The Rio Tinto Mars Analogue site: An extremophilic Raman spectroscopic study

Abstract

The Rio Tinto site is recognised as a terrestrial Mars analogue because of the presence of jarosite and related sulfates which have recently been identified by the NASA Mars Exploration Rover "Opportunity" in the El Capitan region of Meridiani Planum on Mars. It has long been known that acidophilic microbial action is responsible for the deep blood-red colour of the water in Rio Tinto, where the pH varies from about 1.5 to 3.0 and the water is rich in iron and sulfur. Following recent Raman spectroscopic characterisation of the mineral phases of the Rio Tinto system, we report here a study of the biological components found in several specimens of deposited minerals and near the waterside that were collected during a GeoRaman VI Conference organized field trip in 2006. Key biosignatures were found for carotenoids, scytonemin and mycosporine-like amino acids, which are indicative of the biological colonisation of exposed mineral substrates; information from this study will be useful for targeting Martian sites using a miniaturized Raman instrument where the biosignatures of relict or extant life could remain in the geological record.

Potential and limits of Raman spectroscopy for carotenoid detection in microorganisms: implications for astrobiology

“…For detecting them in the frame of future Mars missions, the application of Raman spectroscopy was proposed [38][39][40]. In fact, it was shown that on the Earth carotenoids can unambiguously be detected in lichen encrustations [41][42][43][44].…”

Raman Spectroscopy of Microbial Pigments

“…Based on the characteristics of UV absorption by MAAs, several studies have suggested that these compounds can act as natural screens of UV radiation and should be considered photoprotectants (66,67). The Raman spectrum assigned to a mycosporine-like amino acid compound was reported for a jarosite matrix originating from Rio Tinto, Spain (68) and from hyperarid (Atacama, Chile) shallow subsurface layers (69).…”

“…Raman microspectrometry permits the direct study of pigment type and distribution in endolithic zones in the frame of natural stony samples without sample treatment or extractions. Microbial communities inhabiting rocks from various extreme environments were studied: Antarctic habitats (82-84), volcanic rocks as well as travertines on Svalbard (Norway) (80,85) as well as halophiles from a hot desert (68,86). Raman spectroscopy revealed differences in pigment distribution in chasmolithic and endolithic colonizations of differing lithologies, including those from dolomite, gypsum, or altered orthoquartzite (83,86).…”

Remote Raman Spectroscopy for Planetary Exploration: A Review

“…48 Finally, in 2007 Edwards et al took a portable system to the Rio Tinto, a river rich in iron and sulfates with an acidic pH. 49 This site is widely considered an analog to the El Capitan region of the Meridiani Planum on Mars. Within the river, key biomarkers, such as carotenoids and scytonemin, and minerals, such as jarosite and gypsum, were detected.…”

“…71 Other important minerals include pyroxene, olivine, quartz, jarosite, and gypsum. 49,72,73 Ice is another very important geological sample that could hold key biomarkers and is unique in that water can exist as a solid, liquid, or gas in the atmosphere. Raman has been able to distinguish between different forms of ice with conventional Raman spectrometers 18 and in remote systems (Fig.…”