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Measured atmospheric 36Ar/38Ar, 20Ne/22Ne, 36Ar/22Ne noble gas isotope and bulk K/U ratios constrain the early evolution of Venus and Earth.

Lammer, H and Leizinger, M and Scherf, M and Odert, P. and Burger, C. and Kubyshkina, Daria and Johnstone, Colin and Maindl, T. and Schäfer, C.M. and Güdel, Manuel and Tosi, Nicola and Nikolaou, Athanasia and Marq, E and Erkaev, N. V. and Noack, L and Kislyakova, K. G. and Fossati, L. and Pilat-Lohinger, Elke and Ragossing, F and Dorfi, E.A. (2019) Measured atmospheric 36Ar/38Ar, 20Ne/22Ne, 36Ar/22Ne noble gas isotope and bulk K/U ratios constrain the early evolution of Venus and Earth. Icarus. Elsevier. DOI: 10.1016/j.icarus.2019.113551 ISSN 0019-1035

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Official URL: https://www.sciencedirect.com/science/article/abs/pii/S0019103519301290

Abstract

The atmospheric noble gas isotope and elemental bulk ratios on Venus and Earth provide important information on their origin and evolution. If the protoplanets grew to a certain mass (i.e. > 0.5 MEarth), they could have captured H2-dominated primordial atmospheres by accreting gas from the circumstellar disk during the formation of the Solar System, which were then quickly lost by hydrodynamic escape after the disk dissipated. In such a case, the EUV-driven hydrodynamic flow of H atoms dragged heavier elements with it at different rates, leading to changes in their initial isotope ratios. For reproducing Earth and Venus present atmospheric 36Ar/38Ar, 20Ne/22Ne, 36Ar/22Ne, isotope and bulk K/U ratios we applied hydrodynamic upper atmosphere escape and Smooth Particle Hydrodynamics (SPH) impact models for the calculation of captured H2-dominated primordial atmospheres for various protoplanetary masses. We investigated a wide range of possible EUV evolution tracks of the young Sun and initial atmospheric compositions based on mixtures of captured nebula gas, outgassed and delivered material from ureilite, enstatite and carbonaceaous chondrites. Depending on the disk lifetime of ≈ 3-5 Myr (Bollard et al., 2017; Wang et al., 2017) and the composition of accreted material after disk dispersal, we find from the reproduction of the present atmospheric Ar, Ne, and bulk K/U ratios, that early Earth’s evolution can be explained if proto-Earth had accreted masses between ≈ 0.53 − 0.58 MEarth by the time the nebula gas dissipated. If proto-Earth would have accreted a higher mass during the disk lifetime the present atmospheric Ar and Ne isotope ratios can not be reproduced with our model approach. For masses > 0.75MEarth, Earth would have had a problem to get get rid of its primordial atmosphere. If proto-Earth accreted ≈ 0.53 − 0.58MEarth of enstatite-dominated material as suggested by Dauphas (2017) during the disk lifetime, it would have captured a tiny primordial atmosphere that was lost ≈3 Myr after the disk dissipated. In such a case we find that the present-day atmospheric Ar and Ne isotope ratios can be best reproduced if the post-nebula impactors contained ≈ 5% weakly depleted carbonaceous chondritic material and ≈ 95% enstatite chondrites that are strongly depleted in Ar, Ne and moderately volatile elements like potassium. If higher amounts of carbonaceous chondrites were involved in early Earth’s accretion as recently suggested by Schiller et al. (2018), then the Earth’s present atmospheric Ar and Ne ratios can only be reproduced if the involved carbonaceous chondritic post-nebula material was also highly depleted in these noble gases and/or had to be partially be delivered as long as the primordial atmosphere was yet escaping. As long as primordial atmospheres surround the growing protoplanets the abundance of their volatile elements is overwritten by their respective captured solar-like atmospheric abundances. Therefore the initial composition of the protoplanets at the disk dispersal time can not be identified by our method. For masses less than 0.5 MEarth atmospheric escape cannot explain the present-day ratios, i.e. if Earth grew slower then these ratios have to be explained differently (Marty, 2012). If proto-Venus captured a primordial atmosphere it should have grown to masses of ≈ 0.8 − 1.0 MVenus during the time until the disk dissipated and if early Venus accreted its main mass during the disk lifetime than the present atmospheric Ar and Ne isotope ratios and the observed K/U ratios on Venus surface can also be reproduced by the escape of a captured primordial atmosphere that is lost within ≤ 100 Myr, if the Sun was born between a weakly and moderately active young G star. New precise re-measurements of atmospheric noble gases are necessary by future Venus missions to better constrain the material that was involved in the planet’s accretion history and possibly also the EUV activity evolution of the young Sun. In addition, measurements of other moderately volatile element and isotope ratios on the surface such as Rb/U, 64Zn/66Zn, and 39K/41K can give an insight on whether Venus accreted slow or fast, i.e. almost to its final mass within the disk lifetime.

Item URL in elib:https://elib.dlr.de/132018/
Document Type:Article
Additional Information:Bishr nur online erschienen
Title:Measured atmospheric 36Ar/38Ar, 20Ne/22Ne, 36Ar/22Ne noble gas isotope and bulk K/U ratios constrain the early evolution of Venus and Earth.
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Lammer, HIWF Österreichische Akademie der WissenschaftenUNSPECIFIED
Leizinger, MSpace Research Institute, Austrian Academy of Sciences, Graz, Austria; Institute of Physics/IGAM, University of Graz, AustriaUNSPECIFIED
Scherf, MSpace Research Institute, Austrian Academy of Sciences, Graz, AustriaUNSPECIFIED
Odert, P.Insitute for Physics, Graz, AustriaUNSPECIFIED
Burger, C.Department of Astrophysics, University of Vienna, AustriaUNSPECIFIED
Kubyshkina, DariaSpace Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8041 Graz, Austria 0000-0001-9137-9818UNSPECIFIED
Johnstone, ColinUniversity of Vienna, Department of AstrophysicsUNSPECIFIED
Maindl, T.Department of Astrophysics, University of Vienna, AustriaUNSPECIFIED
Schäfer, C.M.Institute of Astronomy and Astrophysics, University of Tübingen, GermanyUNSPECIFIED
Güdel, ManuelInstitute for Astronomy, University of Vienna, Türkenschanzstr. 17, A-1180 Vienna, AustriaUNSPECIFIED
Tosi, Nicolanicola.tosi (at) dlr.deUNSPECIFIED
Nikolaou, AthanasiaAthanasia.Nikolaou (at) dlr.deUNSPECIFIED
Marq, ELATMOS, Université de Versailles Saint-Quentin-en-Yvelines, Guyancourt, FranceUNSPECIFIED
Erkaev, N. V.Institute for Computational Modelling, Krasnoyarsk, Russian FederationUNSPECIFIED
Noack, LDepartment of Earth Sciences / Institute of Geological Sciences, Free University BerlinUNSPECIFIED
Kislyakova, K. G.University of Vienna, Department of AstrophysicsUNSPECIFIED
Fossati, L.Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042, Graz, AustriaUNSPECIFIED
Pilat-Lohinger, ElkeInstitute of Astrophysics, University of Vienna, Vienna, Austria.UNSPECIFIED
Ragossing, FDepartment of Astrophysics, University of Vienna, AustriaUNSPECIFIED
Dorfi, E.A.Department of Astrophysics, University of Vienna, AustriaUNSPECIFIED
Date:2019
Journal or Publication Title:Icarus
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
DOI :10.1016/j.icarus.2019.113551
Publisher:Elsevier
ISSN:0019-1035
Status:Published
Keywords:Planetary atmospheres, magma oceans, atmospheric escape, nobel gases
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Science and Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Erforschung des Weltraums
DLR - Research theme (Project):R - Vorhaben Exploration des Sonnensystems
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Physics
Deposited By: Tosi, Nicola
Deposited On:04 Dec 2019 13:11
Last Modified:04 Dec 2019 13:11

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