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| {{For|the journal|Astrobiology (journal)}}
| | I am 33 years old and my name is Becky Foos. I life in Riva Presso Chieri (Italy).<br><br>my website: [http://hemorrhoidtreatmentfix.com/thrombosed-hemorrhoid thrombosed hemorrhoids] |
| {{Use dmy dates|date=March 2013}}
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| [[File:ADN animation.gif|thumb|right|upright=1.20|[[Nucleic acids]] may not be the only [[biomolecule]]s in the Universe capable of coding for life processes.<ref name="AstroDNA">{{cite web|url=http://www.astrobio.net/news/article2168.html |title=Launching the Alien Debates (part 1 of 7) | accessdate=2008-10-20 | date=8 December 2006 |work=Astrobiology Magazine |publisher=NASA }}</ref>]]
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| '''Astrobiology''' is the study of the [[abiogenesis|origin]], [[evolution]], distribution, and future of life in the universe: [[extraterrestrial life]] and [[life on Earth]]. This [[interdisciplinary]] field encompasses the search for habitable environments in our [[Solar System]] and [[Planetary habitability|habitable planets]] outside our Solar System, the search for evidence of prebiotic chemistry, laboratory and field research into the origins and early evolution of life on Earth, and studies of the potential for life to adapt to challenges on [[Earth]] and in [[outer space]].<ref>{{cite news | first = [[Charles S. Cockell]] | title = How the search for aliens can help sustain life on Earth | date =4 October 2012 | url = http://edition.cnn.com/2012/10/02/world/europe/astrobiology-aliens-environment-opinion/index.html?hpt=hp_c4 | work = CNN News | accessdate = 2012-10-08}}</ref> Astrobiology addresses the question of whether life exists beyond Earth, and how humans can detect it if it does.<ref name="about">{{cite web|url=http://astrobiology.nasa.gov/about-astrobiology/ |title=About Astrobiology |accessdate=2008-10-20 |date=21 January 2008 |work=NASA Astrobiology Institute |publisher=NASA | archiveurl= http://web.archive.org/web/20081011192341/http://astrobiology.nasa.gov/about-astrobiology/| archivedate= 11 October 2008 <!--DASHBot-->| deadurl= no}}</ref> (The term '''exobiology''' is similar but more specific — it covers the search for life beyond Earth, and the effects of extraterrestrial environments on living things.)<ref>[http://www.merriam-webster.com/dictionary/exobiology Mirriam Webster Dictionary entry "Exobiology"] (accessed 11 April 2013)</ref>
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| Astrobiology makes use of [[physics]], [[chemistry]], [[astronomy]], [[biology]], [[molecular biology]], [[ecology]], [[planetary science]], [[geography]], and [[geology]] to investigate the possibility of life on other worlds and help recognize [[biosphere]]s that might be different from the biosphere on Earth.<ref>[http://www.itwire.com.au/content/view/11647/1066/ iTWire - Scientists will look for alien life, but Where and How?]</ref><ref>{{cite book |title=The life and death of planet Earth |last=Ward |first=P. D. |authorlink= |coauthors=Brownlee, D. |year=2004 |publisher=Owl Books |location=New York |isbn=0-8050-7512-7 |pages= }}</ref> Astrobiology concerns itself with interpretation of existing [[Scientific method|scientific data]]; given more detailed and reliable data from other parts of the universe, the roots of astrobiology itself—physics, chemistry and biology—may have their theoretical bases challenged. Although speculation is entertained to give context, astrobiology concerns itself primarily with [[hypotheses]] that fit firmly into existing [[Theory#Science|scientific theories]].
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| Earth is the only place in the universe known to harbor life.<ref>{{Cite journal | first = Robert W. Graham | contribution = Extraterrestrial Life in the Universe | title = NASA Technical Memorandum 102363 | publisher = NASA | place = Lewis Research Center, Ohio | date = February 1990| id = | contribution-url = http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19900013148_1990013148.pdf | format = PDF }}</ref><ref>{{cite book| last=Altermann| first=Wladyslaw| editors=Joseph Seckbach, Maud Walsh| year=2008| title=From Fossils to Astrobiology: Records of Life on Earth and the Search for Extraterrestrial Biosignatures|chapter=From Fossils to Astrobiology - A Roadmap to Fata Morgana?|volume=12|isbn=1-4020-8836-1|page=xvii}}</ref> However, recent advances in planetary science have changed fundamental assumptions about the possibility of life in the universe, raising the estimates of [[habitable zone]]s around other stars and the search for extraterrestrial microbial life.<ref>{{cite book|last=Horneck|first=Gerda|coauthor=Petra Rettberg|year=2007|title=Complete Course in Astrobiology|publisher=Wiley-VCH|isbn=3-527-40660-3}}</ref><ref name="NYT-20131118">{{cite news |last=Davies |authorlink=Paul Davies |first=Paul |title=Are We Alone in the Universe? |url=http://www.nytimes.com/2013/11/19/opinion/are-we-alone-in-the-universe.html |date=18 November 2013 |work=[[New York Times]] |accessdate=20 November 2013 }}</ref> On 4 November 2013, astronomers reported, based on [[Kepler (spacecraft)|''Kepler'' space mission]] data, that there could be as many as 40 billion [[Terrestrial planet|Earth-sized]] [[extrasolar planets|planets]] orbiting in the [[habitable zone]]s of [[sun-like|sun-like stars]] and [[red dwarf stars]] within the [[Milky Way Galaxy]].<ref name="NYT-20131104">{{cite news |last=Overbye |first=Dennis|title=Far-Off Planets Like the Earth Dot the Galaxy|url=http://www.nytimes.com/2013/11/05/science/cosmic-census-finds-billions-of-planets-that-could-be-like-earth.html |date=4 November 2013 |work=[[New York Times]] |accessdate=5 November 2013 }}</ref><ref name="PNAS-20131031">{{cite journal |last1=Petigura |first1=Eric A.|last2=Howard |first2=Andrew W. |last3=Marcy |first3=Geoffrey W. |title=Prevalence of Earth-size planets orbiting Sun-like stars|url=http://www.pnas.org/content/early/2013/10/31/1319909110 |date=31 October 2013 |journal=[[Proceedings of the National Academy of Sciences of the United States of America]]|doi=10.1073/pnas.1319909110 |accessdate=5 November 2013 }}</ref> 11 billion of these estimated planets may be orbiting sun-like stars.<ref name="LATimes-20131104">{{cite news |last=Khan |first=Amina |title=Milky Way may host billions of Earth-size planets |url=http://www.latimes.com/science/la-sci-earth-like-planets-20131105,0,2673237.story |date=4 November 2013 |work=[[Los Angeles Times]] |accessdate=5 November 2013 }}</ref> The nearest such planet may be 12 light-years away, according to the scientists.<ref name="NYT-20131104" /><ref name="PNAS-20131031"/>
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| It has been proposed that [[viruses]] are likely to be encountered on other life-bearing planets.<ref name="Astro-20130814">{{cite journal |last=Griffin |first=Dale Warren |title=The Quest for Extraterrestrial Life: What About the Viruses? |url=http://online.liebertpub.com/doi/abs/10.1089/ast.2012.0959 |date=14 August 2013 |journal=[[Astrobiology (journal)]] |volume=13 |issue=8 |pages=774–783 |doi=10.1089/ast.2012.0959 |accessdate=6 September 2013 |bibcode = 2013AsBio..13..774G }}</ref> Efforts to discover current or past [[life on Mars (planet)|life on Mars]], is an active area of research.
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| On 24 January 2014, NASA reported that [[Timeline of Mars Science Laboratory#Current status|current studies]] on the planet [[Mars]] by the [[Curiosity (rover)|''Curiosity'']] and [[Opportunity (rover)|''Opportunity'']] [[Mars rover|rovers]] will now be searching for evidence of ancient life, including a [[biosphere]] based on [[Autotroph|autotrophic]], [[Chemotroph|chemotrophic]] and/or [[Lithotroph#Chemolithotrophs|chemolithoautotrophic]] [[microorganism]]s, as well as ancient water, including [[Lacustrine plain|fluvio-lacustrine environments]] ([[plain]]s related to ancient [[river]]s or [[lake]]s) that may have been [[Planetary habitability|habitable]].<ref name="SCI-20140124a">{{cite journal |last=Grotzinger |first=John P. |title=Introduction to Special Issue - Habitability, Taphonomy, and the Search for Organic Carbon on Mars |url=http://www.sciencemag.org/content/343/6169/386 |journal=[[Science (journal)|Science]] |date=24 January 2014 |volume=343 |number=6169 |pages=386-387 |doi=10.1126/science.1249944 |accessdate=24 January 2014 }}</ref><ref name="SCI-20140124special">{{cite journal |authors=Various |title=Special Issue - Table of Contents - Exploring Martian Habitability |url=http://www.sciencemag.org/content/343/6169.toc#SpecialIssue |date=24 January 2014|journal=[[Science (journal)|Science]] |volume=343 |number=6169 |pages=345-452 |accessdate=24 January 2014 }}</ref><ref name="SCI-20140124">{{cite journal |authors=Various |title=Special Collection - Curiosity - Exploring Martian Habitability |url=http://www.sciencemag.org/site/extra/curiosity/|date=24 January 2014 |journal=[[Science (journal)|Science]] |accessdate=January 24, 2014 }}</ref><ref name="SCI-20140124c">{{cite journal |authors=Grotzinger, J.P. et al. |title=A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars |url=http://www.sciencemag.org/content/343/6169/1242777 |date=24 January 2014 |journal=[[Science (journal)|Science]] |volume=343 |number=6169 |doi=10.1126/science.1242777 |accessdate=24 January 2014 }}</ref> The search for evidence of [[Planetary habitability|habitability]], [[taphonomy]] (related to [[fossils]]), and [[organic carbon]] on the planet [[Mars]] is now a primary [[NASA]] objective.<ref name="SCI-20140124a" />
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| == Overview ==
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| [[Image:Plagiomnium affine laminazellen.jpeg|thumb|right|220px|It is not known whether life elsewhere in the universe would utilize cell structures like those found on Earth. ([[Chloroplast]]s within plant cells shown here.)<ref>{{cite web|url=http://www.nasa.gov/centers/goddard/news/topstory/2007/spectrum_plants.html |title=NASA Predicts Non-Green Plants on Other Planets |accessdate=2008-10-20 |last=Gutro |first=Robert |date=4 November 2007 |publisher=Goddard Space Flight Center | archiveurl= http://web.archive.org/web/20081006023937/http://www.nasa.gov/centers/goddard/news/topstory/2007/spectrum_plants.html| archivedate= 6 October 2008 <!--DASHBot-->| deadurl= no}}</ref>]] [[Image:ALH84001 structures.jpg|thumb|right|220px|The [[Mars|Martian]] [[meteorite]] [[ALH84001]] shows microscopic formations that may have been created by life.]]
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| ''Astrobiology'' is etymologically derived from the [[Ancient Greek|Greek]] {{lang|grc|ἄστρον}}, ''astron'', "constellation, star"; {{lang|grc|βίος}}, ''bios'', "life"; and {{lang|grc|-λογία}}, ''[[wiktionary:-logia|-logia]]'', ''study''. The synonyms of astrobiology are diverse; however, the synonyms were structured in relation to the most important sciences implied in its development: [[astronomy]] and [[biology]]. A close synonym is ''exobiology'' from the Greek {{lang|grc|Έξω}}, "external"; Βίος, ''bios'', "life"; and λογία, -logia, ''study''. The term exobiology was first coined by molecular biologist [[Joshua Lederberg]]. Exobiology is considered to have a narrow scope limited to search of life external to earth, whereas subject area of astrobiology is wider and investigates the link between life and the [[universe]], which includes the search for extraterrestrial life, but also includes the study of life on earth, its origin, evolution and limits. Exobiology as a term has tended to be replaced by astrobiology.
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| Another term used in the past is '''xenobiology''', ("biology of the foreigners") a word used in 1954 by science fiction writer [[Robert Heinlein]] in his work [[The Star Beast]].<ref>{{cite journal |author=Heinlein R and Harold W |title=Xenobiology |journal=Science |date=21 July 1961 |pages=223, 225 | doi=10.1126/science.134.3473.223 |jstor=1708323 |volume=134 |issue=3473|bibcode = 1961Sci...134..223H }}</ref>
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| The term ''[[xenobiology]]'' is now used in a more specialized sense, to mean "biology based on foreign chemistry", whether of extraterrestrial or terrestrial (possibly synthetic) origin. Since alternate chemistry analogs to some life-processes have been created in the laboratory, xenobiology is now considered as an extant subject.<ref>{{cite journal | author=Markus Schmidt | title=Xenobiology: A new form of life as the ultimate biosafety tool | journal=BioEssays | date=9 Mar 2010 | pages=322–331 | doi=10.1002/bies.200900147 | volume=32 | issue=4 | url=http://onlinelibrary.wiley.com/doi/10.1002/bies.200900147/abstract | pmid=20217844 | pmc=2909387 }}</ref>
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| While it is an emerging and developing field, the question of whether [[life]] exists elsewhere in the universe is a verifiable hypothesis and thus a valid line of [[science|scientific]] inquiry. Though once considered outside the mainstream of scientific inquiry, astrobiology has become a formalized field of study. Planetary scientist [[David Grinspoon]] calls astrobiology a field of natural philosophy, grounding speculation on the unknown, in known scientific theory.<ref>Grinspoon 2004</ref> [[NASA]]'s interest in exobiology first began with the development of the U.S. Space Program. In 1959, NASA funded its first exobiology project, and in 1960, NASA founded an Exobiology Program; Exobiology research is now one of four elements of NASA's current Astrobiology Program.<ref name="about" /><ref>{{cite book |title=The Living Universe: NASA and the Development of Astrobiology |author=Steven J. Dick and James E. Strick |publisher=Rutgers University Press |location=New Brunswick, NJ |year=2004}}</ref> In 1971, NASA funded the [[Search for Extra-Terrestrial Intelligence]] (SETI) to search radio frequencies of the electromagnetic spectrum for [[interstellar communication|signals]] being transmitted by [[extraterrestrial life]] outside the Solar System. NASA's [[Viking program|Viking missions]] to Mars, launched in 1976, included [[Viking biological experiments|three biology experiments]] designed to look for [[biosignature|possible signs]] of present [[life on Mars (planet)|life on Mars]]. The [[Mars Pathfinder]] lander in 1997 carried a scientific payload intended for exopaleontology in the hopes of finding microbial fossils entombed in the rocks.<ref>{{cite journal | url=http://exobiology.nasa.gov/ssx/Selected_Research/exopaleo_for_pathfinder.html | title=Exopaleontology at the Pathfinder Landing Site | publisher=[[NASA Ames Research Center]] | date=5 September 1996 | accessdate=2009-11-21| author=Jack D. Famer, David J. Des Marais, and Ronald Greeley | bibcode=1995LPI....26..393F | last2=Des Marais | last3=Greeley | volume=26 | pages=393 | journal=Abstracts of the Lunar and Planetary Science Conference}}</ref>
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| In the 21st century, astrobiology is a focus of a growing number of NASA and [[European Space Agency]] Solar System exploration missions. The first European workshop on astrobiology took place in May 2001 in Italy,<ref>{{cite web|url=http://www.esa.int/esaCP/Pr_27_2001_p_EN.html |title=First European Workshop on Exo/Astrobiology |accessdate=2008-10-20 |year=2001 |work=ESA Press Release |publisher=European Space Agency }}</ref> and the outcome was the [[Aurora programme]].<ref>{{cite journal |title=ESA Embraces Astrobiology |journal=Science |date=1 June 2001 |volume=292 |issue=5522 |pages=1626–1627 |url=http://www.sciencemag.org/cgi/content/summary/292/5522/1626?maxtosho= |doi=10.1126/science.292.5522.1626 |last1=Gavaghan |first1=H. |pmid=11387447}}</ref> Currently, NASA hosts the [[NASA Astrobiology Institute]] and a growing number of universities in the United States (e.g., [[University of Arizona]], [[Penn State University]], [[Montana State University – Bozeman]], [[University of Washington]], and [[Arizona State University]]),<ref name="astrobiology.asu.edu">[http://astrobiology.asu.edu/Astrobiology/Home/Home.html Astrobiology at Arizona State University]</ref> Britain (e.g., The [[University of Glamorgan]], [[Buckingham University]]),<ref name="case.glam.ac.uk">[http://case.glam.ac.uk/CASE/Degrees/AstroBio.html CASE Undergraduate Degrees]</ref> Canada, Ireland, and Australia (e.g., The [[University of New South Wales]])<ref name="aca.unsw.edu.au">[http://aca.unsw.edu.au The Australian Centre for Astrobiology, University of New South Wales]</ref> now offer graduate degree programs in astrobiology. The [[International Astronomical Union]] regularly organizes international conferences through its Bioastronomy Commission.<ref>[http://www.ifa.hawaii.edu/~meech/iau/ Commission 51: Bioastronomy]</ref>
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| Advancements in the fields of astrobiology, observational astronomy and discovery of large varieties of [[extremophile]]s with extraordinary capability to thrive in the harshest environments on Earth, have led to speculation that life may possibly be thriving on many of the extraterrestrial bodies in the universe. A particular focus of current astrobiology research is the search for [[life on Mars (planet)|life on Mars]] due to its proximity to Earth and geological history. There is a growing body of evidence to suggest that Mars has previously had a considerable amount of [[Water on Mars|water on its surface]], water being considered an essential precursor to the development of carbon-based life.<ref name="autogenerated1">[http://www.pbs.org/wgbh/nova/mars/essential.html NOVA | Mars | Life's Little Essential | PBS]</ref>
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| Missions specifically designed to search for life include the [[Viking program]] and [[Beagle 2]] probes, both directed to Mars. The Viking results were inconclusive,<ref>{{cite journal |title=The Viking Biological Investigation: Preliminary Results |journal=Science |date=1 October 1976 |author=Klein HP and Levin GV |volume=194 |issue=4260 |pages=99–105 |doi=10.1126/science.194.4260.99 |url=http://www.sciencemag.org/cgi/content/abstract/194/4260/99|format= |accessdate=2008-08-15 |pmid=17793090 |bibcode = 1976Sci...194...99K }}</ref> and Beagle 2 failed to transmit from the surface and is assumed to have crashed.<ref>{{cite web|url=http://www.esa.int/esaCP/SEMAPB8A9HE_Life_0.html |title=Possible evidence found for Beagle 2 location |accessdate=2008-08-18 |date=21 December 2005 |publisher=European Space Agency | archiveurl= http://web.archive.org/web/20080930130433/http://www.esa.int/esaCP/SEMAPB8A9HE_Life_0.html| archivedate= 30 September 2008 <!--DASHBot-->| deadurl= no}}</ref> A future mission with a strong astrobiology role would have been the [[Jupiter Icy Moons Orbiter]], designed to study the frozen moons of Jupiter—some of which may have liquid water—had it not been cancelled. In late 2008, the [[Phoenix (spacecraft)|Phoenix lander]] probed the environment for past and present [[planetary habitability]] of [[microbe|microbial]] [[life on Mars (planet)|life on Mars]], and to research the history of water there.
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| In November 2011, NASA launched the [[Mars Science Laboratory]] (MSL) rover, nicknamed ''[[Curiosity rover|Curiosity]]'', which [[Curiosity rover#Landing|landed]] on Mars at [[Gale (crater)|Gale Crater]] in August 2012.<ref name="Gale Crater">{{cite web |last1=Webster |first1=Guy |last2=Brown |first2=Dwayne |title=NASA's Next Mars Rover To Land At Gale Crater |date=22 July 2011 |publisher=[[NASA JPL]] |url=http://www.jpl.nasa.gov/news/news.cfm?release=2011-222#1 |accessdate=2011-07-22 }}</ref><ref name="Gale Crater2">{{cite web |last1= Chow |first1=Dennis |title=NASA's Next Mars Rover to Land at Huge Gale Crater |url=http://www.space.com/12394-nasa-mars-rover-landing-site-unveiled.html |date=22 July 2011 |publisher=[[Space.com]] |accessdate=2011-07-22 }}</ref><ref name="Gale Crater3">{{cite news |last1=Amos |first1=Jonathan |title=Mars rover aims for deep crater |date=22 July 2011 |url=http://www.bbc.co.uk/news/science-environment-14249524 |work=[[BBC News]] |accessdate = 2011-07-22| archiveurl= http://web.archive.org/web/20110722170810/http://www.bbc.co.uk/news/science-environment-14249524| archivedate= 22 July 2011 <!--DASHBot-->| deadurl= no}}</ref> ''Curiosity'' rover is currently probing the environment for past and present [[planetary habitability]] of [[microbe|microbial]] [[life on Mars (planet)|life on Mars]]. On December 9, 2013, NASA reported that, based on evidence from ''Curiosity'' studying [[Aeolis Palus]], [[Gale (crater)|Gale Crater]] contained an ancient [[freshwater lake]] which could have been a hospitable environment for [[microbial life]].<ref name="NYT-20131209">{{cite news |last=Chang |first=Kenneth |title=On Mars, an Ancient Lake and Perhaps Life |url=http://www.nytimes.com/2013/12/10/science/space/on-mars-an-ancient-lake-and-perhaps-life.html |date=December 9, 2013 |work=[[New York Times]]|accessdate=December 9, 2013 }}</ref><ref name="SCI-20131209">{{cite journal |authors=Various |title=Science - Special Collection - Curiosity Rover on Mars |url=http://www.sciencemag.org/site/extra/curiosity/ |date=December 9, 2013 |journal=[[Science (journal)|Science]] |accessdate=December 9, 2013 }}</ref>
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| The [[European Space Agency]] is currently collaborating with the [[Russian Federal Space Agency]] (Roscosmos) and developing the [[ExoMars]] astrobiology rover, which is to be launched in 2018.<ref name='ESA signed'>{{cite news | title = ExoMars: ESA and Roscosmos set for Mars missions | date = 14 March 2013 | url = http://www.esa.int/Our_Activities/Space_Science/ExoMars_ESA_and_Roscosmos_set_for_Mars_missions | work = European Space Agency (ESA) | accessdate = 2013-03-14}}</ref>
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| ==Methodology==
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| === Planetary habitability ===
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| {{Main|Planetary habitability}}
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| When looking for life on other planets like the earth, some simplifying assumptions are useful to reduce the size of the task of the astrobiologist. One is to assume that the vast majority of life forms in our galaxy are based on [[Carbon-based life|carbon chemistries]], as are all life forms on Earth.<ref>{{cite web|url=http://library.thinkquest.org/C003763/index.php?page=interview07 |title= Polycyclic Aromatic Hydrocarbons: An Interview With Dr. Farid Salama |accessdate=2008-10-20 |year=2000 |work=Astrobiology magazine }}</ref> Carbon is well known for the unusually wide variety of [[molecule]]s that can be formed around it. Carbon is the [[Abundance of the chemical elements|fourth most abundant element]] in the universe and the energy required to make or break a bond is just at an appropriate level for building molecules which are not only stable, but also reactive. The fact that carbon atoms bond readily to other carbon atoms allows for the building of arbitrarily long and [[organic compound|complex molecules]].
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| The presence of liquid water is a useful assumption, as it is a common molecule and provides an excellent environment for the formation of complicated carbon-based molecules that could eventually lead to the emergence of life.<ref>{{cite web|url=http://www.bookrags.com/research/astrobiology-spsc-04/ |title=Astrobiology |accessdate=2008-10-20 |year=2006 |publisher=Macmillan Science Library: Space Sciences. }}</ref> Some researchers posit environments of [[ammonia]], or more likely, water-ammonia mixtures.<ref>{{cite web|url=http://www.astrobio.net/news/article2057.html |title=The Ammonia-Oxidizing Gene |accessdate=2008-10-20 |first=Penn State |date=19 August 2006 |publisher=Astrobiology Magazine }}</ref>
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| A third assumption is to focus on [[sun]]-like [[star]]s. This comes from the idea of [[planetary habitability]].<ref>{{cite web|url=http://www.solstation.com/habitable.htm |title=Stars and Habitable Planets |accessdate=2008-10-20 |year=2007 |publisher=Sol Company | archiveurl= http://web.archive.org/web/20081001194624/http://www.solstation.com/habitable.htm| archivedate= 1 October 2008 <!--DASHBot-->| deadurl= no}}</ref> Very big stars have relatively short lifetimes, meaning that life would not likely have time to evolve on [[planet]]s orbiting them. Very small stars provide so little heat and warmth that only planets in very close orbits around them would not be frozen solid, and in such close orbits these planets would be [[Tidal lock|tidally "locked"]] to the star.<ref>{{cite web|url=http://www.redorbit.com/news/display/?id=223364&source=r |title=M Dwarfs: The Search for Life is On |accessdate=2008-10-20 |date=29 August 2005 |publisher=Red Orbit & Astrobiology Magazine }}</ref> Without a thick [[atmosphere]], one side of the planet would be perpetually baked and the other perpetually frozen. In 2005, the question was brought back to the attention of the [[scientific community]], as the long lifetimes of [[red dwarf]]s could allow some biology on planets with thick atmospheres. This is significant, as red dwarfs are extremely common. (See [[Habitability of red dwarf systems]]).
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| It is estimated that 10% of the stars in our galaxy are sun-like; there are about a thousand such stars within 100 light-years of our [[Sun]]. These stars would be useful [[Project Phoenix (SETI)|primary targets]] for interstellar listening. Since Earth is the only planet known to harbor [[life]], there is no evident way to know if any of the simplifying assumptions are correct.
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| ===Communication attempts===
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| {{Main|Communication with extraterrestrial intelligence}}
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| [[File:Pioneer10-plaque tilt.jpg|right|thumb|The illustration on the [[Pioneer plaque]] ]]
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| Research on communication with extraterrestrial intelligence ([[Communication with extraterrestrial intelligence|CETI]]) focuses on composing and deciphering messages that could theoretically be understood by another technological civilization. Communication attempts by humans have included broadcasting mathematical languages, pictorial systems such as the [[Arecibo message]] and computational approaches to detecting and deciphering 'natural' language communication. The [[SETI]] program, for example, uses both [[radio telescope]]s and [[optical telescope]]s to search for deliberate signals from [[extraterrestrial intelligence]].
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| While some high-profile scientists, such as [[Carl Sagan]], have advocated the transmission of messages,<ref>Sagan, Carl. Communication with Extraterrestrial Intelligence. MIT Press, 1973, 428 pgs.</ref><ref>[http://www.lightspeedmagazine.com/nonfiction/you-never-get-a-seventh-chance-to-make-a-first-impression-an-awkward-history-of-our-space-transmissions/ An Awkward History of Our Space Transmissions]</ref> scientist [[Stephen Hawking]] has warned against it, suggesting that aliens might simply raid Earth for its resources and then move on.<ref>[http://www.timesonline.co.uk/tol/news/science/space/article7107207.ece Don’t talk to aliens, warns Stephen Hawking. (April 25, 2010)]</ref>
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| ===Elements of astrobiology===
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| ==== Astronomy ====
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| {{Main|Astronomy}}
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| [[Image:OGLE-2005-BLG-390Lb planet.jpg|thumb|right|200px|Artist's impression of the [[extrasolar planet]] [[OGLE-2005-BLG-390Lb]] orbiting its star 20,000 [[light-years]] from [[Earth]]; this planet was discovered with [[gravitational microlensing]].]]
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| [[Image:Telescope Kepler-NASA.jpeg|thumb|right|200px|The [[NASA]] [[Kepler mission]], launched in March 2009, searches for [[extrasolar planets]].]]
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| Most astronomy-related astrobiological research falls into the category of [[extrasolar planet]] (exoplanet) detection, the hypothesis being that if life arose on Earth, then it could also arise on other planets with similar characteristics. To that end, a number of instruments designed to detect Earth-sized exoplanets have been considered, most notably [[NASA]]'s [[Terrestrial Planet Finder]] (TPF) and [[European Space Agency|ESA's]] [[Darwin (ESA)|Darwin]] programs, both of which have been cancelled. Additionally, NASA has launched the [[Kepler mission]] in March 2009, and the [[French Space Agency]] has launched the [[COROT]] space mission in 2006.<ref>{{cite web|url=http://kepler.nasa.gov/ |title=Kepler Mission |accessdate=2008-10-20 |year=2008 |publisher=NASA | archiveurl= http://web.archive.org/web/20081031070350/http://kepler.nasa.gov/| archivedate= 31 October 2008 <!--DASHBot-->| deadurl= no}}</ref><ref>{{cite web|url=http://smsc.cnes.fr/COROT/ |title=The COROT space telescope |accessdate=2008-10-20 |date=2008-10-17 |publisher=CNES | archiveurl= http://web.archive.org/web/20081108130307/http://smsc.cnes.fr/COROT/| archivedate= 8 November 2008 <!--DASHBot-->| deadurl= no}}</ref> There are also several less ambitious ground-based efforts underway. (See [[exoplanet]]).
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| The goal of these missions is not only to detect Earth-sized planets, but also to directly detect light from the planet so that it may be studied [[spectroscopy|spectroscopically]]. By examining planetary spectra, it would be possible to determine the basic composition of an extrasolar planet's atmosphere and/or surface; given this knowledge, it may be possible to assess the likelihood of life being found on that planet. A NASA research group, the Virtual Planet Laboratory,<ref>{{cite web|url=http://vpl.astro.washington.edu/main/about_vpl.html |title=The Virtual Planet Laboratory |accessdate=2008-10-20 |year=2008 |publisher=NASA }}</ref> is using computer modeling to generate a wide variety of virtual planets to see what they would look like if viewed by TPF or Darwin. It is hoped that once these missions come online, their spectra can be cross-checked with these virtual planetary spectra for features that might indicate the presence of life. The [[photometry (astronomy)|photometry]] temporal variability of extrasolar planets may also provide clues to their surface and atmospheric properties.
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| An estimate for the number of planets with ''intelligent'' [[extraterrestrial life]] can be gleaned from the [[Drake equation]], essentially an equation expressing the probability of intelligent life as the product of factors such as the fraction of planets that might be habitable and the fraction of planets on which life might arise:<ref>{{cite web|url=http://www.setileague.org/general/drake.htm |title=What is the Drake Equation? |accessdate=2008-10-20 |last=Ford |first=Steve |date=August 1995 |publisher=SETI League | archiveurl= http://web.archive.org/web/20081029212425/http://www.setileague.org/general/drake.htm| archivedate= 29 October 2008 <!--DASHBot-->| deadurl= no}}</ref>
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| <math>N = R^{*} ~ \times ~ f_{p} ~ \times ~ n_{e} ~ \times ~ f_{l} ~ \times ~ f_{i} ~ \times ~ f_{c} ~ \times ~ L</math><br>
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| where, '''N''' = The number of communicative civilizations, '''R*''' = The rate of formation of suitable stars (stars such as our Sun), '''fp''' = The fraction of those stars with planets. (Current evidence indicates that planetary systems may be common for stars like the Sun), '''ne''' = The number of Earth-sized worlds per planetary system, '''fl''' = The fraction of those Earth-sized planets where life actually develops, '''fi''' = The fraction of life sites where intelligence develops, '''fc''' = The fraction of communicative planets (those on which electromagnetic communications technology develops), '''L''' = The "lifetime" of communicating civilizations.
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| However, whilst the rationale behind the equation is sound, it is unlikely that the equation will be constrained to reasonable error limits any time soon. The first term, Number of Stars, is generally constrained within a few orders of magnitude. The second and third terms, Stars with Planets and Planets with Habitable Conditions, are being evaluated for the sun's neighborhood. The problem of the formula is that it is not usable to emit [[hypothesis]] because it contains units that can never be verified. Drake originally formulated the equation merely as an agenda for discussion at the Green Bank conference,<ref>{{cite web|url=http://www.planetary.org/explore/topics/seti/seti_history_07.html|author=Amir Alexander|title=The Search for Extraterrestrial Intelligence: A Short History - Part 7: The Birth of the Drake Equation}}</ref> but some applications of the formula had been taken literally and related to simplistic or [[pseudoscientific]] arguments.<ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = 26 September 2006 | publisher = Biology Cabinet| archiveurl= http://web.archive.org/web/20101212184044/http://biocab.org/Astrobiology.html| archivedate= 12 December 2010 <!--DASHBot-->| deadurl= no}}</ref> Another associated topic is the [[Fermi paradox]], which suggests that if intelligent life is common in the [[universe]], then there should be obvious signs of it. This is the purpose of projects like [[SETI]], which tries to detect signs of radio transmissions from intelligent extraterrestrial civilizations.
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| Another active research area in astrobiology is [[planetary system]] formation. It has been suggested that the peculiarities of our [[Solar System]] (for example, the presence of [[Jupiter]] as a protective shield)<ref>{{cite web|url=http://www.europlanet-eu.org/demo/index.php?option=com_content&task=view&id=58&Itemid=999 |title=Jupiter: Friend or foe? |accessdate=2008-10-20 |last=Horner |first=Jonathan |coauthors=Barrie Jones |date=24 August 2007 |publisher=Europlanet }}</ref> may have greatly increased the probability of intelligent life arising on our planet.<ref>{{cite web|url=http://www.spaceref.com/news/viewsr.html?pid=3910 |title=The Role Of Astrobiology in Solar System Exploration |accessdate=2008-10-20 |last=Jakosky |first=Bruce |coauthors=David Des Marais, ''et al.'' |date=14 September 2001 |work=NASA |publisher=SpaceRef.com }}</ref><ref>{{cite web|url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1222 |title=Coming Soon: "Good" Jupiters |accessdate=2008-10-20 |last=Bortman |first=Henry |date=29 September 2004 |work=Astrobiology Magazine }}</ref> No firm conclusions have been reached so far.
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| ====Biology====
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| {{See also|Abiogenesis|Biology|Extremophile|List of interstellar and circumstellar molecules}}
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| [[Image:Blacksmoker in Atlantic Ocean.jpg|thumb|right|200px|[[Hydrothermal vent]]s are able to support [[extremophile|extremophile bacteria]] on [[Earth]] and may also support life in other parts of the cosmos.]]
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| Biology and chemistry, as opposed to physics, do not admit ideological contexts: either the biological phenomena are real, or they are abstract. Biologists cannot say that a process or phenomenon, by being mathematically possible, have to exist forcibly in the real nature. For biologists, the ground of speculations is well noticeable, and biologists specify what is speculative and what is not.<ref name=BC/>
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| Until the 1970s, [[life]] was believed to be entirely dependent on energy from the [[Sun]]. Plants on Earth's surface capture energy from sunlight to [[photosynthesis|photosynthesize]] sugars from carbon dioxide and water, releasing oxygen in the process, and are then eaten by oxygen-respiring animals, passing their energy up the [[food chain]]. Even life in the ocean depths, where sunlight cannot reach, was believed to obtain its nourishment either from consuming [[marine snow|organic detritus rained down from the surface waters]] or from eating animals that did.<ref name="smoker">{{cite web |title= Black Smokers and Giant Worms |author=Chamberlin, Sean |year=1999 |work=Fullerton College |url=http://www.courseworld.com/ocean/smokers.html |accessdate=11 February 2011 }}</ref> A world's ability to support life was thought to depend on its access to [[sunlight]]. However, in 1977, during an exploratory dive to the [[Galapagos Rift]] in the deep-sea exploration submersible ''[[DSV Alvin|Alvin]]'', scientists discovered colonies of [[giant tube worm]]s, [[clam]]s, [[crustacean]]s, [[mussel]]s, and other assorted creatures clustered around undersea volcanic features known as [[black smoker]]s.<ref name="smoker"/> These creatures thrive despite having no access to sunlight, and it was soon discovered that they comprise an entirely independent food chain. Instead of plants, the basis for this food chain is a form of [[bacterium]] that derives its energy from oxidization of reactive chemicals, such as [[hydrogen]] or [[hydrogen sulfide]], that bubble up from the Earth's interior. This [[chemosynthesis]] revolutionized the study of biology by revealing that life need not be sun-dependent; it only requires water and an energy gradient in order to exist.
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| [[Extremophiles]] (organisms able to survive in extreme environments) are a core research element for astrobiologists. Such organisms include [[Biota (ecology)|biota]] which are able to survive several kilometers below the ocean's surface near [[hydrothermal vent]]s and [[microbe]]s that thrive in highly acidic environments.<ref>{{cite web|url=http://www.livescience.com/animalworld/050207_extremophiles.html |title=Wild Things: The Most Extreme Creatures |accessdate=2008-10-20 |last=Carey |first=Bjorn |date=7 February 2005 |work=Live Science }}</ref> It is now known that extremophiles thrive in ice, boiling water, acid, the water core of nuclear reactors, salt crystals, toxic waste and in a range of other extreme habitats that were previously thought to be inhospitable for life.<ref name=Cavicchioli >{{cite journal|title=Extremophiles and the search for extraterrestrial life|journal=Astrobiology|date=Fall 2002 |first=R. |last=Cavicchioli |coauthors= |volume=2 |issue=3|pages=281–92 |pmid=12530238 |format=|doi=10.1089/153110702762027862 |bibcode = 2002AsBio...2..281C }}</ref> It opened up a new avenue in astrobiology by massively expanding the number of possible extraterrestrial habitats. Characterization of these organisms—their environments and their evolutionary pathways—is considered a crucial component to understanding how life might evolve elsewhere in the universe. According to astrophysicist Dr. Steinn Sigurdsson, "There are viable bacterial spores that have been found that are 40 million years old on Earth - and we know they're very hardened to radiation."<ref>{{cite web|author=BBC Staff |title=Impacts 'more likely' to have spread life from Earth |url=http://www.bbc.co.uk/news/science-environment-14637109 |date=23 August 2011 |publisher=[[BBC]] |accessdate=2011-08-24}}</ref> Some organisms able to withstand exposure to the vacuum and radiation of space include the lichen fungi ''[[Rhizocarpon geographicum]]'' and ''[[Xanthoria elegans]]'',<ref>[http://www.highbeam.com/doc/1P3-979261711.html Article: Lichens survive in harsh environment of outer space]</ref> the bacterium ''[[Bacillus safensis]]'',<ref name=ThePlanetaryReport >The Planetary Report, Volume XXIX, number 2, March/April 2009, "We make it happen! Who will survive? Ten hardy organisms selected for the LIFE project, by Amir Alexander</ref> ''[[Deinococcus radiodurans]]'',<ref name=ThePlanetaryReport /> ''[[Bacillus subtilis]]'',<ref name=ThePlanetaryReport /> yeast ''[[Saccharomyces cerevisiae]]'',<ref name=ThePlanetaryReport /> seeds from ''[[Arabidopsis thaliana]]'' ('mouse-ear cress'),<ref name=ThePlanetaryReport /> as well as the invertebrate animal [[Tardigrade]].<ref name=ThePlanetaryReport /> On 29 April 2013, French scientists, funded by [[NASA]], reported that, during [[spaceflight]], [[microbes]] (like [[Pseudomonas aeruginosa]]) seem to adapt to the [[space environment]] in ways "not observed on Earth" and can increase in "[[virulence]]".<ref name="PLos-20130429">{{cite journal |author=Tengra FK et al. |title=Spaceflight Promotes Biofilm Formation by Pseudomonas aeruginosa |url=http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0062437 |date=29 April 2013 |journal=[[PLOS ONE]] |volume=8 |issue=4 |page=e6237 |doi=10.1371/journal.pone.0062437 |accessdate=5 July 2013 |bibcode = 2013PLoSO...862437K }}</ref> On 27 June 2011, it was reported that a new [[Escherichia coli|E. coli]] bacterium was produced from an engineered [[DNA]] in which approximately 90% of its [[thymine]] was replaced with the synthetic building block 5-chlorouracil, a substance "toxic to other organisms".<ref>{{cite journal |last1=Marlière |first1=Philippe |last2=Patrouix |first2=Julien |last3=Döring |first3=Volker |last4=Herdewijn |first4=Piet |last5=Tricot |first5=Sabine |last6=Cruveiller |first6=Stéphane |last7=Bouzon |first7=Madeleine |last8=Mutzel |first8=Rupert |title=Chemical Evolution of a Bacterium's Genome |journal=[[Angewandte Chemie]] |date=27 June 2011 |doi=10.1002/anie.201100535 |volume=50 |issue=31 |pages=7109 }}</ref><ref>{{cite web |author=Staff |title=Bacterium Engineered With DNA in Which Thymine Is Replaced by Synthetic Building Block |date=29 June 2011 |url=http://www.sciencedaily.com/releases/2011/06/110628132438.htm |publisher=[[Science Daily]] |accessdate=2011-06-30 }}</ref>
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| Jupiter's moon, [[Europa (moon)|Europa]],<ref name=Cavicchioli/><ref>{{cite web |title= Jupiter's Moon Europa Suspected Of Fostering Life|url=http://www.unisci.com/stories/20021/0211026.htm|author=| work=Daily University Science News|year=2002 |accessdate=2009-08-08 |format=PDF}}</ref><ref name=galileo /><ref>{{cite journal|title=Extremophiles and the search for extraterrestrial life|journal=Astrobiology|date=Fall 2002|first=R. |last=Cavicchioli|coauthors=|volume=2|issue=3|pages=281–92.|pmid=12530238|format=|doi=10.1089/153110702762027862 |bibcode = 2002AsBio...2..281C}}</ref><ref>{{cite news | first=Leonard | last=David | coauthors= |title=Europa Mission: Lost In NASA Budget | date=7 February 2006 |publisher=Space.com | url =http://www.space.com/news/060207_europa_budget.html | work = | pages = |accessdate = 2009-08-08 | language = }}</ref><ref>{{cite news | first= |last= | coauthors= | title=Clues to possible life on Europa may lie buried in Antarctic ice | date=5 March 1998 | publisher=NASA | url =http://science.nasa.gov/newhome/headlines/ast05mar98_1.htm | work =Marshal Space Flight Center | pages = | accessdate = 2009-08-08 | language =| archiveurl= http://web.archive.org/web/20090731015842/http://science.nasa.gov/newhome/headlines/ast05mar98_1.htm| archivedate= 31 July 2009 <!--DASHBot-->| deadurl= no}}</ref> and Saturn's moon, [[Enceladus (moon)|Enceladus]],<ref>{{cite journal |last1=Lovett |first1=Richard A. |title=Enceladus named sweetest spot for alien life|url=http://www.nature.com/news/2011/110531/full/news.2011.337.html|date=31 May 2011 |publisher=[[Nature (journal)|Nature]]|accessdate=2011-06-03 |doi=10.1038/news.2011.337 |journal=Nature}}</ref><ref name="Kazan" /> are now considered the most likely locations for extant extraterrestrial life in the [[solar system]].
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| The origin of life, known as [[abiogenesis]], distinct from the [[Evolution#Evolution of life|evolution of life]], is another ongoing field of research. [[Oparin]] and [[J. B. S. Haldane|Haldane]] postulated that the conditions on the early Earth were conducive to the formation of [[organic compound]]s from [[inorganic chemistry|inorganic elements]] and thus to the formation of many of the chemicals common to all forms of life we see today. The study of this process, known as prebiotic chemistry, has made some progress, but it is still unclear whether or not life could have formed in such a manner on Earth. The alternative hypothesis of [[panspermia]] is that the first elements of life may have formed on another planet with even more favorable conditions (or even in interstellar space, asteroids, etc.) and then have been carried over to Earth by a variety of means. Somewhat related to such a hypothesis, [[NIH|NIH scientists]] reported [[Panspermia#Complexity|studies]] that [[life]] began {{val|9.7|2.5}} billion years ago, billions of years before the [[Earth]] was formed, based on extrapolating the "genetic complexity of organisms" [from "major phylogenetic lineages"] to earlier times.<ref name="arXiv-20130328">{{cite journal |last1=Sharov |first1=Alexei A. |last2=Gordon|first2=Richard |title=Life Before Earth |url=http://arxiv.org/ftp/arxiv/papers/1304/1304.3381.pdf |date=28 March 2013 |journal=[[arXiv]] |arxiv=1304.3381v1 |accessdate=16 April 2013 }}</ref><ref name="NIH-20060612">{{cite journal |last=Sharov |first=Alexei A. |title=Genome increase as a clock for the origin and evolution of life |journal=[[Biology Direct]] |volume=1 |pages=1–17 |date=12 June 2006 |issue= |doi=10.1186/1745-6150-1-17|pmc=1526419}}</ref> (also see [[Abiogenesis#Coenzyme world]])
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| In October 2011, scientists found that the [[cosmic dust]] permeating the universe contains complex [[organic compound|organic]] matter ("amorphous organic solids with a mixed [[aromatic]]-[[aliphatic]] structure") that could be created naturally, and rapidly, by [[stars]].<ref name="Space-20111026">{{cite web |last=Chow |first=Denise |title=Discovery: Cosmic Dust Contains Organic Matter from Stars |url=http://www.space.com/13401-cosmic-star-dust-complex-organic-compounds.html |date=26 October 2011 |publisher=[[Space.com]] |accessdate=2011-10-26 }}</ref><ref name="ScienceDaily-20111026">{{cite web |author=[[ScienceDaily]] Staff |title=Astronomers Discover Complex Organic Matter Exists Throughout the Universe |url=http://www.sciencedaily.com/releases/2011/10/111026143721.htm |date=26 October 2011 |publisher=[[ScienceDaily]] |accessdate=2011-10-27 }}</ref><ref name="Nature-20111026">{{cite journal |last1=Kwok |first1=Sun |last2=Zhang |first2=Yong |title=Mixed aromatic–aliphatic organic nanoparticles as carriers of unidentified infrared emission features |date=26 October 2011 |journal=[[Nature (journal)|Nature]] |doi=10.1038/nature10542 |bibcode = 2011Natur.479...80K |volume=479 |issue=7371 |pages=80–3 |pmid=22031328}}</ref> As one of the scientists noted, "[[Coal]] and [[kerogen]] are products of life and it took a long time for them to form ... How do stars make such complicated organics under seemingly unfavorable conditions and [do] it so rapidly?"<ref name="Space-20111026"/> Further, the scientist suggested that these compounds may have been related to the development of life on earth and said that, "If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life."<ref name="Space-20111026"/> In September 2012, [[NASA|NASA scientists]] reported that [[polycyclic aromatic hydrocarbons|polycyclic aromatic hydrocarbons (PAHs)]], subjected to [[Interstellar medium|interstellar medium (ISM)]] conditions, are transformed, through [[hydrogenation]], [[oxygenation (environmental)|oxygenation]] and [[hydroxylation]], to more complex [[organic compound|organics]] - "a step along the path toward [[amino acid]]s and [[nucleotide]]s, the raw materials of [[protein]]s and [[DNA]], respectively".<ref name="Space-20120920">{{cite web |author=Staff |title=NASA Cooks Up Icy Organics to Mimic Life's Origins |url=http://www.space.com/17681-life-building-blocks-nasa-organic-molecules.html |date=September 20, 2012 |publisher=[[Space.com]] |accessdate=September 22, 2012 }}</ref><ref name="AJL-20120901">{{cite journal |last1=Gudipati |first1=Murthy S. |last2=Yang |first2=Rui |title=In-Situ Probing Of Radiation-Induced Processing Of Organics In Astrophysical Ice Analogs—Novel Laser Desorption Laser Ionization Time-Of-Flight Mass Spectroscopic Studies |url=http://iopscience.iop.org/2041-8205/756/1/L24 |date=September 1, 2012 |journal=[[The Astrophysical Journal Letters]] |volume=756 |doi=10.1088/2041-8205/756/1/L24 |accessdate=September 22, 2012 |issue=1 |pages=L24 |bibcode = 2012ApJ...756L..24G }}</ref> Further, as a result of these transformations, the PAHs lose their [[Spectroscopy|spectroscopic signature]] which could be one of the reasons "for the lack of PAH detection in [[interstellar ice]] [[Cosmic dust#Dust grain formation|grains]], particularly the outer regions of cold, dense clouds or the upper molecular layers of [[protoplanetary disks]]."<ref name="Space-20120920" /><ref name="AJL-20120901" />
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| On August 29, 2012, and in a world first, astronomers at [[Copenhagen University]] reported the detection of a specific sugar molecule, [[glycolaldehyde]], in a distant star system. The molecule was found around the [[protostar|protostellar]] binary ''IRAS 16293-2422'', which is located 400 light years from Earth.<ref name="NG-20120829">{{cite journal|title=Sugar Found In Space|journal=National Geographic |last=Than |first=Ker |date=August 29, 2012 |url=http://news.nationalgeographic.com/news/2012/08/120829-sugar-space-planets-science-life/ |accessdate=August 31, 2012 }}</ref><ref name="AP-20120829">{{cite web |author=Staff |title=Sweet! Astronomers spot sugar molecule near star |url=http://apnews.excite.com/article/20120829/DA0V31D80.html |date=August 29, 2012 |publisher=[[AP News]] |accessdate=August 31, 2012 }}</ref> Glycolaldehyde is needed to form [[ribonucleic acid]], or [[RNA]], which is similar in function to [[DNA]]. This finding suggests that complex organic molecules may form in stellar systems prior to the formation of planets, eventually arriving on young planets early in their formation.<ref>{{cite journal|title=Detection of the simplest sugar, glycolaldehyde, in a solar-type protostar with ALMA|author=Jørgensen, J. K.|coauthors=Favre, C.; Bisschop, S.; Bourke, T.; Dishoeck, E.; Schmalzl, M.|version=eprint |year=2012|url=http://www.eso.org/public/archives/releases/sciencepapers/eso1234/eso1234a.pdf|bibcode=2012ApJ...757L...4J|last2=Favre|last3=Bisschop|last4=Bourke|last5=Van Dishoeck|last6=Schmalzl|volume=757|pages=L4|journal=The Astrophysical Journal Letters|doi=10.1088/2041-8205/757/1/L4|arxiv = 1208.5498 }}</ref>
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| ====Astroecology====
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| {{Main|Astroecology}}
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| [[Astroecology]] concerns the interactions of life with space environments and resources, in [[planets]], [[asteroids]] and [[comets]]. On a larger scale, astroecology concerns resources for life about [[stars]] in the [[galaxy]] through the cosmological future. Astroecology attempts to quantify future life in space, addressing this area of astrobiology.
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| Experimental astroecology investigates resources in planetary soils, using actual space materials in [[meteorites]].<ref name = "AstroecologyIcarus2002">{{Cite journal | last = Mautner | first = Michael N. | title = Planetary bioresources and astroecology. 1. Planetary microcosm bioessays of Martian and meteorite materials: soluble electrolytes, nutrients, and algal and plant responses|journal = Icarus |volume = 158 | pages = 72–86 | year = 2002 | doi=10.1006/icar.2002.6841 | bibcode=2002Icar..158...72M | url = http://www.astro-ecology.com/PDFBioresourcesIcarus2002Paper.pdf | pmid=12449855}}</ref> The results suggest that Martian and carbonaceous chondrite materials can support [[bacteria]], [[algae]] and plant (asparagus, potato) cultures, with high soil fertilities. The results support that life could have survived in early aqueous asteroids and on similar materials imported to Earth by dust, comets and meteorites, and that such asteroid materials can be used as soil for future space colonies.<ref name = "AstroecologyIcarus2002" /><ref name = "AstroecologyAstrobiology2002">{{Cite journal | last = Mautner | first = Michael N. | title = Planetary resources and astroecology. Planetary microcosm models of asteroid and meteorite interiors: electrolye solutions and microbial growth. Implications for space populations and panspermia |journal = Astrobiology |volume = 2 | pages = 59–76 | year = 2002 | doi=10.1006/icar.2002.6841 | bibcode=2002Icar..158...72M | url = http://www.astro-ecology.com/PDFBioresourcesIcarus2002Paper.pdf | pmid = 12449855 | issue = 1 }}</ref>
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| On the largest scale, cosmoecology concerns life in the universe over cosmological times. The main sources of energy may be red giant stars and white and red dwarf stars, sustaining life for 10<sup>20</sup> years.<ref name = "AstroecologyIcarus2002" /><ref name = "AstroecologyIcarus2002" /><ref name = "AstroecologyJBIS2005">{{Cite journal|last = Mautner |first = Michael N. | title = Life in the cosmological future: Resources, biomass and populations | journal = Journal of the British Interplanetary Society | year = 2005 | volume = 58 | pages = 167–180 | url=http://www.astro-ecology.com/PDFCosmologyJBIS2005Paper.pdf|bibcode = 2005JBIS...58..167M }}</ref> Astroecologists suggest that their mathematical models may quantify the immense potential amounts of future life in space, allowing a comparable expansion in biodiversity, potentially leading to diverse intelligent life-forms.<ref>{{Cite book | last = Mautner | first = Michael N. | title = Seeding the Universe with Life: Securing Our Cosmological Future | publisher = Legacy Books (www.amazon.com) | location = Washington D. C. | year = 2000 | isbn = 0-476-00330-X | url = http://www.astro-ecology.com/PDFSeedingtheUniverse2005Book.pdf }}</ref>
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| ==== Astrogeology ====
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| {{Main|Geology of solar terrestrial planets}}
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| [[Geology of solar terrestrial planets|Astrogeology]] is a [[planetary science]] discipline concerned with the [[geology]] of the [[celestial bodies]] such as the [[planet]]s and their [[moon]]s, [[asteroid]]s, [[comet]]s, and [[meteorite]]s. The information gathered by this discipline allows the measure of a [[planet]]'s or a [[natural satellite]]'s potential to develop and sustain [[life]], or [[planetary habitability]].
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| An additional discipline of astrogeology is [[geochemistry]], which involves study of the [[chemistry|chemical]] composition of the [[Earth]] and other [[planet]]s, chemical processes and reactions that govern the composition of [[Rock (geology)|rock]]s and [[soil]]s, the cycles of matter and energy and their interaction with the [[hydrosphere]] and the [[atmosphere]] of the planet. Specializations include [[cosmochemistry]], [[biochemistry]] and [[organic geochemistry]].
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| The [[fossil record]] provides the oldest known evidence for [[life on Earth]].<ref>{{cite web|url=http://pubs.usgs.gov/gip/fossils/succession.html |title=Fossil SUccession |accessdate=2008-10-20 |date=14 August 1997 |publisher=U.S. Geological Survey | archiveurl= http://web.archive.org/web/20081014190106/http://pubs.usgs.gov/gip/fossils/succession.html| archivedate= 14 October 2008 <!--DASHBot-->| deadurl= no}}</ref> By examining the fossil evidence, [[paleontologists]] are able to better understand the types of organisms that arose on the early Earth. Some regions on Earth, such as the [[Pilbara]] in [[Western Australia]] and the [[McMurdo Dry Valleys]] of Antarctica, are also considered to be geological analogs to regions of Mars, and as such, might be able to provide clues on how to search for past [[Life on Mars (planet)|life on Mars]].
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| Consistent with the above, the earliest evidence for [[life on Earth]] are [[graphite]] found to be [[Biogenic substance|biogenic]] in 3.7 billion-year-old [[Metasediment|metasedimentary rocks]] discovered in [[Western Greenland]]<ref name="NG-20131208">{{cite web |url =http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2025.html|authors= Yoko Ohtomo, Takeshi Kakegawa, Akizumi Ishida, Toshiro Nagase, Minik T. Rosing| title =Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks |publisher =''[[Nature Geoscience]]''|doi=10.1038/ngeo2025|date=8 December 2013|accessdate =9 Dec 2013 }}</ref> and [[microbial mat]] [[fossils]] found in 3.48 billion-year-old [[sandstone]] discovered in [[Western Australia]].<ref name="AP-20131113">{{cite news |last=Borenstein |first=Seth|title=Oldest fossil found: Meet your microbial mom|url=http://apnews.excite.com/article/20131113/DAA1VSC01.html |date=13 November 2013 |work=[[AP News]]|accessdate=15 November 2013 }}</ref><ref name="AST-20131108">{{cite journal |last1=Noffke|first1=Nora|last2=Christian |first2=Daniel |last3=Wacey |first3=David |last4=Hazen |first4=Robert M.|title=Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia|url=http://online.liebertpub.com/doi/abs/10.1089/ast.2013.1030 |date=8 November 2013 |journal=[[Astrobiology (journal)]] |doi=10.1089/ast.2013.1030 |accessdate=15 November 2013 }}</ref>
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| ==Life in the Solar System==
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| {{See also|Life on Mars (planet){{!}}Life on Mars|Life on Europa|Life on Titan|Hypothetical types of biochemistry}}
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| [[Image:PIA01130 Interior of Europa.jpg|thumb|200px|right|[[Europa (moon)|Europa]], due to the ocean that exists under its icy surface, might host some form of [[bacteria|microbial life]].]]
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| People have long speculated about the possibility of life in settings other than Earth, however, speculation on the nature of life elsewhere often has paid little heed to constraints imposed by the nature of biochemistry.<ref name='Pace'>{{cite journal|title=The universal nature of biochemistry|journal=Proceedings of the National Academy of Sciences of the USA|date=30 January 2001|first=Norman R.|last=Pace|coauthors=|volume=98|issue=3|pages=805–808 |id= |url=http://www.pnas.org/content/98/3/805.full|format=|accessdate=2010-03-20|pmid=11158550|doi=10.1073/pnas.98.3.805|pmc=33372 |bibcode = 2001PNAS...98..805P }}</ref> The likelihood that life throughout the universe is probably carbon-based is encouraged by the fact that carbon is one of the most abundant of the higher elements. Only two of the natural atoms, [[carbon]] and [[silicon]], are known to serve as the backbones of molecules sufficiently large to carry biological information. As the structural basis for life, one of carbon's important features is that unlike silicon it can readily engage in the formation of chemical bonds with many other atoms, thereby allowing for the chemical versatility required to conduct the reactions of biological metabolism and propagation.
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| The various organic functional groups, composed of hydrogen, oxygen, nitrogen, phosphorus, sulfur, and a host of metals, such as iron, magnesium, and zinc, provide the enormous diversity of chemical reactions necessarily catalyzed by a living organism. Silicon, in contrast, interacts with only a few other atoms, and the large silicon molecules are monotonous compared with the combinatorial universe of organic macromolecules.<ref name=BC/><ref name='Pace'/> Indeed, it seems likely that the basic building blocks of life anywhere will be similar to our own, in the generality if not in the detail.<ref name='Pace'/> Although terrestrial life and life that might arise independently of Earth are expected to use many similar, if not identical, building blocks, they also are expected to have some biochemical qualities that are unique. If life has had a comparable impact elsewhere in the solar system, the relative abundances of chemicals key for its survival - whatever they may be - could betray its presence. Whatever extraterrestrial life may be, its tendency to chemically alter its environment might just give it away.<ref>{{cite news | first = Michael Marshall | title = Telltale chemistry could betray ET | date = 21 January 2011 | url = http://www.newscientist.com/article/mg20927962.700-telltale-chemistry-could-betray-et.html | work = New Scientists | accessdate = 2011-01-22}}</ref>
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| Thought on where in the Solar System life might occur was limited historically by the belief that life relies ultimately on light and warmth from the Sun and, therefore, is restricted to the surfaces of planets.<ref name='Pace'/> The three most likely candidates for life in the Solar System are the planet [[Mars]], the Jovian moon [[Europa (moon)|Europa]], and Saturn's moon [[Titan (moon)|Titan]].<ref name=Europa>{{cite web|url=http://people.msoe.edu/~tritt/sf/europa.life.html |title=Possibility of Life on Europa |accessdate=2008-10-20 |last=Tritt |first=Charles S. |year=2002 |publisher=MilwaukeeSchool of Engineering }}</ref><ref name=EuroUpdate>{{cite web|url=http://www.planetary.org/programs/projects/explore_europa/update_12142005.html |title=Projects: Europa Mission Campaign |accessdate=2008-10-20 |last=Friedman |first=Louis |date=14 December 2005 |publisher=The Planetary Society | archiveurl= http://web.archive.org/web/20080920110348/http://www.planetary.org/programs/projects/explore_europa/update_12142005.html| archivedate= 20 September 2008 <!--DASHBot-->| deadurl= no}}</ref><ref>{{cite web|url=http://www.space.com/news/europa_story_991109.html |title=Move Over Mars -- Europa Needs Equal Billing |accessdate=2008-10-20 |last=David |first=Leonard |date=10 November 1999 |publisher=Space.com }}</ref><ref>{{cite web|url=http://www.space.com/businesstechnology/070228_tw_mars_massspec.html |title=New Instrument Designed to Sift for Life on Mars |accessdate=2008-10-20 |last=Than |first=Ker |date=28 February 2007 |publisher=Space.com }}</ref><ref name="Titan1">{{cite news | first=Ker | last=Than | coauthors= | title=Scientists Reconsider Habitability of Saturn's Moon | date=13 September 2005 | publisher= | url =http://www.space.com/1544-scientists-reconsider-habitability-saturn-moon.html | work =Science.com | pages = | accessdate = 11 February 2011 | language = }}</ref> More recently, Saturn's moon [[Enceladus (moon)|Enceladus]] may be considered a likely candidate as well.<ref name="Kazan">{{cite web|last1=Kazan |first1=Casey |title=Saturn's Enceladus Moves to Top of "Most-Likely-to-Have-Life" List|url=http://www.dailygalaxy.com/my_weblog/2011/06/saturns-enceladus-moves-to-top-of-most-likely-to-have-life-list.html|date= 2 June 2011 |publisher=The Daily Galaxy|accessdate=2011-06-03}}</ref><ref name="Lovett">{{cite journal |last1=Lovett |first1=Richard A. |title=Enceladus named sweetest spot for alien life |url=http://www.nature.com/news/2011/110531/full/news.2011.337.html |date=31 May 2011 |publisher=[[Nature (journal)|Nature]] |accessdate=2011-06-03|doi=10.1038/news.2011.337 |journal=Nature}}</ref> This speculation of likely candidates of life is primarily based on the fact that (in the cases of Mars and Europa) the [[List of planetary bodies|planetary bodies]] may have liquid water, a molecule essential for life as we know it, for its use as a [[solvent]] in cells.<ref name="autogenerated1"/>
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| Water on Mars is found in its polar ice caps, and newly carved gullies recently observed on [[Mars]] suggest that liquid water may exist, at least transiently, on the planet's surface.<ref>{{cite news | first= | last= | coauthors= | title=NASA Images Suggest Water Still Flows in Brief Spurts on Mars | year=2006 | publisher=NASA | url =http://www.nasa.gov/mission_pages/mars/news/mgs-20061206.html | work = | pages = | accessdate = 2008-10-20 | language = | archiveurl= http://web.archive.org/web/20081016211222/http://www.nasa.gov/mission_pages/mars/news/mgs-20061206.html| archivedate= 16 October 2008 <!--DASHBot-->| deadurl= no}}</ref><ref>{{cite news | first= | last= | coauthors= | title=Water ice in crater at Martian north pole | date=28 July 2005 | publisher=European Space Agency | url =http://www.esa.int/SPECIALS/Mars_Express/SEMGKA808BE_0.html | work = | pages = | accessdate = 2008-10-20 | language = | archiveurl= http://web.archive.org/web/20080923103534/http://www.esa.int/SPECIALS/Mars_Express/SEMGKA808BE_0.html| archivedate= 23 September 2008 <!--DASHBot-->| deadurl= no}}</ref> At the Martian low temperatures and low pressure, liquid water is likely to be highly saline.<ref>{{cite journal|title=Martian Water: Are There Extant Halobacteria on Mars?|journal=Astrobiology|date=1 June 2001|first=Geoffrey A.|last=Landis|coauthors=|volume=1|issue=2|pages=161–164|doi= 10.1089/153110701753198927|url=http://www.liebertonline.com/doi/abs/10.1089/153110701753198927?prevSearch=allfield%3A%28Halobacteria+on+Mars%29|format=|accessdate=2008-10-20|pmid=12467119 |bibcode = 2001AsBio...1..161L }}</ref> As for Europa, liquid water likely exists beneath the moon's icy outer crust.<ref name=galileo >{{cite news | first=Maia | last=Weinstock | coauthors= | title=Galileo Uncovers Compelling Evidence of Ocean On Jupiter's Moon Europa | date=24 August 2000 | publisher= | url =http://www.space.com/scienceastronomy/solarsystem/europa_ocean_000824.html | work =Space.com | pages = | accessdate = 2008-10-20 | language = }}</ref><ref name=Europa /><ref name=EuroUpdate /> This water may be warmed to a liquid state by volcanic vents on the ocean floor (an especially intriguing theory considering the various types of extremophiles that live near Earth's volcanic vents), but the primary source of heat is probably [[tidal heating]].<ref>{{cite news | first=Karl | last=Kruszelnicki | coauthors= | title=Life on Europa, Part 1 | date=5 November 2001 | publisher=ABC Science | url =http://www.abc.net.au/science/articles/2001/11/05/94459.htm?site=science/greatmomentsinscience | work = | pages = | accessdate = 2008-10-20 | language = }}</ref> On December 11, 2013, NASA reported the detection of "[[Clay minerals|clay-like minerals]]" (specifically, [[phyllosilicates]]), often associated with [[organic materials]], on the icy crust of [[Europa (moon)|Europa]].<ref name="NASA-20131211">{{cite web |last=Cook |first=Jia-Rui c. |title=Clay-Like Minerals Found on Icy Crust of Europa |url=http://www.jpl.nasa.gov/news/news.php?release=2013-362 |date=December 11, 2013 |work=[[NASA]] |accessdate=December 11, 2013 }}</ref> The presence of the minerals may have been the result of a collision with an [[asteroid]] or [[comet]] according to the scientists.<ref name="NASA-20131211" />
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| Another [[List of planetary bodies|planetary body]] that could potentially sustain extraterrestrial life is [[Saturn]]'s largest moon, [[Titan (moon)|Titan]].<ref name="Titan1"/> Titan has been described as having conditions similar to those of early Earth.<ref>{{cite news | first= | last= | coauthors= | title=Titan: Life in the Solar System? | date= | publisher= | url =http://www.bbc.co.uk/science/space/life/looking/titan.shtml | work =BBC - Science & Nature | pages = | accessdate = 2008-10-20 | language = }}</ref> On its surface, scientists have discovered the first liquid lakes outside of Earth, but they seem to be composed of [[ethane]] and/or [[methane]], not water.<ref>{{cite news | first=Robert Roy | last=Britt | coauthors= | title=Lakes Found on Saturn's Moon Titan | date=28 July 2006 | publisher= | url =http://www.space.com/scienceastronomy/060728_titan_lake.html | work =Space.com | pages = | accessdate = 2008-10-20 | language = | archiveurl= http://web.archive.org/web/20081004201650/http://www.space.com/scienceastronomy/060728_titan_lake.html| archivedate= 4 October 2008 <!--DASHBot-->| deadurl= no}}</ref> After Cassini data was studied, it was reported on March 2008 that Titan may also have an underground ocean composed of liquid [[water]] and [[ammonia]].<ref>{{cite news | first=Richard A. | last=Lovett | coauthors= | title=Saturn Moon Titan May Have Underground Ocean | date=20 March 2008 | publisher= | url =http://news.nationalgeographic.com/news/2008/03/080320-titan-ocean.html | work =National Geographic News | pages = | accessdate = 2008-10-20 | language = | archiveurl= http://web.archive.org/web/20080924193047/http://news.nationalgeographic.com/news/2008/03/080320-titan-ocean.html| archivedate= 24 September 2008 <!--DASHBot-->| deadurl= no}}</ref> Additionally, Saturn's moon [[Enceladus (moon)|Enceladus]] may have an ocean below its icy surface<ref>{{cite news | author = | title = Saturn moon 'may have an ocean'
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| | date = 2006-03-10 | work = [[BBC News]] | url = http://news.bbc.co.uk/2/hi/science/nature/4790126.stm
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| | accessdate = 2008-08-05 }}</ref> and, according to NASA scientists in May 2011, "is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it".<ref name="Kazan"/><ref name="Lovett"/>
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| On 26 April 2012, scientists reported that [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of [[photosynthesis|photosynthetic activity]] within the [[simulation|simulation time]] of 34 days under [[Life on Mars (planet)|Martian conditions]] in the Mars Simulation Laboratory (MSL) maintained by the [[German Aerospace Center]] (DLR).<ref name="Skymania-20120426">{{cite web |last=Baldwin |first=Emily |title=Lichen survives harsh Mars environment |url=http://www.skymania.com/wp/2012/04/lichen-survives-harsh-martian-setting.html |date=26 April 2012 |publisher=Skymania News |accessdate=27 April 2012 }}</ref><ref name="EGU-20120426">{{cite web |last1=de Vera |first1=J.-P. |last2=Kohler |first2=Ulrich |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |url=http://media.egu2012.eu/media/filer_public/2012/04/05/10_solarsystem_devera.pdf |date=26 April 2012 |publisher=[[European Geosciences Union]] |accessdate=27 April 2012 }}</ref> In June, 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of [[Life on Mars (planet)|life on Mars]].<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |url=http://www.pnas.org/content/109/25/9750.abstract |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |accessdate=June 27, 2012 |bibcode = 2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web|author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H<sub>2</sub>/CH<sub>4</sub> ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet t Boötis b |url=http://www.nature.com/nature/journal/v486/n7404/full/nature11161.html?WT.ec_id=NATURE-20120628 |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |accessdate=June 28, 2012 |arxiv = 1206.6109 |bibcode = 2012Natur.486..502B |issue=7404 }}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref>
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| == Rare Earth hypothesis ==
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| {{Main|Rare Earth hypothesis}}
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| This hypothesis states that based on astrobiological findings, multi-cellular life forms found on Earth may actually be more of a rarity than scientists initially assumed. It provides a possible answer to the Fermi paradox which suggests, "If extraterrestrial aliens are common, why aren't they obvious?" It is apparently in opposition to the [[principle of mediocrity]], assumed by famed astronomers [[Frank Drake]], [[Carl Sagan]], and others. The Principle of Mediocrity suggests that life on Earth is not exceptional, but rather that life is more than likely to be found on innumerable other worlds.
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| The [[anthropic principle]] states that fundamental laws of the universe work specifically in a way that life would be possible. The anthropic principle supports the Rare Earth Hypothesis by arguing the overall elements that are needed to support life on Earth are so fine-tuned that it is nearly impossible for another just like it to exist by random chance (note that these terms are used by scientists in a different way from the vernacular conception of them). However, [[Stephen Jay Gould]] compared the claim that the universe is fine-tuned for the benefit of our kind of life to saying that sausages were made long and narrow so that they could fit into modern [[hot dog bun]]s, or saying that ships had been invented to house [[barnacle]]s.<ref>{{cite conference| last=Gould| first=Stephen Jay| year =1998| title=Clear Thinking in the Sciences |booktitle=Lectures at Harvard University}}</ref><ref>{{cite book| last=Gould| first=Stephen Jay | year= 2002 | title=Why People Believe Weird Things: Pseudoscience, Superstition, and Other Confusions of Our Time}}</ref>
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| ==Research==
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| {{see also|Extraterrestrial life|Life#Extraterrestrial life}}
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| The systematic search for possible life outside of Earth is a valid multidisciplinary scientific endeavor.<ref>[http://astrobiology.nasa.gov/nai/ NASA Astrobiology Institute]</ref> The [[University of Glamorgan]], UK, started just such a degree in 2006,<ref name="case.glam.ac.uk"/> and the American government funds the [[NASA Astrobiology Institute]]. However, characterization of non-Earth life is unsettled; hypotheses and predictions as to its existence and origin vary widely, but at the present, the development of theories to inform and support the exploratory search for life may be considered astrobiology's most concrete practical application.
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| [[Biologist]] [[Jack Cohen (scientist)|Jack Cohen]] and [[mathematician]] [[Ian Stewart (mathematician)|Ian Stewart]], amongst others, consider '''[[xenobiology]]''' separate from astrobiology. Cohen and Stewart stipulate that astrobiology is the search for Earth-like life outside of our solar system and say that xenobiologists are concerned with the possibilities open to us once we consider that life need not be carbon-based or oxygen-breathing, so long as it has the defining [[characteristics of life]]. (See [[carbon chauvinism]]).
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| === Research outcomes ===
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| [[Image:951 Gaspra.jpg|thumb|right|220px|Asteroid(s) may have transported life to [[Earth]].]]
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| {{As of|2014}}, no evidence of extraterrestrial life has been identified. Examination of the [[Allan Hills 84001]] meteorite, which was recovered in [[Antarctica]] in 1984 and believed to have originated from [[Mars]], is thought by [[David S. McKay|David McKay]], Chief Scientist for Astrobiology at [[NASA]]'s [[Johnson Space Center]], as well as other scientists, to contain [[Fossil#Microfossils|microfossils]] of extraterrestrial origin; this interpretation is controversial.<ref name=disbelief>{{cite web |title=Experts: Little Evidence of Life on Mars | url=http://dsc.discovery.com/news/2006/08/08/marslife_spa.html?category=space&guid=20060808100030 |last=Crenson |first=Matt |publisher=[[Associated Press]] (on [http://dsc.discovery.com discovery.com]) |date=2006-08-06 |accessdate=2011-03-08 | archiveurl= http://web.archive.org/web/20110416094930/http://dsc.discovery.com/news/2006/08/08/marslife_spa.html?category=space&guid=20060808100030| archivedate= 16 April 2011 <!--DASHBot-->| deadurl= no}}</ref><ref name="life">{{cite journal|title= Search for past life on Mars: Possible relic biogenic activity in Martian meteorite ALH84001|author= McKay DS, Gibson EK, ThomasKeprta KL, Vali H, Romanek CS, Clemett SJ, Chillier XDF, Maechling CR, Zare RN |journal=Science|volume= 273|pages=924–930|year=1996|doi= 10.1126/science.273.5277.924|pmid= 8688069|issue= 5277|bibcode = 1996Sci...273..924M }}</ref><ref name=McKay>{{cite journal |title=Life on Mars: new evidence from martian meteorites |author=McKay DS, Thomas-Keprta KL, Clemett, SJ, Gibson, EK Jr, Spencer L, Wentworth SJ |journal=[[Proc. SPIE]] |volume=7441 |year=2009 |url=http://spiedigitallibrary.org/proceedings/resource/2/psisdg/7441/1/744102_1?isAuthorized=no |doi=10.1117/12.832317 |accessdate=2011-03-08 |issue=1 |series=Proceedings of SPIE |last4=Gibson |pages=744102 |editor1-last=Hoover |editor1-first=Richard B |editor2-last=Levin |editor2-first=Gilbert V |editor3-last=Rozanov |editor3-first=Alexei Y |editor4-last=Retherford |editor4-first=Kurt D}}</ref> On 5 March 2011, [[Richard B. Hoover]], a scientist with the [[Marshall Space Flight Center]], speculated on the finding of alleged microfossils similar to [[cyanobacteria]] in [[CI1 fossils|CI1]] carbonaceous [[meteorites]].<ref name=Tenney>{{cite web |last=Tenney |first=Garrett |title=Exclusive: NASA Scientist Claims Evidence of Alien Life on Meteorite |url=http://www.foxnews.com/scitech/2011/03/05/exclusive-nasa-scientists-claims-evidence-alien-life-meteorite/ |publisher=[[FoxNews]] |date=5 March 2011 |accessdate=2011-03-06 | archiveurl= http://web.archive.org/web/20110306082448/http://www.foxnews.com/scitech/2011/03/05/exclusive-nasa-scientists-claims-evidence-alien-life-meteorite/| archivedate= 6 March 2011 <!--DASHBot-->| deadurl= no}}</ref><ref name=Hoover>{{cite journal |title=Fossils of Cyanobacteria in CI1 Carbonaceous Meteorites: Implications to Life on Comets, Europa, and Enceladus |last=Hoover |first=Richard B. |journal=Journal of Cosmology |volume=13 |pages=xxx |year=2011 |url=http://journalofcosmology.com/Life100.html |accessdate=2011-03-06 }}</ref> However, NASA formally distanced itself from Hoover's claim.<ref>{{cite news | first = Kerry Sheridan | title = NASA shoots down alien fossil claims | date = 7 March 2011 | url = http://www.abc.net.au/news/stories/2011/03/08/3157645.htm | work = ABC News | accessdate = 2011-03-07}}</ref><ref name=Borenstein>{{cite web |last=Borenstein |first=Seth |title=Scientists skeptical of meteorite alien life claim |url=http://www.starnewsonline.com/article/20110307/APA/1103071081 |publisher=[[Associated Press]] (on [http://www.starnewsonline.com Starnewsonline.com]) |date=7 March 2011 |accessdate=2011-03-07 }}</ref><ref name="Redfield">{{cite web |last=Redfield |first=Rosemary |title=Is this claim of bacteria in a meteorite any better than the 1996 one? |work=[http://rrresearch.blogspot.com/ RR Research blog] |date=6 March 2011 |url=http://rrresearch.blogspot.com/2011/03/is-this-claim-of-bacteria-in-meteorite.html |accessdate=7 March 2011 | archiveurl= http://web.archive.org/web/20110308050727/http://rrresearch.blogspot.com/2011/03/is-this-claim-of-bacteria-in-meteorite.html| archivedate= 8 March 2011 <!--DASHBot-->| deadurl= no}}</ref> According to American astrophysicist [[Neil deGrasse Tyson]]: "At the moment, life on Earth is the only known life in the Universe, but there are compelling arguments to suggest we are not alone."<ref>{{cite web | url = http://astrobiology.nasa.gov/articles/the-search-for-life-in-the-universe/ | title = The Search for Life in the Universe | accessdate = 2011-03-07 | first = Neil deGrasse Tyson | date = 23 July 2001 | work = Department of Astrophysics and Hayden Planetarium | publisher = NASA}}</ref>
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| ;Extreme environments on the Earth
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| On 17 March 2013, researchers reported data that suggested [[microbes|microbial life forms]] thrive in the [[Mariana Trench]], the deepest spot on the Earth.<ref name="LS-20130317">{{cite web |last=Choi |first=Charles Q. |title=Microbes Thrive in Deepest Spot on Earth |url=http://www.livescience.com/27954-microbes-mariana-trench.html |date=17 March 2013 |publisher=[[LiveScience]] |accessdate=17 March 2013 }}</ref><ref name="NG-20130317">{{cite journal |last1=Glud |first1=Ronnie |last2=Wenzhöfer |first2=Frank |last3=Middleboe |first3=Mathias |last4=Oguri |first4=Kazumasa |last5=Turnewitsch |first5=Robert |last6=Canfield |first6=Donald E. |last7=Kitazato |first7=Hiroshi |title=High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth |url=http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1773.html |doi=10.1038/ngeo1773 |date=17 March 2013 |journal=[[Nature Geoscience]] |accessdate=17 March 2013 |bibcode = 2013NatGe...6..284G }}</ref> Other researchers reported related studies that microbes thrive inside rocks up to 1900 feet below the sea floor under 8500 feet of ocean off the coast of the northwestern United States.<ref name="LS-20130317" /><ref name="LS-20130314">{{cite web |last=Oskin |first=Becky |title=Intraterrestrials: Life Thrives in Ocean Floor |url=http://www.livescience.com/27899-ocean-subsurface-ecosystem-found.html |date=14 March 2013 |publisher=[[LiveScience]] |accessdate=17 March 2013 }}</ref> According to one of the researchers,"You can find microbes everywhere — they're extremely adaptable to conditions, and survive wherever they are."<ref name="LS-20130317" />
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| ;Methane
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| In 2004, the spectral signature of [[methane]] was detected in the Martian atmosphere by both Earth-based telescopes as well as by the [[Mars Express]] probe. Because of [[solar radiation]] and [[cosmic radiation]], methane is predicted to disappear from the Martian atmosphere within several years, so the gas must be actively replenished in order to maintain the present concentration.<ref name="results">
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| {{cite journal | title = Some problems related to the origin of methane on Mars | author = Vladimir A. Krasnopolsky | journal = Icarus | volume = 180 | issue = 2 | pages = 359–367 |date=February 2005
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| | url = http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4HTCW36-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=a614a9e35a422b94cc2611ccdc4bf180
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| | doi = 10.1016/j.icarus.2005.10.015 | bibcode=2006Icar..180..359K}}</ref><ref name="fourier-spec">[http://www.pfs-results.it/ Planetary Fourier Spectrometer website] (ESA, Mars Express)</ref> The [[Mars Science Laboratory]] rover will perform precision measurements of oxygen and carbon [[isotope]] ratios in carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>) in the [[Atmosphere of mars#Methane|atmosphere of Mars]] in order to distinguish between a [[Geochemistry|geochemical]] and a [[biology|biological]] origin.<ref name="SAM">{{cite web|url=http://ael.gsfc.nasa.gov/marsSAM.shtml |title=Sample Analysis at Mars (SAM) Instrument Suite |accessdate=2008-10-09 |date=October 2008 |publisher=NASA | archiveurl= http://web.archive.org/web/20081007102918/http://ael.gsfc.nasa.gov/marsSAM.shtml| archivedate= 7 October 2008 <!--DASHBot-->| deadurl= no}}</ref><ref>{{cite web|url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |title=Making Sense of Mars Methane |accessdate=2008-10-08 |last=Tenenbaum |first=David |date=9 June 2008|work=Astrobiology Magazine | archiveurl= http://web.archive.org/web/20080923195833/http://astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0| archivedate= 23 September 2008 <!--DASHBot-->| deadurl= no}}</ref><ref>{{cite journal | title=Multilaser Herriott cell for planetary tunable laser spectrometers | author=Tarsitano CG and Webster CR | journal=Applied Optics, | volume=46 | pages=6923–6935 | year=2007 | doi=10.1364/AO.46.006923| issue=28|bibcode = 2007ApOpt..46.6923T | pmid=17906720}}</ref>
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| ;Planetary systems
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| It is possible that some planets, like the gas giant [[Jupiter]] in our [[solar system]], may have moons with solid surfaces or liquid oceans that are more hospitable. Most of the planets so far discovered outside our solar system are hot gas giants thought to be inhospitable to life, so it is not yet known whether our solar system, with a warm, rocky, metal-rich inner planet such as Earth, is of an aberrant composition. Improved detection methods and increased observing time will undoubtedly discover more planetary systems, and possibly some more like ours. For example, [[NASA]]'s [[Kepler Mission]] seeks to discover Earth-sized planets around other stars by measuring minute changes in the star's [[light curve]] as the planet passes between the star and the spacecraft. Progress in [[infrared astronomy]] and [[submillimeter astronomy]] has revealed the constituents of other [[star system]]s. Infrared searches have detected belts of dust and [[asteroid]]s around distant stars, underpinning the formation of planets.
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| ;Planetary habitability
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| {{main|Planetary habitability}}
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| Efforts to answer questions such as the abundance of potentially habitable planets in [[habitable zone]]s and chemical precursors have had much success. Numerous [[extrasolar planet]]s have been detected using the [[Doppler spectroscopy|wobble method]] and transit method, showing that planets around other [[star]]s are more numerous than previously postulated. The first Earth-sized extrasolar planet to be discovered within its star's habitable zone is [[Gliese 581 c]], which was found using [[radial velocity]].<ref name="Gliese">{{cite news | first=Ker | last=Than | coauthors= | title=Major Discovery: New Planet Could Harbor Water and Life | date=24 April 2007 | publisher=Space.com | url =http://www.space.com/scienceastronomy/070424_hab_exoplanet.html | work = | pages = | accessdate = 2008-10-20 | language = | archiveurl= http://web.archive.org/web/20081015075030/http://www.space.com/scienceastronomy/070424_hab_exoplanet.html| archivedate= 15 October 2008 <!--DASHBot-->| deadurl= no}}</ref>
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| == Missions ==
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| Research into the environmental limits of life and the workings of extreme [[ecosystem]]s is ongoing, enabling researchers to better predict what planetary environments might be most likely to harbor life. Missions such as the [[Phoenix (spacecraft)|Phoenix lander]], [[Mars Science Laboratory]], [[ExoMars]] to Mars, and the [[Cassini probe]] to [[Saturn]]'s moon [[Titan (moon)|Titan]] hope to further explore the possibilities of life on other [[planet]]s in our [[solar system]].
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| ===Viking program===
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| {{main|Viking biological experiments}}
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| [[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] posing with a model of the Viking Lander.]]
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| The two [[Viking program|Viking spacecraft]] each carried four types of [[biological]] [[experiment]]s to the surface of [[Mars]] in the late 1970s. These were the only Mars landers to carry out experiments to look specifically for [[biosignature]]s of [[Life on Mars (planet)|life on Mars]]. The landers used a robotic arm to put soil samples into sealed test containers on the craft. The two landers were identical, so the same tests were carried out at two places on Mars' surface; [[Viking 1]] near the equator and [[Viking 2]] further north.<ref name="Chambers">{{Cite book
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| | first = Paul
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| | last = Chambers
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| | title = Life on Mars; The Complete Story
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| | place = London
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| | publisher = Blandford
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| | year = 1999
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| | isbn = 0-7137-2747-0
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| }}</ref> The result was inconclusive,<ref>Levin, G and P. Straaf. 1976. Viking Labeled Release Biology Experiment: Interim Results. Science: 194. 1322-1329.</ref> and is still disputed by some scientists.<ref name="Bianciardi-2012">{{cite journal |last1=Bianciardi |first1=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |title=Complexity Analysis of the Viking Labeled Release Experiments |url=http://ijass.org/PublishedPaper/year_abstract.asp?idx=132 |journal=IJASS |date=March 2012 |volume=13 |issue=1 |pages=14–26 |id = |accessdate=15 April 2012 |bibcode=2012IJASS..13...14B |doi=10.5139/IJASS.2012.13.1.14}}</ref><ref name="Discovery-20120412">{{cite web |last=Klotz |first=Irene |title=MARS VIKING ROBOTS 'FOUND LIFE' |url=http://news.discovery.com/space/mars-life-viking-landers-discovery-120412.html |date=12 April 2012 |publisher=[[Discovery Channel|DiscoveryNews]] |accessdate=16 April 2012 }}</ref><ref name="Navarro">{{Cite journal|last=Navarro-González|first=R.|authorlink=|year=2006|month=|title=The limitations on organic detection in Mars-like soils by thermal volatilization–gas chromatography–MS and their implications for the Viking results| journal=[[PNAS]]|volume=103| issue=44| pages=16089–16094| doi=10.1073/pnas.0604210103| url= http://www.pnas.org/content/103/44/16089.full.pdf+html |accessdate= April 2, 2012 |quote=| pmid=17060639 |pmc=1621051| bibcode = 2006PNAS..10316089N|display-authors=1|last2=Navarro| first2=K. F.|last3=Rosa |first3=J. d. l.| last4=Iniguez|first4=E.| last5=Molina|first5=P.|last6=Miranda| first6=L. D.|last7=Morales|first7=P.| last8=Cienfuegos|first8=E.| last9=Coll|first9=P. }}</ref><ref name="Paepe">{{Cite journal|title=The Red Soil on Mars as a proof for water and vegetation| journal=Geophysical Research Abstracts|year=2007|first=Ronald| last=Paepe| coauthors=|volume=9| issue=1794|pages=|id=| url=http://www.cosis.net/abstracts/EGU2007/01794/EGU2007-J-01794.pdf?PHPSESSID=e| format=PDP| accessdate=May 2, 2012}}</ref>
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| | |
| === Beagle 2 ===
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| {{main|Beagle 2}}
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| [[Image:Beagle 2 replica.jpg|thumb|Replica of the 33.2 kg ''Beagle-2'' lander]]
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| [[File:Msl20110519 PIA14156-full.jpg|thumb|[[Mars Science Laboratory]] rover concept artwork]]
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| ''Beagle 2'' was an unsuccessful [[United Kingdom|British]] Mars lander that formed part of the [[European Space Agency]]'s 2003 [[Mars Express]] mission. Its primary purpose was to search for signs of [[Life on Mars (planet)|life on Mars]], past or present. All contact with it was lost upon its entry into the atmosphere.<ref>[http://beagle2.open.ac.uk/index.htm Beagle 2 lander]</ref>
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| ===Mars Science Laboratory===
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| {{main|Mars Science Laboratory}}
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| The Mars Science Laboratory (MSL) mission landed a [[Rover (space exploration)|rover]] that is currently in operation on [[Mars]].<ref name="MSLNameWebsite">{{cite web|title=Name NASA's Next Mars Rover |url=http://marsrovername.jpl.nasa.gov/ |publisher=NASA/JPL |date=May 27, 2009 |accessdate=2009-05-27 | archiveurl= http://web.archive.org/web/20090522004939/http://marsrovername.jpl.nasa.gov/| archivedate= 22 May 2009 | deadurl= no}}</ref> It was launched November 26, 2011, and landed at [[Gale (crater)|Gale Crater]] on August 6, 2012.<ref name="Gale Crater3"/> Mission objectives are to help assess Mars' [[Planetary habitability|habitability]] and in doing so, determine whether Mars is or has ever been able to support [[Life on Mars (planet)|life]],<ref name="MSL-main_page">{{cite web |title=Mars Science Laboratory: Mission |url=http://marsprogram.jpl.nasa.gov/msl/mission/| publisher=NASA/JPL | accessdate=2010-03-12 }}</ref> collect data for a future [[Manned mission to Mars|manned mission]], study Martian geology, its climate, and further assess the role that [[Water on Mars|water]], an essential ingredient for life as we know it, played in forming minerals on Mars.
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| | |
| ===ExoMars===
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| {{main|ExoMars}}
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| [[File:ExoMars model at ILA 2006.jpg|thumb|ExoMars rover model]]
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| ExoMars is a robotic mission to Mars to search for possible [[biosignature]]s of [[Life on Mars (planet)|Martian life]], past or present. This astrobiological mission is currently under development by the [[European Space Agency]] (ESA) with likely collaboration by the [[Russian Federal Space Agency]] (Roscosmos); it is planned for a 2018 launch.<ref name='still keen'>{{cite news | first = Jonathan Amos | title = Europe still keen on Mars missions | date = 15 March 2012 | url = http://www.bbc.co.uk/news/science-environment-17390576 | work = BBC News | accessdate = 2012-03-16}}</ref><ref name='Svitak'>{{cite news | first = Amy Svitak | title = Europe Joins Russia on Robotic ExoMars | date = Mar 16, 2012 | url = http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/awx/2012/03/15/awx_03_15_2012_p0-437120.xml&headline=Europe%20Joins%20Russia%20on%20Robotic%20ExoMars | work = Aviation Week | accessdate = 2012-03-16}}</ref><ref name='Selding'>{{cite news | first = Peter B. de Selding | title = ESA Ruling Council OKs ExoMars Funding | date = 15 March 2012 | url = http://www.spacenews.com/civil/120315-esa-council-oks-exomars.html | work = Space News | accessdate = 2012-03-16}}</ref>
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| ===Mars 2020 rover mission===
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| {{main|Mars 2020 rover mission}}
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| | |
| The 'Mars 2020 rover mission' is a concept under study by NASA with a possible launch in 2020. It is intended to investigate astrobiologically relevant environments on Mars, investigate its surface [[Geology of Mars|geological processes]] and history, including the assessment of its past [[Planetary habitability|habitability]] and potential for preservation of [[biosignature]]s within accessible geological materials.<ref name='Cowing'>{{cite web | url = http://spaceref.com/mars/science-definition-team-for-the-2020-mars-rover.html | title = Science Definition Team for the 2020 Mars Rover | accessdate = 21 December 2012 | first = Keith Cowing | date = 21 December 2012 | work = NASA | publisher = Science Ref}}</ref> The Science Definition Team is proposing the rover collect and package as many as 31 samples of rock cores and soil for a later mission to bring back for more definitive analysis in laboratories on Earth. The rover could make measurements and technology demonstrations to help designers of a [[Manned mission to Mars|human expedition]] understand any hazards posed by Martian dust and demonstrate how to collect [[carbon dioxide]] (CO<sub>2</sub>), which could be a resource for making oxygen (O<sub>2</sub>) and [[rocket fuel]]. Improved precision landing technology that enhances the scientific value of robotic missions also will be critical for eventual human exploration on the surface.<ref name='goals'>{{cite news | title = Science Team Outlines Goals for NASA's 2020 Mars Rover | date = 9 July 2013 | publisher = NASA | url = http://www.jpl.nasa.gov/news/news.php?release=2013-217 | work = Jet Propulsion Laboratory | accessdate = 10 July 2013 }}</ref><ref name='FAQ'>{{cite web | url = http://mars.nasa.gov/files/m2020/Mars2020FAQs.pdf | title = Mars 2020 Science Definition Team Report - Frequently Asked Questions | accessdate = 2013-07-10 | date = 9 July 2013 | format = PDF | work = NASA}}</ref>
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| ===Red Dragon===
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| {{main|Red Dragon (spacecraft)}}
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| | |
| Red Dragon is a proposed concept for a low-cost [[Mars]] [[Lander (spacecraft)|lander]] mission that would utilize a [[SpaceX]] [[Falcon Heavy]] launch vehicle, and a modified [[Dragon (spacecraft)|Dragon capsule]] to [[Atmospheric entry|enter]] the [[Martian atmosphere]]. The lander's primary mission would be to search for evidence of [[Life on Mars (planet)|life on Mars]] ([[biosignature]]s), past or present. The concept had been scheduled to propose for funding on 2012/2013 as a [[Discovery Program|NASA Discovery mission]], for launch in 2018.<ref name=sdc20110731>{{cite news |last=Wall|first=Mike |title='Red Dragon' Mission Mulled as Cheap Search for Mars Life |url=http://www.space.com/12489-nasa-mars-life-private-spaceship-red-dragon.html |accessdate=2012-05-01 |newspaper=SPACE.com |date=2011-07-31 }}</ref><ref name='NAC 2011'>{{cite web | url = http://science.nasa.gov/media/medialibrary/2012/01/23/NAC_Science_Meeting_ReportOctober_31-November_1_2011-finalTAGGED.pdf | title = NASA ADVISORY COUNCIL (NAC) - Science Committee Report | accessdate = 2012-05-01 | date = 1 November 2011 | format = PDF | work = Ames Research Center, NASA}}</ref>
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| ===Icebreaker Life===
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| {{main|Icebreaker Life}}
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| | |
| ''Icebreaker Life'' is a lander mission that is being proposed for NASA's [[Discovery Program]] for the 2018 launch opportunity.<ref name='Icebreaker2018'>{{cite journal | title = The ''Icebreaker Life'' Mission to Mars: A Search for Biomolecular Evidence for Life | journal = Astrobiology | date = April 5, 2013 | first = Christopher P. | last = McKay | coauthors = Carol R. Stoker, Brian J. Glass, Arwen I. Davé, Alfonso F. Davila, Jennifer L. Heldmann, Margarita M. Marinova, Alberto G. Fairen, Richard C. Quinn, Kris A. Zacny, Gale Paulsen, Peter H. Smith, Victor Parro, Dale T. Andersen, Michael H. Hecht, Denis Lacelle, and Wayne H. Pollard. | volume = 13 | issue = 4 | pages = 334–353 | doi = 10.1089/ast.2012.0878 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2012.0878 | accessdate = 2013-06-30|bibcode = 2013AsBio..13..334M }}</ref> The stationary lander would be a near copy of the successful 2008 [[Phoenix (spacecraft)|''Phoenix'']] and it would carry an upgraded scientific payload, including a 1 meter-long drill to sample ice-cemented ground in the northern plains to conduct a search for [[organic molecule]]s and evidence of current or past [[life on Mars]].<ref name='AstrobioMag'>{{cite news | first = Charles Q. Choi | title = Icebreaker Life Mission | date = 16 May 2013 | url = http://www.astrobio.net/exclusive/5476/mars-icebreaker-life-mission | work = Astrobiology Magazine | accessdate = 2013-07-01}}</ref><ref name='LPI 2012'>{{citation | first = C. P. |last = McKay | coauthors = Carol R. Stoker, Brian J. Glass, Arwen I. Davé, Alfonso F. Davila, Jennifer L. Heldmann, Margarita M. Marinova, Alberto G. Fairen, Richard C. Quinn, Kris A. Zacny, Gale Paulsen, Peter H. Smith, Victor Parro, Dale T. Andersen, Michael H. Hecht, Denis Lacelle, and Wayne H. Pollard. | contribution = THE ICEBREAKER LIFE MISSION TO MARS: A SEARCH FOR BIOCHEMICAL EVIDENCE FOR LIFE | title = Concepts and Approaches for Mars Exploration | publisher = Lunar and Planetary Institute | year = 2012 | contribution-url = http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4091.pdf | format = PDF | accessdate = 2013-07-01}}</ref> One of the key goals of the ''Icebreaker Life'' mission is to test the [[hypothesis]] that the ice-rich ground in the polar regions has significant concentrations of organics due to protection by the ice from [[Oxidizing agent|oxidants]] and [[Sunlight|radiation]].
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| ===Europa Clipper===
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| {{main|Europa Clipper}}
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| Europa Clipper is a mission concept under study by NASA that would conduct detailed reconnaissance of [[Jupiter]]'s moon [[Europa (moon)|Europa]] and would investigate whether the icy moon could harbor conditions suitable for [[life]].<ref name='missions'> {{cite news | title = Europa Clipper | date = November 2013 | publisher = NASA | url = http://solarsystem.nasa.gov/missions/profile.cfm?MCode=EuropaClipper&Display=ReadMore | work = Jet Propulsion Laboratory | accessdate = 2013-12-13}}</ref><ref name='FPE'> {{cite news | first = Van | last = Kane | title = Europa Clipper Update | date = 26 May 2013 | url = http://futureplanets.blogspot.com/2013/05/europa-clipper-update.html | work = Future Planetary Exploration | accessdate = 2013-12-13}}</ref> It would also aid in the selection of future [[Lander (spacecraft)|landing sites]].<ref name='Europa Lander 2013'> {{cite journal | title = Science Potential from a Europa Lander | journal = Astrobiology | date = 2013 | first = Robert T. | last = Pappalardo | coauthors = S. Vance, F. Bagenal, B.G. Bills, D.L. Blaney, D.D. Blankenship, W.B. Brinckerhoff, ''et al.'' | volume = 13 | issue = 8| id = {{doi | 10.1089/ast.2013.1003}} | url = http://online.liebertpub.com/doi/pdfplus/10.1089/ast.2013.1003 | accessdate = 2013-12-14}}</ref><ref> {{citation | first = D. | last = Senske | contribution = Europa Mission Concept Study Update | title = Presentation to Planetary Science Subcommittee | date = 2 October 2012| id = | contribution-url = http://www.lpi.usra.edu/pss/oct2012/presentations/5_Senske_Europa.pdf | format = PDF | accessdate = 2013-12-14}}</ref>
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| ==See also==
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| {{Portal|Astrobiology}}
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| {| <!--splity as 3 columns for any browser-->
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| | valign=top |
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| * [[Abiogenesis]]
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| * [[Active SETI]]
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| * [[Alien language]]
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| * [[Astrosciences]]
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| * [[Aurelia and Blue Moon]]{{nb5}}
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| * [[Back-contamination]]
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| | valign=top |
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| * [[Cosmic dust]]
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| * [[Extraterrestrial life]]
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| * [[Forward-contamination]]{{nb5}}{{nb5}}
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| * [[Gravitational biology]]
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| * [[Hypothetical types of biochemistry]]
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| * [[List of microorganisms tested in outer space]]
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| | valign=top |
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| * [[Living Interplanetary Flight Experiment]]
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| * [[Planetary habitability]]
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| * [[Purple Earth Hypothesis]]
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| * [[Rare Earth hypothesis]]
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| * [[Shadow biosphere]]
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| |}
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| ==References==
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| <!--You may want to use the automated reference generator for acceptable reference format: http://toolserver.org/~magnus/makeref.php -->
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| {{Reflist|2}}
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| ==Bibliography==
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| * The [http://www.journals.cambridge.org/jid_IJA ''International Journal of Astrobiology''], published by [[Cambridge University Press]], is the forum for practitioners in this interdisciplinary field.
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| * [http://www.liebertpub.com/publication.aspx?pub_id=99 ''Astrobiology''], published by [[Mary Ann Liebert, Inc.]], is a peer-reviewed journal that explores the origins of life, evolution, distribution, and destiny in the universe.
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| * {{cite book |title=Astrobiology: A Very Short Introduction |last=Catling |first=David C. |authorlink= |coauthors= |year=2013 |publisher=Oxford University Press |location=Oxford |isbn=0-19-958645-4 |pages= }}
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| * {{cite book |title=The Living Universe: NASA and the Development of Astrobiology |last=Dick |first=Steven J. |authorlink= |coauthors=James Strick |year=2005 |publisher=Rutgers University Press |location=Piscataway, NJ |isbn=0-8135-3733-9 |pages= }}
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| * {{cite book |title=Lonely planets. The natural philosophy of alien life |last=Grinspoon |first=David |authorlink= |coauthors= |year=2004 |origyear=2003 |publisher=ECCO |location=New York |isbn=0-06-018540-6 |pages= }}
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| * {{Cite book | last = Mautner | first = Michael N. | title = Seeding the Universe with Life: Securing Our Cosmological Future | publisher = Legacy Books (www.amazon.com) | location = Washington D. C. | year = 2000 | isbn = 0-476-00330-X | url = http://www.astro-ecology.com/PDFSeedingtheUniverse2005Book.pdf }}
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| * {{cite book |title=Science, Society, and the Search for Life in the Universe |last=Jakosky |first=Bruce M. |authorlink= |coauthors= |year=2006 |publisher=University of Arizona Press |location=Tucson |isbn=0-8165-2613-3 |pages= }}
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| * {{cite book |title=Astrobiology. A Multidisciplinary Approach |last=Lunine |first=Jonathan I. |authorlink= |coauthors= |year=2005 |publisher=Pearson Addison-Wesley |location=San Francisco |isbn=0-8053-8042-6 |pages= }}
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| * {{cite book |title=An introduction to astrobiology |last=Gilmour |first=Iain |authorlink= |coauthors=Mark A. Sephton |year=2004 |publisher=Cambridge Univ. Press |location=Cambridge |isbn=0-521-83736-7 |pages= }}
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| * {{cite book |title=Rare Earth: Why Complex Life is Uncommon in the Universe |last=Ward |first=Peter |authorlink= |coauthors=Brownlee, Donald |year=2000 |publisher=Copernicus |location=New York |isbn=0-387-98701-0 |pages= }}
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| * {{cite doi|10.1146/annurev.astro.43.051804.102202}}
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| ==External links==
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| {{sisterlinks|d=no|voy=no|species=no|b=no|s=no|n=no|q=no|wikt=astrobiology|commons=Category:Astrobiology|v=The Department of Astrobiology}}
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| * [http://astrobiology.nasa.gov Astrobiology.nasa.gov]
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| * [http://cab.inta-csic.es/ Spanish Centro de Astrobiología]
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| * [http://astrobiology.ac.uk/ UK Centre for Astrobiology]
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| ==Further reading==
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| * ''The Search For Life In The Universe'', D. Goldsmith, T. Owen. Second edition. [[ISBN 0-201-56949-3]] Addison-Wesley Publishing Company
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| {{Astrobiology}}
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| {{Astronomy subfields}}
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| {{Biology-footer}}
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| {{Extraterrestrial life}}
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| {{Interstellar messages}}
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| {{DEFAULTSORT:Astrobiology}}
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| [[Category:Astrobiology]]
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| [[Category:Extraterrestrial life]]
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| {{Link FA|tr}}
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