VOSviewer’s time-map analysis results reveal three major emerging clusters in astrophysics research, interconnected at various levels between terms. The first 300 links are represented. The importance of a term is indicated by the size of the circle. – Life is a very big picture
Abstract: Life on our planet may have evolved in the ocean, so alien oceans are prime habitats for searching for extraterrestrial life. We conducted a data-driven bibliographic survey of the astronomy literature to identify emerging research trends with ocean science for future synergies in the search for extraterrestrial life in the outer-oceans.
Based on the search queries, we identified 2,592 items published since 1963. The current literature is divided into three main groups: (1) the search for life on Mars, (2) astronomy and icy moons in our Solar System and their reference exo-oceans, and (3) astronomical and biological parameters for planetary habitability.
We found that the most important research terms focused on three key-groups: (1) using terrestrial environments as proxies for Martian environments, focusing on extremophiles and biosignatures of planets, and (3) atmosphere, magnetic field, and geology related to habitable conditions on planets with a focus on water-based oceans. .
Introduction
Many of the planets and moons in our solar system host large bodies of water known as external oceans [1]Although beneath thick layers of ice, they are mostly Earth-like [2]. Moons of Saturn or Jupiter, such as Enceladus, Europa, Callisto, and Ganymede, may have oceanic environments. [3–12]. Mars once had large lakes and oceans, and its south pole still has underground liquid water, where a saline solution keeps water liquid beneath the ice. [13–15]. Titan is hypothesized to contain water, kept liquid by ammonia, with rivers and oceans of liquid methane and ethane beneath its water-ice crust. [16–18].
More extraterrestrial water-ocean environments may be discovered on exoplanets in the next decade [19–21]. Planets orbiting stars beyond the previously thought habitable range have been hypothesized to have habitable oceans. [22–25]. Living near M-red dwarf stars is problematic because they typically emit dangerous flares [26]In some cases this can be counteracted by a planet’s magnetic field [27]Ozone shields [28]and/or bodies of water [29]. Beyond the traditionally defined interstellar habitable zone, life may also exist in geothermal or tidal friction-heated liquid oceans beneath thick ice sheets. [2].
The Earth’s deep ocean is a vast biome without sunlight, where high pressure and various cyclical hydrodynamic phenomena occur within the water column and seafloor at tidal, passive, and seasonal scales. [30,31]. In the benthic zone, communities of stomatal microbes and multicellular organisms thrive in areas of high geothermal activity. [32].
It is hypothesized that life on Earth may have originated around oceanic hydrothermal vents with significant geothermal activity. [33]These areas represent a habitat that meets the requirements of stable energy and essential chemical element supply, among other favorable conditions [34,35]. Precipitation of vesiculated metal oxides and/or sulfones is thought to create compartments that act as primitive cells, trap organic molecules and achieve concentration capacities across the walls and promote reactions. [36].
Similar ecosystems can be found in the outer oceans of geothermally active mantles and/or cores on moons and planets. [37,38]. These systems may provide environmental conditions similar to Earth’s oceans [39– 44]Water-rock interactions can provide nutrients and trace elements with thermodynamic disequilibrium.
Life could also have originated and evolved there, as speculated on Enceladus and Europa, which are about the same age as Earth. [12]. While alien marine organisms may have evolved to become multicellular and may even show some degree of morphological convergence with terrestrial analogs, the morphological similarity of non-phylogenetic organisms can be predicted from common environmental conditioning factors. [45].
The hypothesis that uni- or multicellular extraterrestrial organisms may have evolved around terrestrial-like hydrothermal vents could conceptually help probe the outer oceans for biosignatures. How do we envision these extraterrestrial life forms (ie, uni- or multicellular, photoautotrophs, chemo-autotrophs, or heterotrophs)? [46–48]) will affect the approach we use to identify them. Since the tremendous success of the Voyager 1 and 2 probes, Galileo and Cassini-Huygens between 1979 and 2017, future missions to Enceladus, Europa, Ganymede, Titan and Ceres are now being conceived. [2,12]Based on robotic platforms for orbital surveying, ice drilling, pelagic navigation, and rock-core seabed sampling, all have different spectrophotometric and imaging sensors for molecular and microbial detection. [49–59].
In particular, exploration of the Earth’s deep oceans is developing technology to drive new autonomous vehicles and their payloads dedicated to environmental exploration and ecological monitoring. [60]. Driven by technological advances and a fundamental interest in submarine life, new geographic habitats and associated ecosystems continue to be discovered along continental margins and basins. [31]. The possibility of submarine exploration is illustrated by the revolutionary discovery of hydrothermal vents in 1977, long after mankind had landed on the moon.
This technological innovation offers new methods for detecting and observing life with potential applications for astronomical research. [60,61]. For example, the development of ship-telescopically operated remotely operated vehicles (ROVs) completely revolutionized research in the deep-sea water column. [62,63].
Similarly, macro- and microscopic imaging, in situ spectroscopy, multibeam sonar imaging, and passive acoustic sensors (hydrophones) play an increasingly important role in the investigation of life. [64]. More recently, new biodetection capabilities have been enabled by the development of eco-genetic sensors based on environmental DNA (eDNA) and providing information on the presence of organisms at a wide range of environmental scales (i.e., from bacteria to whales). ), complementing imaging or acoustics [30,65].
In the case of the outer oceans, such developments could be used to detect DNA-based life forms. In deep-sea research, these image and molecular-based sensors enable assessment not only on ROVs, but also on other autonomous or remotely operated robots (e.g., autonomous underwater vehicles—AUVs, rovers, and crawlers). The existence of species and their relationship to the environment by combining biological data acquisition with coherent oceanographic and geochemical surveys. [61]. In particular, for each image/sound or molecular or eDNA record, one can establish the corresponding environmental condition from measurements with geochemical and oceanographic sensors. [61,65]. Recently, off-the-shelf platforms with such multiparametric sensors have been described in relation to exploring possible marine life on Enceladus and Europa. [61,66,67].
Bibliometric analysis tools such as VOSviewer [68] and CiteSpace represent valuable methods for exploring and analyzing large volumes of scientific data [69], revealing the fields of astrophysics research and shedding light on emerging areas. Previous attempts at the analysis of astronomy research trends through bibliometric methods [70] Associates with faculty, collaborative networks, and research domains; [71] Emerging research topics and their evolution from three major journals; And [72] For biotechnological applications for biomining and bioleaching in long-duration human space exploration.
We approach our bibliographic investigation of exo-life from the perspective of interactions with biological ocean science. Identification of emerging astrophysical research areas and their relationship to marine science can provide a dialogic framework for developing strategies for the discovery and monitoring of uni- and multicellular extraterrestrial organisms under 'sea-like’ conditions. We conducted a data-driven and quantitative bibliographic review of the astronomy literature since its inception (by combining VOSviewer and CiteSpace bibliometric analysis) to identify developing paradigms and research trends in general, and in particular, potential connections with ocean science, for future synergies in research. For extraterrestrial life in the outer oceans.
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Astronomy
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