The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy.
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, or non-human intelligence (NHI), refers to hypothetical intelligent extraterrestrial life. No such life has ever been proven to exist in the Solar System except for humans on Earth, and its existence on other star systems is still speculative. 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.
SETI@home is a project of the Berkeley SETI Research Center to analyze radio signals with the aim of searching for signs of extraterrestrial intelligence. Until March 2020, it was run as an Internet-based public volunteer computing project that employed the BOINC software platform. It is hosted by the Space Sciences Laboratory at the University of California, Berkeley, and is one of many activities undertaken as part of the worldwide SETI effort.
The Wow! signal was a strong narrowband radio signal detected on August 15, 1977, by Ohio State University's Big Ear radio telescope in the United States, then used to support the search for extraterrestrial intelligence. The signal appeared to come from the direction of the constellation Sagittarius and bore expected hallmarks of extraterrestrial origin.
The Allen Telescope Array (ATA), formerly known as the One Hectare Telescope (1hT), is a radio telescope array dedicated to astronomical observations and a simultaneous search for extraterrestrial intelligence (SETI). The array is situated at the Hat Creek Radio Observatory in Shasta County, 290 miles (470 km) northeast of San Francisco, California.
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 2011–2020, and founded the Black Hole Initiative in 2016.
Robert Hansen Gray was an American data analyst, author, and astronomer, and author of The Elusive Wow: Searching for Extraterrestrial Intelligence.
Breakthrough Listen is a project to search for intelligent extraterrestrial communications in the Universe. With $100 million in funding and thousands of hours of dedicated telescope time on state-of-the-art facilities, it is the most comprehensive search for alien communications to date. The project began in January 2016, and is expected to continue for 10 years. It is a component of Yuri Milner's Breakthrough Initiatives program. The science program for Breakthrough Listen is based at Berkeley SETI Research Center, located in the Astronomy Department at the University of California, Berkeley.
Breakthrough Initiatives is a science-based program founded in 2015 and funded by Julia and Yuri Milner, also of Breakthrough Prize, to search for extraterrestrial intelligence over a span of at least 10 years. The program is divided into multiple projects. Breakthrough Listen will comprise an effort to search over 1,000,000 stars for artificial radio or laser signals. A parallel project called Breakthrough Message is an effort to create a message "representative of humanity and planet Earth". The project Breakthrough Starshot, co-founded with Mark Zuckerberg, aims to send a swarm of probes to the nearest star at about 20% the speed of light. The project Breakthrough Watch aims to identify and characterize Earth-sized, rocky planets around Alpha Centauri and other stars within 20 light years of Earth. Breakthrough plans to send a mission to Saturn's moon Enceladus, in search for life in its warm ocean, and in 2018 signed a partnership agreement with NASA for the project.
Tabby's Star is an F-type main-sequence star in the constellation Cygnus approximately 1,470 light-years from Earth. A distant red dwarf companion has been reported, making Tabby's Star a binary stellar system.
HD 164595 is a wide binary star system in the northern constellation of Hercules. The primary component of this pair hosts an orbiting exoplanet. The system is located at a distance of 92 light years from the Sun based on parallax measurements, and is drifting further away with a radial velocity of 2.0 km/s. Although it has an absolute magnitude of +4.81, at that distance it is too faint to be viewed with the naked eye, having an apparent visual magnitude of 7.07. The brighter star can be found with binoculars or a small telescope less than a degree to the east-northeast of Xi Herculis. HD 164595 has a relatively large proper motion, traversing the celestial sphere at an angular rate of 0.222″ yr−1.
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.
The Berkeley SETI Research Center (BSRC) conducts experiments searching for optical and electromagnetic transmissions from intelligent extraterrestrial civilizations. The center is based at the University of California, Berkeley.
The NIROSETI is an astronomical program to search for artificial signals in the optical (visible) and near infrared (NIR) wavebands of the electromagnetic spectrum. It is the first dedicated near-infrared SETI experiment. The instrument was created by a collaboration of scientists from the University of California, San Diego, Berkeley SETI Research Center at the University of California, Berkeley, University of Toronto, and the SETI Institute. It uses the Anna Nickel 1-m telescope at the Lick Observatory, situated on the summit of Mount Hamilton, east of San Jose, California, USA. The instrument was commissioned on 15 March 2015 and has been operated for more than 150 nights, and is still operational today.
BLC1 was a candidate SETI radio signal detected and observed during April and May 2019, and first reported on 18 December 2020, spatially coincident with the direction of the Solar System's closest star, Proxima Centauri.
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:
