Thermodynamic Constrains for Life Based on Non-Aqueous Polar Solvents on Free-Floating Planets

Abstract

Free-floating planets (FFPs) might originate either around a star or in solitary fashion. These bodies can retain molecular gases atmospheres which, upon cooling, have basal pressures of tens of bars or more. Pressure-induced opacity of these gases prevents such a body from eliminating its internal radioactive heat and its surface temperature can exceed for a long term the melting temperature of a life-supporting solvent. In this paper two non-aqueous but still polar solvents are considered: hydrogen sulfide and ammonia. Thermodynamic requirements to be fulfilled by a hypothetic gas constituent of a life-supporting FFP's atmosphere are studied. The three gases analyzed here (nitrogen, methane and ethane) are candidates. We show that bodies with ammonia oceans are possible in interstellar space. This may happen on FFPs of (significantly) smaller or larger mass than the Earth. Generally, in case of FFP smaller in size than the Earth, the atmosphere exhibits a convective layer near the surface and a radiative layer at higher altitudes while the atmosphere of FFPs larger in size than Earth does not exhibit a convective layer. The atmosphere mass of a life-hosting FFP of Earth size is two or three orders of magnitude larger than the mass of Earth atmosphere. For FFPs larger than the Earth and specific values of surface pressure and temperature, there are conditions for condensation (in the ethane atmosphere). Some arguments induce the conclusion than the associated surface pressures and temperatures should be treated with caution as appropriate life conditions.

Presence of water on exomoons orbiting free-floating planets: a case study

“…Although it has been discussed that an FFP with an atmosphere rich in molecular hydrogen could harbour life (Stevenson 1999), it is paramount to model the chemical composition and evolution of CO 2 and water to determine the opacity of the atmosphere that might allow liquid water on its surface. Badescu (2010) analyses four gases (nitrogen, carbon dioxide, methane and ethane) as the main component of the FFP atmosphere to study the long-term thermal stability of a liquid solvent on the surface, and Badescu (2011aBadescu ( , 2011bBadescu ( , 2011c studied the possibility for an FFP to host life by calculating the thermal profiles and the solubility properties of condensed gas. It is also shown that these gases produces more effective opacities than H 2 , as originally suggested by Stevenson (1999).…”