Origin and loss of nebula-captured hydrogen envelopes from ‘sub’- to ‘super-Earths’ in the habitable zone of Sun-like stars
By H. Lammer, A. Stökl, N. Erkaev, E. Dorfi, P. Odert, M. Gudel, Y. Kulikov, K. Kislyakova, M. Leitzinger. 2014
137 citations recorded by the source corpus.
We investigate the origin and loss of captured hydrogen envelopes from protoplanets having masses in a range between ‘sub-Earth’-like bodies of 0.1 M⊕ and ‘super-Earths’ with 5 M⊕ in the habitable zone at 1 au of a Sun-like G star, assuming that their rocky cores had formed before the nebula gas dissipated. We model the gravitational attraction and accumulation of nebula gas around a planet’s core as a function of protoplanetary luminosity during accretion and calculate the resulting surface temperature by solving the hydrostatic structure equations for the protoplanetary nebula. Depending on nebular properties, such as the dust grain depletion factor, planetesimal accretion rates, and resulting luminosities, for planetary bodies of 0.1– 1M ⊕ we obtain hydrogen envelopes with masses between ∼2.5 × 10 19 and 1.5 × 10 26 g. For ‘super-Earths’ with masses between 2 and 5 M ⊕ more massive hydrogen envelopes within the mass range of ∼7.5 × 10 23 –1.5 × 10 28 g can be captured from the nebula. For studying the escape of these accumulated hydrogen-dominated protoatmospheres, we apply a hydrodynamic upper atmosphere model and calculate the loss rates due to the heating by the high soft-X-ray and extreme ultraviolet (XUV) flux of the young Sun/star. The results of our study indicate that under most nebula conditions ‘sub-Earth’ and Earth-mass planets can lose their captured hydrogen envelopes by thermal escape during the first ∼100 Myr after the disc dissipated. However, if a nebula has a low dust depletion factor or low accretion rates resulting in low protoplanetary luminosities, it is possible that even protoplanets with Earth-mass cores may keep their hydrogen envelopes during their whole lifetime. In contrast to lower mass protoplanets, more massive ‘super-Earths’, which can accumulate a huge amount of nebula gas, lose only tiny fractions of their primordial hydrogen envelopes. Our results agree with the fact that Venus, Earth, and Mars are not surrounded by dense hydrogen envelopes, as well as with the recent discoveries of low density ‘super-Earths’ that most likely could not get rid of their dense protoatmospheres.
Subfields: Astronomy and Astrophysics
View Paper: https://www.semanticscholar.org/paper/5f496ddd4faf44def0860bf1c31b5c3ed56cf5cb
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In Astronomy and Astrophysics
Citations in the corpus
- Origin and evolution of the atmospheres of early Venus, Earth and Mars (2018, background): “More massive protoplanets can accumulate a huge amount of nebula gas, which can not be lost during the planet’s life time (Lammer et al. 2014; Johnstone et al. 2015a; Owen and Mohanty 2016).”
- Stellar winds on the main-sequence - II. The evolution of rotation and winds (2015, background): “It is possible that the primordial Earth formed with a dense hydrogen atmosphere captured during the Sun’s classical T Tauri phase (Hayashi et al. 1979; Lammer et al. 2014) which must have been lost early in the Earth’s evolution.”
- The Extreme Ultraviolet and X-Ray Sun in Time: High-Energy Evolutionary Tracks of a Solar-Like Star (2015, background): “For this case, Lammer et al. (2014) calculateḋMpl from the atmosphere of 3.5 × 1032mH s−1 with FEUV = 100 erg s−1 cm−2, wheremH is the mass of a hydrogen atom (see the fifth case in their Table 4).”
- Atmospheric Escape and the Evolution of Close-In Exoplanets (2018, background): “Yelle (2004) and Tian et al. (2005)’s approach of a constant heating efficiency has been adopted by a wide number of further calculations studying both hot-Jupiters (Garćıa Muñoz 2007) and super-Earth/mini-Neptune mass planets (Lammer et al. 2013, 2014, 2016; Erkaev et al. 2013, 2016).”
- PLANETARY POPULATION SYNTHESIS COUPLED WITH ATMOSPHERIC ESCAPE: A STATISTICAL VIEW OF EVAPORATION (2014, background): “…flux can drive hydrodynamic evaporation in the atmosphere of close-in planets and yield a substantially higher mass-loss rate than for planets in the Jeans escape regime (Lammer et al. 2003; Baraffe et al. 2 2004; Murray-Clay et al. 2009; Owen & Jackson 2012; Lopez et al. 2012; Lammer et al. 2014).”