Abstract:For life-forms like us, the most important feature of Earth is its habitability. Understanding habitability and using that knowledge to locate the nearest habitable planet may be crucial for our survival as a species. During the past decade, expectations that the universe could be filled with habitable planets have been bolstered by the increasingly large overlap between terrestrial environments known to harbor life and the variety of environments on newly detected rocky exoplanets. The inhabited and uninhabit… Show more
“…Most proteins can exist up to 50°C, while some can exist up to 120°C (see e.g. Lineweaver & Chopra 2012). A detailed review of the concept of habitability can be found in Cockell et al (2016).…”
Context. Plate tectonics is considered a fundamental component for the habitability of the Earth. Yet whether it is a recurrent feature of terrestrial bodies orbiting other stars or unique to the Earth is unknown. The stagnant lid may rather be the most common tectonic expression on such bodies. Aims. To understand whether a stagnant-lid planet can be habitable, i.e. host liquid water at its surface, we model the thermal evolution of the mantle, volcanic outgassing of H 2 O and CO 2 , and resulting climate of an Earth-like planet lacking plate tectonics. Methods. We used a 1D model of parameterized convection to simulate the evolution of melt generation and the build-up of an atmosphere of H 2 O and CO 2 over 4.5 Gyr. We then employed a 1D radiative-convective atmosphere model to calculate the global mean atmospheric temperature and the boundaries of the habitable zone (HZ).Results. The evolution of the interior is characterized by the initial production of a large amount of partial melt accompanied by a rapid outgassing of H 2 O and CO 2 . The maximal partial pressure of H 2 O is limited to a few tens of bars by the high solubility of water in basaltic melts. The low solubility of CO 2 instead causes most of the carbon to be outgassed, with partial pressures that vary from 1 bar or less if reducing conditions are assumed for the mantle to 100-200 bar for oxidizing conditions. At 1 au, the obtained temperatures generally allow for liquid water on the surface nearly over the entire evolution. While the outer edge of the HZ is mostly influenced by the amount of outgassed CO 2 , the inner edge presents a more complex behaviour that is dependent on the partial pressures of both gases. Conclusions. At 1 au, the stagnant-lid planet considered would be regarded as habitable. The width of the HZ at the end of the evolution, albeit influenced by the amount of outgassed CO 2 , can vary in a non-monotonic way depending on the extent of the outgassed H 2 O reservoir. Our results suggest that stagnant-lid planets can be habitable over geological timescales and that joint modelling of interior evolution, volcanic outgassing, and accompanying climate is necessary to robustly characterize planetary habitability.
“…Most proteins can exist up to 50°C, while some can exist up to 120°C (see e.g. Lineweaver & Chopra 2012). A detailed review of the concept of habitability can be found in Cockell et al (2016).…”
Context. Plate tectonics is considered a fundamental component for the habitability of the Earth. Yet whether it is a recurrent feature of terrestrial bodies orbiting other stars or unique to the Earth is unknown. The stagnant lid may rather be the most common tectonic expression on such bodies. Aims. To understand whether a stagnant-lid planet can be habitable, i.e. host liquid water at its surface, we model the thermal evolution of the mantle, volcanic outgassing of H 2 O and CO 2 , and resulting climate of an Earth-like planet lacking plate tectonics. Methods. We used a 1D model of parameterized convection to simulate the evolution of melt generation and the build-up of an atmosphere of H 2 O and CO 2 over 4.5 Gyr. We then employed a 1D radiative-convective atmosphere model to calculate the global mean atmospheric temperature and the boundaries of the habitable zone (HZ).Results. The evolution of the interior is characterized by the initial production of a large amount of partial melt accompanied by a rapid outgassing of H 2 O and CO 2 . The maximal partial pressure of H 2 O is limited to a few tens of bars by the high solubility of water in basaltic melts. The low solubility of CO 2 instead causes most of the carbon to be outgassed, with partial pressures that vary from 1 bar or less if reducing conditions are assumed for the mantle to 100-200 bar for oxidizing conditions. At 1 au, the obtained temperatures generally allow for liquid water on the surface nearly over the entire evolution. While the outer edge of the HZ is mostly influenced by the amount of outgassed CO 2 , the inner edge presents a more complex behaviour that is dependent on the partial pressures of both gases. Conclusions. At 1 au, the stagnant-lid planet considered would be regarded as habitable. The width of the HZ at the end of the evolution, albeit influenced by the amount of outgassed CO 2 , can vary in a non-monotonic way depending on the extent of the outgassed H 2 O reservoir. Our results suggest that stagnant-lid planets can be habitable over geological timescales and that joint modelling of interior evolution, volcanic outgassing, and accompanying climate is necessary to robustly characterize planetary habitability.
“…A significant part of the free energy (typically an amount of ca 100 kJ mol –1 at 300 K for systems with time scales of seconds to years [42,43]) is dissipated so that the loop proceeds unidirectionally, provided that subsequent kinetic barriers remain below that of the activation process. Useful chemical work can be produced from further reactions of intermediate I through its conversion into metabolites (M) but in limited amount (≤ Δ G (I)) compared with the free energy introduced in the system.Scheme 5.Free energy source requirements in living systems (inspired from the figure introduced by Lineweaver & Chopra [45] with a different perspective). Comparison of different sources of energy available in planetary environments: electromagnetic radiations (correspondence with frequency and wavelength in abscissa), thermal energy (black body radiation curves displaying spectral radiance in ordinate: at 647 K, the critical point of water, blue line; 1600 K, representing typical Hadean magma temperatures red line; and 3500 or 6000 K, dark and light orange lines, surface temperatures of examples of M-stars or G-stars as the Sun, respectively) and lightning ( T ≥ 10 4 K).…”
A sudden transition in a system from an inanimate state to the living state—defined on the basis of present day living organisms—would constitute a highly unlikely event hardly predictable from physical laws. From this uncontroversial idea, a self-consistent representation of the origin of life process is built up, which is based on the possibility of a series of intermediate stages. This approach requires a particular kind of stability for these stages—dynamic kinetic stability (DKS)—which is not usually observed in regular chemistry, and which is reflected in the persistence of entities capable of self-reproduction. The necessary connection of this kinetic behaviour with far-from-equilibrium thermodynamic conditions is emphasized and this leads to an evolutionary view for the origin of life in which multiplying entities must be associated with the dissipation of free energy. Any kind of entity involved in this process has to pay the energetic cost of irreversibility, but, by doing so, the contingent emergence of new functions is made feasible. The consequences of these views on the studies of processes by which life can emerge are inferred.
“…Habitability has quickly become the central concept of astrobiology (e.g., Chyba and Hand, 2005;Gonzalez, 2005;Horneck and Rettberg, 2007;Lineweaver and Chopra, 2012;Domagal-Goldman et al, 2016). While research interest is naturally concentrated upon the habitability of newly discovered Earthlike planets around nearby stars, there is also an emerging interest for habitability of other astrophysical systems, in particular galaxies as main building blocks of the universe.…”
The problem of the extent of habitable zones in different kinds of galaxies is one of the outstanding challenges for contemporary astrobiology. In the present study, we investigate habitability in a large sample of simulated galaxies from the Illustris Project in order to at least roughly quantify the hospitality to life of different galactic types. The pioneering study of Dayal et al. (2015) is critically examined and some of its results are amended. In particular, we find a tentative evidence for a second mode of galactic habitability comprising metal-rich dwarfs similar to IC 225, LMC or M32. The role of the galactic environment and the observation selection effects is briefly discussed and prospects for further research on the topic outlined.
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