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Register a new userMonte Carlo estimation of the probability of causal contacts between communicating civilisations
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In this work we address the problem of estimating the probabilities of causal contacts between civilisations in the Galaxy. We make no assumptions regarding the origin and evolution of intelligent life. We simply assume a network of causally connected nodes. These nodes refer somehow to intelligent agents with the capacity of receiving and emitting electromagnetic signals. Here we present a three-parametric statistical Monte Carlo model of the network in a simplified sketch of the Galaxy. Our goal, using Monte Carlo simulations, is to explore the parameter space and analyse the probabilities of causal contacts. We find that the odds to make a contact over decades of monitoring are low for most models, except for those of a galaxy densely populated with long-standing civilisations. We also find that the probability of causal contacts increases with the lifetime of civilisations more significantly than with the number of active civilisations. We show that the maximum probability of making a contact occurs when a civilisation discovers the required communication technology.
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The recent discovery of seven potentially habitable Earth-size planets around the ultra-cool star TRAPPIST-1 has further fueled the hunt for extraterrestrial life. Current methods focus on closely monitoring the host star to look for biomarkers in the transmission signature of exoplanets atmosphere. However, the outcome of these methods remain uncertain and difficult to disentangle with abiotic alternatives. Recent exoplanet direct imaging observations by THIRSTY, an ultra-high contrast coronagraph located in La Trappe (France), lead us to propose a universal and unambiguous habitability criterion which we directly demonstrate for the TRAPPIST-1 system. Within this new framework, we find that TRAPPIST-1g possesses the first unambiguously habitable environment in our galaxy, with a liquid water percentage that could be as large as $sim~90~%$. Our calculations hinge on a new set of biomarkers, CO$_2$ and C$_{x}$H$_{2(x+1)}$O (liquid and gaseous), that could cover up to $sim~10~%$ of the planetary surface and atmosphere. THIRSTY and TRAPPIST recent observations accompanied by our new, unbiased habitability criterion may quench our thirst for the search for extraterrestrial life. However, the search for intelligence must continue within and beyond our Solar System.
The Ad Hoc Committee on SETI Nomenclature was convened at the suggestion of Frank Drake after the Decoding Alien Intelligence Workshop at the SETI Institute in March 2018. The purpose of the committee was to recommend standardized definitions for terms, especially those that are used inconsistently in the literature and the scientific community. The committee sought to recommend definitions and terms that are a compromise among several desirable but occasionally inconsistent properties for such terms: 1) Consistency with the historical literature and common use in the field; 2) Consistency with the present literature and common use in the field; 3) Precision of meaning; 4) Consistency with the natural (i.e. everyday, non-jargon) meanings of terms; 5) Compatibility with non-English terms and definitions. The definitions in this report are restricted to technical, SETI contexts, where they may have jargon senses different from their everyday senses. In many cases we include terms only to deprecate them (in the sense of to withdraw official support for or discourage the use of...in favor of a newer or better alternative, Merriam-Webster sense 4). This is a consensus document that the committee members all endorse; however, in many cases the individual members have (or have expressed in the past) more nuanced opinions on these terms that are not fully reflected here, for instance Almar (2008, Acta Astronautica, 68, 351), Denning (2008, NASA-SP-2009-4802 Ch. 3 pp.63-124), and Wright (2018, arXiv:1803.06972).
Numerous missions planned for the next decade are likely to target a handful of smal sites of interest on the Moons surface, creating risks of crowding and interference at these locations. The Moon presents finite and scarce areas with rare topography or concentrations of resources of special value. Locations of interest to science, notably for astronomy, include the Peaks of Eternal Light, the coldest of the cold traps and smooth areas on the far side. Regions richest in physical resources could also be uniquely suited to settlement and commerce. Such sites of interest are both few and small. Typically, there are fewer than ten key sites of each type, each site spanning a few kilometres across. We survey the implications for different kins of mission and find that the diverse actors pursuing incomptible ends at these sites could soon crowd and interfere with each other, leaving almost all actors worse off. Without proactive measures to prevent these outcomes, lunar actors are likely to experience significant losses of opportunity. We highlight the legal, policy, and ethical ramifications. Insights from research on comparable sites on Earth present a path toward managing lunar crowding and interference grounded in ethical and practical near-term considerations. This article is part of a discussion meeting issue Astronomy from the Moon: the next decades.
In an age of media saturation, how can astronomers succeed in grabbing the publics attention to increase awareness and understanding of astronomy? Here I discuss some creative alternatives to press releases, public lectures, television programs, books, magazine articles, and other traditional ways of bringing astronomy to a wide audience. By thinking outside the box and employing novel tools - from truly terrible sci-fi movies, to modern Stonehenges, to music from the stars - astronomers are finding effective new ways of communicating the wonders of the universe to people of all ages.
We present MCRaT, a Monte Carlo Radiation Transfer code for self-consistently computing the light curves and spectra of the photospheric emission from relativistic, unmagnetized jets. We apply MCRaT to a relativistic hydrodynamic simulation of a long duration gamma-ray burst jet, and present the resulting light-curves and time-dependent spectra for observers at various angles from the jet axis. We compare our results to observational results and find that photospheric emission is a viable model to explain the prompt phase of long-duration gamma-ray bursts at the peak frequency and above, but faces challenges in reproducing the flat spectrum below the peak frequency. We finally discuss possible limitations of these results both in terms of the hydrodynamics and the radiation transfer and how these limitations could affect the conclusions that we present.
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