1,720,973 research outputs found
Beyond mediocrity: how common is life?
No full textThe probability that life spontaneously emerges in a suitable environment (abiogenesis) is one of the major unknowns in astrobiology. Assessing its value is impeded by the lack of an accepted theory for the origin of life, and is further complicated by the existence of selection biases. Appealing uncritically to some version of the 'Principle of Mediocrity' - namely, the supposed typicality of what transpired on Earth - is problematic on empirical or logical grounds. In this paper, we adopt a Bayesian statistical approach to put the inference of lower bounds for the probability of abiogenesis on a rigorous footing, based on current and future evidence. We demonstrate that the single datum that life has appeared at least once on Earth merely sets weak constraints on the minimal probability of abiogenesis. In fact, the a priori probability assigned to this event (viz., optimistic, pessimistic, or agnostic prior) exerts the strongest influence on the final result. We also show that the existence of a large number of habitable worlds does not necessarily imply, by itself, a high probability that life should be common in the universe. Instead, as delineated before, the choice of prior, which is subject to uncertainty (i.e. admits multiple scenarios), strongly influences the likelihood of life being common. If habitable worlds are uncommon, for an agnostic prior, a deterministic scenario for the origin of life might be favoured over one where abiogenesis is a fluke event
Excitation properties of photopigments and their possible dependence on the host star
Full text linkPhotosynthesis is a plausible pathway for the sustenance of a substantial biosphere on an exoplanet. In fact, it is also anticipated to create distinctive biosignatures detectable by next-generation telescopes. In this work, we explore the excitation features of photopigments that harvest electromagnetic radiation by constructing a simple quantum-mechanical model. Our analysis suggests that the primary Earth-based photopigments for photosynthesis may not function efficiently at wavelengths >1.1 mu m. In the context of (hypothetical) extrasolar photopigments, we calculate the potential number of conjugated pi-electrons (N-*) in the relevant molecules, which can participate in the absorption of photons. By hypothesizing that the absorption maxima of photopigments are close to the peak spectral photon flux of the host star, we utilize the model to estimate N-*. As per our formalism, N-* is modulated by the stellar temperature, and is conceivably higher (lower) for planets orbiting stars cooler (hotter) than the Sun; exoplanets around late-type M-dwarfs might require an N-* twice that of the Earth. We conclude the analysis with a brief exposition of how our model could be empirically tested by future observations
A Bayesian Analysis of the Probability of the Origin of Life Per Site Conducive to Abiogenesis
No full textThe emergence of life from nonlife, or abiogenesis, remains a fundamental question in scientific inquiry. In this article, we investigate the probability of the origin of life (per conducive site) by leveraging insights from Earth's environments. If life originated endogenously on Earth, its existence is indeed endowed with informative value, although the interpretation of the attendant significance hinges critically upon prior assumptions. By adopting a Bayesian framework, for an agnostic prior, we establish a direct connection between the number of potential locations for abiogenesis on Earth and the probability of life's emergence per site. Our findings suggest that constraints on the availability of suitable environments for the origin(s) of life on Earth may offer valuable insights into the probability of abiogenesis and the frequency of life in the universe
The Impact of Tidal Disruption Events on Galactic Habitability
Full text linkTidal Disruption Events (TDEs) are characterized by the emission of a short
burst of high-energy radiation. We analyze the cumulative impact of TDEs on
galactic habitability using the Milky Way as a proxy. We show that X-rays and
extreme ultraviolet (XUV) radiation emitted during TDEs can cause hydrodynamic
escape and instigate biological damage. By taking the appropriate variables
into consideration, such as the efficiency of atmospheric escape and distance
from the Galactic center, we demonstrate that the impact of TDEs on galactic
habitability is comparable to that of Active Galactic Nuclei. In particular, we
show that planets within distances of - kpc could lose Earth-like
atmospheres over the age of the Earth, and that some of them might be subject
to biological damage once every yrs. We conclude by highlighting
potential ramifications of TDEs and argue that they should be factored into
future analyses of inner galactic habitability.Comment: MNRAS, in pres
The impact of AGN outflows on the surface habitability of terrestrial planets in the Milky Way
No full textThe Impact of tidal disruption events on galactic habitability
Full text linkTidal disruption events (TDEs) are characterized by the emission of a short burst of high-energy radiation. We analyse the cumulative impact of TDEs on galactic habitability using the Milky Way as a proxy. We show that X-rays and extreme ultraviolet radiation emitted during TDEs can cause hydrodynamic escape and instigate biological damage. By taking the appropriate variables into consideration, such as the efficiency of atmospheric escape and distance from the Galactic centre, we demonstrate that the impact of TDEs on galactic habitability is comparable to that of active galactic nuclei. In particular, we show that planets within distances of similar to 0.1-1 kpc could lose Earth-like atmospheres over the age of the Earth, and that some of them might be subject to biological damage once every greater than or similar to 10(4) yr. We conclude by highlighting potential ramifications of TDEs and argue that they should be factored into future analyses of inner galactic habitability
Feasibility of Detecting Interstellar Panspermia in Astrophysical Environments
No full textThe proposition that life can spread from one planetary system to another (interstellar panspermia) has a long history, but this hypothesis is difficult to test through observations. We develop a mathematical model that takes parameters such as the microbial survival lifetime, the stellar velocity dispersion, and the dispersion of ejecta into account in order to assess the prospects for detecting interstellar panspermia. We show that the correlations between pairs of life-bearing planetary systems (embodied in the pair-distribution function from statistics) may serve as an effective diagnostic of interstellar panspermia, provided that the velocity dispersion of ejecta is greater than the stellar dispersion. We provide heuristic estimates of the model parameters for various astrophysical environments and conclude that open clusters and globular clusters appear to represent the best targets for assessing the viability of interstellar panspermia.LP
A Bayesian Analysis of Technological Intelligence in Land and Oceans
Full text linkCurrent research indicates that (sub)surface ocean worlds essentially devoid of subaerial landmasses (e.g., continents) are common in the Milky Way and that these worlds could host habitable conditions, thence raising the possibility that life and technological intelligence (TI) may arise in such aquatic settings. It is known, however, that TI on Earth (i.e., humans) arose on land. Motivated by these considerations, we present a Bayesian framework to assess the prospects for the emergence of TIs in land- and ocean-based habitats (LBHs and OBHs). If all factors are equally conducive for TIs to arise in LBHs and OBHs, we demonstrate that the evolution of TIs in LBHs (which includes humans) might have very low odds of roughly 1 in 10 ^3 to 1 in 10 ^4 , thus outwardly contradicting the Copernican principle. Hence, we elucidate three avenues whereby the Copernican principle can be preserved: (i) the emergence rate of TIs is much lower in OBHs, (ii) the habitability interval for TIs is much shorter in OBHs, and (iii) only a small fraction of worlds with OBHs comprise appropriate conditions for effectuating TIs. We also briefly discuss methods for empirically falsifying our predictions and comment on the feasibility of supporting TIs in aerial environments
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