analytes.
This approach was tested at a site in Iceland, where
young/active hydrothermal systems are focussed in a
rift environment. Sulphur species are prevalent, in a
range of oxidation states, including sulphates,
sulphides and native sulphur. Thus they are a useful
model for systems that might exist on Mars, where
sulphur species are widespread and therefore likely to
be incorporated into hydrothermal systems. Microbial
colonization of the Iceland sites is evident as
pigmentation, which is amenable to SERS. The
pigments detected by SERS are particularly
phycocyanin, scytonemin and β,β carotene (Fig. 2),
the distribution of which is controlled by water
temperature. A SERS response is obtained from
sinters as well as active hydrothermal discharges.
This successful application of SERS indicates a
potential technique for the exploration for organic
compounds in martian hydrothermal systems.
ph
ph
Brown/purple
sc sc
sc
Orange
b,b
b,b
b,b
C–S, C=S
Green
D2
D1
C–O–C
Sinter
Blank
600
800
1000
1200
1400
1600
1800
2000
Raman Shift (cm-1)
Fig. 2 SERS spectra for pigmented samples and sinter in active hydrothermal system, Iceland. Ph, phycocyanin; sc, scytonemin; b,b, β,β
carotene. Sinter shows bond-types, including D1/D2 organic peaks. Sampling courtesy of K. Jonasson, Iceland Institute of Natural History.
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