Editing Extraterrestrial life (section)

===Recent history===
{{see also|Space exploration}}
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| footer            = Some major international efforts to search for extraterrestrial life, clockwise from top left:
*The search for [[extrasolar planet]]s (image: [[Kepler space telescope|''Kepler'' telescope]])
*[[SETI|Listening for extraterrestrial signals indicating intelligence]] (image: [[Allen Telescope Array|Allen array]])
*[[Robotic spacecraft|Robotic exploration]] of the [[Solar System]] (image: [[Curiosity (rover)|''Curiosity'' rover]] on [[Mars]])
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The search and study of extraterrestrial life became a science of its own, [[astrobiology]]. Also known as ''exobiology'', this discipline is studied by the [[NASA]], the [[ESA]], the [[INAF]], and others. Astrobiology studies life from Earth as well, but with a cosmic perspective. For example, [[abiogenesis]] is of interest to astrobiology, not because of the origin of life on Earth, but for the chances of a similar process taking place in other celestial bodies. Many aspects of life, from its definition to its chemistry, are analyzed as either likely to be similar in all forms of life across the cosmos or only native to Earth.<ref>Aguilera Mochon, pp. 10–11</ref> Astrobiology, however, remains constrained by the current lack of extraterrestrial lifeforms to study, as all life on Earth comes from the same ancestor, and it is hard to infer general characteristics from a group with a single example to analyse.<ref>{{cite web|url= https://www.nasa.gov/vision/universe/starsgalaxies/life%27s_working_definition.html|title= Life's Working Definition: Does It Work?|author= |date= 2002|publisher= NASA|accessdate= January 17, 2022|archive-date= 26 May 2018|archive-url= https://web.archive.org/web/20180526161726/https://www.nasa.gov/vision/universe/starsgalaxies/life%27s_working_definition.html|url-status= dead}}</ref>

The 20th century came with great technological advances, speculations about future [[Hypothetical technology|hypothetical technologies]], and an increased basic knowledge of science by the general population thanks to [[science divulgation]] through the mass media. The public interest in extraterrestrial life and the lack of discoveries by mainstream science led to the emergence of [[pseudoscience]]s that provided affirmative, if questionable, answers to the existence of aliens. [[Ufology]] claims that many [[unidentified flying object]]s (UFOs) would be spaceships from alien species, and [[ancient astronauts]] hypothesis claim that aliens would have visited Earth in antiquity and prehistoric times but people would have failed to understand it by then.<ref>Aguilera Mochon, p. 10</ref> Most UFOs or [[List of UFO sightings|UFO sightings]]<ref>{{cite journal |first=Anne |last=Cross |title=The Flexibility of Scientific Rhetoric: A Case Study of UFO Researchers |journal=Qualitative Sociology |volume=27 |issue=1 |pages=3–34 |doi=10.1023/B:QUAS.0000015542.28438.41 |year=2004|s2cid=144197172 }}</ref> can be readily explained as sightings of Earth-based aircraft (including [[Black project|top-secret aircraft]]), known [[astronomical object]]s or weather phenomenons, or as [[hoax]]es.<ref>{{cite journal |first=Philippe |last=Ailleris |date=January–February 2011 |title=The lure of local SETI: Fifty years of field experiments |journal=Acta Astronautica |volume=68 |issue=1–2 |pages=2–15 |doi=10.1016/j.actaastro.2009.12.011 |bibcode=2011AcAau..68....2A}}</ref>

Looking beyond the psudosciences, [[Lewis White Beck]] strove to elevate the level of public discourse on the topic of extraterrestrial life by tracing the evolution of philosophical thought over the centuries from ancient times into the modern era. His review of the contributions made by [[Lucretius]], [[Plutarch]], [[Aristotle]], [[Copernicus]], [[Immanuel Kant]], [[Thomas Wilkins]], [[Charles Darwin]] and [[Karl Marx]] demonstrated that even in modern times, humanity could be profoundly influenced in its search for extraterrestrial life by subtle and comforting archetypal ideas which are largely derived from firmly held religious, philosophical and existential belief systems. On a positive note, however,  Beck further argued that even if the search for extraterrestrial life proves to be unsuccessful, the endeavor itself could have beneficial consequences by assisting humanity in its attempt to actualize superior ways of living here on Earth.<ref>{{Cite journal |last=Beck |first=Lewis White |date=1971 |title=Extraterrestrial Intelligent Life |url=https://www.jstor.org/stable/3129745 |journal=Proceedings and Addresses of the American Philosophical Association |volume=45 |pages=5–21 |doi=10.2307/3129745|jstor=3129745 }}</ref>
   
By the 21st century, it was accepted that multicellular life in the Solar System can only exist on Earth, but the interest in extraterrestrial life increased regardless. This is a result of the advances in several sciences. The knowledge of planetary habitability allows to consider on scientific terms the likelihood of finding life at each specific celestial body, as it is known which features are beneficial and harmful for life. Astronomy and telescopes also improved to the point exoplanets can be confirmed and even studied, increasing the number of search places. Life may still exist elsewhere in the Solar System in unicellular form, but the advances in spacecraft allow to send robots to study samples in situ, with tools of growing complexity and reliability. Although no extraterrestrial life has been found and life may still be just a rarity from Earth, there are scientific reasons to suspect that it can exist elsewhere, and technological advances that may detect it if it does.<ref>Bennett, p. 4</ref>

Many scientists are optimistic about the chances of finding alien life. In the words of SETI's Frank Drake, "All we know for sure is that the sky is not littered with powerful microwave transmitters".<ref>{{cite web |url=http://antarcticaedu.com/bio2024.htm |title=LECTURE 4: MODERN THOUGHTS ON EXTRATERRESTRIAL LIFE |work=The University of Antarctica |access-date=25 July 2015}}</ref> Drake noted that it is entirely possible that advanced technology results in communication being carried out in some way other than conventional radio transmission. At the same time, the data returned by space probes, and giant strides in detection methods, have allowed science to begin delineating [[Planetary habitability|habitability criteria]] on other worlds, and to confirm that at least other planets are plentiful, though aliens remain a question mark. The [[Wow! signal]], detected in 1977 by a SETI project, remains a subject of speculative debate.<ref>{{Cite web |date=2020-12-02 |title=Did the Wow! signal come from this star? {{!}} Space {{!}} EarthSky |url=https://earthsky.org/space/source-of-wow-signal-in-1977-sunlike-star-2mass-19281982-2640123/ |access-date=2024-05-10 |website=earthsky.org |language=en-US}}</ref>

On the other hand, other scientists are pessimistic. Jacques Monod wrote that "Man knows at last that he is alone in the indifferent immensity of the universe, whence which he has emerged by chance".<ref>{{cite web |url= https://www.scientificamerican.com/article/the-cosmos-might-be-mostly-devoid-of-life/|title= The Cosmos Might Be Mostly Devoid of Life|author= Paul Davies|date= September 1, 2016|publisher= Scientific American|accessdate=July 8, 2022}}</ref> In 2000, geologist and [[paleontologist]] [[Peter Ward (paleontologist)|Peter Ward]] and [[Astrobiology|astrobiologist]] [[Donald Brownlee]] published a book entitled ''[[Rare Earth (book)|Rare Earth: Why Complex Life is Uncommon in the Universe]]''.<ref>{{cite book |title=Rare Earth: Why Complex Life is Uncommon in the Universe |publisher=Copernicus |first1=Peter |last1=Ward |first2=Donald |last2=Brownlee |date=2000 |bibcode=2000rewc.book.....W |isbn=978-0-387-98701-9}}</ref>{{Better source needed|reason=The significance of the book on the history of thoughts about alien life should not be the book itself|date=July 2023}} In it, they discussed the [[Rare Earth hypothesis]], in which they claim that Earth-like life is rare in the [[universe]], whereas [[bacteria|microbial]] life is common. Ward and Brownlee are open to the idea of evolution on other planets that is not based on essential Earth-like characteristics such as DNA and carbon.

As for the possible risks, theoretical physicist [[Stephen Hawking]] warned in 2010 that humans should not try to contact alien life forms. He warned that aliens might pillage Earth for resources. "If aliens visit us, the outcome would be much as when [[Christopher Columbus|Columbus]] landed in [[Americas|America]], which didn't turn out well for the [[Indigenous peoples of the Americas|Native Americans]]", he said.<ref>{{cite news |url=http://news.bbc.co.uk/2/hi/uk_news/8642558.stm |work=BBC News |title=Hawking warns over alien beings |date=25 April 2010 |access-date=2 May 2010}}</ref> [[Jared Diamond]] had earlier expressed similar concerns.<ref>{{cite book |chapter=Chapter 12 |title=The Third Chimpanzee: The Evolution and Future of the Human Animal |publisher=Harper Perennial |first=Jared M. |last=Diamond |date=2006 |isbn=978-0-06-084550-6}}</ref> On 20 July 2015, Hawking and Russian billionaire [[Yuri Milner]], along with the [[SETI Institute]], announced a well-funded effort, called the [[Breakthrough Initiatives]], to expand efforts to search for extraterrestrial life. The group contracted the services of the 100-meter [[Robert C. Byrd]] [[Green Bank Telescope]] in West Virginia in the United States and the 64-meter [[Parkes Telescope]] in New South Wales, Australia.<ref name="AP-20150720">{{cite news |url=http://apnews.excite.com/article/20150720/eu--britain-extraterrestrials-e52c157915.html |title=Searching for ET: Hawking to look for extraterrestrial life |work=Excite! |agency=Associated Press |last=Katz |first=Gregory |date=20 July 2015 |access-date=20 July 2015}}</ref> On 13 February 2015, scientists (including [[Geoffrey Marcy]], [[Seth Shostak]], [[Frank Drake]] and [[David Brin]]) at a convention of the [[American Association for the Advancement of Science]], discussed [[Active SETI]] and whether transmitting a message to possible intelligent extraterrestrials in the [[Cosmos]] was a good idea;<ref name="NYT-20150213">{{cite news |url=https://www.nytimes.com/aponline/2015/02/13/science/ap-us-sci-calling-the-cosmos.html |title=Should We Call the Cosmos Seeking ET? Or Is That Risky? |work=[[The New York Times]] |agency=Associated Press |first=Seth |last=Borenstein |date=13 February 2015 |archive-url=https://web.archive.org/web/20150214152940/http://www.nytimes.com/aponline/2015/02/13/science/ap-us-sci-calling-the-cosmos.html |archive-date=14 February 2015 |url-status=dead }}</ref><ref name="BBC-20150212">{{cite news |last=Ghosh |first=Pallab |title=Scientist: 'Try to contact aliens' |url=https://www.bbc.com/news/science-environment-31442952 |date=12 February 2015 |work=[[BBC News]] |access-date=12 February 2015}}</ref> one result was a statement, signed by many, that a "worldwide scientific, political and humanitarian discussion must occur before any message is sent".<ref name="UCB-20150213">{{cite web |url=http://setiathome.berkeley.edu/meti_statement_0.html |title=Regarding Messaging To Extraterrestrial Intelligence (METI) / Active Searches For Extraterrestrial Intelligence (Active SETI) |publisher=[[University of California, Berkeley]] |date=13 February 2015 |access-date=14 February 2015}}</ref>