Test Your Knowledge on the Search for Extraterrestrial Life

Extraterrestrial life refers to life that may exist outside of Earth and has not originated on Earth. The existence of such life has not yet been conclusively detected, but research efforts are underway. Extraterrestrial life may range from simple forms like prokaryotes to intelligent beings, possibly bringing forth civilizations that might be far more advanced than humankind. The Drake equation speculates about the existence of sapient life elsewhere in the universe, and the science of extraterrestrial life is known as astrobiology. The concept of extraterrestrial life has had a major cultural impact, especially extraterrestrials in fiction. The Rare Earth hypothesis maintains that life on Earth is possible because of 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 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. Life on Earth requires water in a liquid state as a solvent in which biochemical reactions take place. 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. The evolution from simple cells to eukaryotes, and from them to multicellular lifeforms, is not guaranteed. 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.The Search for Extraterrestrial Life: Direct and Indirect Methods

• Astrobiology is the science that studies life in the universe, using the combined perspectives of several scientific disciplines.

• Direct search methods include studying planetary surfaces, examining meteorites, and searching for biosignatures within the Solar System.

• Indirect search methods include monitoring the galaxy for electromagnetic interstellar communications from civilizations on other worlds.

• Over 4,000 exoplanets have been discovered, and astronomers search for terrestrial planets within the habitable zones of their stars.

• The Kepler space telescope has detected a few thousand candidate planets, of which about 11% may be false positives.

• The presence of heavy elements in a star's light-spectrum is another potential biosignature.

• The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.

• Cosmic pluralism, the plurality of worlds, describes the philosophical belief in numerous "worlds" in addition to Earth, which might harbor extraterrestrial life.

• Giordano Bruno was an early proponent of extraterrestrial life, arguing for an infinite universe in which every star is surrounded by its own planetary system.

• Early modern indirect search methods for extraterrestrial life included using telescopes to study the Moon, Mars, and Venus.

• The Fermi paradox describes the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for such civilizations.

• The discovery of life on Earth in 4.1 billion-year-old rocks in Western Australia suggests that life could be common in the universe.A Brief History of the Search for Extraterrestrial Life

• Early musings on extraterrestrial life by Anton Maria Schyrleus of Rheita and Cyrano de Bergerac

• The emergence of the idea of cosmic pluralism in the Enlightenment period, championed by Immanuel Kant and Benjamin Franklin

• The 19th-century speculation about life on Mars, fueled by the discovery of apparent Martian canals, and the subsequent debunking of the canal hypothesis

• The development of the science fiction genre and its influence on public perception of extraterrestrial life

• The emergence of Astrobiology as a science of its own, studying life from Earth with a cosmic perspective

• The emergence of pseudosciences, such as Ufology and the ancient astronaut hypothesis, providing questionable affirmative answers to the existence of aliens

• The emergence of the Rare Earth hypothesis, claiming that Earth-like life is rare in the universe, whereas microbial life is common

• The risks associated with contacting alien life forms, as warned by Stephen Hawking and Jared Diamond

• The governmental responses to the search for extraterrestrial life, including the Outer Space Treaty and the Planetary Protection Office of NASA

• The current research objectives of the Chinese space program and the French space agency

• The probability of detecting life in outer space, according to Isaac Ben-Israel, chairman of the Israel Space Agency.