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'''Extraterrestrial life''' is [[Life science|life]], whether demonstrated, hypothesized, or merely imagined, that did not obviously originate on the [[earth]]. It has been a staple of [[science fiction]] since the [[Edward VII|Edwardian]] era, and has more recently become the subject of scientific debate and even theological debate.

'''Extraterrestrial life''' is [[Life science|life]], whether demonstrated, hypothesized, or merely imagined, that did not obviously originate on the [[Earth]]. It has been a staple of [[science fiction]] since the [[Edward VII|Edwardian]] era, and has more recently become the subject of scientific and even theological debates.

The term ''life'' is here used in its usual manner to connote living things, regardless of complexity or condition of sentience.  However, in [[science fiction]] especially, extraterrestrial life may take unconventional form, such as non-carbon-based life forms or even disembodied intelligence.

The term ''life'' is here used in its usual manner to denote living things, regardless of complexity or sentience.  However, in [[science fiction]] especially, extraterrestrial life may take unconventional forms, such as non-carbon-based life forms or even disembodied intelligence.

The term ''race'' here means a species of sentient individuals (not an ethnographic subdivision of a single species); for example, humans all belong to only one race, the human race.

The term ''race'' here means a species of sentient individuals (not an ethnographic subdivision of a single species); for example, humans all belong to only one race, the human race.

Vigorous scientific research on the subject is fairly limited, and has focused on both the "micro" and "macro" aspects of the problem:

Vigorous scientific research on the subject is fairly limited, and has focused on both the "micro" and "macro" aspects of the problem:

# The genesis, nature, survival, and movement of primitive life forms, including the hazard that spaceborne microbes might pose to [[astronaut]]s or to the earth itself.

# The genesis, nature, survival, and movement of primitive life forms, including the hazard that spaceborne microbes might pose to [[astronaut]]s or to the Earth itself.

# The possibility of prior or future detection, contact, trade, or war with an extraterrestrial [[civilization]].

# The possibility of prior or future detection, contact, trade, or war with an extraterrestrial [[civilization]].

Extraterrestrial microbes have been and remain the subject of much serious scientific speculation. Such speculation has centered on three questions:

Extraterrestrial microbes have been and remain the subject of much serious scientific speculation. Such speculation has centered on three questions:

# Could a microbe of extraterrestrial origin somehow come to earth and cause a killer [[pandemic]]?<ref>This question of ''back-contamination'' was a serious worry in the middle years of [[Project Apollo]]--that is, the time of the first four missions of that project. [[National Aeronautics and Space Administration|NASA]], the launch authority for Apollo, required the crews of the first three missions actually to reach the [[moon]] to spend weeks in [[quarantine]] while under the constant care and watch of a [[physician]]. Only after three crews landed on the moon and returned to earth with no ill effect and no evidence of having contracted any communicable disease on the moon or in space did NASA drop that requirement. (The crew of [[Apollo 13]] did not face this requirement because their in-flight emergency precluded their planned landing.)</ref>

# Could a microbe of extraterrestrial origin somehow come to Earth and cause a killer [[pandemic]]?<ref>This question of ''back-contamination'' was a serious worry in the middle years of [[Project Apollo]]--that is, the time of the first four missions of that project. [[National Aeronautics and Space Administration|NASA]], the launch authority for Apollo, required the crews of the first three missions actually to reach the [[moon]] to spend weeks in [[quarantine]] while under the constant care and watch of a [[physician]]. Only after three crews landed on the moon and returned to Earth with no ill effect and no evidence of having contracted any communicable disease on the Moon or in space did NASA drop that requirement. (The crew of [[Apollo 13]] did not face this requirement because their in-flight emergency precluded their planned landing.)</ref>

# Did life on earth begin with the "seeding" of the earth from outside? This theory, called [[panspermia]], alleges that either (a) the earth acquired the seeds of life by passing through the tail of a [[comet]], or (b) an extraterrestrial ''civilization'' sent the seeds of life ''deliberately'' for one reason or another. Extraterrestrial microbes would be involved in either case.

# Did life on Earth begin with the "seeding" of the earth from outside? This theory, called [[panspermia]], alleges that either (a) the Earth acquired the seeds of life by passing through the tail of a [[comet]], or (b) an extraterrestrial ''civilization'' sent the seeds of life ''deliberately'' for one reason or another. Extraterrestrial microbes would be involved in either case.

# Might a human crew or human-directed robotic explorer find extraterrestrial microbes on another [[planet]]?

# Might a human crew or human-directed robotic explorer find extraterrestrial microbes on another [[planet]]?

With the continued development and perfection of telescopes, [[Astronomy|astronomers]] and [[rocket]] [[science|scientists]] have openly and often feverishly speculated about whether the other planets in our [[solar system]] might harbor forms of life that originated on those planets. This speculation has also extended to [[Titan]], the largest satellite of the planet [[Saturn]].

With the continued development and perfection of telescopes, [[Astronomy|astronomers]] and [[rocket]] [[science|scientists]] have openly and often feverishly speculated about whether the other planets in the [[Solar System]] might harbor forms of life that originated on those planets. This speculation has also extended to [[Titan]], the largest satellite of the planet [[Saturn]].

The major considerations driving such speculation are the requirements of life, and the difficulty with the theory of [[abiogenesis]] as a workable origin of [[life]] on [[earth]]. Most scientists engaged in such speculation seem to agree that life requires at least two things in order to self-generate in any environment:

The major considerations driving such speculation are the requirements of life, and the difficulty with the theory of [[abiogenesis]] as a workable origin of [[life]] on [[Earth]]. Most scientists engaged in such speculation seem to agree that life requires at least two things in order to self-generate in any environment:

# [[Water]]

# [[Water]]

# An [[atmosphere]]

# An [[atmosphere]]

[[Image:Mars_meteorite.jpg|thumb|150px|[[Meteor]]ite believed to have once been a part of [[Mars]] and to contain [[fossil]] evidence that primitive [[life]] may have existed on Mars.[http://spaceflight.nasa.gov/gallery/images/mars/meteorites/html/s94_032549.html Image source] ]]

[[Image:Mars_meteorite.jpg|thumb|150px|[[Meteor]]ite believed to have once been a part of [[Mars]] and to contain [[fossil]] evidence that primitive [[life]] may have existed on Mars.[http://spaceflight.nasa.gov/gallery/images/mars/meteorites/html/s94_032549.html Image source] ]]

Currently the most exciting subject for speculation concerning extraterrestrial life is the planet [[Mars]]. Its atmosphere is quite thin, and this would militate against the presence of life or, more to the point, the presence of standing or flowing water. But photographs taken from orbit and from the surface of Mars reveal erosion channels that strongly suggest that water once flowed on Mars. Indeed, the first graphic above shows changes in a gully in two views of it, taken four years apart--as if liquid water had opened another erosion channel in the meantime. (The operators of the Mars Global Surveyor insist that such pictures might still contain artifacts that make them unsuitable for scientific research, and hence disclaim any definite conclusion that anyone might be tempted to draw from them.) The second graphic shows a [[meteor]]ite, found in [[Antarctica]] in 1984, containing microscopic cavities that once might have held [[microbes]] and that, until recently, was believed to have fallen to earth from Mars.<ref>Donald L. Savage, James Hartsfield, and David Salisbury, "[http://www2.jpl.nasa.gov/snc/nasa1.html Meteorite Yields Evidence of Primitive Life on Early Mars]," ''Mars Meteorite Project'', press release 96-160, August 7, 1996. Retrieved April 17, 2007, from the [[Jet Propulsion Laboratory]] Web servers.</ref>

Currently the most exciting subject for speculation concerning extraterrestrial life is the planet [[Mars]]. Its atmosphere is quite thin, and this would militate against the presence of life or, more to the point, the presence of standing or flowing water. But photographs taken from orbit and from the surface of Mars reveal erosion channels that strongly suggest that water once flowed on Mars. Indeed, the first graphic above shows changes in a gully in two views of it, taken four years apart--as if liquid water had opened another erosion channel in the meantime. (The operators of the Mars Global Surveyor insist that such pictures might still contain artifacts that make them unsuitable for scientific research, and hence disclaim any definite conclusion that anyone might be tempted to draw from them.) The second graphic shows a [[meteor]]ite, found in [[Antarctica]] in 1984, containing microscopic cavities that once might have held [[microbes]] and that, until recently, was believed to have fallen to Earth from Mars.<ref>Donald L. Savage, James Hartsfield, and David Salisbury, "[http://www2.jpl.nasa.gov/snc/nasa1.html Meteorite Yields Evidence of Primitive Life on Early Mars]," ''Mars Meteorite Project'', press release 96-160, August 7, 1996. Retrieved April 17, 2007, from the [[Jet Propulsion Laboratory]] Web servers.</ref>

If one could show that abiogenesis occurred on Mars, then that process was far more likely to have occurred on earth than it would be absent such a showing or finding. Yet apart from the reliability of such evidence is this one inherent weakness for this argument: it assumes that life ''found'' on Mars ''originated'' on Mars. The hydroplate theory of the [[Great Flood]] suggests that large quantities of water, including muddy slurries, were ejected into space during the initial fissure of the original earth's crust, and that these ejecta persist today as [[comet]]s, [[asteroid]]s, and [[meteor]]oids. If such ejected water and mud fell to Mars from above, then they might have held [[microbes]]--and therefore any microbes found on Mars are far more likely to have come from earth during the Noachic Flood than to have originated on Mars.<ref>If such life forms survived, that need not be a great shock to any observer. [[Extremophiles]], or microbes known to thrive under conditions that would kill or render dormant any other form of life, are well-known on earth and have even been the subject of engineering studies attempting to find practical uses for them.</ref>

If one could show that abiogenesis occurred on Mars, then that process was far more likely to have occurred on Earth than it would be absent such a showing or finding. Yet apart from the reliability of such evidence is this one inherent weakness for this argument: it assumes that life ''found'' on Mars ''originated'' on Mars. The hydroplate theory of the [[Great Flood]] suggests that large quantities of water, including muddy slurries, were ejected into space during the initial fissure of the original earth's crust, and that these ejecta persist today as [[comet]]s, [[asteroid]]s, and [[meteor]]oids. If such ejected water and mud fell to Mars from above, then they might have held [[microbes]]--and therefore any microbes found on Mars are far more likely to have come from Earth during the Noachic Flood than to have originated on Mars.<ref>If such life forms survived, that need not be a great shock to any observer. [[Extremophiles]], or microbes known to thrive under conditions that would kill or render dormant any other form of life, are well-known on Earth and have even been the subject of engineering studies attempting to find practical uses for them.</ref>

Space scientists have searched for extraterrestrial microbes for years. To date, no definitive proof of such microbes has been found. The Antarctic meteorite mentioned above, and the alleged bacterial fossils on it, fueled speculation for months, until other scientists finally determined that the microbes involved probably were earthly contaminants.<ref>Rick Lockridge, "[http://www.cnn.com/TECH/9801/15/contaminated.rock/ Scientists dispute NASA's claims about Mars meteorite]", ''The Cable News Network'', January 15, 1998. Retrieved April 17, 2007 from CNN's web servers.</ref>

Space scientists have searched for extraterrestrial microbes for years. To date, no definitive proof of such microbes has been found. The Antarctic meteorite mentioned above, and the alleged bacterial fossils on it, fueled speculation for months, until other scientists finally determined that the microbes involved probably were earthly contaminants.<ref>Rick Lockridge, "[http://www.cnn.com/TECH/9801/15/contaminated.rock/ Scientists dispute NASA's claims about Mars meteorite]", ''The Cable News Network'', January 15, 1998. Retrieved April 17, 2007 from CNN's web servers.</ref>

Nevertheless, the finding of extraterrestrial microbes on [[Mars]] is one of the fondest expressed hopes of NASA planetary scientists<ref>Authors unknown, "[http://mars.jpl.nasa.gov/life/ Do Martians Exist?], ''NASA Mars Exploration'', 05 Oct 2005 04:51:40 UTC. Retrieved April 17, 2007, from [[NASA]].</ref> and of other scientists and advocacy groups<ref>Everett Gibson, Jr., David S. McKay, and Kathie Thomas-Kerpta, "[http://www.marssociety.org/portal/TMS_Library/MAR_98_046/view Life on Mars: Evidence from Martian Meteorites]," ''Proceedings of the Founding Convention of the Mars Society'', R. M. Zubrin and M. Zubrin, eds. 1998. Retrieved April 17, 2007, from [http://www.marssociety.org The Mars Society].</ref> hoping to persuade the [[United States]] government, or perhaps the [[United Nations]], to fund crewed expeditions to Mars. Furthermore, no sane space mission planner could in good conscience ignore the potential hazard of the transport of a microbe to earth and the release of that microbe into earth's [[biosphere]]. Happily, measures for containing such a microbe, perhaps derived from those measures taken during [[Project Apollo]], would contribute a relatively insignificant amount to the total budget of a program of crewed missions to Mars or to any other celestial body.

Nevertheless, the finding of extraterrestrial microbes on [[Mars]] is one of the fondest expressed hopes of NASA planetary scientists<ref>Authors unknown, "[http://mars.jpl.nasa.gov/life/ Do Martians Exist?], ''NASA Mars Exploration'', 05 Oct 2005 04:51:40 UTC. Retrieved April 17, 2007, from [[NASA]].</ref> and of other scientists and advocacy groups<ref>Everett Gibson, Jr., David S. McKay, and Kathie Thomas-Kerpta, "[http://www.marssociety.org/portal/TMS_Library/MAR_98_046/view Life on Mars: Evidence from Martian Meteorites]," ''Proceedings of the Founding Convention of the Mars Society'', R. M. Zubrin and M. Zubrin, eds. 1998. Retrieved April 17, 2007, from [http://www.marssociety.org The Mars Society].</ref> hoping to persuade the [[United States]] government, or perhaps the [[United Nations]], to fund crewed expeditions to Mars. Furthermore, no sane space mission planner could in good conscience ignore the potential hazard of the transport of a microbe to Earth and the release of that microbe into Earth's [[biosphere]]. Happily, measures for containing such a microbe, perhaps derived from those measures taken during [[Project Apollo]], would contribute a relatively insignificant amount to the total budget of a program of crewed missions to Mars or to any other celestial body.

[[Francis Crick]] and [[Leslie Orgel]], in 1973,<ref>Crick, F. H. C., and Orgel, L. E. "Directed Panspermia," ''Icarus'', 19, 341 (1973).</ref> openly speculated on a form of exogenesis called [[Panspermia#Directed panspermia|directed panspermia]], in which such an extraterrestrial nation-state fired a brace of missiles, each laden with [[bacteria]] and/or [[blue-green algae]], in all directions. One such  missile crashed on earth, and we are its by-product, as it were, their theory states.<ref>For a detailed discussion on the logical weaknesses and omissions of such a position, see the main article on [[Panspermia]].</ref>

[[Francis Crick]] and [[Leslie Orgel]], in 1973,<ref>Crick, F. H. C., and Orgel, L. E. "Directed Panspermia," ''Icarus'', 19, 341 (1973).</ref> openly speculated on a form of exogenesis called [[Panspermia#Directed panspermia|directed panspermia]], in which such an extraterrestrial nation-state fired a brace of missiles, each laden with [[bacteria]] and/or [[blue-green algae]], in all directions. One such  missile crashed on Earth, and we are its by-product, as it were, their theory states.<ref>For a detailed discussion on the logical weaknesses and omissions of such a position, see the main article on [[Panspermia]].</ref>

=====Candidates for extraterrestrial life in our Solar System=====

=====Candidates for extraterrestrial life in our Solar System=====

== Extraterrestrial Life in Science Fiction ==

== Extraterrestrial Life in Science Fiction ==

Extraterrestrial life, from nation-states to microbes, has been a staple of [[science fiction]] since the early days of the genre.  Novelist [[H. G. Wells]] speculated on what sort of inventions might carry men into outer space, and what they might discover there.  In ''The First Men in the Moon'', he describes a fictional extraterrestrial civilization on the [[moon]], populated by man-sized insects. Wells also wrote about a Martian nation-state that launched an invasion of Earth (''The War of the Worlds''), only to fail when the invaders fell terminally ill from earthly microbes against which their immune systems had no defense. [[Edgar Rice Burroughs]] indulged in far richer speculation on an entire civilization on Mars, and on semi-regular commerce between his Martians and a select few visitors from earth.

Extraterrestrial life, from nation-states to microbes, has been a staple of [[science fiction]] since the early days of the genre.  Novelist [[H. G. Wells]] speculated on what sort of inventions might carry men into outer space, and what they might discover there.  In ''The First Men in the Moon'', he describes a fictional extraterrestrial civilization on the [[moon]], populated by man-sized insects. Wells also wrote about a Martian nation-state that launched an invasion of Earth (''The War of the Worlds''), only to fail when the invaders fell terminally ill from earthly microbes against which their immune systems had no defense. [[Edgar Rice Burroughs]] indulged in far richer speculation on an entire civilization on Mars, and on semi-regular commerce between his Martians and a select few visitors from Earth.

The middle twentieth century introduced other now-familiar themes, often through the media of comic books, novels, low-budget films, and [[television]]: humans caught up in events on other inhabited worlds, spacefaring starship crews, and extraterrestrial "prophets" appearing on earth with either good intentions or bad.  By the late twentieth century, big-budget films repeated these themes and introduced new ones, sometimes (as in ''[[Star Wars]]'') bypassing Earth altogether in favor of mythlike tales of ancient civilizations. The alleged crash of an extraterrestrial scout craft near Roswell, New Mexico, United States was the subject of another film.

The middle twentieth century introduced other now-familiar themes, often through the media of comic books, novels, low-budget films, and [[television]]: humans caught up in events on other inhabited worlds, spacefaring starship crews, and extraterrestrial "prophets" appearing on earth with either good intentions or bad.  By the late twentieth century, big-budget films repeated these themes and introduced new ones, sometimes (as in ''[[Star Wars]]'') bypassing Earth altogether in favor of mythlike tales of ancient civilizations. The alleged crash of an extraterrestrial scout craft near Roswell, New Mexico, United States was the subject of another film.

The ''[[Star Trek]]'' television franchise created by [[Gene Roddenberry]], with its myriad of extraterrestrial and even trans-galactic empires, is well known. Also in the 1960s, producer Quinn Martin created the series ''The Invaders'' that centered on one man's attempt to warn his government that Eath had been infiltrated with extraterrestrial spies. More recently, Kenneth Johnston created ''V'', a series in which a spaceborne force whose commanding admiral at first puts on a friendly appearance (similar to that of [[Matthew Perry]], the American commodore who first visited [[Japan]]) but then subverts human governmental and media institutions in order to further the aliens' true purpose, which is to steal earth's water and carry away earth's population for food.

The ''[[Star Trek]]'' television franchise created by [[Gene Roddenberry]], with its myriad of extraterrestrial and even trans-galactic empires, is well known. Also in the 1960s, producer Quinn Martin created the series ''The Invaders'' that centered on one man's attempt to warn his government that the Earth had been infiltrated with extraterrestrial spies. More recently, Kenneth Johnston created ''V'', a series in which a spaceborne force whose commanding admiral at first puts on a friendly appearance (similar to that of [[Matthew Perry]], the American commodore who first visited [[Japan]]) but then subverts human governmental and media institutions in order to further the aliens' true purpose, which is to steal earth's water and carry away earth's population for food.

Nor have science fiction writers ignored speculation about the finding of extraterrestrial microbes. Usually they have portrayed such microbes as capable of producing deadly extinction-level pandemics. (See, for example, ''The Andromeda Strain'' by Michael Crichton.) John B. Olson and Randall S. Ingermanson, however, speculated that the first crew to fly to Mars might discover incontrovertible evidence of microbial life--including a culturable microbe. This would engender excitement in the hearts of their launch authorites, but would also inspire such fear in the mind of a [[National Aeronautics and Space Administration|NASA]] engineer that she would actually attempt to strand or murder the crew to stop them from back-contaminating the earth with their culture.

Nor have science fiction writers ignored speculation about the finding of extraterrestrial microbes. Usually they have portrayed such microbes as capable of producing deadly extinction-level pandemics. (See, for example, ''The Andromeda Strain'' by Michael Crichton.) John B. Olson and Randall S. Ingermanson, however, speculated that the first crew to fly to Mars might discover incontrovertible evidence of microbial life--including a culturable microbe. This would engender excitement in the hearts of their launch authorites, but would also inspire such fear in the mind of a [[National Aeronautics and Space Administration|NASA]] engineer that she would actually attempt to strand or murder the crew to stop them from back-contaminating the earth with their culture.

==== Extent of the Creation ====

==== Extent of the Creation ====

The presence of extraterrestrial ''microbes'' on one or more of the other planets in our solar system (most likely Mars) does excite some fear in Christian quarters. But not all Christians harbor such fear, and even [[Young earth creationism|young earth creationists]] are quite confident that they could explain such a finding. For example, if the hydroplate theory is correct and a slurry of mud from the Great Flood traveled to Mars and poured itself out upon it, then such a slurry would almost certainly contain microbes. That some of these might be extremophiles, and thus capable of long-term survival even in such a harsh environment as that of Mars, is entirely possible and would allow complete harmony between the finding of microbes in such locations and the Biblical account of earth pre-history.

The presence of extraterrestrial ''microbes'' on one or more of the other planets in the Solar System (most likely Mars) does cause some fear in Christian quarters. But not all Christians harbor such fear, and even [[Young Earth creationism|young Earth creationists]] are quite confident that they could explain such a finding. For example, if the hydroplate theory is correct and a slurry of mud from the Great Flood traveled to Mars and poured itself out upon it, then such a slurry would almost certainly contain microbes. That some of these might be extremophiles, and thus capable of long-term survival even in such a harsh environment as that of Mars, is entirely possible and would allow complete harmony between the finding of microbes in such locations and the Biblical account of Earth's prehistory.

===Non-Christian Views===

===Non-Christian Views===

#'''Church of [[Scientology]]''' founder [[L. Ron Hubbard]] has lectured on and written accounts of complex extraterrestrial civilizations and alien interventions in earthly events.

#'''Church of [[Scientology]]''' founder [[L. Ron Hubbard]] has lectured on and written accounts of complex extraterrestrial civilizations and alien interventions in earthly events.

#The '''[[Raelism|Raelians]]''' believe that their minds are the once-disembodied souls of extraterrestrial persons (and therefore believe that their minds are extraterrestrial in origin though their bodies are not).

#The '''[[Raelism|Raelians]]''' believe that their minds are the once-disembodied souls of extraterrestrial persons (and therefore believe that their minds are extraterrestrial in origin though their bodies are not).

#The '''Hale-Bopp movement''', whose members committed mass suicide in the season of the close passage near the earth of Comet Hale-Bopp, believed they would be taken away by an alien craft concealed in the comet's tail.

#The '''Hale-Bopp movement''', whose members committed mass suicide in the season of the close passage near the Earth of Comet Hale-Bopp, believed they would be taken away by an alien craft concealed in the comet's tail.

#The '''[[UFO]] movement''', a loose alliance of organizations often having the initials "UFO" (for Unidentified Flying Object) in their names, ''viz.'', "Mutual UFO Network", "Center for UFO Studies," "Fund for UFO Research", express various beliefs concerning the extrterrestrial nature of unidentified flying objects.

#The '''[[UFO]] movement''', a loose alliance of organizations often having the initials "UFO" (for Unidentified Flying Object) in their names, ''viz.'', "Mutual UFO Network", "Center for UFO Studies," "Fund for UFO Research", express various beliefs concerning the extrterrestrial nature of unidentified flying objects.

#The '''[[Nation of Islam]]''', especially when it came under the leadership of [[Louis Farrakhan]], expressed a belief that the original founder of the Nation of Islam lives today in an extraterrestrial spacecraft called the "Mother Wheel," and that Farrakhan himself has been taken on board that vessel for consultations with this person.<ref>Farrakhan seems recently to have abandoned this theory and attempted to steer the movement he now leads toward the orthodox [[Islam]] taught by [[Muhammad]].</ref>

#The '''[[Nation of Islam]]''', especially when it came under the leadership of [[Louis Farrakhan]], expressed a belief that the original founder of the Nation of Islam lives today in an extraterrestrial spacecraft called the "Mother Wheel," and that Farrakhan himself has been taken on board that vessel for consultations with this person.<ref>Farrakhan seems recently to have abandoned this theory and attempted to steer the movement he now leads toward the orthodox [[Islam]] taught by [[Muhammad]].</ref>