Redox state and interior structure control on the long-term habitability of stagnant-lid planets

A major goal in the search for extraterrestrial life is the detection of liquid water on the surface of exoplanets. On terrestrial planets, volcanic outgassing is a significant source of atmospheric and surface water and a major contributor to the long-term evolution of the atmosphere. The rate of volcanism depends on the interior evolution and on numerous feedback processes between atmosphere and interior, which continuously shape atmospheric composition, pressure, and temperature. We present the results of a comprehensive 1D model of the coupled evolution of the interior and atmosphere of rocky exoplanets that combines central feedback processes between these two reservoirs. We carried out more than \num{280000} simulations over a wide range of mantle redox states and volatile content, planetary masses, interior structures and orbital distances in order to robustly assess the emergence, accumulation and preservation of surface water on rocky planets. To establish a conservative baseline of which types of planets can outgas and sustain water on their surface, we focus here on stagnant-lid planets. We find that only a narrow range of the mantle redox state around the iron-w\"ustite buffer allows the formation of atmospheres that lead to long-term habitable conditions. At oxidizing conditions similar to those of the Earth's mantle, most stagnant-lid planets end up in a hothouse regime akin to Venus due to strong \ce{CO2} outgassing. At more reducing conditions, the amount of outgassed greenhouse gases is often too low to keep surface water from freezing. In addition, Mercury-like planets with large metallic cores are able to sustain habitable conditions at an extended range of orbital distances as a result of lower volcanic activity.Comment: 23 pages, 18 figures, accepted for publication in Astronomy & Astrophysic

Redox state and interior structure control on the long-term habitability of stagnant-lid planets

Context. A major goal in the search for extraterrestrial life is the detection of liquid water on the surface of exoplanets. On terrestrial planets, volcanic outgassing is a significant source of atmospheric and surface water and a major contributor to the long-term evolution of the atmosphere. The rate of volcanism depends on the interior evolution and on numerous feedback processes between the atmosphere and interior, which continuously shape atmospheric composition, pressure, and temperature. Aims. We explore how key planetary parameters, such as planet mass, interior structure, mantle water content, and redox state, shape the formation of atmospheres that permit liquid water on the surface of planets. Methods. We present the results of a comprehensive 1D model of the coupled evolution of the interior and atmosphere of rocky exoplanets that combines central feedback processes between these two reservoirs. We carried out more than 280 000 simulations over a wide range of mantle redox states and volatile content, planetary masses, interior structures, and orbital distances in order to robustly assess the emergence, accumulation, and preservation of surface water on rocky planets. To establish a conservative baseline of which types of planets can outgas and sustain water on their surface, we focus here on stagnant-lid planets. Results. We find that only a narrow range of the mantle redox state around the iron-wüstite buffer allows the formation of atmospheres that lead to long-term habitable conditions. At oxidizing conditions similar to those of the Earth's mantle, most stagnant-lid planets end up in a hothouse regime akin to Venus due to strong CO2 outgassing. At more reducing conditions, the amount of outgassed greenhouse gases is often too low to keep surface water from freezing. In addition, Mercury-like planets with large metallic cores are able to sustain habitable conditions at an extended range of orbital distances as a result of lower volcanic activity

Twelve-month follow-up of left atrial appendage occlusion with Amplatzer Amulet

  Background: The Amplatzer Amulet (St. Jude Medical, Minneapolis, MN, USA) is a second gen­eration Amplatzer device for left atrial appendage (LAA) occlusion (LAAO) for stroke prophylaxis in patients with atrial fibrillation. This research sought to assess the clinical performance of the Amplatzer Amulet device and in follow up for 12 months. Methods: In this single-center registry patients with atrial fibrillation and contraindication to oral anticoagulation underwent LAAO with the Amplatzer Amulet device. Follow-up was performed before discharge, by transesophageal echocardiography (TEE) after 6 weeks and telephone interview after 3, 6 and 12 months. Results: Between October 2014 and August 2015 50 patients (76.1 ± 8.3 years; 30 male) were en­rolled. Procedural success was achieved in 49 (98%) patients. Major periprocedural adverse events were observed in 4 (8%) of patients: 1 device embolization, 2 pericardial effusions requiring pericardiocente­sis and 1 prolonged hospital stay due to retropharyngeal hematoma from the TEE probe. Follow-up TEE was available in 38 of 50 patients showing complete LAA sealing in all. 2 device-related thrombi were also documented. At 12-month follow-up 7 patients had died unrelated to the device. Ischemic stroke occurred in 3 patients. According to neurological examination two were classified as microangiopathic and not cardio-embolic. The other one could not be classified. Bleeding complications (5 minor, 3 major) were documented in 8 patients. Conclusions: Although minimizing procedure-related complications remains challenging, LAAO with the Amplatzer Amulet device showed high procedural success and excellent LAA sealing. (Cardiol J 2017; 24, 2: 131–138

Redox state and interior structure control on the long-term habitability of stagnant-lid planets

A major goal in exoplanet science is the search for planets with the right conditions to support liquid water (1). The habitability of a planet depends strongly on the composition of its atmosphere. Meanwhile, the interior and atmosphere of rocky planets are intricately linked through feedback processes and consequently evolve as a coupled system. In particular, volcanic outgassing of volatile species from the planet's silicate mantle shapes the atmospheric composition, temperature, and pressure, but the exact composition of outgassed species not only depends on the volatile content and redox state of the mantle, but also on the current state of the atmosphere (2, 3). This means that the interior dynamics of planets can not be neglected, especially since much of the surface water on terrestrial planets originates from the planetary mantle. In an extensive parameter study of rocky exoplanets, we investigated the emergence of habitable surface conditions for a wide range of initial conditions, including the planet mass, interior structure, volatile content and redox state, as well as the distance of the planet to its host star. The model accounts for the main mechanisms controlling the global-scale, long-term evolution of stagnant-lid rocky planets (i.e. bodies without plate tectonics), and it includes a large number of atmosphere-interior feedback processes, such as a CO2 weathering cycle, volcanic outgassing, a water cycle between ocean and atmosphere, greenhouse heating, as well as escape processes of H2. We find that only a narrow range of the mantle redox state around the iron-wüstite buffer allows forming atmospheres that lead to long-term habitable conditions. At more oxidizing conditions, most planets instead end up in a runaway greenhouse state (akin to Venus) due to strong CO2 outgassing. On the other hand, on planets with more reducing mantles, the amount of outgassed greenhouse gasses is often too low to keep the surface above the freezing point of water. References: (1) Noack, L., Snellen, I. & Rauer, H. Water in Extrasolar Planets and Implications for Habitability. Space Sci Rev 212, 877-898 (2017). (2) Ortenzi, G. et al. Mantle redox state drives outgassing chemistry and atmospheric composition of rocky planets. Sci Rep 10, 10907 (2020). (3) Gaillard, F. & Scaillet, B. A theoretical framework for volcanic degassing chemistry in a comparative planetology perspective and implications for planetary atmospheres. Earth and Planetary Science Letters 403, 307-316 (2014)

Redox state and interior structure control on the long-term habitability of stagnant-lid planets

A major goal in exoplanet science is the search for planets with the right conditions to support liquid water (1). The habitability of a planet depends strongly on the composition of its atmosphere. Meanwhile, the interior and atmosphere of rocky planets are intricately linked through feedback processes and consequently evolve as a coupled system. In particular, volcanic outgassing of volatile species from the planet's silicate mantle shapes the atmospheric composition, temperature, and pressure, but the exact composition of outgassed species not only depends on the volatile content and redox state of the mantle, but also on the current state of the atmosphere (2, 3). This means that the interior dynamics of planets can not be neglected, especially since much of the surface water on terrestrial planets originates from the planetary mantle. In an extensive parameter study of rocky exoplanets, we investigated the emergence of habitable surface conditions for a wide range of initial conditions, including the planet mass, interior structure, volatile content and redox state, as well as the distance of the planet to its host star. The model accounts for the main mechanisms controlling the global-scale, long-term evolution of stagnant-lid rocky planets (i.e. bodies without plate tectonics), and it includes a large number of atmosphere-interior feedback processes, such as a CO2 weathering cycle, volcanic outgassing, a water cycle between ocean and atmosphere, greenhouse heating, as well as escape processes of H2. We find that only a narrow range of the mantle redox state around the iron-wüstite buffer allows forming atmospheres that lead to long-term habitable conditions. At more oxidizing conditions, most planets instead end up in a runaway greenhouse state (akin to Venus) due to strong CO2 outgassing. On the other hand, on planets with more reducing mantles, the amount of outgassed greenhouse gasses is often too low to keep the surface above the freezing point of water. References: (1) Noack, L., Snellen, I. & Rauer, H. Water in Extrasolar Planets and Implications for Habitability. Space Sci Rev 212, 877-898 (2017). (2) Ortenzi, G. et al. Mantle redox state drives outgassing chemistry and atmospheric composition of rocky planets. Sci Rep 10, 10907 (2020). (3) Gaillard, F. & Scaillet, B. A theoretical framework for volcanic degassing chemistry in a comparative planetology perspective and implications for planetary atmospheres. Earth and Planetary Science Letters 403, 307-316 (2014)

Impact of conscious sedation and general anesthesia on periprocedural outcomes in Watchman left atrial appendage closure

Background: Transcatheter left atrial appendage closure (LAAC) is performed either in conscious sedation (CS) or general anesthesia (GA), and limited data exist regarding clinical outcomes for the two approaches. The aim of the study was to analyze the effect of CS versus GA on acute outcomes in a large patient cohort undergoing LAAC with a Watchman occluder.Methods: A cohort of 521 consecutive patients underwent LAAC with Watchman occluders at two centers (REGIOMED hospitals, Germany) between 2012 and 2018. One site performed 303 consecutive LAAC procedures in GA, and the other site performed 218 consecutive procedures in CS. The safety endpoint was a composite of major periprocedural complications and postoperative pneumonia. The efficacy endpoint was defined as device success.Results: After a 1:1 propensity score matching, 196 (CS) vs. 115 (GA) patients could be compared. In 5 (2.6%) cases CS was converted to GA. The primary safety endpoint (3.5% [CS] vs. 7.0% [GA], p = 0.18) and its components (major periprocedural complications: 2.5% vs. 3.5%, p = 0.73; postoperative pneumonia: 2.6% vs. 4.3%, p = 0.51) did not differ between the groups. Also, device success was comparable (96.9% vs. 93.9%, p = 0.24).Conclusions: In patients undergoing LAAC with the Watchman device, conscious sedation and general anesthesia showed comparable device success rates and safety outcomes. The type of anesthesia for LAAC may therefore be tailored to patient comorbidities, operator experience, and hospital logistics

Reactive fluid flow guided by grain-scale equilibrium reactions during eclogitization of dry crustal rocks

Fluid flow in crystalline rocks in the absence of fractures or ductile shear zones dominantly occurs by grain boundary diffusion, as it is faster than volume diffusion. It is, however, unclear how reactive fluid flow is guided through such pathways. We present a microstructural, mineral chemical, and thermodynamic analysis of a static fluid-driven reaction from dry granulite to ‘wet’ eclogite. Fluid infiltration resulted in re-equilibration at eclogite-facies conditions, indicating that the granulitic protolith was out of equilibrium, but unable to adjust to changing P–T conditions. The transformation occurred in three steps: (1) initial hydration along plagioclase grain boundaries, (2) complete breakdown of plagioclase and hydration along phase boundaries between plagioclase and garnet/clinopyroxene, and (3) re-equilibration of the rock to an eclogite-facies mineral assemblage. Thermodynamic modelling of local compositions reveals that this reaction sequence is proportional to the local decrease of the Gibbs free energy calculated for ‘dry’ and ‘wet’ cases. These energy differences result in increased net reaction rates and the reactions that result in the largest decrease of the Gibbs free energy occur first. In addition, these reactions result in a local volume decrease leading to porosity formation; i.e., pathways for new fluid to enter the reaction site thus controlling net fluid flow. Element transport to and from the reaction sites only occurs if it is energetically beneficial, and enough transport agent is available. Reactive fluid flow during static re-equilibration of nominally impermeable rocks is thus guided by differences in the energy budget of the local equilibrium domains

Reactive fluid flow guided by grain-scale equilibrium reactions during eclogitization of dry crustal rocks

Fluid flow in crystalline rocks in the absence of fractures or ductile shear zones dominantly occurs by grain boundary diffusion, as it is faster than volume diffusion. It is, however, unclear how reactive fluid flow is guided through such pathways. We present a microstructural, mineral chemical, and thermodynamic analysis of a static fluid-driven reaction from dry granulite to ‘wet’ eclogite. Fluid infiltration resulted in re-equilibration at eclogite-facies conditions, indicating that the granulitic protolith was out of equilibrium, but unable to adjust to changing P–T conditions. The transformation occurred in three steps: (1) initial hydration along plagioclase grain boundaries, (2) complete breakdown of plagioclase and hydration along phase boundaries between plagioclase and garnet/clinopyroxene, and (3) re-equilibration of the rock to an eclogite-facies mineral assemblage. Thermodynamic modelling of local compositions reveals that this reaction sequence is proportional to the local decrease of the Gibbs free energy calculated for ‘dry’ and ‘wet’ cases. These energy differences result in increased net reaction rates and the reactions that result in the largest decrease of the Gibbs free energy occur first. In addition, these reactions result in a local volume decrease leading to porosity formation; i.e., pathways for new fluid to enter the reaction site thus controlling net fluid flow. Element transport to and from the reaction sites only occurs if it is energetically beneficial, and enough transport agent is available. Reactive fluid flow during static re-equilibration of nominally impermeable rocks is thus guided by differences in the energy budget of the local equilibrium domains

Volcanic chemical gas speciation and atmospheric redistribution on terrestrial planets

The internal constitution of rocky exoplanets can be inferred only indirectly via their atmospheric composition. To address this issue with confidence requires the coupling of interior and atmospheric models to each other. In the past, various atmospheric redistribution models were developed to determine the composition of exoplanetary atmospheres by varying element abundance, temperature and pressure. However, these models neglect that present-day atmospheres were formed via volcanic degassing and, consequently, element abundances are limited by thermodynamic processes accompanying magma ascent and volatile release. Here we combine volcanic outgassing with an atmospheric chemistry model to simulate the evolution of C-H-O-N atmospheres in thermal equilibrium below 650 K. These volatiles can be stored in significant amounts in basaltic magmas and are the most commonly degassed species. Sulfur molecules are not stable at low atmospheric temperatures and are therefore not included in our calculations. For the present study, we built a basic model to calculate possible atmospheric compositions by varying oxygen fugacity, melt and surface temperature and volatile abundances. Furthermore, we consider the solubility of each phase, atmospheric processes such as water condensation, graphite precipitation, hydrogen escape and the effect an already existing atmosphere may have on further degassing. Our model suggests that the most common atmospheric type is composed of CO2, N2, CH4, and (dependent on surface temperature) H2O. Furthermore, we show that the evolving atmospheric pressure and composition are highly dependent on the oxygen fugacity of the melt because of its influence on gas speciation and solubility. Reduced conditions produce H2, NH3, CH4 and H2O dominated atmospheres with extremely low atmospheric pressures. Oxidized conditions lead to atmospheres consisting of H2O, CO2, N2 and small amount of CH4 with high atmospheric pressures. O2 is never produced since carbon or hydrogen are still available in sufficient amounts to form H2O, CO or CO2. Hence it is not possible to form abiotically O2 dominated atmospheres unless O2 degassing occurs in the case of super oxidized magmas with low carbon and hydrogen abundances. Low hydrogen abundances are found to produce another atmospheric type consisting of CO2, CO, CH4 and N2. (This leads us to conclude that also the depth of the source region of a magma may have a significant effect on atmospheric compositions because of the different pressure dependence of the solubilities of the degassed species.