Composition and Habitability of Europa’s Ocean Over Time

Introduction: Europa is proposed to host a global liquid water ocean that is in contact with a silicate interior [1]. Understanding the composition of this ocean and the underlying rock is crucial for evaluating the habitability of Europa. However, the presence of an ice shell impedes direct observation or analysis of the ocean and rock, leaving their compositions largely unknown. Previous modelling work has shown that, if Europa accreted entirely from CI or CM chondritic material, sufficient volatiles could be released during prograde metamorphism to account for the current size of the hydrosphere [2]. However, thermal models predict that temperatures in Europa’s interior would gradually increase over billions of years [e.g. 3], where the progressive release of volatiles would change the ocean composition over time. In this study, possible ocean compositions were explored using computer modelling to simulate the thermal evolution of Europa’s interior over its ~4.5 Gyr lifetime and assess the volatiles released from the starting material as it is heated. Methods: The composition of Murchison (a CM chondrite) was chosen to represent the silicate material that accreted to form Europa because the CMs: formed close to early Jupiter (unlike the CIs [4]), contain sufficient water (largely held within hydrated silicates [5]), and can produce fluid compositions consistent with salts observed on Europa’s surface [2, 6]. A 1-dimensional thermal evolution code was used to model the temperatures achieved within Europa’s interior [3]. Temperature-depth profiles were then extracted at two points in time to reflect the formation of the proto-ocean (i.e. ~1600 Myr since the calcium-aluminium-rich inclusions (CAIs)) and the current-day ocean (~4568 Myr since the CAIs). Rcrust [7] and Perple_X [8] were used to predict the electrolytic fluid speciation from the starting material when heated to the temperatures predicted by the first temperature-depth profile (Stage 1; 4 – ~1600 Myr) and then the second (Stage 2; ~1600 – ~4568 Myr). Pyrrhotite was extracted from the starting material past the Fe-FeS eutectic temperature (which was also calculated using Rcrust and Perple_X) to approximate core formation. The volatiles forming the proto-ocean (i.e. those released in Stage 1) were then equilibrated using CHIM-XPT [9], where supersaturated gases were exsolved and minerals precipitated. The further volatiles (i.e. those released in Stage 2) were then added to the proto-ocean in CHIM-XPT, forming the current-day ocean. Results and Discussion: Released volatiles for the proto-ocean are predicted to form a ~77.9 km deep layer around Europa. With the addition of the further volatiles, the current-day ocean would be ~84.8 km deep. The extraction of pyrrhotite, which occurs after proto-ocean formation, would form a metallic core of ~271.5 km radius by the current day. The current-day ocean depth and core radius predicted here agree with those inferred for current-day Europa based on observations [3]. The model predicts that both the proto- and current-day oceans would be rich in Na+, Cl-, and CO32-, which may explain the recent observation of NaCl and CO2 in geologically-disrupted regions of Europa’s surface [10, 11]. Large concentrations of NH3 and NH4+ are predicted for both the proto- and current-day oceans, despite the lack of any clear detection of nitrogen species on the surface. However, this abundance may be explained by the absence of thermodynamic data for solid nitrogen-bearing phases in the model resulting in an overestimation of nitrogen release during metamorphism (mainly as NH3). A key difference between the proto- and current-day oceans is their HS- concentration, where the current-day ocean has only ~0.2% that of the proto-ocean. This is due to the addition of the iron-rich Stage 2 volatiles to the proto-ocean causing the precipitation of pyrite (removing HS- from solution). Conclusion: We find that Europa’s ocean composition would have varied over time as a result of continued prograde metamorphism, with particular changes in HS- concentration. The significant decrease in HS- content could affect the potential for energy generation by sulfide-oxidising microbes in the current-day ocean and, thus, would have implications for Europa’s continuous habitability. References: [1] Běhounková M. et al. (2021) Geophys. Res. Lett., 48. [2] Melwani Daswani M. et al. (2021) Geophys. Res. Lett., 48. [3] Trinh K. T. et al. (2023) Sci. Adv., 9, eadf3955. [4] Desch S. J. et al. (2018), ApJS. 238, 11. [5] Howard K. T. et al. (2011) Geochim. Cosmochim. Acta., 75, 2735–2751. [6] Fanale F. P. et al. (2001) J. Geophys. Res., 106, 14595–14600. [7] Mayne M. J. et al. (2016), J. Metamorph. Geol., 34, 663–682. [8] Connolly J. A. D. (2005) Earth Planet. Sci. Lett., 236, 524–541. [9] Reed M. H. et al. (2010) J. Chem. Inf. Model., 53, 1689–1699. [10] Trumbo S. K. et al. (2019) Sci. Adv., 5, eaaw7123. [11] Villanueva G. L. et al. (2023) Science., 381, 1305–1308. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration

Containers, sensors and samples to understand desert weathering

Our study is motivated by two aspects: i) the scientific motivation is to a) expand on previous studies of heavy noble gases in samples from terrestrial hot and cold deserts, thus to collect surface and subsurface (20 cm depth) samples from wind-blown desert soil and to b) study clay rich soil horizons for their microbiology and potential to serve as Mars analogue; and the ii) technological motivation is to field-test a prototype sampling container for crew-based sample return missions to Mars, the Moon, or other celestial bodies

Gratitude and hospitality: Tamil refugee employment in London and the conditional nature of integration

Healy, R. L. 2014. The definitive, peer-reviewed and edited version of this article is published in Environment and Planning A, 2014, 46(3), pp. 614-628, http:dx/doi.org/10.1068/a4655The policy of integration attempts to address different elements of exclusion, yet relatively little research has considered what integration means to the refugees themselves. This paper explores one key area for supporting integration: employment.ESRC PTA-030-2005-0082

Differential proteomic response of Sydney rock oysters (Saccostrea glomerata) to prolonged environmental stress

Exposure to prolonged environmental stress can have impacts on the cellular homeostasis of aquatic organisms. The current study employed two-dimensional electrophoresis (2-DE) to test whether exposure to impaired water quality conditions in the Sydney Harbour estuary has significantly altered the proteomes of the resident Sydney rock oyster (Saccostrea glomerata). Adult S. glomerata were sampled from four bays in the estuary. Each bay consisted of a “high-impact” site adjacent to point sources of chemical contamination (e.g., storm drains/canals or legacy hotspots) and a “low-impact” site located ~5 km away from point sources. A mixture of environmental stressors differed significantly between high- and low-impact sites. Specifically, PAHs, PCBs, tributyltin, Pb, and Zn were significantly elevated in oyster tissues from high-impact sites, together with depleted dissolved oxygen and low pH in the water column. A 2-DE proteomics analysis subsequently identified 238 protein spots across 24 2-DE gels, of which 27–50 spots differed significantly in relative intensity between high- and low-impact sites per bay. Twenty-five percent of the differential spots were identified in more than one bay. The identities of 80 protein spots were determined by mass spectrometry. HSP 70, PPIB, and radixin were the three most highly expressed differential proteins. Despite the largely unique proteomes evident in each bay, functional annotations revealed that half of the differentially expressed proteins fell into just two subcellular functional categories—energy metabolism and the cytoskeleton. These findings provide a framework to further investigate adaptation of cellular mechanisms to prolonged stress in S. glomerata.10 page(s

Rapid transcriptional acclimation following transgenerational exposure of oysters to ocean acidification

Marine organisms need to adapt in order to cope with the adverse effects of ocean acidification and warming. Transgenerational exposure to CO2₂ stress has been shown to enhance resilience to ocean acidification in offspring from a number of species. However, the molecular basis underlying such adaptive responses is currently unknown. Here, we compared the transcriptional profiles of two genetically distinct oyster breeding lines following transgenerational exposure to elevated CO₂ in order to explore the molecular basis of acclimation or adaptation to ocean acidification in these organisms. The expression of key target genes associated with antioxidant defence, metabolism and the cytoskeleton was assessed in oysters exposed to elevated CO₂ over three consecutive generations. This set of target genes was chosen specifically to test whether altered responsiveness of intracellular stress mechanisms contributes to the differential acclimation of oyster populations to climate stressors. Transgenerational exposure to elevated CO₂ resulted in changes to both basal and inducible expression of those key target genes (e.g. ecSOD, catalase and peroxiredoxin 6), particularly in oysters derived from the disease-resistant, fast-growing B2 line. Exposure to CO₂ stress over consecutive generations produced opposite and less evident effects on transcription in a second population that was derived from wild-type (nonselected) oysters. The analysis of key target genes revealed that the acute responses of oysters to CO₂ stress appear to be affected by population-specific genetic and/or phenotypic traits and by the CO₂ conditions to which their parents had been exposed. This supports the contention that the capacity for heritable change in response to ocean acidification varies between oyster breeding lines and is mediated by parental conditioning.14 page(s

The Biology of environmental stress : molecular biomarkers in Sydney rock oysters (Saccostrea glomerata)

This review describes our recent work on environmental stress in Sydney rock oysters, focusing on the identification of molecular biomarkers for ecotoxicological analysis. We begin by describing the environmental pressures facing coastal estuaries in Australia, with particular reference to Sydney Harbour. After providing that context, we summarise our transcriptional and proteomic analyses of Sydney rock oysters responding to chemical contamination and other forms of environmental stress. This work has shown that the intracellular processes of oysters are highly responsive to environmental threats. Our data agree with the broader literature, which suggests that there is a highly conserved intracellular stress response in oysters involving a limited number of biological processes. We conclude that many effective molecular markers for environmental biomonitoring are likely to lie within these biological pathways. Correction can be found in Environmental science : processes and impacts, Vol. 18. p. 1359, doi: http://dx.doi.org/10.1039/C6EM90036D11 page(s

Meta-Analysis of Studies Using Suppression Subtractive Hybridization and Microarrays to Investigate the Effects of Environmental Stress on Gene Transcription in Oysters

<div><p>Many microarray and suppression subtractive hybridization (SSH) studies have analyzed the effects of environmental stress on gene transcription in marine species. However, there have been no unifying analyses of these data to identify common stress response pathways. To address this shortfall, we conducted a meta-analysis of 14 studies that investigated the effects of different environmental stressors on gene expression in oysters. The stressors tested included chemical contamination, hypoxia and infection, as well as extremes of temperature, pH and turbidity. We found that the expression of over 400 genes in a range of oyster species changed significantly after exposure to environmental stress. A repeating pattern was evident in these transcriptional responses, regardless of the type of stress applied. Many of the genes that responded to environmental stress encoded proteins involved in translation and protein processing (including molecular chaperones), the mitochondrial electron transport chain, anti-oxidant activity and the cytoskeleton. In light of these findings, we put forward a consensus model of sub-cellular stress responses in oysters.</p></div

Schematic representation of the workflow used in this study.

<p>Schematic representation of the workflow used in this study.</p