Astrobiology seeks to understand the origin, evolution, distribution, and future of life in the universe and thus to integrate biology with planetary science, astronomy, cosmology, and the other physical sciences. The discipline emerged in the late 20th century, partly in response to the development of space exploration programs in the United States, Russia, and elsewhere. Many astrobiologists are now involved in the search for life on Mars, Europa, Enceladus, and beyond. However, research in astrobiology does not presume the existence of extraterrestrial life, for which there is no compelling evidence; indeed, it includes the study of life on Earth in its astronomical and cosmic context. Moreover, the absence of observed life from all other planetary bodies requires a scientific explanation, and suggests several hypotheses amenable to further observational, theoretical, and experimental investigation under the aegis of astrobiology. Despite the apparent uniqueness of Earth’s biosphere— the “n = 1 problem”—astrobiology is increasingly driven by large quantities of data. Such data have been provided by the robotic exploration of the Solar System, the first observations of extrasolar planets, laboratory experiments into prebiotic chemistry, spectroscopic measurements of organic molecules in extraterrestrial environments, analytical advances in the biogeochemistry and paleobiology of very ancient rocks, surveys of Earth’s microbial diversity and ecology, and experiments to delimit the capacity of organisms to survive and thrive in extreme conditions.
Ingo Baumann, Jan Helge Mey, and Erik Pellander
The space industry has witnessed a tremendous commercialization wave. Flagged with the (disputable) term “NewSpace,” numerous start-up companies are emerging in the leading space nations as well as in nontraditional space countries. These companies are attracting private investments as never before. In addition to such private financing, strong public market interest in the space sector has enabled a number of leading space start-ups to access large amounts of capital through Special Purpose Acquisition Companies’ initial public offerings (IPOs). One economic consultancy company has predicted that the space economy will grow significantly by 2030—perhaps as much as 74%—with others suggesting even higher estimates. With such strong economic growth and developments in new business models, there is a need to examine industry practices, particularly in contractual agreements. Such an examination is critical for the oversight of public spending, research and development funding, and space procurement for all public (government) and private stakeholders. The main public stakeholders on European level are the European Union, the European Space Agency, and the national space agencies of the member states, each of which has its dedicated legal frameworks and procedures.
The thin layer known as the Earth’s crust contains an even thinner layer that is suitable for sustaining life. The boundary conditions that define where we can find life in the deep subsurface depend on the physical space and water availability, accessibility to suitable substrates for energy and growth, in addition to tolerable temperature and pressure. The prevailing rather extreme conditions in the deep subsurface dictate that it is mainly inhabited by prokaryotic microorganisms. In fact, most of Earth’s microbial biomass is dwelling in the deep subsurface. Understanding the microbial diversity, dynamics and ecology in the Earth’s crust provides knowledge on the role of microbes in global elemental cycling. These capacities are investigated with cultivation-based experiments or molecular biological methods. Using genetic material of the microbes to reveal insights into metabolic processes, community structure and evolutionary history of microorganisms is state-of the-art in the deep biosphere research. Upgraded cultivation methods, such as those mimicking the physical and chemical conditions of the deep subsurface, and especially the combination of different methodologies have proven to be a useful approach in unraveling the way of microbial life in the depths. Partly the same fundamentals that define the habitability in the deep subsurface, dictate the potential of finding life outside Earth. Thus, studying the deep biosphere may help us to understand and explore the potential of microbial life to survive and thrive in extreme environments and therefore be useful for future space missions trying to find life on other planetary objects. The study can also help us draw conclusions on our own planet’s history and how life originated on early Earth.
Stanley Miller demonstrated in 1953 that it was possible to form amino acids from methane, ammonia, and hydrogen in water, thus launching the ambitious hope that chemists would be able to shed light on the origins of life by recreating a simple life form in a test tube. However, it must be acknowledged that the dream has not yet been accomplished, despite the great volume of effort and innovation put forward by the scientific community. A minima, primitive life can be defined as an open chemical system, fed with matter and energy, capable of self-reproduction (i.e., making more of itself by itself), and also capable of evolving. The concept of evolution implies that chemical systems would transfer their information fairly faithfully but make some random errors. If we compared the components of primitive life to parts of a chemical automaton, we could conceive that, by chance, some parts self-assembled to generate an automaton capable of assembling other parts to produce a true copy. Sometimes, minor errors in the building generated a more efficient automaton, which then became the dominant species. Quite different scenarios and routes have been followed and tested in the laboratory to explain the origin of life. There are two schools of thought in proposing the prebiotic supply of organics. The proponents of a metabolism-first call for the spontaneous formation of simple molecules from carbon dioxide and water to rapidly generate life. In a second hypothesis, the primeval soup scenario, it is proposed that rather complex organic molecules accumulated in a warm little pond prior to the emergence of life. The proponents of the primeval soup or replication first approach are by far the more active. They succeeded in reconstructing small-scale versions of proteins, membranes, and RNA. Quite different scenarios have been proposed for the inception of life: the RNA world, an origin within droplets, self-organization counteracting entropy, or a stochastic approach merging chemistry and geology. Understanding the emergence of a critical feature of life, its one-handedness, is a shared preoccupation in all these approaches.
Jiannan Zhao, Yutong Shi, and Long Xiao
Analog study is a convenient and effective way to understand the geomorphic features and geological processes of other planets. The Qaidam Basin, an intramontane basin in the northeastern Tibetan Plateau, northwest China, is a new and unique Mars analog study site. The basin hosts the highest and one of the driest deserts on the Earth, and its environment is characterized as cold, arid, of high altitude, of high UV radiation, and of high soil salinity. A variety of landforms that are comparable to those on the Martian surface have been identified, such as dunes, yardangs, valleys, gullies, lakes, and playas, providing opportunities to study the formation and evolution of similar Martian geomorphic features. Aqueous minerals including chlorides, sulfates, carbonates, and phyllosilicates are concentrated in the saline lakes and playas of the basin. Analog studies on the mineral assemblages of the Qaidam playas and Martian paleolakes and playas will help researchers better understand the hydrological environment and climate of the ancient Mars. The extreme environment of the Qaidam Basin also makes it an ideal site for astrobiological study. Detection of biomarkers and the isolation of microorganisms in the basin could provide clues for the search for life and a habitable environment on Mars. In addition, the accessibility of the Qaidam Basin makes the basin a potential testing ground for instruments and study methods to be used in future Mars missions.
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article. Astrobiologists are engaged in the search for signs of extraterrestrial life in all forms, known as biosignatures, as well as specific signs of extraterrestrial technology, known as technosignatures. The search for technosignatures and biosignatures attempts to identify characteristic evidence of life on other planets that could be detected using astronomical methods. The first scientific searches for technosignatures took place in the 1960s and used radio telescopes to examine nearby star systems for evidence of narrow-band transmissions used for communication. The search for extraterrestrial intelligence and for anomalous radio and optical signals that would indicate intentional or unintentional extraterrestrial communication continues. Advances in ground- and space-based spectroscopy have enabled searches for technosignatures in exoplanetary systems, such as atmospheric pollution, city lights, large-scale surface structures, and orbiting satellites. Some technosignature searches also attempt to search for nonterrestrial artifacts within the solar system on planetary bodies or in stable orbits. Researchers use known technology on Earth as a starting point for thinking about what might be plausible and detectable in extraterrestrial systems. Technology is a relatively recent phenomenon in the history of life on Earth, so the search for technosignatures also employs methods of future projection to explore numerous trajectories for extensions of known technology. The range of possibilities considered by technosignature science can include any known or plausible technology that could be remotely detected and would not violate any known physical laws. Megastructures are examples of theoretical large-scale planetary engineering or astroengineering projects that could be detectable in exoplanetary systems through infrared excesses or gravitational effects. Many other technosignatures are possible, even if they do not draw upon Earth projections, but most astrobiological studies of technosignatures focus on predictions that could be tested with current or near-future missions. The discovery of extraterrestrial technology could be of great significance to humanity, but technosignature searches that yield negative results still provide value by placing qualitative upper limits on the prevalence of certain types of extraterrestrial technology.