Evolution and Spectral Response of a Steam Atmosphere for Early Earth with a coupled climate-interior model

The evolution of Earth's early atmosphere and the emergence of habitable conditions on our planet are intricately coupled with the development and duration of the magma ocean phase during the early Hadean period (4 to 4.5 Ga). In this paper, we deal with the evolution of the steam atmosphere during the magma ocean period. We obtain the outgoing longwave radiation using a line-by-line radiative transfer code GARLIC. Our study suggests that an atmosphere consisting of pure H$_{2}$O, built as a result of outgassing extends the magma ocean lifetime to several million years. The thermal emission as a function of solidification timescale of magma ocean is shown. We study the effect of thermal dissociation of H$_{2}$O at higher temperatures by applying atmospheric chemical equilibrium which results in the formation of H$_{2}$ and O$_{2}$ during the early phase of the magma ocean. A 1-6\% reduction in the OLR is seen. We also obtain the effective height of the atmosphere by calculating the transmission spectra for the whole duration of the magma ocean. An atmosphere of depth ~100 km is seen for pure water atmospheres. The effect of thermal dissociation on the effective height of the atmosphere is also shown. Due to the difference in the absorption behavior at different altitudes, the spectral features of H$_{2}$ and O$_{2}$ are seen at different altitudes of the atmosphere. Therefore, these species along with H$_{2}$O have a significant contribution to the transmission spectra and could be useful for placing observational constraints upon magma ocean exoplanets.Comment: 22 pages, 17 Figures, accepted for publication in ApJ on March

What factors affect the duration and outgassing of the terrestrial magma ocean?

The magma ocean (MO) is a crucial stage in the build-up of terrestrial planets. Its solidification and the accompanying outgassing of volatiles set the conditions for important processes occurring later or even simultaneously, such as solid-state mantle convection and atmospheric escape. To constrain the duration of a global-scale Earth MO we have built and applied a 1D interior model coupled alternatively with a grey H2O/CO2 atmosphere or with a pure H2O atmosphere treated with a line-by-line model described in a companion paper by Katyal et al. (2019). We study in detail the effects of several factors affecting the MO lifetime, such as the initial abundance of H2O and CO2, the convection regime, the viscosity, the mantle melting temperature, and the longwave radiation absorption from the atmosphere. In this specifically multi-variable system we assess the impact of each factor with respect to a reference setting commonly assumed in the literature. We find that the MO stage can last from a few thousand to several million years. By coupling the interior model with the line-by-line atmosphere model, we identify the conditions that determine whether the planet experiences a transient magma ocean or it ceases to cool and maintains a continuous magma ocean. We find a dependence of this distinction simultaneously on the mass of the outgassed H2O atmosphere and on the MO surface melting temperature. We discuss their combined impact on the MO's lifetime in addition to the known dependence on albedo, orbital distance and stellar luminosity and we note observational degeneracies that arise thereby for target exoplanets

Detection of early warning signals in paleoclimate data using a genetic time series segmentation algorithm

This paper proposes a time series segmentation algorithm combining a clustering technique and a genetic algorithm to automatically find segments sharing common statistical characteristics in paleoclimate time series. The segments are transformed into a six-dimensional space composed of six statistical measures, most of which have been previously considered in the detection of warning signals of critical transitions. Experimental results show that the proposed approach applied to paleoclimate data could effectively analyse Dansgaard–Oeschger (DO) events and uncover commonalities and differences in their statistical and possibly their dynamical characterisation. In particular, warning signals were robustly detected in the GISP2 and NGRIP δ18O ice core data for several DO events (e.g. DO 1, 4, 8 and 12) in the form of an order of magnitude increase in variance, autocorrelation and mean square distance from a linear approximation (i.e. the mean square error). The increase in mean square error, suggesting nonlinear behaviour, has been found to correspond with an increase in variance prior to several DO events for ∼90 % of the algorithm runs for the GISP2 δ18O dataset and for ∼100 % of the algorithm runs for the NGRIP δ18O dataset. The proposed approach applied to well-known dynamical systems and paleoclimate datasets provides a novel visualisation tool in the field of climate time series analysi

Origin and evolution of the atmospheres of early Venus, Earth and Mars

We review the origin and evolution of the atmospheres of Earth, Venus and Mars from the time when their accreting bodies were released from the protoplanetary disk a few million years after the origin of the Sun. If the accreting planetary cores reached masses ≥0.5 MEarth before the gas in the disk disappeared, primordial atmospheres consisting mainly of H2 form around the young planetary body, contrary to late-stage planet formation, where terrestrial planets accrete material after the nebula phase of the disk. The differences between these two scenarios are explored by investigating non-radiogenic atmospheric noble gas isotope anomalies observed on the three terrestrial planets. The role of the young Sun’s more efficient EUV radiation and of the plasma environment into the escape of early atmospheres is also addressed. We discuss the catastrophic outgassing of volatiles and the formation and cooling of steam atmospheres after the solidification of magma oceans and we describe the geochemical evidence for additional delivery of volatile-rich chondritic materials during the main stages of terrestrial planet formation. The evolution scenario of early Earth is then compared with the atmospheric evolution of planets where no active plate tectonics emerged like on Venus and Mars. We look at the diversity between early Earth, Venus and Mars, which is found to be related to their differing geochemical, geodynamical and geophysical conditions, including plate tectonics, crust and mantle oxidation processes and their involvement in degassing processes of secondary N2 atmospheres. The buildup of atmospheric N2, O2, and the role of greenhouse gases such as CO2 and CH4 to counter the Faint Young Sun Paradox (FYSP), when the earliest life forms on Earth originated until the Great Oxidation Event ≈ 2.3 Gyr ago, are addressed. This review concludes with a discussion on the implications of understanding Earth’s geophysical and related atmospheric evolution in relation to the discovery of potential habitable terrestrial exoplanets.PostprintPeer reviewe

Enabling planetary science across light-years. Ariel Definition Study Report

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution

Numerische Modellierung der Erstarrung von Magma-Ozeanen und der gleichzeitigen Bildung von Atmosphäre

Magma ocean is a crucial stage in the build-up of terrestrial planets. Its solidification and the accompanying outgassing of volatiles set the conditions for important processes that occur later or even simultane-ously, such as solid state mantle convection and atmospheric escape. In order to constrain the duration of a global scale magma ocean on Earth I have built and applied a 1D interior model coupled alternatively with either a grey H2O/CO2 atmosphere or with a pure H2O atmosphere treated with a line-by-line radiative transfer approach. This study examines the effects of several factors affecting the magma ocean lifetime, such as the initial abundance of H2O and CO2 , the convection regime, the viscosity, the mantle’s melting temperature, and the longwave radiation absorption from the atmosphere. In this specifically multi-variable system I assess the impact of each factor with respect to a reference setting commonly assumed in the literature. This setting is intended to be a benchmark and it is deliberately kept low in complexity. Such approach helps emphasize the potential role of each additional modeled process in the solidification time.It is found that the magma ocean stage can last from a few thousand to several million years for a rocky planet of terrestrial size and composition. By coupling the interior model with the line-byline radiative transfer treatment in the atmosphere, I identify the conditions that determine whether the planet experiences a transient magma ocean or it ceases to cool and maintains a magma ocean,conditional on the assumption that atmospheric mass is conserved. I find a dependence of this distinction simultaneously on the mass of outgassed H2O atmosphere and on the magma ocean surface melting temperature. The present work discusses their combined impact on the magma ocean lifetime in addition to the known dependence on albedo, orbital distance and stellar luminosity and notes observational degeneracies that arise thereby for target exoplanets. A potential magma ocean case for Venus and Mars is shortly discussed and is put in perspective with the study findings.Der Magma-Ozean ist eine entscheidende Phase beim Aufbau von terrestrischen Planeten. Seine Verfestigung und die damit einhergehende Ausgasung flüchtiger Stoffe schaffen die Voraussetzungen für wichtige Prozesse, die später oder sogar gleichzeitig ablaufen, wie die Konvektion des Festkörpermantels und das Entweichen der Atmosphäre. Um die Dauer eines Magma-Ozeans im globalen Maßstab auf der Erde einzuschränken, habe ich ein 1D-Modell des Inneren erstellt und angewendet, das wahlweise mit einer grauen H2O/CO2 - Atmosphäre oder mit einer reinen H2O-Atmosphäre gekoppelt ist, die mit einem Spektralrechnungs-Ansatz behandelt wurde. Diese Studie untersucht die Auswirkungen verschiedener Faktoren, die die Lebensdauer des Magma-Ozeans beeinflussen, wie etwa die anfängliche Häufigkeit von H2O und CO2 , das Konvektionsregime, die Viskosität, die Schmelztemperatur des Mantels und die Absorption langwelliger Strahlung aus der Atmosphäre. In diesem spezifischen multivariablen System bewerte ich die Auswirkung jedes Faktors im Hinblick auf eine in der Literatur allgemein angenommene Referenzkonfiguration. Diese Konfiguration soll als Richtwert dienen und ist bewusst wenig komplex gehalten. Ein solcher Ansatz hilft dabei, die potenzielle Rolle jedes zusätzlich modellierten Prozesses in der Erstarrungszeit hervorzuheben. Es wurde festgestellt, dass die Magma-Ozean-Phase für einen felsigen Planeten von irdischer Größe und Zusammensetzung einige tausend bis mehrere Millionen Jahre dauern kann. Indem ich das Modell des Inneren mit dem Spektralrechnungs-Verfahren in der Atmosphäre verbinde, identifiziere ich die Bedingungen, die bestimmen, ob der Planet einem vorübergehenden Magma-Ozean ausgesetzt ist oder aufgehört hat abzukühlen und einen Magma-Ozean beibehält – unter der Annahme, dass atmosphärische Masse erhalten bleibt. Ich stelle eine Abhängigkeit dieser Unterscheidung gleichzeitig von der Masse der ausgegasten H2O-Atmosphäre und von der Schmelztemperatur der Magma-Ozean-Oberfläche fest. Die vorliegende Arbeit diskutiert den gemeinsamen Einfluss von beidem auf die Lebensdauer des Magma-Ozeans zusätzlich zu den bekannten Abhängigkeiten von Albedo, Umlaufdistanz und Sternhelligkeit und stellt Beobachtungs-Entartungen fest, die dadurch für Ziel-Exoplaneten entstehen. Ein möglicher Magma-Ozean-Fall wird kurz für Venus und Mars diskutiert und mit den Ergebnissen der Untersuchung in Beziehung gesetzt