Day 1748

Tuesday, Wednesday, Thursday, Friday.

2008.08671

Stable partial ice cover possible for any obliquity: effects of obliquity, albedo, and heat transport on  ice cover dynamics

Landgren, Nadeau

The Snowball state refers to when a planet is completely or almost completely covered in ice. The Earth may have passed through several Snowball events in its history which may have been crucial for increasing complexity of life. As we turn our focus to habitable planets outside of our solar system, the question then arises, what planetary characteristics permit a Snowball state and how do they impact the severity of this state? One factor determining planetary ice cover is the distribution of mean annual incoming solar radiation, which in turn depends on the planetary obliquity. In this study, we use an analytical energy balance model with explicit dependence on obliquity to study the probability of a catastrophic transition from partial ice cover to a stable Snowball State. We show that transitions to the Snowball state is more severe but less likely for higher values of the albedo contrast and energy transport across latitudes and that stable partial ice cover is possible at any obliquity. Additionally, this work is general enough to apply to any rapidly rotating planet and could be used to study the likelihood of Snowball transitions on planets within the habitable region of other stars.

2008.08709

Potential for liquid water biochemistry deep under the surfaces of the Moon, Mars and beyond

Lingam, Loeb

We investigate the prospects for the past or current existence of habitable conditions deep underneath the surfaces of the Moon and Mars as well as generic bound and free-floating extrasolar rocky objects. We construct a simple model that takes into account the thermal limits of life as well as the size, surface temperature, and relative radionuclide abundance of a given object and yields the spatial extent of the subsurface habitable region. We also investigate the constraint imposed by pressure on habitability, and show that it is unlikely to rule out the prospects for life altogether. We estimate the maximum biomass that might be sustainable in deep subsurface environments as a function of the aforementioned parameters from an energetic perspective. We find that it might be a few percent that of Earth's subsurface biosphere, and three orders of magnitude smaller than Earth's global biomass, under ideal circumstances. We conclude with a brief exposition of the prevalence of rocky objects with deep biospheres and methods for detecting signatures of biological activity through forthcoming missions to visit the Moon and Mars.