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95-702: Tharg is depicted as an alien from Quaxxann, a fictional planet that orbits the star Betelgeuse . The character has green skin, a white mohawk hairstyle and a red device called the rosette of Sirius on his forehead. He is written and performed for comic effect as an authoritarian egoist. He eats polystyrene cups. Tharg writes the comic's introduction, answers letters, and doles out prizes to readers (for artwork or story suggestions) - winners could choose payment either in pounds sterling or in "galactic groats". Tharg speaks mostly in English , but with various pithy Betelgusian aphorisms thrown in for colour. In addition to

190-416: A basic component of the development of a potential extraterrestrial technological civilization, as it is on Earth. Fossil fuels may likely be generated and used on such worlds as well. The abundance of chlorofluorocarbons in the atmosphere can also be a clear technosignature, considering their role in ozone depletion . Light pollution may be another technosignature, as multiple lights on the night side of

285-611: A catalog of microorganisms, with the way each one reacts to sunlight. The goal is to help with the search for similar organisms in exoplanets, as the starlight reflected by planets rich in such organisms would have a specific spectrum, unlike that of starlight reflected from lifeless planets. If Earth was studied from afar with this system, it would reveal a shade of green, as a result of the abundance of plants with photosynthesis. In August 2011, NASA studied meteorites found on Antarctica, finding adenine , guanine , hypoxanthine and xanthine . Adenine and guanine are components of DNA, and

380-404: A character. The plots often concern Tharg's conflict with Thrillsuckers, a plague of psychic pests that attempt to steal 2000 AD' s Thrillpower, his abuse of his droid staff, and his battles against The Dictators of Zrag, rulers of the dull cube-shaped planet Zrag. This trio of incompetent alien warlords hope to usurp Tharg's position and use the comic's powers to revitalise their planet. Tharg uses

475-481: A living entity must have the capacity to replicate itself, the capacity to avoid damage/decay, and the capacity to acquire and process resources in support of the first two capacities. Life on Earth started with an RNA world and later evolved to its current form, where some of the RNA tasks were transferred to DNA and proteins . Extraterrestrial life may still be stuck using RNA, or evolve into other configurations. It

570-446: A major cultural impact, especially extraterrestrials in fiction . Science fiction has communicated scientific ideas, imagined a range of possibilities, and influenced public interest in and perspectives on extraterrestrial life. One shared space is the debate over the wisdom of attempting communication with extraterrestrial intelligence. Some encourage aggressive methods to try to contact intelligent extraterrestrial life. Others – citing

665-534: A math equation, none of its values were known at the time. Although some values may eventually be measured, others are based on social sciences and are not knowable by their very nature. This does not allow one to make noteworthy conclusions from the equation. Based on observations from the Hubble Space Telescope , there are nearly 2 trillion galaxies in the observable universe. It is estimated that at least ten per cent of all Sun-like stars have

760-472: A mixed aromatic - aliphatic structure") that could be created naturally, and rapidly, by stars . It is still unclear if those compounds played a role in the creation of life on Earth, but Sun Kwok, of the University of Hong Kong, thinks so. "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." In August 2012, and in

855-507: A more particular case of extraterrestrial intelligence. It is the possible long-term result of intelligent and specifically sapient extraterrestrial life. The Copernican principle is generalized to the relativistic concept that humans are not privileged observers of the universe. Many prominent scientists, including Stephen Hawking have proposed that the sheer scale of the universe makes it improbable for intelligent life not to have emerged elsewhere. However, Fermi's Paradox highlights

950-650: A planetary system formed by a star at the center, the Sun , and the objects that orbit it: other planets, moons, asteroids, and comets. The sun is part of the Milky Way , a galaxy . The Milky Way is part of the Local Group , a galaxy group that is in turn part of the Laniakea Supercluster . The universe is composed of all similar structures in existence. The immense distances between celestial objects

1045-466: A potential explanation to the Fermi paradox. If extraterrestrial life exists, it could range from simple microorganisms and multicellular organisms similar to animals or plants, to complex alien intelligences akin to humans . When scientists talk about extraterrestrial life, they consider all those types. Although it is possible that extraterrestrial life may have other configurations, scientists use

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1140-570: A reasonable scientific explanation for any gathered data. In 1961, astronomer and astrophysicist Frank Drake devised the Drake equation as a way to stimulate scientific dialogue at a meeting on the search for extraterrestrial intelligence (SETI). The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilisations in the Milky Way galaxy . The Drake equation is: where: and Drake's proposed estimates are as follows, but numbers on

1235-443: A result has been conceived, even if hypothetical. Evolution requires life to be divided into individual organisms, and no alternative organisation has been satisfactorily proposed either. At the basic level, membranes define the limit of a cell, between it and its environment, while remaining partially open to exchange energy and resources with it. The evolution from simple cells to eukaryotes, and from them to multicellular lifeforms,

1330-505: A rocky planet can be a sign of advanced technological development. However, modern telescopes are not strong enough to study exoplanets with the required level of detail to perceive it. Extraterrestrial intelligence Extraterrestrial intelligence ( ETI ) refers to hypothetical intelligent extraterrestrial life . No such life has ever been verifiably observed to exist. The question of whether other inhabited worlds might exist has been debated since ancient times. The modern form of

1425-468: A scale. Life on Earth is quite ubiquitous across the planet and has adapted over time to almost all the available environments in it, extremophiles and the deep biosphere thrive at even the most hostile ones. As a result, it is inferred that life in other celestial bodies may be equally adaptive. However, the origin of life is unrelated to its ease of adaptation, and may have stricter requirements. A celestial body may not have any life on it, even if it

1520-476: A series of factors that range from the location in the galaxy and the configuration of the Solar System to local characteristics of the planet, and that it is unlikely that all such requirements are simultaneously met by another planet. The proponents of this hypothesis consider that very little evidence suggests the existence of extraterrestrial life, and that at this point it is just a desired result and not

1615-579: A solvent other than water. The low temperatures required would add an extra problem, the difficulty to kickstart a process of abiogenesis to create life in the first place. Norman Horowitz , head of the Jet Propulsion Laboratory bioscience section for the Mariner and Viking missions from 1965 to 1976 considered that the great versatility of the carbon atom makes it the element most likely to provide solutions, even exotic solutions, to

1710-440: A star's light and heat, and so its lifeforms would not grow beyond a certain complexity. There is also research in assessing the capacity of life for developing intelligence. It has been suggested that this capacity arises with the number of potential niches a planet contains, and that the complexity of life itself is reflected in the information density of planetary environments, which in turn can be computed from its niches. It

1805-660: A system of planets, i.e. there are 6.25 × 10 stars with planets orbiting them in the observable universe. Even if it is assumed that only one out of a billion of these stars has planets supporting life, there would be some 6.25 billion life-supporting planetary systems in the observable universe. A 2013 study based on results from the Kepler spacecraft estimated that the Milky Way contains at least as many planets as it does stars, resulting in 100–400 billion exoplanets. The apparent contradiction between high estimates of

1900-461: A world first, astronomers at Copenhagen University reported the detection of a specific sugar molecule, glycolaldehyde , in a distant star system. The molecule was found around the protostellar binary IRAS 16293-2422 , which is located 400 light years from Earth. Glycolaldehyde is needed to form ribonucleic acid , or RNA, which is similar in function to DNA. This finding suggests that complex organic molecules may form in stellar systems prior to

1995-428: Is sophoncy , being wise or wiser, first coined by Karen Anderson and published in the 1966 works by her husband Poul Anderson . Sentience , like consciousness , is a concept sometimes mistakenly used to refer to the concept of intelligence and sapience, since it does not exclude forms of life that are non-sapient (or more broadly non-intelligent or non-conscious). The term extraterrestrial civilization frames

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2090-402: Is life that originates from another world rather than on Earth . No extraterrestrial life has yet been scientifically conclusively detected. Such life might range from simple forms such as prokaryotes to intelligent beings , possibly bringing forth civilizations that might be far more advanced than humans. The Drake equation speculates about the existence of sapient life elsewhere in

2185-450: Is "Extraterrestrial Technological Instantiations" (ETI). The term was coined to avoid the use of terms such as "civilizations" "species" and "intelligence", as those may prove to be ambiguous and open to interpretation, or simply inapplicable in its local context. Intelligence is, along with the more precise concept of sapience , used to describe extraterrestrial life with similar cognitive abilities as humans. Another interchangeable term

2280-601: Is a difficulty for the study of extraterrestrial life. So far, humans have only set foot on the Moon and sent robotic probes to other planets and moons in the Solar System. Although probes can withstand conditions that may be lethal to humans, the distances cause time delays: the New Horizons took nine years after launch to reach Pluto . No probe has ever reached extrasolar planetary systems. The Voyager 2 has left

2375-501: Is also conceivable that there are forms of life whose solvent is a liquid hydrocarbon , such as methane , ethane or propane . Another unknown aspect of potential extraterrestrial life would be the chemical elements that would compose it. Life on Earth is largely composed of carbon, but there could be other hypothetical types of biochemistry . A replacement for carbon would need to be able to create complex molecules, store information required for evolution, and be freely available in

2470-416: Is being carried out both directly and indirectly. As of September 2017 , 3,667 exoplanets in 2,747 systems have been identified , and other planets and moons in the Solar System hold the potential for hosting primitive life such as microorganisms . As of 8 February 2021, an updated status of studies considering the possible detection of lifeforms on Venus (via phosphine ) and Mars (via methane )

2565-403: Is common knowledge that the conditions on other planets in the solar system, in addition to the many galaxies outside of the Milky Way galaxy , are very harsh and seem to be too extreme to harbor any life. The environmental conditions on these planets can have intense UV radiation paired with extreme temperatures, lack of water, and much more that can lead to conditions that don't seem to favor

2660-485: Is complex and defined by several factors. Being in the habitable zone is not enough for a planet to be habitable, not even to actually have such liquid water. Venus is located in the habitable zone of the Solar System but does not have liquid water because of the conditions of its atmosphere. Jovian planets or gas giants are not considered habitable even if they orbit close enough to their stars as hot Jupiters , due to crushing atmospheric pressures. The actual distances for

2755-412: Is contacted, be it electromagnetic radiation, direct physical interaction, extraterrestrial artefact, or otherwise, may also influence the results of contact. Incorporating these factors, various systems have been created to assess the implications of extraterrestrial contact. The implications of extraterrestrial contact, particularly with a technologically superior civilization, have often been likened to

2850-520: Is embodied in the Copernican principle , which states that Earth does not occupy a unique position in the Universe, and the mediocrity principle , which states that there is nothing special about life on Earth. Other authors consider instead that life in the cosmos, or at least multicellular life, may be actually rare. The Rare Earth hypothesis maintains that life on Earth is possible because of

2945-463: Is largely speculative. The extraterrestrial hypothesis is the idea that some UFOs are vehicles containing or sent by extraterrestrial beings (usually called aliens in this context). As an explanation for UFOs, ETI is sometimes contrasted with EDI (extradimensional intelligence) , for example by J. Allen Hynek . In 2023, House lawmakers held a hearing to examine how the executive branch handles reports of UFOs . The theories and reception of

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3040-439: Is likely devoid of life. However, Venus is still of interest to astrobiologists, as it is a terrestrial planet that was likely similar to Earth in its early stages and developed in a different way. There is a greenhouse effect , the surface is the hottest in the Solar System, sulfuric acid clouds, all surface liquid water is lost, and it has a thick carbon-dioxide atmosphere with huge pressure. Comparing both helps to understand

3135-444: Is no guarantee that it is transmitting radio communications in the direction of Earth. The length of time required for a signal to travel across space means that a potential answer may arrive decades or centuries after the initial message. The atmosphere of Earth is rich in nitrogen dioxide as a result of air pollution , which can be detectable. The natural abundance of carbon, which is also relatively reactive, makes it likely to be

3230-657: Is not guaranteed. The Cambrian explosion took place thousands of millions of years after the origin of life, and its causes are not fully known yet. On the other hand, the jump to multicellularity took place several times, which suggests that it could be a case of convergent evolution , and so likely to take place on other planets as well. Palaeontologist Simon Conway Morris considers that convergent evolution would lead to kingdoms similar to our plants and animals, and that many features are likely to develop in alien animals as well, such as bilateral symmetry , limbs , digestive systems and heads with sensory organs . Scientists from

3325-466: Is that the chemical elements that make up life, such as carbon and water, are ubiquitous in the universe. The third is that the physical laws are universal, which means that the forces that would facilitate or prevent the existence of life would be the same ones as on Earth. According to this argument, made by scientists such as Carl Sagan and Stephen Hawking , it would be improbable for life not to exist somewhere else other than Earth. This argument

3420-421: Is that there are natural sources of such signals as well, such as gamma-ray bursts and supernovae, and the difference between a natural signal and an artificial one would be in its specific patterns. Astronomers intend to use artificial intelligence for this, as it can manage large amounts of data and is devoid of biases and preconceptions. Besides, even if there is an advanced extraterrestrial civilization, there

3515-570: Is the attempt to send messages to intelligent extraterrestrial life. Active SETI messages are usually sent in the form of radio signals. Physical messages like that of the Pioneer plaque may also be considered an active SETI message. Communication with extraterrestrial intelligence (CETI) is a branch of the search for extraterrestrial intelligence that focuses on composing and deciphering messages that could theoretically be understood by another technological civilization. The best-known CETI experiment

3610-447: Is unclear if our biochemistry is the most efficient one that could be generated, or which elements would follow a similar pattern. However, it is likely that, even if cells had a different composition to those from Earth, they would still have a cell membrane . Life on Earth jumped from prokaryotes to eukaryotes and from unicellular organisms to multicellular organisms through evolution . So far no alternative process to achieve such

3705-778: The Rio Tinto river in Spain. NASA officials soon distanced NASA from the scientists' claims, and Stoker herself backed off from her initial assertions. In November 2011, NASA launched the Mars Science Laboratory that landed the Curiosity rover on Mars. It is designed to assess the past and present habitability on Mars using a variety of scientific instruments. The rover landed on Mars at Gale Crater in August 2012. A group of scientists at Cornell University started

3800-604: The Vector 13 story "Case Ten: Case Closed?" The role of Tharg has been performed by the following editors: 2000 AD regularly features self-contained, science-fiction short stories called Tharg's Future Shocks . Tharg is generally characterised as the host or presenter of these one-shots. The format also sub-divides into genre-specific variants including: Tharg's 3rillers , Tharg's Alien Invasions , Tharg's Dragon Tales , and Tharg's Terror Tales . On occasion 2000 AD includes short humorous strips that feature Tharg as

3895-459: The hydrothermal vents found on the ocean floor are known to support many chemosynthetic processes which allow organisms to utilize energy through reduced chemical compounds that fix carbon. In return, these reactions will allow for organisms to live in relatively low oxygenated environments while maintaining enough energy to support themselves. The early Earth environment was reducing and therefore, these carbon fixing compounds were necessary for

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3990-485: The 15th century, acknowledged the possibility Jesus could have visited extraterrestrial worlds to redeem their inhabitants. Nicholas of Cusa wrote in 1440 that Earth is "a brilliant star" like other celestial objects visible in space; which would appear similar to the Sun , from an exterior perspective, due to a layer of "fiery brightness" in the outer layer of the atmosphere. He theorised all extraterrestrial bodies could be inhabited by men, plants, and animals, including

4085-505: The Dictators as convenient scapegoats whom he can blame for printing errors and plot holes. Tharg occasionally uses words and phrases from a fictional language . This slang has become part of the vocabulary of 2000 AD fan culture , particularly in fan interactions with Tharg. The following is a short list, with approximate translations: Extraterrestrial life Extraterrestrial life , or alien life (colloquially, alien ),

4180-478: The Solar System at a speed of 50,000 kilometers per hour, if it headed towards the Alpha Centauri system, the closest one to Earth at 4.4 light years, it would reach it in 100,000 years. Under current technology such systems can only be studied by telescopes, which have limitations. It is estimated that dark matter has a larger amount of combined matter than stars and gas clouds, but as it plays no role on

4275-478: The Sun. Descartes wrote that there was no means to prove the stars were not inhabited by "intelligent creatures", but their existence was a matter of speculation. When considering the atmospheric composition and ecosystems hosted by extraterrestrial bodies, extraterrestrial life can seem more speculation than reality, due to the harsh conditions and disparate chemical composition of the atmospheres, when compared to

4370-625: The University of Oxford analysed it from the perspective of evolutionary theory and wrote in a study in the International Journal of Astrobiology that aliens may be similar to humans. The planetary context would also have an influence: a planet with higher gravity would have smaller animals, and other types of stars can lead to non-green photosynthesizers . The amount of energy available would also affect biodiversity , as an ecosystem sustained by black smokers or hydrothermal vents would have less energy available than those sustained by

4465-415: The amount of energy a civilization is able to utilize. The Drake equation is a probabilistic framework used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy . There has been a search for signals from extraterrestrial intelligence for several decades, with no significant results. Active SETI (Active Search for Extra-Terrestrial Intelligence)

4560-428: The apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilization and humanity's lack of contact with, or evidence for, such civilizations. So far, there is no observation of extraterrestrial life, including intelligent extraterrestrial life. The Kardashev scale is a speculative method of measuring a civilization 's level of technological advancement, based on

4655-410: The area surrounding these hydrothermal vents which can suggest that some form of life can be supported even in the harshest of environments like the other planets in the solar system. The aspects of these harsh environments that make them ideal for the origin of life on Earth, as well as the possibility of creation of life on other planets, is the chemical reactions forming spontaneously. For example,

4750-568: The atom speeds, either too fast or too slow, make it difficult for specific ones to meet and start chemical reactions. A liquid medium also allows the transport of nutrients and substances required for metabolism. Sufficient quantities of carbon and other elements, along with water, might enable the formation of living organisms on terrestrial planets with a chemical make-up and temperature range similar to that of Earth. Life based on ammonia rather than water has been suggested as an alternative, though this solvent appears less suitable than water. It

4845-474: The best candidate for an extraterrestrial radio signal ever detected, though the fact that no similar signal has ever been observed again makes attribution of the signal to any cause difficult if not impossible. On 14 June 2022 astronomers working with China's FAST telescope reported the possibility of having detected artificial (presumably alien) signals, but cautions that further studies are required to determine if some kind of natural radio interference may be

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4940-402: The cold temperatures would make such chemistry take place at a very slow pace. Water is rock-solid on the surface, but Titan does have a subsurface water ocean like several other moons. However, it is of such a great depth that it would be very difficult to access it for study. The science that searches and studies life in the universe, both on Earth and elsewhere, is called astrobiology . With

5035-566: The concept emerged when the Copernican Revolution demonstrated that the Earth was a planet revolving around the Sun, and other planets were, conversely, other worlds. The question of whether other inhabited planets or moons exist was a natural consequence of this new understanding. It has become one of the most speculative questions in science and is a central theme of science fiction and popular culture. An alternative name for it

5130-469: The creation or maintenance of extraterrestrial life. However, there has been much historical evidence that some of the earliest and most basic forms of life on Earth originated in some extreme environments that seem unlikely to have harbored life at least at one point in Earth's history. Fossil evidence as well as many historical theories backed up by years of research and studies have marked environments like hydrothermal vents or acidic hot springs as some of

5225-444: The difficulty for life to appear was not the temperature, but the scarcity of free heavy elements. Planetary systems emerged, and the first organic compounds may have formed in the protoplanetary disk of dust grains that would eventually create rocky planets like Earth. Although Earth was in a molten state after its birth and may have burned any organics that fell in it, it would have been more receptive once it cooled down. Once

5320-413: The editorial duties in 2000 AD being attributed to Tharg, all writing, art, lettering, sub-editing and PR is attributed to malcontent, feckless and long-suffering droids that appear as caricatures of their actual counterparts. In one episode, a Tharg suit in the comic's office was explained as a skin that Tharg had shed . The concept of using a fictional character to host the comic is comparable to

5415-413: The end, the star blows much of its content back into the stellar medium, where it would join clouds that would eventually become new generations of stars and planets. Many of those materials are the raw components of life on Earth. As this process takes place in all the universe, said materials are ubiquitous in the cosmos and not a rarity from the Solar System. Earth is a planet in the Solar System ,

5510-403: The first hominids appeared 60 million years ago. Life on other planets may have started, evolved, given birth to extraterrestrial intelligences, and perhaps even faced a planetary extinction event millions or even billions of years ago. The brief times of existence of Earth's species, when considered from a cosmic perspective, may suggest that extraterrestrial life may be equally fleeting under such

5605-466: The first places that life could have originated on Earth. These environments can be considered extreme when compared to the typical ecosystems that the majority of life on Earth now inhabit, as hydrothermal vents are scorching hot due to the magma escaping from the Earth's mantle and meeting the much colder oceanic water. Even in today's world, there can be a diverse population of bacteria found inhabiting

5700-410: The formation of planets, eventually arriving on young planets early in their formation. In December 2023, astronomers reported the first time discovery, in the plumes of Enceladus , moon of the planet Saturn , of hydrogen cyanide , a possible chemical essential for life as we know it, as well as other organic molecules , some of which are yet to be better identified and understood. According to

5795-455: The giant planets themselves are highly unlikely to have life, there is much hope to find it on moons orbiting these planets. Europa , from the Jovian system, has a subsurface ocean below a thick layer of ice. Ganymede and Callisto also have subsurface oceans, but life is less likely in them because water is sandwiched between layers of solid ice. Europa would have contact between the ocean and

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5890-404: The habitable zones vary according to the type of star, and even the solar activity of each specific star influences the local habitability. The type of star also defines the time the habitable zone will exist, as its presence and limits will change along with the stars stellar evolution. The Big Bang took place 14 billion years ago, the Solar System was formed 4 and a half billion years ago, and

5985-571: The hierarchy of lifeforms from Earth for simplicity, as it is the only one known to exist. The first basic requirement for life is an environment with non-equilibrium thermodynamics , which means that the thermodynamic equilibrium must be broken by a source of energy. The traditional sources of energy in the cosmos are the stars, such as for life on Earth, which depends on the energy of the sun. However, there are other alternative energy sources, such as volcanoes , plate tectonics , and hydrothermal vents . There are ecosystems on Earth in deep areas of

6080-440: The life-abundant Earth. However, there are many extreme and chemically harsh ecosystems on Earth that do support forms of life and are often hypothesized to be the origin of life on Earth. Hydrothermal vents , acidic hot springs, and volcanic lakes are examples of life forming under difficult circumstances, provide parallels to the extreme environments on other planets and support the possibility of extraterrestrial life. Since

6175-543: The medium. To create DNA , RNA , or a close analog, such an element should be able to bind its atoms with many others, creating complex and stable molecules. It should be able to create at least three covalent bonds: two for making long strings and at least a third to add new links and allow for diverse information. Only nine elements meet this requirement: boron , nitrogen , phosphorus , arsenic , antimony (three bonds), carbon , silicon , germanium and tin (four bonds). As for abundance, carbon, nitrogen, and silicon are

6270-474: The meeting of two vastly different human cultures on Earth, a historical precedent being the Columbian Exchange . Such meetings have generally led to the destruction of the civilization receiving contact (as opposed to the "contactor", which initiates contact), and therefore destruction of human civilization is a possible outcome. However, the absence of any such contact to date means such conjecture

6365-478: The mid-20th century, active research has taken place to look for signs of extraterrestrial life, encompassing searches for current and historic extraterrestrial life, and a narrower search for extraterrestrial intelligent life . Depending on the category of search, methods range from analysis of telescope and specimen data to radios used to detect and transmit communications. The concept of extraterrestrial life, and particularly extraterrestrial intelligence, has had

6460-572: The most abundant ones in the universe, far more than the others. On Earth's crust the most abundant of those elements is silicon, in the Hydrosphere it is carbon and in the atmosphere, it is carbon and nitrogen. Silicon, however, has disadvantages over carbon. The molecules formed with silicon atoms are less stable, and more vulnerable to acids, oxygen, and light. An ecosystem of silicon-based lifeforms would require very low temperatures, high atmospheric pressure , an atmosphere devoid of oxygen, and

6555-504: The native planet that may not be caused by natural causes. There are three main types of techno-signatures considered: interstellar communications , effects on the atmosphere, and planetary-sized structures such as Dyson spheres . Organizations such as the SETI Institute search the cosmos for potential forms of communication. They started with radio waves , and now search for laser pulses as well. The challenge for this search

6650-418: The ocean that do not receive sunlight, and take energy from black smokers instead. Magnetic fields and radioactivity have also been proposed as sources of energy, although they would be less efficient ones. Life on Earth requires water in a liquid state as a solvent in which biochemical reactions take place. It is highly unlikely that an abiogenesis process can start within a gaseous or solid medium:

6745-568: The origin of extraterrestrial life. The Solar System has a wide variety of planets, dwarf planets, and moons, and each one is studied for its potential to host life. Each one has its own specific conditions that may benefit or harm life. So far, the only lifeforms found are those from Earth. No extraterrestrial intelligence other than humans exists or has ever existed within the Solar System. Astrobiologist Mary Voytek points out that it would be unlikely to find large ecosystems, as they would have already been detected by now. The inner Solar System

6840-468: The others are used in other biological processes. The studies ruled out pollution of the meteorites on Earth, as those components would not be freely available the way they were found in the samples. This discovery suggests that several organic molecules that serve as building blocks of life may be generated within asteroids and comets. In October 2011, scientists reported that cosmic dust contains complex organic compounds ("amorphous organic solids with

6935-553: The planetary core ceased to generate a magnetic field, solar winds removed the atmosphere and the planet became vulnerable to solar radiation. Ancient life-forms may still have left fossilised remains, and microbes may still survive deep underground. As mentioned, the gas giants and ice giants are unlikely to contain life. The most distant solar system bodies, found in the Kuiper Belt and outwards, are locked in permanent deep-freeze, but cannot be ruled out completely. Although

7030-511: The precise differences that lead to beneficial or harmful conditions for life. And despite the conditions against life on Venus , there are suspicions that microbial life-forms may still survive in high-altitude clouds. Mars is a cold and almost airless desert, inhospitable to life. However, recent studies revealed that water on Mars used to be quite abundant, forming rivers, lakes, and perhaps even oceans. Mars may have been habitable back then, and life on Mars may have been possible. But when

7125-456: The probability of the existence of extraterrestrial civilisations and the lack of evidence for such civilisations is known as the Fermi paradox . Dennis W. Sciama claimed that life's existence in the universe depends on various fundamental constants. Zhi-Wei Wang and Samuel L. Braunstein suggest that a random universe capable of supporting life is likely to be just barely able to do so, giving

7220-476: The probe to study ocean water. Still, Cassini detected complex organic molecules, salts, evidence of hydrothermal activity, hydrogen, and methane. Titan is the only celestial body in the Solar System besides Earth that has liquid bodies on the surface. It has rivers, lakes, and rain of hydrocarbons, methane, and ethane, and even a cycle similar to Earth's water cycle . This special context encourages speculations about lifeforms with different biochemistry, but

7315-438: The problems of survival of life on other planets. However, he also considered that the conditions found on Mars were incompatible with carbon based life. Even if extraterrestrial life is based on carbon and uses water as a solvent, like Earth life, it may still have a radically different biochemistry . Life is generally considered to be a product of natural selection . It has been proposed that to undergo natural selection

7410-433: The researchers, "these [newly discovered] compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life ." Although most searches are focused on the biology of extraterrestrial life, an extraterrestrial intelligence capable enough to develop a civilization may be detectable by other means as well. Technology may generate technosignatures , effects on

7505-426: The right conditions on Earth were met, life started by a chemical process known as abiogenesis . Alternatively, life may have formed less frequently, then spread – by meteoroids , for example – between habitable planets in a process called panspermia . During most of its stellar evolution stars combine hydrogen nuclei to make helium nuclei by stellar fusion, and the comparatively lighter weight of helium allows

7600-405: The right side of the equation are agreed as speculative and open to substitution: 10,000 = 5 ⋅ 0.5 ⋅ 2 ⋅ 1 ⋅ 0.2 ⋅ 1 ⋅ 10,000 {\displaystyle 10{,}000=5\cdot 0.5\cdot 2\cdot 1\cdot 0.2\cdot 1\cdot 10{,}000} The Drake equation has proved controversial since, although it is written as

7695-422: The rocky surface, which helps the chemical reactions. It may be difficult to dig so deep in order to study those oceans, though. Enceladus , a tiny moon of Saturn with another subsurface ocean, may not need to be dug, as it releases water to space in eruption columns . The space probe Cassini flew inside one of these, but could not make a full study because NASA did not expect this phenomenon and did not equip

7790-532: The same samples suggests that a non-biological reaction is a more likely hypothesis. In February 2005 NASA scientists reported they may have found some evidence of extraterrestrial life on Mars. The two scientists, Carol Stoker and Larry Lemke of NASA's Ames Research Center , based their claim on methane signatures found in Mars's atmosphere resembling the methane production of some forms of primitive life on Earth, as well as on their own study of primitive life near

7885-699: The source. On 18 June 2022 Dan Werthimer , chief scientist for several SETI -related projects, reportedly noted that “These signals are from radio interference; they are due to radio pollution from earthlings, not from E.T.” The potential changes from extraterrestrial contact could vary greatly in magnitude and type, based on the extraterrestrial civilization's level of technological advancement, degree of benevolence or malevolence, and level of mutual comprehension between itself and humanity. Some theories suggest that an extraterrestrial civilization could be advanced enough to dispense with biology, living instead inside of advanced computers. The medium through which humanity

7980-399: The star to release the extra energy. The process continues until the star uses all of its available fuel, with the speed of consumption being related to the size of the star. During its last stages, stars start combining helium nuclei to form carbon nuclei. The higher-sized stars can further combine carbon nuclei to create oxygen and silicon, oxygen into neon and sulfur, and so on until iron. In

8075-482: The stellar evolution of stars and planets, it is usually not taken into account by astrobiology. There is an area around a star, the circumstellar habitable zone or "Goldilocks zone", where water may be at the right temperature to exist in liquid form at a planetary surface. This area is neither too close to the star, where water would become steam, nor too far away, where water would be frozen as ice. However, although useful as an approximation, planetary habitability

8170-508: The study of Earth's life, the only known form of life, astrobiology seeks to study how life starts and evolves and the requirements for its continuous existence. This helps to determine what to look for when searching for life in other celestial bodies. This is a complex area of study, and uses the combined perspectives of several scientific disciplines, such as astronomy , biology , chemistry , geology , oceanography , and atmospheric sciences . The scientific search for extraterrestrial life

8265-539: The survival and possible origin of life on Earth . With the little amount of information that scientists have found regarding the atmosphere on other planets in the Milky Way galaxy and beyond, the atmospheres are most likely reducing or with very low oxygen levels, especially when compared with Earth's atmosphere. If there were the necessary elements and ions on these planets, the same carbon fixing, reduced chemical compounds occurring around hydrothermal vents could also occur on these planets' surfaces and possibly result in

8360-636: The tendency of technologically advanced human societies to enslave or destroy less advanced societies – argue it may be dangerous to actively draw attention to Earth. Initially, after the Big Bang the universe was too hot to allow life. 15 million years later , it cooled to temperate levels, but the elements that make up living things did not exist yet. The only freely available elements at that point were hydrogen and helium . Carbon and oxygen (and later, water ) would not appear until 50 million years later, created through stellar fusion. At that point,

8455-544: The tradition of hosts in horror comics . It was commonplace in British comics in the 1970s when 2000 AD began publication. For example, Warlord was supposedly edited by Lord Peter Flint and Bullet by a character named Fireball. 2000 AD' s short-lived sister title Starlord used a similar device with the eponymous alien Starlord as did Tornado with Big E. Pat Mills created Tharg but since regrets it, in 2015 describing him as an anachronism. In 1996 David Bishop

8550-608: The universe. The science of extraterrestrial life is known as astrobiology . Speculation about the possibility of inhabited worlds beyond Earth dates back to antiquity. Early Christian writers discussed the idea of a "plurality of worlds" as proposed by earlier thinkers such as Democritus ; Augustine references Epicurus 's idea of innumerable worlds "throughout the boundless immensity of space" in The City of God . Pre-modern writers typically assumed extraterrestrial "worlds" are inhabited by living beings. William Vorilong , in

8645-445: The unusual properties of the meteorite were eventually explained as the result of inorganic processes, the controversy over its discovery laid the groundwork for the development of astrobiology. An experiment on the two Viking Mars landers reported gas emissions from heated Martian soil samples that some scientists argue are consistent with the presence of living microorganisms. Lack of corroborating evidence from other experiments on

8740-557: Was determined to get rid of Tharg and challenge the status quo, so replaced him as host in #1014 with the Vector 13 Men in Black . Reader reaction was "strong and vitriolic" and Tharg was reinstated in #1032. Bishop came to realise that Tharg is an intrinsic part of 2000 AD and that the Men in Black were "a tiresome encumbrance". Tharg's return and the ousting of the Men in Black was covered in

8835-417: Was habitable. It is unclear if life and intelligent life are ubiquitous in the cosmos or rare. The hypothesis of ubiquitous extraterrestrial life relies on three main ideas. The first one, the size of the universe allows for plenty of planets to have a similar habitability to Earth, and the age of the universe gives enough time for a long process analog to the history of Earth to happen there. The second

8930-399: Was reported. Scientists search for biosignatures within the Solar System by studying planetary surfaces and examining meteorites . Some claim to have identified evidence that microbial life has existed on Mars. In 1996, a controversial report stated that structures resembling nanobacteria were discovered in a meteorite, ALH84001 , formed of rock ejected from Mars . Although all

9025-606: Was the 1974 Arecibo message composed by Frank Drake and Carl Sagan . There are multiple independent organizations and individuals engaged in CETI research. The U.S. government 's position, in line with that of most relevant experts, is that "chances of contact with an extraterrestrial intelligence are extremely small, given the distances involved." This line of thinking has led some to conclude that first contact might be made with extraterrestrial artificial intelligence, rather than with biological beings. The Wow! signal remains

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