Escape of planetary atmospheres: physical processes and numerical models

Abstract

We address the problem of the dissipation (escape) of planetary atmospheres and discuss the physical mechanisms controlling the nature of the relevant processes and review the mathematical models and numerical methods used in the analysis of this phenomenon, taking the limitations imposed by available experimental data into account. The structural and dynamic features of the aeronomy of Earth and terrestrial planets are discussed in detail; they are key in determining the energy absorption rate and the atmosphere escape rate. A kinetic Monte Carlo method developed by the authors for investigating the thermal and nonthermal processes of atmospheric escape is presented. Using this approach and spacecraft data, atomic loss rates from the Venusian and Martian atmospheres via a variety of escape processes are estimated, and their role at the current and early evolutionary stages of these planets is discussed. The discovery of exosolar planets, model studies of the dissipation of their gas envelopes, and the likely impact of the dissipation mechanisms on the planetary atmosphere and climate evolution have stimulated the study of this field and made it a topical research subject.

Lava Worlds: From Early Earth to Exoplanets

“…The rates of escape depend on the behavior of the star and the interaction with the planet and any magnetic field, as well as XUV heating of the upper atmosphere, which determines its vertical structure. The kinetic energy imparted to the atom is variously derived from recombination after photoionization or even photodissociation (Shematovich and Marov, 2018;Howe et al, 2020), collisions with ions from star or planet planetary ions accelerated by the magnetic field in the stellar wind (Lundin et al, 2007), or electromagnetic interactions with the stellar wind (Catling and Kasting, 2017). The foundations of a better understanding of these phenomena is being laid with statistical determinations of flaring rates of stars with a range of spectral type and rotation rates/ages.…”

Neutral atmospheric escape in the Solar and extrasolar planetary systems

“…by sputtering and/or precipitation). Escape rates of neutral particles have been indirectly estimated using a combination of measurements of the atmospheric reservoirs for escape and models (Shematovich & Marov 2018, Jakosky et al 2018. The total atmospheric escape from both ions and neutrals varies with the same drivers observed to modify the solar wind interaction region.…”

“…Neutral O escaping flux due to the photochemistry is about (0.5 -1.0)×10 7 cm −2 s −1 depending on the solar activity level (Shematovich & Marov 2018, Jakosky et al 2018. Recently the neutral O escaping flux due to the H + and H precipitation was estimated by the values about (0.7 -30.0)×10 5 cm −2 s −1 (Shematovich 2017) when the energy spectra of the precipitating protons measured by MEX ASPERA-3 instrument at low solar activity level were used as the inputs at upper boundary.…”

“…These results have shaped a new basis for the physics of the upper atmosphere, i.e., the aeronomy that is directly linked to planetary cosmogony. In particular, they have allowed to infer a conclusion that dissipation of a planetary atmosphere (or atmospheric escape) plays an important role in the evolution of planets primarily of terrestrial planets of the Solar System, although many details of those events are not fully clear and remain the topic of active discussions (Shematovich & Marov 2018). Observations and theoretical models of the exoplanet atmospheres exposed to the extreme fluxes of X-ray and UV radiation of the parent star provide a remarkable opportunity to test theoretical understanding of the key processes -thermal and non-thermal escape.…”

Comparative Analysis of the Model for Exoplanet Atmosphere Outflow

“…Under strong stellar UV radiation, the upper planetary atmosphere can be expanded over large distances from the center of the planet. This results in rapid atmospheric losses, with their efficiency being determined by the physics and chemistry of the atmosphere Johnson et al (2008); Shematovich, Bisikalo & Ionov (2015); Shematovich & Marov (2018). For example, the so-called gasdynamic outflow (or the planetary wind) was studied theoretically for planets of the Solar System at early stages of their evolution Watson, Donahue & Walker (1981); Hunten, Pepin & Walker (1987); Chassefière (1996); Volkov (2016).Only recent decades have proposed opportunities for observing the gas-dynamic outflow from several close exoplanets Vidal-Madjar et al (2003; Linsky et al (2010); Kulow et al (2014).…”