Extraterrestrial life, or alien life, is life which does not originate from Earth. No extraterrestrial life has yet been 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 the universe. The science of extraterrestrial life is known as astrobiology.
The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. As a 2015 article put it, "If life is so easy, someone from somewhere must have come calling by now."
The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other planets.
Frank Donald Drake was an American astrophysicist and astrobiologist.
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 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.
Ufology, sometimes written UFOlogy, is the investigation of unidentified flying objects (UFOs) by people who believe that they may be of extraordinary origins. While there are instances of government, private, and fringe science investigations of UFOs, ufology is generally regarded by skeptics and science educators as an example of pseudoscience.
Jill Cornell Tarter is an American astronomer best known for her work on the search for extraterrestrial intelligence (SETI). Tarter is the former director of the Center for SETI Research, holding the Bernard M. Oliver Chair for SETI at the SETI Institute. In 2002, Discover magazine recognized her as one of the 50 most important women in science.
Abraham "Avi" Loeb is an Israeli-American theoretical physicist who works on astrophysics and cosmology. Loeb is the Frank B. Baird Jr. Professor of Science at Harvard University, where since 2007 he has been Director of the Institute for Theory and Computation at the Center for Astrophysics. He chaired the Department of Astronomy from 2011 to 2020, and founded the Black Hole Initiative in 2016.
Active SETI is the attempt to send messages to intelligent extraterrestrial life. Active SETI messages are predominantly sent in the form of radio signals. Physical messages like that of the Pioneer plaque may also be considered an active SETI message. Active SETI is also known as METI.
An interstellar object is an astronomical object in interstellar space that is not gravitationally bound to a star. This term can also be applied to an object that is on an interstellar trajectory but is temporarily passing close to a star, such as certain asteroids and comets. In the latter case, the object may be called an interstellar interloper.
The cultural impact of extraterrestrial contact is the corpus of changes to terrestrial science, technology, religion, politics, and ecosystems resulting from contact with an extraterrestrial civilization. This concept is closely related to the search for extraterrestrial intelligence (SETI), which attempts to locate intelligent life as opposed to analyzing the implications of contact with that life.
Technosignature or technomarker is any measurable property or effect that provides scientific evidence of past or present technology. Technosignatures are analogous to biosignatures, which signal the presence of life, whether intelligent or not. Some authors prefer to exclude radio transmissions from the definition, but such restrictive usage is not widespread. Jill Tarter has proposed that the search for extraterrestrial intelligence (SETI) be renamed "the search for technosignatures". Various types of technosignatures, such as radiation leakage from megascale astroengineering installations such as Dyson spheres, the light from an extraterrestrial ecumenopolis, or Shkadov thrusters with the power to alter the orbits of stars around the Galactic Center, may be detectable with hypertelescopes. Some examples of technosignatures are described in Paul Davies's 2010 book The Eerie Silence, although the terms "technosignature" and "technomarker" do not appear in the book.
ʻOumuamua is the first interstellar object detected passing through the Solar System. Formally designated 1I/2017 U1, it was discovered by Robert Weryk using the Pan-STARRS telescope at Haleakalā Observatory, Hawaii, on 19 October 2017, approximately 40 days after it passed its closest point to the Sun on 9 September. When it was first observed, it was about 33 million km from Earth and already heading away from the Sun.
Douglas A. Vakoch is an American astrobiologist, search for extraterrestrial intelligence (SETI) researcher, psychologist, and president of METI International, a nonprofit research and educational organization devoted to transmitting intentional signals to extraterrestrial civilizations. Vakoch led METI's participation in Sónar Calling GJ 273b, which transmitted a series of interstellar messages to Luyten's Star, located 12.4 light years from Earth. Vakoch advocates ongoing transmission projects, arguing that this does not increase risks of an alien invasion as suggested by British cosmologist Stephen Hawking. He has participated in several SETI observation programs, and after sixteen years at the SETI Institute, where he was director of Interstellar Message Composition, Vakoch founded METI International. He has edited over two dozen books in SETI, astrobiology, the psychology of space exploration, ecocriticism, COVID, and transgender studies. Vakoch helped design the message included on NASA's Europa Clipper spacecraft. He is general editor of three book series in ecocriticism and in the intersection of space and society. Vakoch has appeared widely on television and radio as a commentator on SETI and astrobiology. He is an emeritus professor of clinical psychology at the California Institute of Integral Studies (CIIS).
Extraterrestrial: The First Sign of Intelligent Life Beyond Earth is a popular science book written by American theoretical physicist and Harvard University astronomer Avi Loeb, published by Houghton Mifflin Harcourt on 26 January 2021.
CNEOS 2014-01-08, also known as Interstellar meteor 1 (IM1), was a 0.45 m (1.5 ft) meteor that impacted Earth on 8 January 2014 near the northeast coast of Papua New Guinea. It was claimed to be an interstellar object in a 2019 preprint by astronomers Amir Siraj and Abraham Loeb, and this was published in 2022. This was confirmed by the U.S. Space Command in 2022 based on the object's velocity relative to the Sun. Other astronomers doubt this, and still other experts found Earth-related explanations for the purported meteorite impact instead.
Alberto Caballero is a Spanish astronomer and science communicator. He is known for having identified a Sun-like star in the sky region where the Wow! signal came from as one of the possible sources of the radio signal. Caballero is also known for founding and coordinating the Habitable Exoplanet Hunting Project, an international effort consisting of more than 30 observatories searching for nearby potentially habitable exoplanets. Data is collected 24/7 from specific stars by observatories located both in the Northern and Southern hemispheres, and an initial list of exoplanet candidates was made public in 2020.
The following outline is provided as an overview of and topical guide to extraterrestrial life:
The firstborn hypothesis is a proposed solution to the Fermi paradox which states that no extraterrestrial intelligent life has been discovered because humanity is the first form of intelligent life in the universe.
The Galileo Project is an international scientific research project to search for extraterrestrial intelligence or extraterrestrial technology on and near Earth and to identify the nature of anomalous Unidentified Flying Objects/Unidentified Aerial Phenomena (UFOs/UAP).
