Composition des océans des lunes de Jupiter et Saturne - Approches thermodynamique et expérimentale

The existence of subsurface aqueous oceans in Jupiter and Saturn's large icy moons, theorized in the 1970s, has been confirmed by data collected by the Voyager, Galileo and Cassini-Huygens missions. The composition of chondritic and cometary materials and the data from these missions suggest that magnesium sulfate and carbon dioxide may be major components of these extra-terrestrial oceans. In order to understand the implications of the presence of these two constituents, new experiments were carried out in the H2O-CO2 and H2O-MgSO4 systems at the high pressures (0 - 2 GPa), low temperatures (250 - 350 K) and compositions (water-rich systems) expected in the hydrospheres of Ganymede, Callisto and Titan. The results from these experiments led to the first global description of the H2O-CO2 system at these conditions. The domain of stability of the two CO2 hydrates and the solubility of CO2 in water at high pressure bring new constraints on the trapping and transfer of this volatile in large icy moons. These data now make possible the high-pressure thermodynamic modeling of the CO2-CH4 sI clathrate hydrate, a phase likely involved in the segregation of these main volatile carbon molecules throughout the hydrospheres of icy moons. The first set of data acquired to constrain the eutectic composition of the H2O-MgSO4 system at high pressures complete available density data and provide the means to understand the evolution of dense oceans within massive hydrospheres. These data support the recent hypothesis of deep oceans at the bottom of the icy mantles of large icy satellites, giving a new perspective on the evolution and dynamics of these bodies.L'existence d'océans aqueux sous les surfaces des grands satellites de glace de Jupiter et Saturne, théorisée durant les années 1970, est aujourd'hui confirmée par les données des missions Voyager, Galileo et Cassini-Huygens. La composition des matériaux chondritiques et cométaires et les données des missions spatiales érigent aujourd'hui le sulfate de magnésium et le dioxyde de carbone parmi les principaux contaminants pouvant être attendus dans ces océans extra-terrestres. Pour éclaircir les implications de la présence de ces constituants, des expériences ont été menées afin de compléter l'exploration encore partielle des systèmes H2O-CO2 et H2O-MgSO4 aux conditions de haute pression (0 - 2 GPa), de basse température (250 - 350 K) et de composition (systèmes riches en eau) attendues dans les hydrosphères de Ganymède, Callisto et Titan. Les données acquises ont permis d'établir la première description globale du système H2O-CO2 à ces conditions. Les domaines de stabilité des deux hydrates de CO2 et la solubilité du CO2 dans l'eau éclairent les mécanismes de stockage et de transfert de ce volatil dans les grands satellites de glace. Ces données ont également ouvert la voie à la modélisation thermodynamique du clathrate sI de CO2-CH4, acteur potentiel de la ségrégation du carbone volatil dans les hydrosphères des lunes. Les premières données acquises pour contraindre l'eutectique du système H2O-MgSO4 permettent d'aborder la question de l'évolution d'océans denses au sein des hydrosphères. Ces données précisent l'hypothèse récente de l'existence de domaines océaniques profonds à la base des manteaux glacés des grands satellites, offrant une nouvelle vue de leur dynamique

Biological functions at high pressure: transcriptome response of Shewanella oneidensis MR-1 to hydrostatic pressure relevant to Titan and other icy ocean worlds

High hydrostatic pressure (HHP) is a key driver of life's evolution and diversification on Earth. Icy moons such as Titan, Europa, and Enceladus harbor potentially habitable high-pressure environments within their subsurface oceans. Titan, in particular, is modeled to have subsurface ocean pressures ≥ 150 MPa, which are above the highest pressures known to support life on Earth in natural ecosystems. Piezophiles are organisms that grow optimally at pressures higher than atmospheric (0.1 MPa) pressure and have specialized adaptations to the physical constraints of high-pressure environments – up to ~110 MPa at Challenger Deep, the highest pressure deep-sea habitat explored. While non-piezophilic microorganisms have been shown to survive short exposures at Titan relevant pressures, the mechanisms of their survival under such conditions remain largely unelucidated. To better understand these mechanisms, we have conducted a study of gene expression for Shewanella oneidensis MR-1 using a high-pressure experimental culturing system. MR-1 was subjected to short-term (15 min) and long-term (2 h) HHP of 158 MPa, a value consistent with pressures expected near the top of Titan's subsurface ocean. We show that MR-1 is metabolically active in situ at HHP and is capable of viable growth following 2 h exposure to 158 MPa, with minimal pressure training beforehand. We further find that MR-1 regulates 264 genes in response to short-term HHP, the majority of which are upregulated. Adaptations include upregulation of the genes argA, argB, argC, and argF involved in arginine biosynthesis and regulation of genes involved in membrane reconfiguration. MR-1 also utilizes stress response adaptations common to other environmental extremes such as genes encoding for the cold-shock protein CspG and antioxidant defense related genes. This study suggests Titan's ocean pressures may not limit life, as microorganisms could employ adaptations akin to those demonstrated by terrestrial organisms

Composition des océans des lunes de Jupiter et Saturne : approches thermodynamique et expérimentale

L existence d océans aqueux sous les surfaces des grands satellites de glace de Jupiter et Saturne, théorisée durant les années 1970, est aujourd hui confirmée par les données des missions Voyager, Galileo et Cassini-Huygens. La composition des matériaux chondritiques et cométaires et les données des missions spatiales érigent aujourd hui le sulfate de magnésium et le dioxyde de carbone parmi les principaux contaminants pouvant être attendus dans ces océans extra-terrestres. Pour éclaircir les implications de la présence de ces constituants, des expériences ont été menées afin de compléter l'exploration encore partielle des systèmes H2O CO2 et H2O MgSO4 aux conditions de haute pression (0 2 GPa), de basse température (250 350 K) et de composition (systèmes riches en eau) attendues dans les hydrosphères de Ganymède, Callisto et Titan. Les données acquises ont permis d'établir la première description globale du système H2O CO2 à ces conditions. Les domaines de stabilité des deux hydrates de CO2 et la solubilité du CO2 dans l eau éclairent les mécanismes de stockage et de transfert de ce volatil dans les grands satellites de glace. Ces données ont également ouvert la voie à la modélisation thermodynamique du clathrate sI de CO2 CH4, acteur potentiel de la ségrégation du carbone volatil dans les hydrosphères des lunes. Les premières données acquises pour contraindre l'eutectique du système H2O MgSO4 permettent d aborder la question de l évolution d océans denses au sein des hydrosphères. Ces données précisent l'hypothèse récente de l'existence de domaines océaniques profonds à la base des manteaux glacés des grands satellites, offrant une nouvelle vue de leur dynamique.The existence of subsurface aqueous oceans in Jupiter and Saturn s large icy moons, theorized in the 1970s, has been confirmed by data collected by the Voyager, Galileo and Cassini-Huygens missions. The composition of chondritic and cometary materials and the data from these missions suggest that magnesium sulfate and carbon dioxide may be major components of these extra-terrestrial oceans. In order to understand the implications of the presence of these two constituents, new experiments were carried out in the H2O CO2 and H2O MgSO4 systems at the high pressures (0 2 GPa), low temperatures (250 350 K) and compositions (water-rich systems) expected in the hydrospheres of Ganymede, Callisto and Titan. The results from these experiments led to the first global description of the H2O CO2 system at these conditions. The domain of stability of the two CO2 hydrates and the solubility of CO2 in water at high pressure bring new constraints on the trapping and transfer of this volatile in large icy moons. These data now make possible the high-pressure thermodynamic modeling of the CO2 CH4 sI clathrate hydrate, a phase likely involved in the segregation of these main volatile carbon molecules throughout the hydrospheres of icy moons. The first set of data acquired to constrain the eutectic composition of the H2O MgSO4 system at high pressures complete available density data and provide the means to understand the evolution of dense oceans within massive hydrospheres. These data support the recent hypothesis of deep oceans at the bottom of the icy mantles of large icy satellites, giving a new perspective on the evolution and dynamics of these bodies. a priori conditions, the transition zone appears to be isotropic, along the investigated pathNANTES-BU Sciences (441092104) / SudocSudocFranceF

Laboratory infrared reflection spectrum of carbon dioxide clathrate hydrates for astrophysical remote sensing applications

International audienc

Carbonic acid monohydrate

In the water-carbon dioxide system, above a pressure of 4.4 GPa, a crystalline phase consisting of an adduct of the two substances can be observed to exist in equilibrium with the aqueous fluid. The phase had been found to be triclinic, and its unit-cell parameters determined, but the full crystalline and even molecular structure remained undetermined. Here, we report new diamond-anvil cell, X-ray diffraction data of a quality sufficient to allow us to propose a full structure. The crystal exists in the P1 space group. Unit-cell parameters (at 6.5 GPa and 140 °C) are a = 5.8508(14), b = 6.557(5), c = 6.9513(6) Å, α = 88.59(2)°, β = 79.597(13)°, and $γ$ = 67.69(4)°. Direct solution for the heavy atoms (carbon and oxygen) revealed CO$_3$ units, with co-planar, but isolated, O units. Construction of a hydrogen network, in accordance with the requirements of hydrogen bonding and with minimum allowed distances between non-bonded atoms, indicates that the phase consists of a monohydrate of carbonic acid (H$_2$CO$_3$·H$_2$O) with the carbonic acid molecule in the cis-trans configuration. This is the first experimental determination of the crystalline structure of a H$_2$CO$_3$ compound. The structure serves as a guide for ab initio calculations that have until now explored only anhydrous H$_2$CO$_3$ solids, while validating calculations that indicated that high pressures should stabilize H$_2$CO$_3$ in the solid state. If 4.4 GPa is the lowest pressure at which the phase is thermodynamically stable, this probably precludes its existence in our solar system, although it may exist on larger, volatile-rich exoplanets. If, however, its range of stability extends to lower pressures at lower temperatures (which possibility has not yet been adequately explored), then it might have been be a stable form of CO$_2$ within the water-rich moons and dwarf planets prior to differentiation and might still exist on an undifferentiated Callisto

Phase equilibria in the H2O–CO2 system between 250–330K and 0–1.7GPa: Stability of the CO2 hydrates and H2O-ice VI at CO2 saturation

International audienc

Image_3_Biological functions at high pressure: transcriptome response of Shewanella oneidensis MR-1 to hydrostatic pressure relevant to Titan and other icy ocean worlds.pdf

High hydrostatic pressure (HHP) is a key driver of life's evolution and diversification on Earth. Icy moons such as Titan, Europa, and Enceladus harbor potentially habitable high-pressure environments within their subsurface oceans. Titan, in particular, is modeled to have subsurface ocean pressures ≥ 150 MPa, which are above the highest pressures known to support life on Earth in natural ecosystems. Piezophiles are organisms that grow optimally at pressures higher than atmospheric (0.1 MPa) pressure and have specialized adaptations to the physical constraints of high-pressure environments – up to ~110 MPa at Challenger Deep, the highest pressure deep-sea habitat explored. While non-piezophilic microorganisms have been shown to survive short exposures at Titan relevant pressures, the mechanisms of their survival under such conditions remain largely unelucidated. To better understand these mechanisms, we have conducted a study of gene expression for Shewanella oneidensis MR-1 using a high-pressure experimental culturing system. MR-1 was subjected to short-term (15 min) and long-term (2 h) HHP of 158 MPa, a value consistent with pressures expected near the top of Titan's subsurface ocean. We show that MR-1 is metabolically active in situ at HHP and is capable of viable growth following 2 h exposure to 158 MPa, with minimal pressure training beforehand. We further find that MR-1 regulates 264 genes in response to short-term HHP, the majority of which are upregulated. Adaptations include upregulation of the genes argA, argB, argC, and argF involved in arginine biosynthesis and regulation of genes involved in membrane reconfiguration. MR-1 also utilizes stress response adaptations common to other environmental extremes such as genes encoding for the cold-shock protein CspG and antioxidant defense related genes. This study suggests Titan's ocean pressures may not limit life, as microorganisms could employ adaptations akin to those demonstrated by terrestrial organisms.</p

Table_3_Biological functions at high pressure: transcriptome response of Shewanella oneidensis MR-1 to hydrostatic pressure relevant to Titan and other icy ocean worlds.XLSX

High hydrostatic pressure (HHP) is a key driver of life's evolution and diversification on Earth. Icy moons such as Titan, Europa, and Enceladus harbor potentially habitable high-pressure environments within their subsurface oceans. Titan, in particular, is modeled to have subsurface ocean pressures ≥ 150 MPa, which are above the highest pressures known to support life on Earth in natural ecosystems. Piezophiles are organisms that grow optimally at pressures higher than atmospheric (0.1 MPa) pressure and have specialized adaptations to the physical constraints of high-pressure environments – up to ~110 MPa at Challenger Deep, the highest pressure deep-sea habitat explored. While non-piezophilic microorganisms have been shown to survive short exposures at Titan relevant pressures, the mechanisms of their survival under such conditions remain largely unelucidated. To better understand these mechanisms, we have conducted a study of gene expression for Shewanella oneidensis MR-1 using a high-pressure experimental culturing system. MR-1 was subjected to short-term (15 min) and long-term (2 h) HHP of 158 MPa, a value consistent with pressures expected near the top of Titan's subsurface ocean. We show that MR-1 is metabolically active in situ at HHP and is capable of viable growth following 2 h exposure to 158 MPa, with minimal pressure training beforehand. We further find that MR-1 regulates 264 genes in response to short-term HHP, the majority of which are upregulated. Adaptations include upregulation of the genes argA, argB, argC, and argF involved in arginine biosynthesis and regulation of genes involved in membrane reconfiguration. MR-1 also utilizes stress response adaptations common to other environmental extremes such as genes encoding for the cold-shock protein CspG and antioxidant defense related genes. This study suggests Titan's ocean pressures may not limit life, as microorganisms could employ adaptations akin to those demonstrated by terrestrial organisms.</p