Did high-energy astrophysical sources contribute to Martian atmospheric loss?

Abstract

Mars is believed to have had a substantial atmosphere in the past. Atmospheric loss led to depressurization and cooling, and is thought to be the primary driving force responsible for the loss of liquid water from its surface. Recently, MAVEN observations have provided new insight into the physics of atmospheric loss induced by ICMEs and solar wind interacting with the Martian atmosphere. In addition to solar radiation, it is likely that its atmosphere has been exposed to radiation bursts from high-energy astrophysical sources which become highly probable on timescales of ∼Gy and beyond. These sources are capable of significantly enhancing the rates of photoionization and charged particle-induced ionization in the upper atmosphere. We use Monte Carlo simulations to model the interaction of charged particles and photons from astrophysical sources in the upper Martian atmosphere and discuss its implications on atmospheric loss. Our calculations suggest that the passage of the solar system though dense interstellar clouds is the most significant contributor to atmospheric loss among the sources considered here.

Does the planetary dynamo go cycling on? Re-examining the evidence for cycles in magnetic reversal rate

“…The rate of geomagnetic reversals could potentially be relevant to life on Earth and its extinctions (Wei et al 2014), especially since a magnetic reversal occurring during transit of a dense interstellar cloud could be catastrophic (Pavlov et al 2005). The question of reversal probability will be even more relevant for the long term potential for life to survive (or the type of life that survives) around M stars (Atri et al 2013;Atri 2017) due to intense flare activity. Fourier analysis of the magnetic reversal record reveals multiple significant periodic components, some of which seem to interact in a complex way and thus may be spurious, but one periodic component may actually be significant and possibly finds physical explanation.…”

“…Still, atmospheric loss on the Earth during reversals has been hypothesized (Wei et al 2014; for the case of Mars see Atri 2016). Further, planets orbiting M stars are subject to a high flux of moderate energy cosmic rays and thus loss of the protection of a magnetic field could be disastrous for any life there (Atri 2017;Atri et al 2013). Therefore, the possibility of gaining insight into whether or not magnetic field reversals are periodic on Earth might have broader relevance.…”

“…Thus, any evidence for a potential temporal association between the periodicity of magnetic reversals and biodiversity cycles may be tenuous, at least based on current theoretical understanding. Still, atmospheric loss on the Earth during reversals has been hypothesized (Wei et al 2014; for the case of Mars see Atri 2013). Further, planets orbiting M stars are subject to a high flux of moderate energy cosmic rays and thus loss of the protection of a magnetic field could be disastrous for any life there (Atri 2017; Atri et al 2013).…”

Stellar proton event-induced surface radiation dose as a constraint on the habitability of terrestrial exoplanets

“…The code tracks one particle at a time, and as a result, for the same spectrum, the radiation dose scales linearly with fluence (Agostinelli et al 2003). The radiation dose is primarily dependent on the overall column density of the atmosphere whereas the atmospheric composition is not crucial as in case of photochemistry or atmospheric loss (Atri et al 2013;Atri 2016b). Since little is known about the atmospheres of terrestrial exoplanets, parameters from the Earth's atmosphere were used (along with mass, radius, and gravity), except for the atmospheric depth (1036 g cm −2 ), which is a free parameter in this study.…”

Black hole spin-orbit misalignment in the X-ray binary MAXI J1820+070

“…On the other hand, the leading model for the low-frequency quasi-periodic oscillations observed in black hole x-ray binaries in the x-rays and optical, the Lense-Thirring solid-body precession of the hot flow around black hole (3)(4)(5), is based on the assumption that the misalignment is significant. Significant misalignment is also expected in x-ray binaries which have potentially high kick velocities acquired during formation (6). The large degree of misalignment puts strong constraints on the supernova explosion and black hole formation mechanisms, as it can only decrease during the accretion stage (7).…”