Astrobiology (alsoxenology orexobiology) is a scientific field within thelife andenvironmental sciences that studies theorigins,early evolution, distribution, and future oflife in theuniverse by investigating its deterministic conditions and contingent events.[2] As a discipline, astrobiology is founded on the premise that life may exist beyond Earth.[3]
The field of astrobiology has its origins in the 20th century with the advent ofspace exploration and the discovery ofexoplanets. Early astrobiology research focused on the search for extraterrestrial life and the study of the potential for life to exist on other planets.[2] In the 1960s and 1970s, NASA began its astrobiology pursuits within theViking program, which was the first US mission to land on Mars and search forsigns of life.[4] This mission, along with other early space exploration missions, laid the foundation for the development of astrobiology as a discipline.
Regardinghabitable environments, astrobiology investigates potential locations beyond Earth that could support life, such asMars,Europa, andexoplanets, through research into theextremophiles populating austere environments on Earth, like volcanic and deep sea environments. Research within this topic is conducted utilising the methodology of the geosciences, especiallygeobiology, for astrobiological applications.
The search forbiosignatures involves the identification of signs of past or present life in the form oforganic compounds, isotopic ratios, or microbial fossils. Research within this topic is conducted utilising the methodology ofplanetary andenvironmental science, especiallyatmospheric science, for astrobiological applications, and is often conducted throughremote sensing and in situ missions.
Astrobiology also concerns the study of theorigin andearly evolution of life on Earth to try to understand the conditions that are necessary for life to form on other planets.[5] This research seeks to understand how life emerged from non-living matter and how it evolved to become the diverse array of organisms we see today. Research within this topic is conducted utilising the methodology of paleosciences, especiallypaleobiology, for astrobiological applications.
Astrobiology is a rapidly developing field with a strong interdisciplinary aspect that holds many challenges and opportunities for scientists. Astrobiology programs and research centres are present in many universities and research institutions around the world, and space agencies likeNASA andESA have dedicated departments and programs for astrobiology research.
The term astrobiology was first proposed by theRussian astronomerGavriil Tikhov in 1953.[6] It is etymologically derived from theGreekἄστρον, "star";βίος, "life"; and-λογία,-logia, "study". A close synonym is exobiology from theGreek Έξω, "external";βίος, "life"; and-λογία,-logia, "study", coined by American molecular biologistJoshua Lederberg; exobiology is considered to have a narrow scope limited to search of life external to Earth.[7] Another associated term isxenobiology, from the Greek ξένος, "foreign";βίος, "life"; and -λογία, "study", coined by American science fiction writerRobert Heinlein in his workThe Star Beast;[8] xenobiology is now used in a more specialised sense, referring to 'biology based on foreign chemistry', whether of extraterrestrial or terrestrial (typically synthetic) origin.[9]
While the potential for extraterrestrial life, especially intelligent life, has been explored throughout human history within philosophy and narrative, the question is a verifiablehypothesis and thus a valid line ofscientific inquiry;[10][11] planetary scientist David Grinspoon calls it a field of natural philosophy, grounding speculation on the unknown in known scientific theory.[12]
The modern field of astrobiology can be traced back to the 1950s and 1960s with the advent ofspace exploration, when scientists began to seriously consider the possibility of life on other planets. In 1957, theSoviet Union launchedSputnik 1, the first artificial satellite, which marked the beginning of theSpace Age. This event led to an increase in the study of the potential for life on other planets, as scientists began to consider the possibilities opened up by the new technology of space exploration. In 1959, NASA funded its first exobiology project, and in 1960, NASA founded the Exobiology Program, now one of four main elements of NASA's current Astrobiology Program.[13] In 1971, NASA fundedProject Cyclops,[14] part of thesearch for extraterrestrial intelligence, to search radio frequencies of the electromagnetic spectrum for interstellar communications transmitted by extraterrestrial life outside the Solar System. In the 1960s-1970s, NASA established theViking program, which was the first US mission to land on Mars and search for metabolic signs of present life; the results were inconclusive.
In the 1980s and 1990s, the field began to expand and diversify as new discoveries and technologies emerged. The discovery of microbial life in extreme environments on Earth, such as deep-sea hydrothermal vents, helped to clarify the feasibility of potential life existing in harsh conditions. The development of new techniques for the detection of biosignatures, such as the use of stable isotopes, also played a significant role in the evolution of the field.
The contemporary landscape of astrobiology emerged in the early 21st century, focused on utilising Earth and environmental science for applications within comparate space environments. Missions included the ESA'sBeagle 2, which failed minutes after landing on Mars, NASA'sPhoenix lander, which probed the environment for past and present planetary habitability of microbial life on Mars and researched the history of water, and NASA'sCuriosity rover, currently probing the environment for past and present planetary habitability of microbial life on Mars.
Astrobiological research makes a number of simplifying assumptions when studying the necessary components for planetary habitability.
Carbon and Organic Compounds: Carbon is thefourth most abundant element in the universe and the energy required to make or break a bond is at just the appropriate level for building molecules which are not only stable, but also reactive. The fact that carbon atoms bond readily to other carbon atoms allows for the building of extremely long and complex molecules. As such, astrobiological research presumes that the vast majority of life forms in the Milky Way galaxy are based oncarbon chemistries, as are all life forms on Earth.[15][16] However, theoretical astrobiology entertains the potential for otherorganic molecular bases for life, thus astrobiological research often focuses on identifying environments that have the potential to support life based on the presence of organic compounds.
Liquid water: Liquidwater is a common molecule that provides an excellent environment for theformation of complicated carbon-based molecules, and is generally considered necessary for life as we know it to exist. Thus, astrobiological research presumes that extraterrestrial life similarly depends upon access to liquid water, and often focuses on identifying environments that have the potential to support liquid water.[17][18] Some researchers posit environments of water-ammonia mixtures as possible solvents forhypothetical types of biochemistry.[19]
Environmental stability: Where organisms adaptively evolve to the conditions of the environments in which they reside, environmental stability is considered necessary for life to exist. This presupposes the necessity of a stabletemperature, pressure, andradiation levels; resultantly, astrobiological research focuses on planets orbitingSun-likered dwarfstars.[20][16] This is because very large stars have relatively short lifetimes, meaning that life might not have time to emerge on planets orbiting them; very small stars provide so little heat and warmth that only planets in very close orbits around them would not be frozen solid, and in such close orbits these planets would betidally locked to the star;[21] whereas the long lifetimes ofred dwarfs could allow the development of habitable environments on planets with thick atmospheres.[22] This is significant as red dwarfs are extremely common. (See also:Habitability of red dwarf systems).
Energy source: It is assumed that any life elsewhere in the universe would also require an energy source. Previously, it was assumed that this would necessarily be from asun-like star, however with developments withinextremophile research contemporary astrobiological research often focuses on identifying environments that have the potential to support life based on the availability of an energy source, such as the presence of volcanic activity on a planet or moon that could provide a source of heat and energy.
It is important to note that these assumptions are based on our current understanding of life on Earth and the conditions under which it can exist. As our understanding of life and the potential for it to exist in different environments evolves, these assumptions may change.
Astrobiological research concerning the study of habitable environments in our solar system and beyond utilises methods within the geosciences. Research within this branch primarily concerns the geobiology of organisms that can survive in extreme environments on Earth, such as in volcanic or deep sea environments, to understand the limits of life, and the conditions under which life might be able to survive on other planets. This includes, but is not limited to:
Deep-sea extremophiles: Researchers are studying organisms that live in the extreme environments of deep-sea hydrothermal vents and cold seeps.[23] These organisms survive in the absence of sunlight, and some are able to survive in high temperatures and pressures, and use chemical energy instead of sunlight to produce food.
Desert extremophiles: Researchers are studying organisms that can survive in extreme dry, high temperature conditions, such as in deserts.[24]
Microbes in extreme environments: Researchers are investigating the diversity and activity of microorganisms in environments such as deep mines, subsurface soil, cold glaciers[25] and polar ice,[26] and high-altitude environments.
Research also regards the long-term survival of life on Earth, and the possibilities and hazards of life on other planets, including:
Biodiversity and ecosystem resilience: Scientists are studying how the diversity of life and the interactions between different species contribute to the resilience of ecosystems and their ability to recover from disturbances.[27]
Climate change and extinction: Researchers are investigating the impacts of climate change on different species and ecosystems, and how they may lead to extinction or adaptation.[28] This includes the evolution of Earth's climate and geology, and their potential impact on the habitability of the planet in the future, especially for humans.
Human impact on the biosphere: Scientists are studying the ways in which human activities, such as deforestation, pollution, and the introduction of invasive species, are affecting the biosphere and the long-term survival of life on Earth.[29]
Long-term preservation of life: Researchers are exploring ways to preserve samples of life on Earth for long periods of time, such as cryopreservation and genomic preservation, in the event of a catastrophic event that could wipe out most of life on Earth.[30]
Emerging astrobiological research concerning the search for planetary biosignatures of past or present extraterrestrial life utilise methodologies within planetary sciences. These include:
Scientists are using data from Mars rover missions to study the composition of the subsurface ofMars, searching for biosignatures of past or present microbial life.[31]The study of liquid bodies on icy moons:
Discoveries of surface and subsurface bodies of liquid on moons such asEuropa,[32][33][34]Titan[35] andEnceladus[36][37] showed possible habitability zones, making them viable targets for the search for extraterrestrial life. As of September 2024[update], missions likeEuropa Clipper andDragonfly are planned to search for biosignatures within these environments.
Scientists are studying the potential for life to exist in the atmospheres of planets, with a focus on the study of the physical and chemical conditions necessary for such life to exist, namely the detection of organic molecules and biosignature gases; for example, the study of the possibility of life in the atmospheres of exoplanets that orbit red dwarfs and the study of the potential for microbial life in the upper atmosphere of Venus.[38]
Telescopes and remote sensing of exoplanets: The discovery of thousands of exoplanets has opened up new opportunities for the search for biosignatures. Scientists are using telescopes such as theJames Webb Space Telescope and theTransiting Exoplanet Survey Satellite to search for biosignatures on exoplanets. They are also developing new techniques for the detection of biosignatures, such as the use of remote sensing to search for biosignatures in the atmosphere of exoplanets.[39]
Scientists search for signals from intelligent extraterrestrial civilizations using radio and optical telescopes within the discipline ofextraterrestrial intelligence communications (CETI). CETI focuses on composing and deciphering messages that could theoretically be understood by another technological civilization. Communication attempts by humans have included broadcasting mathematical languages, pictorial systems such as theArecibo message, and computational approaches to detecting and deciphering 'natural' language communication. While some high-profile scientists, such asCarl Sagan, have advocated the transmission of messages,[40][41] theoretical physicistStephen Hawking warned against it, suggesting that aliens may raid Earth for its resources.[42]
Emerging astrobiological research concerning the study of the origin and early evolution of life on Earth utilises methodologies within the palaeosciences. These include:
The study of the early atmosphere: Researchers are investigating the role of the early atmosphere in providing the right conditions for the emergence of life, such as the presence of gases that could have helped to stabilise the climate and the formation of organic molecules.[43]
The study of the early magnetic field: Researchers are investigating the role of the early magnetic field in protecting the Earth from harmful radiation and helping to stabilise the climate.[44] This research has immense astrobiological implications where the subjects of current astrobiological research like Mars lack such a field.
The study of prebiotic chemistry: Scientists are studying the chemical reactions that could have occurred on the early Earth that led to the formation of the building blocks of life- amino acids, nucleotides, and lipids- and how these molecules could have formed spontaneously under early Earth conditions.[45]
Chart showing the theorized origin of thechemical elements that make up the human body
The study of impact events: Scientists are investigating the potential role of impact events- especially meteorites- in the delivery of water and organic molecules to early Earth.[46]
Researchers are investigating the conditions and ingredients that were present on the early Earth that could have led to the formation of the first living organisms, such as the presence of water and organic molecules, and how these ingredients could have led to the formation of the first living organisms.[47] This includes the role of water in the formation of the first cells and in catalysing chemical reactions.
The study of the role of minerals: Scientists are investigating the role of minerals like clay in catalysing the formation of organic molecules, thus playing a role in the emergence of life on Earth.[48]
The study of the role of energy and electricity: Scientists are investigating the potential sources of energy and electricity that could have been available on the early Earth, and their role in the formation of organic molecules, thus the emergence of life.[49]
The study of the early oceans: Scientists are investigating the composition and chemistry of the early oceans and how it may have played a role in the emergence of life, such as the presence of dissolved minerals that could have helped to catalyse the formation of organic molecules.[50]
The study of hydrothermal vents: Scientists are investigating the potential role of hydrothermal vents in the origin of life, as these environments may have provided the energy and chemical building blocks needed for its emergence.[51]
The study of plate tectonics: Scientists are investigating the role of plate tectonics in creating a diverse range of environments on the early Earth.[52]
The study of the early biosphere: Researchers are investigating the diversity and activity of microorganisms in the early Earth, and how these organisms may have played a role in the emergence of life.[53]
The study of microbial fossils: Scientists are investigating the presence of microbial fossils in ancient rocks, which can provide clues about the early evolution of life on Earth and the emergence of the first organisms.[54]
The systematic search for possible life outside Earth is a valid multidisciplinary scientific endeavor.[55] However, hypotheses and predictions as to its existence and origin vary widely, and at the present, the development of hypotheses firmly grounded on science may be considered astrobiology's most concrete practical application. It has been proposed thatviruses are likely to be encountered on other life-bearing planets,[56][57] and may be present even if there are no biological cells.[58]
As of 2024[update], no evidence of extraterrestrial life has been identified.[59] Examination of theAllan Hills 84001 meteorite, which was recovered inAntarctica in 1984 and originated fromMars, is thought byDavid McKay, as well as few other scientists, to containmicrofossils of extraterrestrial origin; this interpretation is controversial.[60][61][62]
Yamato 000593, thesecond largestmeteorite fromMars, was found on Earth in 2000. At a microscopic level,spheres are found in the meteorite that are rich incarbon compared to surrounding areas that lack such spheres. The carbon-rich spheres may have been formed bybiotic activity according to some NASA scientists.[63][64][65]
Most astronomy-related astrobiology research falls into the category ofextrasolar planet (exoplanet) detection, the hypothesis being that if life arose on Earth, then it could also arise on other planets with similar characteristics. To that end, a number of instruments designed to detect Earth-sized exoplanets have been considered, most notablyNASA'sTerrestrial Planet Finder (TPF) andESA'sDarwin programs, both of which have been cancelled. NASA launched theKepler mission in March 2009, and theFrench Space Agency launched theCOROT space mission in 2006.[70][71] There are also several less ambitious ground-based efforts underway.
The goal of these missions is not only to detect Earth-sized planets but also to directly detect light from the planet so that it may be studiedspectroscopically. By examining planetary spectra, it would be possible to determine the basic composition of an extrasolar planet's atmosphere and/or surface.[72] Given this knowledge, it may be possible to assess the likelihood of life being found on that planet. A NASA research group, the Virtual Planet Laboratory,[73] is using computer modeling to generate a wide variety of virtual planets to see what they would look like if viewed by TPF or Darwin. It is hoped that once these missions come online, their spectra can be cross-checked with these virtual planetary spectra for features that might indicate the presence of life.
An estimate for the number of planets with intelligentcommunicativeextraterrestrial life can be gleaned from theDrake equation, essentially an equation expressing the probability of intelligent life as the product of factors such as the fraction of planets that might be habitable and the fraction of planets on which life might arise:[74]
where:
N = The number of communicative civilizations
R* = The rate of formation of suitable stars (stars such as the Sun)
fp = The fraction of those stars with planets (current evidence indicates that planetary systems may be common for stars like the Sun)
ne = The number of Earth-sized worlds per planetary system
fl = The fraction of those Earth-sized planets where life actually develops
fi = The fraction of life sites where intelligence develops
fc = The fraction of communicative planets (those on which electromagnetic communications technology develops)
L = The "lifetime" of communicating civilizations
However, whilst the rationale behind the equation is sound, it is unlikely that the equation will be constrained to reasonable limits of error any time soon. The problem with the formula is that it is not used to generate or supporthypotheses because it contains factors that can never be verified. The first term,R*, number of stars, is generally constrained within a few orders of magnitude. The second and third terms,fp, stars with planets andfe, planets with habitable conditions, are being evaluated for the star's neighborhood. Drake originally formulated the equation merely as an agenda for discussion at the Green Bank conference,[75] but some applications of the formula had been taken literally and related to simplistic orpseudoscientific arguments.[76] Another associated topic is theFermi paradox, which suggests that if intelligent life is common in theuniverse, then there should be obvious signs of it.
Another active research area in astrobiology isplanetary system formation. It has been suggested that the peculiarities of theSolar System (for example, the presence ofJupiter as a protective shield)[77] may have greatly increased the probability of intelligent life arising on Earth.[78][79]
Biology cannot state that a process or phenomenon, by being mathematically possible, has to exist forcibly in an extraterrestrial body. Biologists specify what is speculative and what is not.[76] The discovery ofextremophiles, organisms able to survive in extreme environments, became a core research element for astrobiologists, as they are important to understand four areas in the limits of life in planetary context: the potential forpanspermia, forward contamination due to human exploration ventures, planetary colonization by humans, and the exploration of extinct and extant extraterrestrial life.[80]
Until the 1970s,life was thought to be entirely dependent on energy from theSun. Plants on Earth's surface capture energy fromsunlight tophotosynthesize sugars from carbon dioxide and water, releasing oxygen in the process that is then consumed by oxygen-respiring organisms, passing their energy up thefood chain. Even life in the ocean depths, where sunlight cannot reach, was thought to obtain its nourishment either from consumingorganic detritus rained down from the surface waters or from eating animals that did.[81] The world's ability to support life was thought to depend on its access tosunlight. However, in 1977, during an exploratory dive to theGalapagos Rift in the deep-sea exploration submersibleAlvin, scientists discovered colonies ofgiant tube worms,clams,crustaceans,mussels, and other assorted creatures clustered around undersea volcanic features known asblack smokers.[81] These creatures thrive despite having no access to sunlight, and it was soon discovered that they form an entirely independentecosystem. Although most of these multicellular lifeforms need dissolved oxygen (produced by oxygenic photosynthesis) for their aerobic cellular respiration and thus are not completely independent from sunlight by themselves, the basis for their food chain is a form ofbacterium that derives its energy fromoxidization of reactive chemicals, such ashydrogen orhydrogen sulfide, that bubble up from the Earth's interior. Other lifeforms entirely decoupled from the energy from sunlight are green sulfur bacteria which are capturing geothermal light for anoxygenic photosynthesis or bacteria running chemolithoautotrophy based on the radioactive decay of uranium.[82] Thischemosynthesis revolutionized the study of biology and astrobiology by revealing that life need not be sunlight-dependent; it only requires water and an energy gradient in order to exist.
Biologists have found extremophiles that thrive in ice, boiling water, acid, alkali, the water core of nuclear reactors, salt crystals, toxic waste and in a range of other extreme habitats that were previously thought to be inhospitable for life.[83][84] This opened up a new avenue in astrobiology by massively expanding the number of possible extraterrestrial habitats. Characterization of these organisms, their environments and their evolutionary pathways, is considered a crucial component to understanding how life might evolve elsewhere in the universe. For example, some organisms able to withstand exposure to the vacuum and radiation of outer space include the lichen fungiRhizocarpon geographicum andRusavskia elegans,[85] the bacteriumBacillus safensis,[86]Deinococcus radiodurans,[86]Bacillus subtilis,[86] yeastSaccharomyces cerevisiae,[86] seeds fromArabidopsis thaliana ('mouse-ear cress'),[86] as well as the invertebrate animalTardigrade.[86] Whiletardigrades are not considered true extremophiles, they are considered extremotolerant microorganisms that have contributed to the field of astrobiology. Their extreme radiation tolerance and presence of DNA protection proteins may provide answers as to whether life can survive away from the protection of the Earth's atmosphere.[87]
The origin of life, known asabiogenesis, distinct from theevolution of life, is another ongoing field of research.Oparin andHaldane postulated that the conditions on the early Earth were conducive to the formation oforganic compounds frominorganic elements and thus to the formation of many of the chemicals common to all forms of life we see today. The study of this process, known as prebiotic chemistry, has made some progress, but it is still unclear whether or not life could have formed in such a manner on Earth. The alternative hypothesis ofpanspermia is that the first elements of life may have formed on another planet with even more favorable conditions (or even in interstellar space, asteroids, etc.) and then have been carried over to Earth.
Thecosmic dust permeating the universe contains complexorganic compounds ("amorphous organic solids with a mixedaromatic-aliphatic structure") that could be created naturally, and rapidly, bystars.[93][94][95] Further, a scientist suggested that these compounds may have been related to the development of life on Earth and said that, "If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life."[93]
In October 2020, astronomers proposed the idea of detecting life on distant planets by studying the shadows of trees at certain times of the day to find patterns that could be detected through observation of exoplanets.[99][100]
David Grinspoon called astrobiology a field of natural philosophy.[101] Astrobiology intersects withphilosophy by raising questions about the nature and existence of life beyond Earth. Philosophical implications include the definition oflife itself, issues in thephilosophy of mind andcognitive science in case intelligent life is found,epistemological questions about the nature of proof,ethical considerations of space exploration, along with the broader impact of discovering extraterrestrial life on human thought and society.
Dunér[102] has emphasized philosophy of astrobiology as an ongoing existential exercise in individual and collective self-understanding, whose major task is constructing and debating concepts such as the concept of life. Key issues, for Dunér, are questions of resource money and monetary planning,epistemological questions regarding astrobiological knowledge,linguistics issues about interstellar communication,cognitive issues such as the definition ofintelligence, along with the possibility ofinterplanetary contamination.Persson[103] also emphasized key philosophical questions in astrobiology. They include ethical justification of resources, the question of life in general, the epistemological issues and knowledge about being alone in the universe, ethics towards extraterrestrial life, the question ofpolitics and governing uninhabited worlds, along with questions ofecology.
For von Hegner,[104] the question of astrobiology and the possibility ofastrophilosophy differs. For him, the discipline needs to bifurcate into astrobiology and astrophilosophy since discussions made possible by astrobiology, but which have been astrophilosophical in nature, have existed as long as there have been discussions about extraterrestrial life. Astrobiology is a self-corrective interaction among observation, hypothesis, experiment, and theory, pertaining to the exploration of all natural phenomena. Astrophilosophy consists of methods of dialectic analysis and logical argumentation, pertaining to the clarification of the nature of reality. Šekrst[105] argues that astrobiology requires the affirmation of astrophilosophy, but not as a separate cognate to astrobiology. The stance of conceptual speciesm, according to Šekrst, permeates astrobiology since the very name astrobiology tries to talk about not justbiology, but about life in a general way, which includes terrestrial life as a subset. This leads us to either redefine philosophy, or consider the need for astrophilosophy as a more general discipline, to which philosophy is just a subset that deals with questions such as the nature of the human mind and otheranthropocentric questions.
Most of the philosophy of astrobiology deals with two main questions: the question of life and the ethics of space exploration. Kolb[106] specifically emphasizes the question ofviruses, for which the question whether they are alive or not is based on the definitions of life that includeself-replication. Schneider[107] tried to defined exo-life, but concluded that we often start with our own prejudices and that defining extraterrestrial life seems futile using human concepts. For Dick, astrobiology relies onmetaphysical assumption that there is extraterrestrial life, which reaffirms questions in thephilosophy of cosmology, such asfine-tuning or theanthropic principle.
The Rare Earth hypothesis postulates that multicellular life forms found on Earth may actually be more of a rarity than scientists assume. According to this hypothesis, life on Earth (and more, multi-cellular life) is possible because of a conjunction of the right circumstances (galaxy and location within it,planetary system, star, orbit, planetary size, atmosphere, etc.); and the chance for all those circumstances to repeat elsewhere may be rare. It provides a possible answer to theFermi paradox which wonders: if extraterrestrial aliens are common, why aren't they obvious? It is apparently in opposition to theprinciple of mediocrity, assumed by famed astronomersFrank Drake,Carl Sagan, and others. The principle of mediocrity suggests that life on Earth is not exceptional, and it is more than likely to be found on innumerable other worlds.
Research into the environmental limits of life and the workings of extremeecosystems is ongoing, enabling researchers to better predict what planetary environments might be most likely to harbor life. Missions such as thePhoenix lander,Mars Science Laboratory,ExoMars,Mars 2020 rover to Mars, and theCassini probe toSaturn's moons aim to further explore the possibilities of life on other planets in the Solar System.
The twoViking landers each carried four types of biological experiments to the surface of Mars in the late 1970s. These were the only Mars landers to carry out experiments looking specifically formetabolism by current microbiallife on Mars. The landers used a robotic arm to collect soil samples into sealed test containers on the craft. The two landers were identical, so the same tests were carried out at two places on Mars' surface;Viking 1 near the equator andViking 2 further north.[108] The result was inconclusive,[109] and is still disputed by some scientists.[110][111][112][113]
Norman Horowitz was the chief of theJet Propulsion Laboratory bioscience section for theMariner andViking missions from 1965 to 1976. Horowitz considered that the great versatility of the carbon atom makes it the element most likely to provide solutions, even exotic solutions, to the problems of survival of life on other planets.[114] However, he also considered that the conditions found on Mars were incompatible with carbon based life.
Beagle 2 was an unsuccessfulBritish Mars lander that formed part of theEuropean Space Agency's 2003Mars Express mission. Its primary purpose was to search for signs oflife on Mars, past or present. Although it landed safely, it was unable to correctly deploy its solar panels and telecom antenna.[115]
TheMars Science Laboratory (MSL) mission landed theCuriosityrover that is currently in operation onMars.[119] It was launched 26 November 2011, and landed atGale Crater on 6 August 2012. Mission objectives are to help assess Mars'habitability and in doing so, determine whether Mars is or has ever been able to supportlife,[120] collect data for a futurehuman mission, study Martian geology, its climate, and further assess the role thatwater, an essential ingredient for life as we know it, played in forming minerals on Mars.
Tanpopo
TheTanpopo mission is an orbital astrobiology experiment investigating the potential interplanetary transfer of life,organic compounds, and possible terrestrial particles in the low Earth orbit. The purpose is to assess thepanspermia hypothesis and the possibility of natural interplanetary transport of microbial life as well as prebiotic organic compounds. Early mission results show evidence that some clumps of microorganism can survive for at least one year in space.[121] This may support the idea that clumps greater than 0.5 millimeters of microorganisms could be one way for life to spread from planet to planet.[121]
Mars 2020 successfully landed its roverPerseverance inJezero Crater on 18 February 2021. It will investigate environments on Mars relevant to astrobiology, investigate its surfacegeological processes and history, including the assessment of its pasthabitability and potential for preservation ofbiosignatures andbiomolecules within accessible geological materials.[126] The Science Definition Team is proposing the rover collect and package at least 31 samples of rock cores and soil for a later mission to bring back for more definitive analysis in laboratories on Earth. The rover could make measurements and technology demonstrations to help designers of ahuman expedition understand any hazards posed by Martian dust and demonstrate how to collectcarbon dioxide (CO2), which could be a resource for making molecular oxygen (O2) androcket fuel.[127][128]
Europa Clipper
Europa Clipper is a mission launched by NASA on 14 October 2024 that will conduct detailed reconnaissance ofJupiter's moonEuropa beginning in 2030, and will investigate whether its internal ocean could harbor conditions suitable for life.[129][130][131] It will also aid in the selection of futurelanding sites.[132][133]
Dragonfly
Dragonfly is a NASA mission scheduled to land onTitan in 2036 to assess its microbial habitability and study its prebiotic chemistry. Dragonfly is arotorcraft lander that will perform controlled flights between multiple locations on the surface, which allows sampling of diverse regions and geological contexts.[134]
Icebreaker Life is a lander mission that was proposed for NASA'sDiscovery Program for the 2021 launch opportunity,[135] but it was not selected for development. It would have had a stationary lander that would be a near copy of the successful 2008Phoenix and it would have carried an upgraded astrobiology scientific payload, including a 1-meter-long core drill to sample ice-cemented ground in the northern plains to conduct a search fororganic molecules and evidence of current or pastlife on Mars.[136][137] One of the key goals of theIcebreaker Life mission is to test thehypothesis that the ice-rich ground in the polar regions has significant concentrations of organics due to protection by the ice fromoxidants andradiation.
Life Investigation For Enceladus (LIFE) is a proposed astrobiology sample-return mission concept. The spacecraft would enter intoSaturn orbit and enable multiple flybys through Enceladus' icy plumes to collect icy plume particles and volatiles and return them to Earth on a capsule. The spacecraft may sample Enceladus' plumes, theE ring of Saturn, and the upper atmosphere ofTitan.[143][144][145]
Oceanus
Oceanus is an orbiter proposed in 2017 for theNew Frontiers mission No. 4. It would travel to the moon ofSaturn,Titan, to assess itshabitability.[146]Oceanus' objectives are to reveal Titan'sorganic chemistry, geology, gravity, topography, collect 3D reconnaissance data, catalog theorganics and determine where they may interact with liquid water.[147]
Forward-contamination – Biological contamination of a planetary body by a space probe or spacecraftPages displaying short descriptions of redirect targets
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Astrobiology, published byMary Ann Liebert, Inc., is a peer-reviewed journal that explores the origins of life, evolution, distribution, and destiny in the universe.
Catling, David C. (2013).Astrobiology: A Very Short Introduction. Oxford: Oxford University Press.ISBN978-0-19-958645-5.
Cockell, Charles S. (2015).Astrobiology: Understanding Life in the Universe. NJ: Wiley-Blackwell.ISBN978-1-118-91332-1.
Kolb, Vera M., ed. (2015).Astrobiology: An Evolutionary Approach. Boca Raton: CRC Press.ISBN978-1-4665-8461-7.
Kolb, Vera M., ed. (2019).Handbook of Astrobiology. Boca Raton: CRC Press.ISBN978-1-138-06512-3.
Dick, Steven J.; James Strick (2005).The Living Universe: NASA and the Development of Astrobiology. Piscataway, NJ: Rutgers University Press.ISBN978-0-8135-3733-7.
Grinspoon, David (2004) [2003].Lonely planets. The natural philosophy of alien life. New York: ECCO.ISBN978-0-06-018540-4.
