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What is extraterrestrial life?
Extraterrestrial life, also known as alien life or aliens, is life that does not originate from Earth. Learn about the scientific and cultural aspects of this topic, from the Drake equation to the Fermi paradox, and the history of speculation and research.
- UFOs are real (and the government knows it) In June, the Pentagon released a highly anticipated report detailing 144 UFO encounters between 2004 and 2021.
- Black holes could be alien powerhouses. While alien hunters spend plenty of time searching for habitable planets beyond our solar system, a study published in July in the journal Monthly Notices of the Royal Astronomical Society warns that scientists shouldn't overlook nature's most extreme objects: Black holes.
- Alien planets may look nothing like Earth. Typically, the search for alien life begins with the search for Earth-like planets — but there may be another class of alien world that is just as conducive to life, a study published in the Astrophysical Journal in August contends.
- One of Saturn's moon still holds potential for life. The methane wafting from Enceladus, Saturn's sixth largest moon, may be a sign that life teems in the moon's subsurface sea, a June study found.
Sep 10, 2021 · Do aliens exist? Extraterrestrial life has never been discovered, but that doesn’t mean it doesn’t exist. At NASA, astrobiologists like Lindsay Hays are trying to answer one of the most profound questions ever: Is there life beyond Earth?
Sep 15, 2024 · Explore the latest research and news on the search for alien life beyond Earth. Learn about the possibilities, challenges and methods of finding intelligent or microbial aliens in our galaxy and beyond.
- Overview
- Universal criteria
extraterrestrial life, life that may exist or may have existed in the universe outside of Earth. The search for extraterrestrial life encompasses many fundamental scientific questions. What are the basic requirements for life? Could life have arisen elsewhere in the solar system? Are there other planets like Earth? How likely is the evolution of intelligent life?
(Read Britannica’s biography of Carl Sagan, co-author of this entry.)
No one knows which aspects of living systems are necessary, in the sense that living systems everywhere must have them, and which are contingent, in the sense that they are the result of evolutionary accidents such that elsewhere a different sequence of events might have led to different properties of life. In this respect the discovery of even a single example of extraterrestrial life, no matter how elementary in form or substance, would represent a fundamental revolution in science. Do a vast array of biological themes and counterpoints exist in the universe, or are there places with living fugues, compared with which Earth’s one tune is a bit thin and reedy? Or is Earth’s the only tune around?
Life on Earth, structurally based on carbon, hydrogen, nitrogen, and other elements, uses water as its interaction medium. Phosphorus, as phosphate bound to an organic residue, is required for energy storage and transport; sulfur is involved in the three-dimensional configuration of protein molecules; and other elements are present in smaller concentrations. Must these particular atoms be the atoms of life everywhere, or might there be a wide range of atomic possibilities in extraterrestrial organisms? What are the general physical constraints on extraterrestrial life?
In approaching these questions, several criteria can be used. The major atoms should tend to have a high cosmic abundance. Structural molecules of organisms at the temperature of the planet in question should not be so extremely stable that chemical reactions are impossible, but neither should they be extremely unstable, or else the organism would fall to pieces. A medium for molecular interaction must be present. Solids are inappropriate because of their inertness. The medium, most likely a liquid but possibly a very dense gas, must be stable in a number of respects. It should have a large temperature range (for a liquid, the temperature difference between freezing point and boiling point should be large). The liquid should be difficult to vaporize and to freeze; in general, it should be difficult to change its temperature. The interaction medium needs to be an excellent solvent. A fluid phase must be present on the planet in question, for material must cycle to the organism as food and away from the organism as waste.
The planet should therefore have an atmosphere and some liquid near the surface, although not necessarily a water ocean. If the intensity of ultraviolet light or charged particles from its sun is intense at the planetary surface, then some area, perhaps below the surface, should be shielded from this radiation (although some forms or intensity of radiation might permit useful chemical reactions to occur). Finally, it is imperative that conditions allow the existence of autotrophy (the ability of an organism to synthesize at least some of its own nutrients) or other means of net production of necessary compounds.
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Nov 25, 2023 · Aliens are having a moment. But the evidence says all possibilities remain in play, including the possibility that we are alone.
Extraterrestrials: Everything you need to know about the hunt for alien life | BBC Science Focus. Scientists are becoming increasingly optimistic that extraterrestrial life is out there. Here, an astrobiologist explains why.
