No Arabic abstract
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.
Monitoring of vibrational eigenmodes of an elastic body excited by gravitational waves was one of the first concepts proposed for the detection of gravitational waves. At laboratory scale, these experiments became known as resonant-bar detectors first developed by Joseph Weber in the 1960s. Due to the dimensions of these bars, the targeted signal frequencies were in the kHz range. Weber also pointed out that monitoring of vibrations of Earth or Moon could reveal gravitational waves in the mHz band. His Lunar Surface Gravimeter experiment deployed on the Moon by the Apollo 17 crew had a technical failure rendering the data useless. In this article, we revisit the idea and propose a Lunar Gravitational-Wave Antenna (LGWA). We find that LGWA could become an important partner observatory for joint observations with the space-borne, laser-interferometric detector LISA, and at the same time contribute an independent science case due to LGWAs unique features. Technical challenges need to be overcome for the deployment of the experiment, and development of inertial vibration sensor technology lays out a future path for this exciting detector concept.
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).
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.
Lunar occultation, which occurs when the Moon crosses sight-lines to distant sources, has been studied extensively through apparent intensity pattern resulting from Fresnel diffraction, and has been successfully used to measure angular sizes of extragalactic sources. However, such observations to-date have been mainly over narrow bandwidth, or averaged over the observing band, and the associated intensity pattern in time has rarely been examined in detail as a function of frequency over a wide band. Here, we revisit the phenomenon of lunar occultation with a view to study the associated intensity pattern as a function of both time and frequency. Through analytical and simulation approach, we examine the variation of intensity across the dynamic spectra, and look for chromatic signatures which could appear as discrete dispersed signal tracks, when the diffraction pattern is adequately smoothed by a finite source size. We particularly explore circumstances in which such diffraction pattern might closely follow the interstellar dispersion law followed by pulsars and transients, such as the Fast Radio Bursts (FRBs), which remain a mystery even after a decade of their discovery. In this paper, we describe details of this investigation, relevant to radio frequencies at which FRBs have been detected, and discuss our findings, along with their implications. We also show how a band-averaged light curve suffers from temporal smearing, and consequent reduction in contrast of intensity variation, with increasing bandwidth. We suggest a way to recover the underlying diffraction signature, as well as the sensitivity improvement commensurate with usage of large bandwidths.