Olga Prieto-Ballesteros

Interglacial clathrate destabilization on Mars: Possible contributing source of its atmospheric methane

The presence of methane has been recently detected in the martian atmosphere, suggesting a contemporary source such as volcanism or microbial activity. Here we show that methane may be released by the destabilization of methane clathrate hydrates, triggered by the interglacial climate change starting 0.4 Ma. Clathrate hydrates are nonstoichiometric crystalline compounds in which a water ice lattice forms cages that contain apolar gas molecules, such as methane [CH4· n H2O] and carbon dioxide [CO2· n H2O]. The loss of shallow ground ice eliminates confining pressure, initiating the destabilization of clathrate hydrates and the release of methane to the atmosphere. This alternative process does not restrict the methanes age to 430 yr (maximum residence time of methane gas in martian atmosphere), because clathrate hydrates can preserve (encage) methane of ancient origin for long time periods.

The 2005 MARTE Robotic Drilling Experiment in Río Tinto, Spain: Objectives, Approach, and Results of a Simulated Mission to Search for Life in the Martian Subsurface

The Mars Astrobiology Research and Technology Experiment (MARTE) simulated a robotic drilling mission to search for subsurface life on Mars. The drill site was on Peña de Hierro near the headwaters of the Río Tinto river (southwest Spain), on a deposit that includes massive sulfides and their gossanized remains that resemble some iron and sulfur minerals found on Mars. The mission used a fluidless, 10-axis, autonomous coring drill mounted on a simulated lander. Cores were faced; then instruments collected color wide-angle context images, color microscopic images, visible-near infrared point spectra, and (lower resolution) visible-near infrared hyperspectral images. Cores were then stored for further processing or ejected. A borehole inspection system collected panoramic imaging and Raman spectra of borehole walls. Life detection was performed on full cores with an adenosine triphosphate luciferin-luciferase bioluminescence assay and on crushed core sections with SOLID2, an antibody array-based instrument. Two remotely located science teams analyzed the remote sensing data and chose subsample locations. In 30 days of operation, the drill penetrated to 6 m and collected 21 cores. Biosignatures were detected in 12 of 15 samples analyzed by SOLID2. Science teams correctly interpreted the nature of the deposits drilled as compared to the ground truth. This experiment shows that drilling to search for subsurface life on Mars is technically feasible and scientifically rewarding.

SOLID2: an antibody array-based life-detector instrument in a Mars Drilling Simulation Experiment (MARTE).

A field prototype of an antibody array-based life-detector instrument, Signs Of LIfe Detector (SOLID2), has been tested in a Mars drilling mission simulation called MARTE (Mars Astrobiology Research and Technology Experiment). As one of the analytical instruments on the MARTE robotic drilling rig, SOLID2 performed automatic sample processing and analysis of ground core samples (0.5 g) with protein microarrays that contained 157 different antibodies. Core samples from different depths (down to 5.5 m) were analyzed, and positive reactions were obtained in antibodies raised against the Gram-negative bacterium Leptospirillum ferrooxidans, a species of the genus Acidithiobacillus (both common microorganisms in the Río Tinto area), and extracts from biofilms and other natural samples from the Río Tinto area. These positive reactions were absent when the samples were previously subjected to a high-temperature treatment, which indicates the biological origin and structural dependency of the antibody-antigen reactions. We conclude that an antibody array-based life-detector instrument like SOLID2 can detect complex biological material, and it should be considered as a potential analytical instrument for future planetary missions that search for life.

A chamber for studying planetary environments and its applications to astrobiology

We have built a versatile environmental simulation chamber capable of reproducing atmospheric compositions and surface temperatures for most of the planetary objects. It has been especially developed to make feasible in situ irradiation and characterization of the sample under study. The total pressure in the chamber can range from 5 to 5 × 10−9 mbar. The required atmospheric composition is regulated via a residual gas analyser with ca ppm precision. Temperatures can be set from 4 K to 325 K. The sample under study can be irradiated with ion and electron sources, a deuterium ultraviolet (UV) lamp and a noble-gas discharge UV lamp. One of the main technological challenges of this device is to provide the user the possibility of performing ion and electron irradiation at a total pressure of 0.5 mbar. This is attained by means of an efficient differential pumping system. The in situ analysis techniques implemented are UV spectroscopy and infrared spectroscopy (IR). This machine is especially suitable for following the chemical changes induced in a particular sample by irradiation in a controlled environment. Therefore, it can be used in different disciplines such as planetary geology, astrobiology, environmental chemistry, materials science and for instrumentation testing.

Subsurface Geomicrobiology of the Iberian Pyritic Belt

Terrestrial subsurface geomicrobiology is a matter of growing interest. On a fundamental level, it seeks to determine whether life can be sustained in the absence of radiation, whereas it also aims to develop practical applications in environmental biotechnology. Subsurface ecosystems are also intriguing exobiological models , useful for the re-creation of life on early Earth (Widdel et al. 1993) or the representation of life as it would occur in other planetary bodies (Boston et al. 1992). Subsurface ecosystems were originally reported in basalt aquifers (Stevens and McKinley 1995; Chapelle et al. 2002) and later in sedimentary aquifers, petroleum reservoirs, and alkaline and saline goldmine groundwater (Lin et al. 2006). Results obtained by deep-sea subsurface exploration initiatives are widening the scope of our knowledge in this field (D’Hondt et al. 2004). In this field there is a serious debate on whether the source of electron donors and/or acceptors is dependent on radiation-mediated reactions and also on contamination problems associated with drilling technologies, their mitigation, and control. In spite of the interest of subsurface ecosystems, information concerning microbial abundance, diversity, and sustainability is still scarce, mainly due to methodological limitations. Among the different minerals, the metallic sulfides have the potential to be a good source of energy for subsurface chemolithotrophs . The micro-organisms that aerobically oxidize iron sulfides are well characterized (Gonzalez-Toril et al. 2003), however, little is known about the possibility of subsurface chemolithoautotrophic metabolism in anoxic conditions. The Mars Analog Research and Technology Experiment (MARTE) project (Stoker et al. 2004; Fernandez-Remolar et al. 2005a) outlined in this chapter was designed to search for this type of life in the nonporous volcanically hosted massive sulfide deposits (VHMS) of the Rio Tinto basement at Pena de Hierro (Iberian Pyritic Belt).

Quantitative Raman spectroscopy as a tool to study the kinetics and formation mechanism of carbonates.

We have carried out a systematic study of abiotic precipitation at different temperatures of several Mg and Ca carbonates (calcite, nesquehonite, hydrocalcite) present in carbonaceous chondrites. This study highlights the capability of Raman spectroscopy as a primary tool for performing full mineralogical analysis. The precipitation reaction and the structure of the resulting carbonates were monitored and identified with Raman spectroscopy. Raman spectroscopy enabled us to confirm that the precipitation reaction is very fast (minutes) when Ca(II) is present in the solution, whereas for Mg(II) such reactions developed at rather slow rates (weeks). We also observed that both the composition and the reaction mechanisms depended on temperature, which might help to clarify several issues in the fields of planetology and geology, because of the environmental implications of these carbonates on both terrestrial and extraterrestrial objects.

Raman spectroscopy as a tool to study the solubility of CO2 in magnesium sulphate brines: application to the fluids of Europa’s cryomagmatic reservoirs

The solubility of CO 2 in water at different temperature and pressure conditions has been studied for more than 150 years because of the common presence of this system in the Earth, and its importance for engineering and in several biological and geological processes. However, there are many contradictions in the literature with regard to the solubility of CO 2 in salt-rich aqueous solutions, and associated effects such as the salting out have been studied in detail for only few salts such as NaCl or Na 2 SO 4 . In this study we introduce Raman spectroscopy as a useful tool to measure gas solubility in brines. We have obtained the solubility of CO 2 in aqueous solution of MgSO 4 at different concentrations (5 and 17 wt %), in the range of temperatures from 5 to 20 °C and pressures up to 50 bar. The results allow one to approach different aqueous reactions and processes that are relevant in geochemical phenomena of some planetary objects. Thus, we have modelled the degassing processes that could occur through the crust of Europa, a satellite of Jupiter.

Characterization of Salting-Out Processes during CO2-Clathrate Formation Using Raman Spectroscopy: Planetological Application

ABSTRACT Clathrate hydrates are particular solids that planetologists study in detail because those solids may be present in several bodies of the solar system, such as Mars, comets, and the icy satellites. The solids are formed by solid H2O, like common water ice, but adopt open structures with cavities containing gas molecules. Clathrate hydrates are usually stable at relatively low temperature and high pressure, which are the typical conditions present inside these planetary objects. Their interest for astrobiology is that they represent potential sources of liquid water and gases when they decompose. The present work is focused on the crystallization of clathrates in Europas (icy satellite of Jupiter) interior conditions. We postulate that clathrate hydrates may play an important role in its crust mineralogy and that it can explain some features of the satellites surface due to their formation/destabilization. An in situ kinetic study by Raman Spectroscopy of the clathrate formation from salty solutions was performed in our laboratory. The chemical composition that we used mimics those obtained from Europas surface during the Galileo mission. An effect of the salting-out process in the solution was monitored through the clathrate formational path. Our results demonstrate that this process may have geological consequences on Europa and confirm the suitability of Raman spectroscopy for planetary detection of clathrate hydrates and other ices.

Viable cyanobacteria in the deep continental subsurface

Significance Cyanobacteria were responsible for the origin of oxygenic photosynthesis, and have since come to colonize almost every environment on Earth. Here we show that their ecological range is not limited by the presence of sunlight, but also extends down to the deep terrestrial biosphere. We report the presence of microbial communities dominated by cyanobacteria in the continental subsurface using microscopy, metagenomics, and antibody microarrays. These cyanobacteria were related to surface rock-dwelling lineages known for their high tolerance to environmental and nutritional stress. We discuss how these adaptations allow cyanobacteria to thrive in the dark underground, a lifestyle that might trace back to their nonphotosynthetic ancestors. Cyanobacteria are ecologically versatile microorganisms inhabiting most environments, ranging from marine systems to arid deserts. Although they possess several pathways for light-independent energy generation, until now their ecological range appeared to be restricted to environments with at least occasional exposure to sunlight. Here we present molecular, microscopic, and metagenomic evidence that cyanobacteria predominate in deep subsurface rock samples from the Iberian Pyrite Belt Mars analog (southwestern Spain). Metagenomics showed the potential for a hydrogen-based lithoautotrophic cyanobacterial metabolism. Collectively, our results suggest that they may play an important role as primary producers within the deep-Earth biosphere. Our description of this previously unknown ecological niche for cyanobacteria paves the way for models on their origin and evolution, as well as on their potential presence in current or primitive biospheres in other planetary bodies, and on the extant, primitive, and putative extraterrestrial biospheres.

Fluvial Bedform Generation by Biofilm Activity in the Berrocal Segment of Río Tinto: Acidic Biofilms and Sedimentation

In the acidic environment of Rio Tinto, there is a close relationship between microbial mat growth and channel configuration. This extreme environment is characterized by solutions with a low pH (1–3) and high Eh (300–450 mV), and high concentration in ferric iron (0.5–30 g l−1) and sulfates (1–120 g l−1). Under these conditions, biofilms have several morphologies that adapt to the local parameters controlled by the water flow, light, and hydrochemistry. Seasonal water availability induces different rates in the oxidation degree and concentration of water chemicals. Therefore, seasonal changes favor cycles between high increment in microbial mass and late preservation under coating by inorganic polymers mainly composed by ferric iron and sulfate. Under these circumstances, massive coating of biofilms during the dry season induce clear changes in the river bed in the form of pool and riffle corrugated pattern that has some impact on the river flow. Moreover, sediment accretion and lateral progradation is also found in those areas where the river has a meandering patter or floods on the lower bank. In this last case, lateral sedimentation is favored by the mineralization on biofilms.