Modeling a Transient Secondary Paleolunar Atmosphere: 3‐D Simulations and Analysis

Abstract

The lunar history of water deposition, loss, and transport postaccretion has become an important consideration in relation to the possibility of a human outpost on the Moon. Very recent work has shown that a secondary primordial atmosphere of up to 10 mbar could have been emplaced ∼3.5×109 years ago due to volcanic outgassing from the maria. Using a zero‐dimensional chemistry model, we demonstrate the temperature dependence of the resulting major atmospheric components (CO or CO2). We use a three‐dimensional general circulation model to test the viability of such an atmosphere and derive its climatological characteristics. Based on these results, we then conjecture on its capability to transport volatiles outgassed from the maria to the permanently shadowed regions at the poles. Our preliminary results demonstrate that atmospheres as low as 1 mbar are viable and that permanent cold trapping of volatiles is only possible at the poles.

Volcanically Induced Transient Atmospheres on the Moon: Assessment of Duration, Significance, and Contributions to Polar Volatile Traps

“…As part of an extensive review of three possible types of lunar atmosphere, Stern (1999; his section 5.2.2) treated a hypothetical volcanically induced atmosphere with a total gas mass of 10 11 kg and adopted the loss rate calculated by Vondrak (1974) of 10 kg s −1 . The same loss rate is estimated in a recent more general analysis by Aleinov et al (2019) treating much more massive, at least ~10 15 kg, atmospheres with surface pressures >100 Pa. Using a 10 kg s −1 loss rate leads to the typical timescales for atmospheric decay, τ d , shown in Table 2, between ~2,000 and ~6,000 years.…”

“…We also conclude that these low volatile release volumes and rates are not conducive to optimizing the transport of released volatiles from the eruption site to the poles to enhance the accumulation of volatiles in polar cold traps (see also Aleinov et al, 2019), nor of creating temporary environments that might favor astrobiological activity (Schulze-Makuch & Crawford, 2018). Our results suggest that most volatiles in lunar polar cold traps originated from volatile-rich impacts, rather than volatile release from volcanic eruptions, similar to findings about polar cold-trap volatile deposits on Mercury (e.g., Deutsch et al, 2019Deutsch et al, , 2020Ernst et al, 2018).…”

Atmospheric Escape Processes and Planetary Atmospheric Evolution

“…It is important to note that while the Jeans parameter is the main parameter of thermal escape, the location of the exobase is extremely important. In the case of Titan or a possible early Moon atmosphere (Aleinov et al., 2019) the altitude of the exobase is nonnegligible compared to the radius of the planet, and while the flux per unit surface is small, it can become the most important source of loss when taking the whole exobase surface into account.…”

“…In Aleinov et al. (2019), a study of the thermal escape was made, showing the limitations of the creation of such an atmosphere, as well as the climatic conditions an atmosphere would have had. These conditions are interesting since they show the transport of volatiles to the poles.…”

Anthony Del Genio: Climates of Planets Near and Far

“…Led by my GISS colleague Mike Way and with contributions from many others in the GISS Earth GCM group (Way et al, ), a generalized planetary version of the GISS GCM has been developed. We have used it to explore the possibility that ancient Venus under the faint young Sun may have been habitable (Way et al, ); to understand the processes that put excessive water vapor into the stratosphere as incident stellar flux increases, a precursor to the eventual loss of a planet's oceans (Fujii et al, ); to determine how the thermal inertia and heat transport of a dynamic ocean might render a planet continuously habitable in the face of oscillations in planet eccentricity (Way & Georgakarakos, ); to examine scenarios for a possible habitable climate on the known exoplanet closest to Earth (Del Genio et al, ); to determine how the carbonate‐silicate cycle feedback that regulates CO 2 and allowed Earth to remain habitable over most of its history might vary as precipitation and runoff change with insolation and planet rotation (Jansen et al, ); to understand the transport of volatiles to permanently shadowed polar regions early in the Moon's history (Aleinov et al, ); to predict the planetary albedos and surface temperatures of exoplanets from sparse available information using Earth climate concepts (Del Genio, Kiang , et al, ); and to understand how high obliquity allows weakly illuminated planets to remain habitable (Colose et al, ). We have also tried to set a standard for data sharing by making the GCM output files and metadata for our published papers publicly available, as described in Way et al ().…”