Modification of the radioactive heat budget of Earth-like exoplanets by the loss of primordial atmospheres

Author(s)

Nikolai Erkaev, Manuel Scherf, Oliver Herbort, Helmut Lammer, Darya Kubyshkina, Martin Leitzinger, C. O'Neill, Peter Woitke

Abstract

The initial abundance of radioactive heat producing isotopes in the interior of terrestrial planets are important drivers of its thermal evolution and the related tectonics and possible evolution to an Earth-like habitat. The moderately volatile element K can be outgassed from a magma ocean into H

₂-dominated primordial atmospheres of protoplanets with assumed masses between 0.55 and 1.0M

_Earth at the time when the gas disc evaporated. We estimate this outgassing and let these planets grow through impacts of depleted and non-depleted material that resembles the same

⁴⁰K abundance of average carbonaceous chondrites until the growing protoplanets reach 1.0M

_Earth. We examine different atmospheric compositions and, as a function of pressure and temperature, calculate the proportion of K by Gibbs Free Energy minimization using the GGCHEM code. We find that for H

₂-envelopes and for magma ocean surface temperatures that are ≥ 2500 K, no K condensates are thermally stable, so that outgassed

⁴⁰K can populate the atmosphere to a great extent. However, due to magma ocean turnover time and the limited diffusion of

⁴⁰K into the upper atmosphere, from the entire

⁴⁰K in the magma ocean only a fraction may be available for escaping into space. The escape rates of the primordial atmospheres and the dragged

⁴⁰K are simulated for different stellar EUV activities with a multispecies hydrodynamic upper atmosphere evolution model. Our results show that one can expect that different initial abundances of heat producing elements will result in different thermal and tectonic histories of terrestrial planets and their habitability conditions.

Organisation(s)

Department of Astrophysics

External organisation(s)

Russian Academy of Sciences, Österreichische Akademie der Wissenschaften (ÖAW), Karl-Franzens-Universität Graz, Macquarie University, Siberian Federal University, Technische Universität Graz, University of St. Andrews

Journal

Monthly Notices of the Royal Astronomical Society

Volume

518

Pages

3703-3721

No. of pages

19

ISSN

0035-8711

DOI

https://doi.org/10.1093/mnras/stac3168

Publication date

01-2023

Peer reviewed

Yes

Austrian Fields of Science 2012

103004 Astrophysics

Keywords

ASJC Scopus subject areas

Astronomy and Astrophysics, Space and Planetary Science

Portal url

https://ucrisportal.univie.ac.at/en/publications/c15df3bb-059e-4206-a8c5-bc54af0a1391