View source for Interplanetary contamination

{{Short description|Biological contamination of a planetary body by a space probe or spacecraft}}
'''Interplanetary contamination''' refers to [[biological contamination]] of a [[planetary body]] by a [[space probe]] or [[spacecraft]], either deliberate or unintentional.

There are two types of interplanetary contamination:
*'''''Forward contamination''''' is the transfer of life and other forms of contamination from Earth to another celestial body. 
*'''''Back contamination''''' is the introduction of [[Extraterrestrial life|extraterrestrial]] organisms and other forms of contamination into [[Earth]]'s [[biosphere]]. It also covers infection of humans and human habitats in space and on other celestial bodies by extraterrestrial organisms, if such organisms exist.

The main focus is on [[microbial life]] and on potentially [[invasive species]]. Non-biological forms of contamination have also been considered, including contamination of sensitive deposits (such as lunar polar ice deposits) of scientific interest.<ref>{{cite journal|author=S.T. Shipley |author2=P.T. Metzger|author3=J.E. Lane|name-list-style=amp|title=Lunar Cold Trap Contamination by Landing Vehicles| url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140017853.pdf|website=Earth and Space 2014 - Proceedings of the 14th Biennial ASCE Conference on Engineering, Science, Construction, and Operations in Challenging Environments|date=27 October 2014}}</ref> In the case of back contamination, multicellular life is thought unlikely but has not been ruled out. In the case of forward contamination, contamination by multicellular life (e.g. lichens) is unlikely to occur for robotic missions, but it becomes a consideration in [[Human mission to Mars|crewed missions to Mars]].<ref name="PHYS-20180227">{{cite web |author=Purdue University Staff |author-link=Purdue University |title=Tesla in space could carry bacteria from Earth |url=https://phys.org/news/2018-02-tesla-space-bacteria-earth.html |date=27 February 2018 |work=[[phys.org]] |access-date=28 February 2018 }}</ref>

Current space missions are governed by the [[Outer Space Treaty]] and the [[COSPAR]] guidelines for [[planetary protection]]. Forward contamination is prevented primarily by sterilizing the spacecraft. In the case of [[sample-return mission]]s, the aim of the mission is to return extraterrestrial samples to Earth, and sterilization of the samples would make them of much less interest. So, back contamination would be prevented mainly by containment, and breaking the chain of contact between the planet of origin and Earth. It would also require [[quarantine]] procedures for the materials and for anyone who comes into contact with them.

==Overview ==

Most of the [[Solar System]] appears hostile to life as we know it. No extraterrestrial life has ever been discovered. But if extraterrestrial life exists, it may be vulnerable to interplanetary contamination by foreign microorganisms. Some [[extremophile]]s may be able to survive space travel to another planet, and foreign life could possibly be introduced by spacecraft from Earth. If possible, some believe this poses scientific and ethical concerns.

Locations within the Solar System where life might exist today include the oceans of liquid water beneath the icy surface of [[Europa (moon)|Europa]], [[Enceladus]],
and [[Titan (moon)|Titan]] (its surface has oceans of liquid [[ethane]] / [[methane]], but it may also have liquid water below the surface and [[cryovolcano|ice volcanoes]]).<ref name=smallsolarsystembodies>[http://www.gwu.edu/~spi/COSPAR_OP_PP_Workshop_final_Aug2009.pdf COSPAR Workshop on Planetary Protection for Outer Planet Satellites and Small Solar System Bodies] European Space Policy Institute (ESPI), 15–17 April 2009</ref><ref>[https://science.nasa.gov/media/medialibrary/2011/06/29/Rummel_COSPAR_COPUOS_PPS_9May11_-_TAGGED.pdf COSPAR power point type presentation, gives good overview of the detailed category decisions] {{webarchive|url=https://web.archive.org/web/20131019160210/http://science.nasa.gov/media/medialibrary/2011/06/29/Rummel_COSPAR_COPUOS_PPS_9May11_-_TAGGED.pdf |date=2013-10-19 }}</ref>

There are multiple consequences for both forward- and back-contamination. If a planet becomes contaminated with Earth life, it might then be difficult to tell whether any lifeforms discovered originated there or came from Earth.<ref>{{cite web|url = http://motherboard.vice.com/en_uk/read/if-there-are-microbes-on-mars-we-could-have-put-them-there |title = If there Are Microbes on Mars, We Might Have Put Them There |first = Victoria|last = Turk|work = Motherboard|date = 20 May 2014|publisher = Vice}}</ref> Furthermore, the organic chemicals produced by the introduced life would confuse sensitive searches for [[biosignature]]s of living or ancient native life. The same applies to other more complex biosignatures. Life on other planets could have a common origin with Earth life, since in the early Solar System there was much exchange of material between the planets which could have transferred life as well. If so, it might be based on [[nucleic acid]]s too ([[RNA]] or [[DNA]]).

The majority of the species isolated are not well understood or characterized and cannot be cultured in labs, and are known only from DNA fragments obtained with swabs.<ref>{{cite journal | url=http://www.nature.com/ismej/journal/v2/n1/full/ismej200798a.html | doi=10.1038/ismej.2007.98 | title=Archaeal diversity analysis of spacecraft assembly clean rooms | date=2008 | last1=Moissl | first1=Christine | last2=Bruckner | first2=James C. | last3=Venkateswaran | first3=Kasthuri | journal=The ISME Journal | volume=2 | issue=1 | pages=115–119 | pmid=18180750 | bibcode=2008ISMEJ...2..115M }}</ref> On a contaminated planet, it might be difficult to distinguish the [[DNA]] of extraterrestrial life from the DNA of life brought to the planet by the exploring. Most species of microorganisms on Earth are not yet well understood or DNA sequenced. This particularly applies to the unculturable [[archaea]], and so are difficult to study. This can be either because they depend on the presence of other microorganisms, are slow growing, or depend on other conditions not yet understood. In [[Agar plate|typical habitats]], 99% of microorganisms are not [[Microbiological culture|culturable]].<ref>{{cite journal | pmid = 12004133 | doi=10.1126/science.1070633 | volume=296 | issue=5570 | title=Isolating "uncultivable" microorganisms in pure culture in a simulated natural environment | journal=Science | pages=1127–9 | last1 = Kaeberlein | first1 = T | last2 = Lewis | first2 = K | last3 = Epstein | first3 = SS|bibcode = 2002Sci...296.1127K | year=2002 | s2cid=28437864 }}</ref>  Introduced Earth life could contaminate resources of value for future human missions, such as water.<ref name="groundwatercontamination">{{Cite news |url=https://www.bbc.co.uk/news/uk-northern-ireland-27526981 |quote=No-one has yet proved that there is deep groundwater on Mars, but it is plausible as there is certainly surface ice and atmospheric water vapour, so we wouldn't want to contaminate it and make it unusable by the introduction of micro-organisms. |title=Queens University Belfast scientist helps NASA Mars project |work=BBC News |date=23 May 2014 }}</ref>

[[Invasive species]] could out compete native life or consume it, if there is life on the planet.<ref name=martianrabbit>Rachel Courtland [https://www.newscientist.com/article/dn16546-should-mars-be-treated-like-a-wildlife-preserve.html#.UgZ6qpJMu84 Should Mars be treated like a wildlife preserve?] New Scientist, February 2009.</ref> However, the experience on earth shows that species moved from one continent to another may be able to out compete the native life adapted to that continent.<ref name=martianrabbit /> Additionally, evolutionary processes on Earth might have developed biological pathways different from extraterrestrial organisms, and so may be able to out-compete it. The same is also possible the other way around for contamination introduced to Earth's [[biosphere]].

In addition to science research concerns, there are also attempts to raise ethical and moral concerns regarding intentional or unintentional interplanetary transport of life.<ref>{{Cite journal |last1=Rummel |first1=J.D. |last2=Race |first2=M.S. |last3=Horneck, and the Princeton Workshop |first3=G. |date=November 2012 |title=Ethical Considerations for Planetary Protection in Space Exploration: A Workshop |journal=Astrobiology |language=en |volume=12 |issue=11 |pages=1017–1023 |doi=10.1089/ast.2012.0891 |pmid=23095097 |pmc=3698687 |bibcode=2012AsBio..12.1017R }}</ref><ref>{{cite journal | url=https://www.sciencedirect.com/science/article/abs/pii/S0265964605000767 | doi=10.1016/j.spacepol.2005.08.003 | title=Planetary protection—A microbial ethics approach | journal=Space Policy | date=November 2005 | volume=21 | issue=4 | pages=287–292 | last1=Cockell | first1=Charles S. | bibcode=2005SpPol..21..287C }}</ref><ref>[https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/need-of-an-ethics-of-planetary-sustainability/C5BF69491F2B3F743022CD1EF54DB281 The need of an ethics of planetary sustainability]. Andreas Losch. ''International Journal of Astrobiology''. 10 January 2018. {{doi|10.1017/S1473550417000490}}</ref><ref name=RestorationEcology>Christopher P. McKay [http://esseacourses.strategies.org/EcosynthesisMcKay2008ReviewAAAS.pdf Planetary Ecosynthesis on Mars: Restoration Ecology and Environmental Ethics] {{Webarchive|url=https://web.archive.org/web/20200401190045/http://esseacourses.strategies.org/EcosynthesisMcKay2008ReviewAAAS.pdf |date=2020-04-01 }} NASA Ames Research Center</ref>

== Evidence for possible habitats outside Earth ==

[[Enceladus]] and [[Europa (moon)|Europa]] show the best evidence for current habitats, mainly due to the possibility of their hosting liquid water and organic compounds.

=== Mars ===
{{Further|Life on Mars}}
There is ample evidence to suggest that Mars once offered habitable conditions for microbial life.<ref name="NYT-20131209">{{cite news |last=Chang |first=Kenneth |title=On Mars, an Ancient Lake and Perhaps Life |url=https://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]] }}</ref><ref name="SCI-20131209">{{cite journal |author=Various |title=Science - Special Collection - Curiosity Rover on Mars |url=https://www.science.org/action/doSearch?AllField=Curiosity+Mars |date=December 9, 2013 |journal=[[Science (journal)|Science]] }}</ref> It is therefore possible that microbial life may have existed on Mars, although no evidence has been found.<ref>{{Cite journal |quote=Finally, our results indicate that liquid water could form on the surface during the spring where snow has been deposited on saline soils [Martínez et al., 2012; Möhlmann, 2011]. These results have important implications for the understanding of the habitability of Mars because liquid water is essential for life as we know it, and halophilic terrestrial bacteria can thrive in brines |doi=10.1002/2014GL060302 |title=Experimental evidence for the formation of liquid saline water on Mars |year=2014 |last1=Fischer |first1=Erik |last2=Martínez |first2=Germán M. |last3=Elliott |first3=Harvey M. |last4=Rennó |first4=Nilton O. |journal=Geophysical Research Letters |volume=41 |issue=13 |pages=4456–4462 |pmid=25821267 |pmc=4373172 |bibcode=2014GeoRL..41.4456F }}</ref><ref>{{cite journal | url=https://link.springer.com/article/10.1007%2Fs11214-012-9956-3/fulltext.html | doi=10.1007/s11214-012-9956-3 | title=Water and Brines on Mars: Current Evidence and Implications for MSL | year=2013 | last1=Martínez | first1=G. M. | last2=Renno | first2=N. O. | journal=Space Science Reviews | volume=175 | issue=1–4 | pages=29–51 | bibcode=2013SSRv..175...29M | s2cid=255073809 | doi-access=free }}</ref><ref name="Biosignatures 2011">{{cite journal | doi=10.1089/ast.2010.0506 | quote=There is general consensus that extant microbial life on Mars would probably exist (if at all) in the subsurface and at low abundance. | title=Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group | date=2011 | last1=Summons | first1=Roger E. | last2=Amend | first2=Jan P. | last3=Bish | first3=David | last4=Buick | first4=Roger | last5=Cody | first5=George D. | last6=Des Marais | first6=David J. | last7=Dromart | first7=Gilles | last8=Eigenbrode | first8=Jennifer L. | last9=Knoll | first9=Andrew H. | last10=Sumner | first10=Dawn Y. | display-authors=8|author-link8=Jennifer Eigenbrode | journal=Astrobiology | volume=11 | issue=2 | pages=157–81 | pmid=21417945 | bibcode = 2011AsBio..11..157S | url=https://dash.harvard.edu/bitstream/handle/1/13041033/66876195.pdf?sequence=2 | hdl=1721.1/66519 | s2cid=9963677 | hdl-access=free }}</ref><ref name="Parnell">{{cite news | first=JohnThomas |last=Didymus | title=Scientists find evidence Mars subsurface could hold life | date=January 21, 2013 | url=http://digitaljournal.com/article/341801 | work = Digital Journal – Science | quote=There can be no life on the surface of Mars because it is bathed in radiation and it's completely frozen. However, life in the subsurface would be protected from that. - Prof. Parnell.}}</ref><ref>{{cite news | title=Mars: 'Strongest evidence' planet may have supported life, scientists say | date=January 20, 2013 | url=https://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-21063817 | work=BBC News }}</ref><ref>{{cite journal |doi=10.1038/ngeo1706 |title=Groundwater activity on Mars and implications for a deep biosphere |date=2013 |last1=Michalski |first1=Joseph R. |last2=Cuadros |first2=Javier |last3=Niles |first3=Paul B. |last4=Parnell |first4=John |last5=Deanne Rogers |first5=A. |last6=Wright |first6=Shawn P. |journal=Nature Geoscience |volume=6 |issue=2 |pages=133–8|bibcode = 2013NatGe...6..133M }}</ref><ref>{{Cite journal |url=https://arxiv.org/ftp/astro-ph/papers/0507/0507317.pdf |title=RADIATIVE HABITABLE ZONES IN MARTIAN POLAR ENVIRONMENTS|quote=Finally there are other harmful radiation sources reaching Mars: ionizing and neutron radiation caused by galactic cosmic radiation and solar particle events. Due to the lack of a magnetic field and the low shielding of the Martian atmosphere (the Martian overhead airmass is 16 g cm-2 instead of the terrestrial 1000 g cm-2) the doses of ionizing radiation at the surface of Mars reach values about 100 times higher than those on the Earth. However, since a great variety of microbes tolerate this type of radiation at similar or even greater doses than those found on Mars, ionizing radiation cannot be considered a limiting factor for microbial life on Mars and thus here we will limit our study to solar UV shielding and VIS radiation pentration.}}</ref>

It is thought that many bacterial spores ([[endospores]]) from Earth were transported on Mars spacecraft.<ref name=Debus>{{cite journal |bibcode=2005AdSpR..35.1648D |title=Estimation and assessment of Mars contamination |last1=Debus |first1=A. |volume=35 |date=2005 |pages=1648–53 |journal=Advances in Space Research |doi=10.1016/j.asr.2005.04.084 |pmid=16175730 |issue=9}}</ref><ref name=Beaty>{{cite journal |bibcode=2006AsBio...6..677M |title=Findings of the Mars Special Regions Science Analysis Group |author1=MEPAG Special Regions-Science Analysis Group |last2=Beaty |first2=D. |last3=Buxbaum |first3=K. |last4=Meyer |first4=M. |last5=Barlow |first5=N. |last6=Boynton |first6=W. |last7=Clark |first7=B. |last8=Deming |first8=J. |last9=Doran |first9=P. T. |last10=Edgett |first10=K. |last11=Hancock |first11=S. |last12=Head |first12=J. |last13=Hecht |first13=M. |last14=Hipkin |first14=V. |last15=Kieft |first15=T. |last16=Mancinelli |first16=R. |last17=McDonald |first17=E. |last18=McKay |first18=C. |last19=Mellon |first19=M. |last20=Newsom |first20=H. |last21=Ori |first21=G. |last22=Paige |first22=D. |last23=Schuerger |first23=A. C. |last24=Sogin |first24=M. |last25=Spry |first25=J. A. |last26=Steele |first26=A. |last27=Tanaka |first27=K. |last28=Voytek |first28=M. |volume=6 |date=2006 |pages=677–732 |journal=Astrobiology |doi=10.1089/ast.2006.6.677 |pmid=17067257 |issue=5|display-authors=9 }}</ref> Some may be protected within Martian rovers and landers on the shallow surface of the planet.<ref>{{cite web |title=Space Station Research Shows That Hardy Little Space Travelers Could Colonize Mars |website=[[NASA]] |archive-url=https://web.archive.org/web/20230620084956/https://www.nasa.gov/mission_pages/station/research/news/eu_tef/ |archive-date=2023-06-20 |url-status=live |url=http://www.nasa.gov/mission_pages/station/research/news/eu_tef/#.U_qEjfmwJcQ}}</ref><ref>[http://www.voanews.com/content/microbes-prove-hearty-enough-for-interplanetary-travel/1908225.html NASA Press Release, May 2014] "In another investigation, spores of Bacillus pumilus SAFR-032 and another spore-forming bacteria, Bacillus subtilis 168, were dried on pieces of spacecraft-quality aluminum and subjected for 1.5 years to the vacuum of space, cosmic and extraterrestrial solar radiation and temperature fluctuations on EuTEF. These samples also were subjected to a simulated Martian atmosphere using EuTEF. Most of the organisms exposed to solar UV radiation in space and in the Mars spectrum were killed, but when UV rays were filtered out and samples were kept in the dark, about 50 percent or more of those subjected to other space- and Mars-like conditions survived. That makes it likely that spores could survive a trip on a spacecraft to Mars if they are sheltered against solar radiation, perhaps in a tiny pocket of the spacecraft surface or underneath a layer of other spores."</ref> In that sense, Mars may have already been contaminated.

Certain [[lichen]]s from the arctic [[permafrost]] are able to [[photosynthesize]] and grow in the absence of any liquid water, simply by using the humidity from the atmosphere. They are also highly tolerant of [[UV radiation]], using [[melanin]] and other more specialized chemicals to protect their cells.<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 |access-date=27 April 2012 |archive-url=https://web.archive.org/web/20120528145425/http://www.skymania.com/wp/2012/04/lichen-survives-harsh-martian-setting.html/ |archive-date=28 May 2012 |url-status=dead }}</ref><ref name="EGU-20120426">{{cite journal|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 |journal=EGU General Assembly Conference Abstracts |volume=14 |pages=2113 |url=http://media.egu2012.eu/media/filer_public/2012/04/05/10_solarsystem_devera.pdf |date=26 April 2012 |publisher=[[European Geosciences Union]] |access-date=27 April 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120504224706/http://media.egu2012.eu/media/filer_public/2012/04/05/10_solarsystem_devera.pdf |archive-date=4 May 2012 |bibcode=2012EGUGA..14.2113D }}</ref>
 
Although numerous studies point to resistance to some of Mars conditions, they do so separately, and none has considered the full range of Martian surface conditions, including temperature, pressure, atmospheric composition, radiation, humidity, oxidizing regolith, and others, all at the same time and in combination.<ref>{{cite journal | doi=10.1089/ast.2017.1772 | title=Is Searching for Martian Life a Priority for the Mars Community? | year=2018 | last1=Fairén | first1=Alberto G. | last2=Parro | first2=Victor | last3=Schulze-Makuch | first3=Dirk | last4=Whyte | first4=Lyle | journal=Astrobiology | volume=18 | issue=2 | pages=101–107 | pmid=29359967 | pmc=5820680 | bibcode=2018AsBio..18..101F }}</ref> Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.<ref name="dust-up">{{cite web|url=http://www.astrobio.net/exclusive/3495/mars-contamination-dust-up |title=Mars Contamination Dust-Up |first=Charles |last=Q. Choi |date=May 17, 2010 |publisher=Astrobiology Magazine |quote=Whenever multiple biocidal factors are combined, the survival rates plummet quickly |url-status=usurped |archive-url=https://web.archive.org/web/20110820212814/http://www.astrobio.net/exclusive/3495/mars-contamination-dust-up |archive-date=August 20, 2011 }}</ref>

Other studies have suggested the potential for life to survive using [[Hygroscopy#Deliquescence|deliquescing salts]]. These, similarly to the lichens, use the humidity of the atmosphere. If the mixture of salts is right, the organisms may obtain liquid water at times of high atmospheric humidity, with salts capturing enough to be capable of supporting life.

Research published in July 2017 shows that when irradiated with a simulated Martian UV flux, [[perchlorate]]s become even more lethal to bacteria ([[bactericide]] effect). Even dormant spores lost viability within minutes.<ref name="bacteriocidal">{{cite journal| pmc=5500590 | pmid=28684729 | doi=10.1038/s41598-017-04910-3 | volume=7 | issue=1 | title=Perchlorates on Mars enhance the bacteriocidal effects of UV light | year=2017 | journal=Sci Rep | page=4662 | last1 = Wadsworth | first1 = J | last2 = Cockell | first2 = CS| bibcode= 2017NatSR...7.4662W }}</ref> In addition, two other compounds of the Martian surface, [[iron oxide]]s and [[hydrogen peroxide]], act in synergy with irradiated perchlorates to cause a 10.8-fold increase in cell death when compared to cells exposed to UV radiation after 60 seconds of exposure.<ref name='bacteriocidal'/><ref name="oxides">{{cite journal | url=https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/shielding-biomolecules-from-effects-of-radiation-by-mars-analogue-minerals-and-soils/C7AB68D3D632E3654A72B0D979ED3FDD | doi=10.1017/S1473550416000331 | title=Shielding biomolecules from effects of radiation by Mars analogue minerals and soils | year=2017 | last1=Ertem | first1=G. | last2=Ertem | first2=M. C. | last3=McKay | first3=C. P. | last4=Hazen | first4=R. M. | journal=International Journal of Astrobiology | volume=16 | issue=3 | pages=280–285 | bibcode=2017IJAsB..16..280E | s2cid=125294279 }}</ref>  It was also found that abraded silicates (quartz and basalt) lead to the formation of toxic [[reactive oxygen species]].<ref>{{cite journal | last1 = Bak | first1 = Ebbe N. | last2 = Larsen | first2 = Michael G. | last3 = Moeller | first3 = Ralf | last4 = Nissen | first4 = Silas B. | last5 = Jensen | first5 = Lasse R. | last6 = Nørnberg | first6 = Per | last7 = Jensen | first7 = Svend J. K. | last8 = Finster | first8 = Kai | title=Silicates Eroded under Simulated Martian Conditions Effectively Kill Bacteria - A Challenge for Life on Mars | journal=Frontiers in Microbiology | date=September 12, 2017 | volume=8 |pages=1709 |doi=10.3389/fmicb.2017.01709 | pmid = 28955310 | pmc = 5601068 | doi-access = free }}</ref> The researchers concluded that "the surface of Mars is lethal to vegetative cells and renders much of the surface and near-surface regions uninhabitable."<ref>{{cite web |url = http://time.com/4845251/mars-life-toxins-microbes/ |title = Why Life on Mars May Be Impossible|first=Jeffrey|last= Kluger|work = Time - Science|date= July 6, 2017}}</ref> This research demonstrates that the present-day surface is more uninhabitable than previously thought,<ref name='bacteriocidal'/><ref name= 'Wall2017'>[https://www.space.com/37402-mars-life-soil-toxic-perchlorates-radiation.html Mars Soil May Be Toxic to Microbes]. Mike Wall. Space.com.  July 6, 2017</ref> and reinforces the notion to inspect at least a few meters into the ground to ensure the levels of radiation would be relatively low.<ref name='Wall2017'/><ref>[http://www.abc.net.au/news/2017-07-07/mars-toxic-soil-could-make-growing-vegies-harder/8687626 Mars soil is likely toxic to cells — does this mean humans won't be able to grow vegetables there?]. David Coady. ''The World Today''. 7 Jul 2017</ref>

=== Enceladus ===

The [[Cassini–Huygens|''Cassini'' spacecraft]] [[Cassini-Huygens#Enceladus flybys|directly sampled]] the plumes escaping from Enceladus. Measured data indicates that these geysers are made primarily of salt rich particles with an 'ocean-like' composition, which is thought to originate from a [[Ocean#Extraterrestrial oceans|subsurface ocean]] of liquid saltwater, rather than from the moon's icy surface.<ref>{{cite web| url = http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Cassini_samples_the_icy_spray_of_Enceladus_water_plumes |title = Cassini samples the icy spray of Enceladus' water plumes|date = June 22, 2011|publisher = European Space Agency}}</ref> Data from the geyser flythroughs also indicate the presence of organic chemicals in the plumes. Heat scans of Enceladus's surface also indicate higher temperatures around the fissures where the geysers originate, with temperatures reaching −93&nbsp;°C (−135&nbsp;°F), which is 115&nbsp;°C (207&nbsp;°F) warmer than the surrounding surface regions.<ref>{{cite web|url = http://www.nasa.gov/mission_pages/cassini/media/cassini-20080326.html |title = Cassini Tastes Organic Material at Saturn's Geyser Moon|date =26 March 2008|publisher = NASA}}</ref>

=== Europa ===

Europa has much indirect evidence for its sub-surface ocean. Models of how Europa is affected by [[tidal heating]] require a subsurface layer of liquid water in order to accurately reproduce the linear fracturing of the surface. Indeed, observations by the [[Galileo (spacecraft)|''Galileo'' spacecraft]] of how Europa's magnetic field interacts with Jupiter's field strengthens the case for a liquid, rather than solid, layer; an [[Dynamo theory|electrically conductive fluid]] deep within Europa would explain these results.<ref>[https://web.archive.org/web/20130106034335/http://solarsystem.nasa.gov/europa/evidence.cfm What Makes Us Think There is an Ocean Beneath Europa's Icy Crust?], Paragraphs 4 - 7</ref> Observations from the [[Hubble Space Telescope]] in December 2012 appear to show an ice plume spouting from Europa's surface,<ref>[https://web.archive.org/web/20150429174058/http://www.newscientist.com/article/mg22129502.700-water-plumes-spark-a-race-to-jupiter-moon-europa.html#.VUEXq3bP1qY Water plumes spark a race to Jupiter moon Europa], Lisa Grossman, New Scientist 31 December 2013</ref> which would immensely strengthen the case for a liquid subsurface ocean. As was the case for Enceladus, vapour geysers would allow for easy sampling of the liquid layer.<ref>[http://www.nasa.gov/content/goddard/hubble-europa-water-vapor Hubble Space Telescope Sees Evidence of Water Vapor Venting off Jupiter Moon], Paragraph 4; December 12, 2013</ref> Unfortunately, there appears to be little evidence that geysering is a frequent event on Europa due to the lack of water in the space near Europa.<ref>[http://www.nasa.gov/jpl/signs-of-europa-plumes-remain-elusive-in-search-of-cassini-data Signs of Europa Plumes Remain Elusive in Search of Cassini Data]; December 17, 2014</ref>

==Planetary protection==
{{main|Planetary protection}}

Forward contamination is prevented by [[Sterilization (microbiology)#Spacecraft|sterilizing space probes]] sent to sensitive areas of the Solar System. Missions are classified depending on whether their destinations are of interest for the search for life, and whether there is any chance that Earth life could reproduce there.

NASA made these policies official with the issuing of Management Manual NMI-4-4-1, ''NASA Unmanned Spacecraft Decontamination Policy'' on September 9, 1963.<ref>{{cite book|last1=Meltzer|first1=Michael|title=When Biospheres Collide: A History of NASA's Planetary Protection Programs|date=May 31, 2012|isbn=978-0-16-085327-2|pages=46–51}}</ref>  Prior to NMI-4-4-1 the same sterilization requirements were required on all outgoing spacecraft regardless of their target.  Difficulties in the sterilization of Ranger probes sent to the Moon are the primary reasons for NASA's change to a target-by-target basis in assessing the likelihood forward contamination.
 
Some destinations such as [[Mercury (planet)|Mercury]] need no precautions at all. Others such as the Moon require documentation but nothing more, while destinations such as Mars require sterilization of the rovers sent there.

Back contamination would be prevented by containment or quarantine. However, there have been no sample-returns thought to have any possibility of a back contamination risk since the [[Apollo program|Apollo missions]]. The Apollo regulations have been rescinded and new regulations have yet to be developed.  See [[#Suggested precautions for sample-returns|Suggested precautions for sample-returns]].

== Crewed spacecraft ==

[[Human spaceflight|Crewed spacecraft]] are of particular concern for interplanetary contamination because of the impossibility to sterilize a human to the same level as a robotic spacecraft. Therefore, the chance of forwarding contamination is higher than for a robotic mission.<ref name=biospherescollide /> Humans are typically [[Host (biology)|host]] to a hundred trillion microorganisms in ten thousand species in the [[human microbiome]] which cannot be removed while preserving the life of the human. Containment seems the only option, but effective containment to the same standard as a robotic rover appears difficult to achieve with present-day technology. In particular, adequate containment in the event of a hard landing is a major challenge.

Human explorers may be potential carriers back to Earth of microorganisms acquired on Mars, if such microorganisms exist.<ref>[http://www.nap.edu/openbook.php?record_id=10360&page=37 Safe on Mars page 37] "Martian biological contamination may occur if astronauts breathe contaminated dust or if they contact material that is introduced into their habitat. If an astronaut becomes contaminated or infected, it is conceivable that he or she could transmit Martian biological entities or even disease to fellow astronauts, or introduce such entities into the biosphere upon returning to Earth. A contaminated vehicle or item of equipment returned to Earth could also be a source of contamination."</ref> Another issue is the contamination of the water supply by Earth microorganisms shed by humans in their stools, skin and breath, which could have a direct effect on the long-term human colonization of Mars.<ref name=groundwatercontamination />

==The Moon ==

The [[Apollo 11]] missions incited public concern about the possibility of microbes on the Moon,<ref>{{Cite news |last=Sullivan |first=Walter |date=June 15, 1969 |title=Science; Guarding Against Moon Bugs |publisher=The New York Times |location=New York |type=Newspaper}}</ref> creating fears about a plague being brought to Earth when the astronauts returned.<ref>{{Cite journal |last=Johnson |first=Jenell |date=January 2, 2020 |title=The End of the World, The Future of the Earth: Bioplurality and the Politics of Human Extinction |journal=Journal for the History of Rhetoric |volume=23 |issue=1 |pages=30-53}}</ref> NASA received thousands of letters from Americans concerned with the potential for back contamination.<ref>{{Cite book |last=Johnson |first=Jenell |title=Every Living Thing: The Politics of Life in Common |publisher=Pennsylvania State University Press |publication-date=April 28, 2023 |pages=114-5}}</ref>

=== As a testbed ===
The [[Moon]] has been suggested as a testbed for new technology to protect sites in the Solar System, and astronauts, from forward and back contamination. Currently, the Moon has no contamination restrictions because it is considered to be "not of interest" for prebiotic chemistry and [[abiogenesis|origins of life]].  Analysis of the contamination left by the [[Apollo program]] astronauts could also yield useful ground truth for planetary protection models.<ref>[http://planetaryprotection.nasa.gov/file_download/53/Conley_Rummel_Acta_Astro_PP_Mars_Moon.pdf Mars and the Moon (C. A. Conley & J. D. Rummel Acta Astronautica 63 1025–1030 (2008))]</ref><ref>[https://www.academia.edu/267154/Biological_contamination_studies_of_lunar_landing_sites_implications_for_future_planetary_protection_and_life_detection_on_the_Moon_and_Mars Biological contamination studies of lunar landing sites: implications for futureplanetary protection and life detectionon the Moon and Mars], D.P. Glavin, J.P. Dworkin, M. Lupisella, G. Kminek and J.D. Rummel, International Journal of Astrobiology (2004) {{doi|10.1017/S1473550404001958}}</ref>

== Non-contaminating exploration methods ==
[[File:Teleroboitcs image2.jpg|thumb|Telerobotics exploration on Mars and Earth]]

One of the most reliable ways to reduce the risk of forward and back contamination during visits to extraterrestrial bodies is to use only [[robotic spacecraft]].<ref name=biospherescollide>[http://www.nasa.gov/connect/ebooks/when_biospheres_collide_detail.html#.U_uVh_mwJcQ When Biospheres Collide - a history of NASA'S Planetary Protection Programs], Michael Meltzer, May 31, 2012. See Chapter 7, Return to Mars. Quote: "One of the most reliable ways to reduce the risk of forward contamination during visits to extraterrestrial bodies is to make those visits only with robotic spacecraft. Sending a person to Mars would be, for some observers, more exciting. But in the view of much of the space science community, robotic missions are the way to accomplish the maximum amount of scientific inquiry since valuable fuel and shipboard power do not have to be expended in transporting and operating the equipment to keep a human crew alive and healthy. And very important to planetary protection goals, robotic craft can be thoroughly sterilized, while humans cannot. Such a difference can be critical in protecting sensitive targets, such as the special regions of Mars, from forward contamination." "Perhaps a change in the public's perspective as to just what today's robotic missions really are would be helpful in deciding what types of missions are important to implement. In the opinion of Terence Johnson, who has played a major role in many of NASA's robotic missions, including serving as the project scientist for the Galileo mission and the planned Europa Orbiter mission, the term "robotic exploration" misses the point. NASA is actually conducting human exploration on these projects.  The mission crews that sit in the control panel at JPL, "as well as everyone else who can log on to the Internet" can observe in near real-time what is going on. The spacecraft instruments, in other words, are becoming more like collective sense organs for humankind. Thus, according to Johnson, when NASA conducts its so-called robotic missions, people all around the world are really "all standing on the bridge of Starship Enterprise". The question must thus be asked, when, if ever, is it necessary for the good of humankind to send people rather than increasingly sophisticated robots to explore other worlds."</ref> Humans in close orbit around the target planet could control equipment on the surface in real time via telepresence, so bringing many of the benefits of a surface mission, without its associated increased forward and back contamination risks.<ref>[https://www.wired.com/category/wiredscience?p=136729 Almost Being There: Why the Future of Space Exploration Is Not What You Think]</ref><ref>[http://telerobotics.gsfc.nasa.gov/  First Exploration Telereobotics Symposium] {{webarchive|url=https://web.archive.org/web/20150705060719/http://telerobotics.gsfc.nasa.gov/ |date=2015-07-05 }}</ref><ref>[HERRO: A Science-Oriented Strategy for Crewed Missions Beyond LEO HERRO: A Science-Oriented Strategy for Crewed Missions Beyond LEO]
</ref>

== Back contamination issues ==

Since the Moon is now generally considered to be free from life, the most likely source of contamination would be from Mars during either a [[Mars sample-return mission]] or as a result of a [[Human mission to Mars|crewed mission to Mars]]. The possibility of new human pathogens, or environmental disruption due to back contamination, is considered to be of extremely low probability but cannot yet be ruled out.

NASA and ESA are actively developing a [[Sample-return mission|Mars Sample Return Program]] to return samples collected by the Perseverance Rover to Earth. The European Space Foundation report cites many advantages of a Mars sample-return. In particular, it would permit extensive analyses on Earth, without the size and weight constraints for instruments sent to Mars on rovers. These analyses could also be carried out without the communication delays for experiments carried out by Martian rovers. It would also make it possible to repeat experiments in multiple laboratories with different instruments to confirm key results.<ref name=esf2012_PP-advanntages>[https://science.nasa.gov/media/medialibrary/2013/01/17/ESF_Mars_Sample_Return_backward_contamination_study.pdf European Science Foundation - Mars Sample Return backward contamination - strategic advice] {{webarchive|url=https://web.archive.org/web/20160602150139/http://science.nasa.gov/media/medialibrary/2013/01/17/ESF_Mars_Sample_Return_backward_contamination_study.pdf |date=2016-06-02 }} July, 2012, {{ISBN|978-2-918428-67-1}} - see 2. From remote exploration to returning samples. (for more details of the document see [http://elib.dlr.de/78092/ abstract] )</ref>

[[Carl Sagan]] was first to publicise back contamination issues that might follow from a Mars sample-return. In ''Cosmic Connection'' (1973) he wrote:
{{blockquote|Precisely because Mars is an environment of great potential biological interest, it is possible that on Mars there are pathogens, organisms which, if transported to the terrestrial environment, might do enormous biological damage.<ref name=cosmicconnection>Carl Sagan,[http://www.e-reading.org.ua/bookreader.php/148581/Sagan_-_The_Cosmic_Connection___An_Extraterrestrial_Perspective.pdf ''The Cosmic Connection - an Extraterrestrial Perspective''] (1973) {{ISBN|0521783038}}</ref>}}
Later in ''Cosmos'' (1980) Carl Sagan wrote:
{{blockquote|Perhaps Martian samples can be safely returned to Earth. But I would want to be very sure before considering a returned-sample mission.<ref>{{cite book|author=Carl Sagan|title=Cosmos|url=https://books.google.com/books?id=EIqoiww1r9sC|year=2011|publisher=Random House Publishing Group|isbn=978-0-307-80098-5}}</ref>}}

NASA and ESA views are similar. The findings were that with present-day technology, Martian samples can be safely returned to Earth provided the right precautions are taken.<ref>{{cite report |title=Assessment of Planetary Protection Requirements for Mars Sample Return Missions |publisher=National Research Council |year=2009|url=http://www.nap.edu/openbook.php?record_id=12576&page=46}}| Quote: "The risks of [[Environmental degradation|environmental disruption]] resulting from the inadvertent contamination of Earth with putative martian microbes are still considered to be low. But since the risk cannot be demonstrated to be zero, due care and caution must be exercised in handling any martian materials returned to Earth."
</ref>

=== Suggested precautions for sample-returns ===

NASA has already had experience with returning samples thought to represent a low back contamination risk when samples were returned for the first time by [[Apollo 11]]. At the time, it was thought that there was a low probability of life on the Moon, so the requirements were not very stringent. The precautions taken then were inadequate by current standards, however. The regulations used then have been rescinded, and new regulations and approaches for a sample-return would be needed.<ref name=race>M. S. Race [http://salegos-scar.montana.edu/docs/Planetary%20Protection/AdvSpaceResVol18(1-2).pdf Planetary Protection, Legal Ambiguity, and the Decision Making Process for Mars Sample Return] {{webarchive|url=https://web.archive.org/web/20100619123320/http://salegos-scar.montana.edu/docs/Planetary%20Protection/AdvSpaceResVol18%281-2%29.pdf |date=2010-06-19 }} Adv. Space Res. vol 18 no 1/2 pp (1/2)345-(1/2)350 1996</ref>

==== Chain of contact ====

A sample-return mission would be designed to break the chain of contact between Mars and the exterior of the sample container, for instance, by sealing the returned container inside another larger container in the vacuum of space before it returns to Earth.<ref name="GTA 2013" /><ref name=mepag_ppt /> In order to eliminate the risk of parachute failure, the capsule could fall at terminal velocity and the impact would be cushioned by the capsule's thermal protection system. The sample container would be designed to withstand the force of the impact.<ref name=mepag_ppt>{{cite web |url=http://mepag.jpl.nasa.gov/meeting/mar-10/Li2-MSR_Dis-for-MEPAG3-17_tech_updates.pdf |title=Mars Sample Return Discussions |date = 23 February 2010|url-status=dead |archive-url=https://web.archive.org/web/20130216181529/http://mepag.jpl.nasa.gov/meeting/mar-10/Li2-MSR_Dis-for-MEPAG3-17_tech_updates.pdf |archive-date=2013-02-16 }}</ref>

==== Receiving facility ====

[[File:NIAID Integrated Research Facility - Positive Pressure Personnel Suit.jpg|thumb|Working inside a BSL-4 laboratory with air hoses providing positive air pressure to their suits]]

To receive, analyze and curate extraterrestrial soil samples, NASA has proposed to build a biohazard containment facility, tentatively known as the Mars Sample Return Receiving Facility (MSRRF).<ref name=samplereceivingfacility>[http://www.lpi.usra.edu/pss/presentations/200803/04-Atlas-PPSonMSR.pdf Mars Sample Return Receiving Facility]. (PDF).</ref> This future facility must be rated [[Biosafety level|biohazard level]] 4 ('''BSL-4''').<ref name=samplereceivingfacility/> While existing BSL-4 facilities deal primarily with fairly well-known organisms, a BSL-4 facility focused on extraterrestrial samples must pre-plan the systems carefully while being mindful that there will be unforeseen issues during sample evaluation and curation that will require independent thinking and solutions.<ref name='Bass 2020'>[https://www.lpi.usra.edu/meetings/lifedetection2012/pdf/6013.pdf Planning for the Analytic Environment to Conduct Life Detection Experiments on Samples Returned from Mars: Observations and Issues (2012)] D. S. Bass, D. W. Beaty, C. C. Allen, A. C. Allwood, L. E. Borg, K. E. Buxbaum1, J. A. Hurowitz and M. D. Schulte. ''Lunar and Planetary Institute''. 2012. Accessed: 19 August 2018.</ref>

The facility's systems must be able to contain unknown biohazards, as the sizes of any putative Martian microorganisms are unknown. In consideration of this, additional requirements were proposed. Ideally it should filter particles of 0.01&nbsp;μm or larger, and release of a particle 0.05&nbsp;μm or larger is unacceptable under any circumstance.<ref name='GTA 2013'>[https://science.nasa.gov/media/medialibrary/2013/01/17/ESF_Mars_Sample_Return_backward_contamination_study.pdf European Science Foundation - Mars Sample Return backward contamination - Strategic advice and requirements] {{webarchive|url=https://web.archive.org/web/20160602150139/http://science.nasa.gov/media/medialibrary/2013/01/17/ESF_Mars_Sample_Return_backward_contamination_study.pdf |date=2016-06-02 }}</ref>

The reason for this extremely small size limit of 0.01&nbsp;μm is for consideration of [[gene transfer agent]]s (GTAs) which are virus-like particles that are produced by some microorganisms that package random segments of [[DNA]] capable of [[horizontal gene transfer]].<ref name='GTA 2013'/> These randomly incorporate segments of the host genome and can transfer them to other evolutionarily distant hosts, and do that without killing the new host. In this way many archaea and bacteria can swap DNA with each other. This raises the possibility that Martian life, if it has a common origin with Earth life in the distant past, could swap DNA with Earth microorganisms in the same way.<ref name='GTA 2013'/> In one experiment reported in 2010, researchers left GTAs (DNA conferring antibiotic resistance) and marine bacteria overnight in natural conditions and found that by the next day up to 47% of the bacteria had incorporated the genetic material from the GTAs.<ref name=naturegta>{{cite journal 
| last = Maxmen | first = Amy | author-link = Amy Maxmen
| date = 2010-09-30
| title = Virus-like particles speed bacterial evolution
| journal = [[Nature (journal)|Nature]]
| doi = 10.1038/news.2010.507 | url = http://www.nature.com/news/2010/100930/full/news.2010.507.html
}}</ref><ref>Lauren D. McDaniel, Elizabeth Young, Jennifer Delaney, Fabian Ruhnau, Kim B. Ritchie, John H. Paul [https://www.science.org/doi/10.1126/science.1192243 High Frequency of Horizontal Gene Transfer in the Oceans] Science 1 October 2010: Vol. 330 no. 6000 p. 50 {{doi|10.1126/science.1192243}}</ref> Another reason for the 0.05&nbsp;μm limit is because of the discovery of [[ultramicrobacteria]] as small as 0.2&nbsp;μm across.<ref name='GTA 2013'/>

The BSL-4 containment facility must also double as a [[cleanroom]] to preserve the scientific value of the samples. A challenge is that, while it is relatively easy to simply contain the samples once returned to Earth, researchers would also want to remove parts of the sample and perform analyses. During all these handling procedures, the samples would need to be protected from Earthly contamination. A [[cleanroom]] is normally kept at a higher pressure than the external environment to keep contaminants out, while a biohazard laboratory is kept at a lower pressure to keep the biohazards in. This would require to compartmentalize the specialized rooms in order to combine these in a single building. Solutions suggested include a triple walled containment facility, and one of the suggestions include extensive robotic handling of the samples.<ref name=MSRRF-clean-room-quote>{{cite report |title=Mars Sample Return Receiving Facility - A Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth |year=2002 |url=http://www.lpi.usra.edu/pss/presentations/200803/04-Atlas-PPSonMSR.pdf| quote=''A Sample Return Facility will require combining technologies used for constructing maximum containment laboratories (e.g. Biosafety Level 4 labs) with cleanroom technologies which will be needed to protect the Mars samples from Earth contamination.}}</ref><ref>[http://www.marsinstitute.info/epo/docs/draft_protocol.pdf A Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth] {{webarchive|url=https://web.archive.org/web/20060222131531/http://www.marsinstitute.info/epo/docs/draft_protocol.pdf |date=2006-02-22 }}</ref><ref>[http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1395.pdf CLEANROOM ROBOTICS – APPROPRIATE TECHNOLOGY FOR A SAMPLE RECEIVING FACILITY 2005 update on the Draft Test Protocol ].</ref><ref>{{cite web|url = http://www.nap.edu/reports/13117/App%20G%2008_Mars-Sample-Return-Orbiter.pdf |title = 2010 Mars Sample Return Orbiter decadal survey|quote = The NASA Planetary Protection Officer commissioned the development of a draft test protocol that would represent one "necessary and sufficient" approach to evaluate the safety of the samples while safeguarding the purity of the samples from terrestrial contamination. A Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth was published in October 2002 [7]. In 2003, three architectural design teams independently examined the scope, approach, cost, and technology required for the SRF, using the Draft Test Protocol for requirements. The approaches varied from allrobotic handling of samples to more traditional glove box implementations. The studies indicated that the principles and techniques required are generally mature. Biosafety laboratories, the NASA Lunar Sample Facility, pharmaceutical laboratories, and electronic fabrication cleanrooms perform most of the required individual functions. However, there are some areas needing early development, such as ensuring sample preservation and bio-safety together, representing new challenges that were addressed by techniques like dual-walled containers (and gloves) with positive pressure clean inert gas in between the walls. This, as well as some further development in ultra-clean sample manipulation, safe and pure transport of samples, and sample sterilization techniques, are planned in the technology program.}}</ref>

The facility would be expected to take 7 to 10 years from design to completion,<ref name='Assessment 2009'>{{cite report |title=Assessment of Planetary Protection Requirements for Mars Sample Return Missions |publisher=National Research Council |year=2009 |chapter=7: Sample-Receiving Facility and Program Oversight |page=59 |chapter-url=http://www.nap.edu/openbook.php?record_id=12576&page=59 |quote=It has been estimated that the planning, design, site selection, environmental reviews, approvals, construction, commissioning, and pre-testing of a proposed safe room facility (SRF) will occur 7 to 10 years before actual operations begin. In addition, 5 to 6 years will likely be required for refinement and maturation of SRF-associated technologies for safely containing and handling samples to avoid contamination and to further develop and refine biohazard-test protocols. Many of the capabilities and technologies will either be entirely new or will be required to meet the unusual challenges of integration into an overall (end-to-end) Mars sample return program.}}</ref><ref name=MSRtaskgroup>[http://planetaryprotection.nasa.gov/summary/msr Mars Sample Return: Issues and Recommendations (Planetary Protection Office Summary)] Task Group on Issues in Sample Return. National Academies Press, Washington, DC (1997)</ref> and an additional two years is recommended for the staff to become accustomed to the facilities.<ref name='Assessment 2009'/><ref name="GTA 2013" />

==== Dissenting views on back contamination ====

Robert Zubrin, from the [[Mars Society]], maintains that the risk of back contamination is negligible. He supports this using an argument based on the possibility of transfer of life from Earth to Mars on meteorites.<ref name=zubrin>Robert Zubrin "Contamination From Mars: No Threat", [http://www.planetary.org/explore/the-planetary-report/ The Planetary Report] July/Aug. 2000, P.4–5</ref><!-- I haven't yet been able to obtain this article --><!-- he says it in this later interview as well however, which is available online--><ref name=zubrin-interview>[http://astronomy.nmsu.edu/cwc/Teaching/SpaceCol/sts497i/Zubrin/transcript.txt transcription of a tele-conference interview with ROBERT ZUBRIN] conducted on March 30, 2001 by the class members of STS497 I, "Space Colonization"; Instructor: Dr. Chris Churchill</ref>

==== Legal process of approval for Mars sample-return ====

Margaret Race has examined in detail the legal process of approval for a MSR.<ref name="race"/> She found that under the National Environmental Policy Act (NEPA) (which did not exist in the Apollo era) a formal environment impact statement is likely to be required, and public hearings during which all the issues would be aired openly. This process is likely to take up to several years to complete.

During this process, she found, the full range of worst accident scenarios, impact, and project alternatives would be played out in the public arena. Other agencies such as the Environment Protection Agency, Occupational Health and Safety Administration, etc., may also get involved in the decision-making process.

The laws on quarantine will also need to be clarified as the regulations for the Apollo program were rescinded. In the Apollo era, NASA delayed announcement of its quarantine regulations until the day Apollo was launched, so bypassing the requirement for public debate - something that would be unlikely to be tolerated today.

It is also probable that the presidential directive NSC-25 will apply which requires a review of large scale alleged effects on the environment and is carried out subsequent to the other domestic reviews and through a long process, leads eventually to presidential approval of the launch.

Then apart from those domestic legal hurdles, there are numerous international regulations and treaties to be negotiated in the case of a Mars sample-return, especially those relating to environmental protection and health. She concluded that the public of necessity has a significant role to play in the development of the policies governing Mars sample-return.

=== Alternatives to sample-returns ===

Several exobiologists have suggested that a Mars sample-return is not necessary at this stage, and that it is better to focus more on in situ studies on the surface first. Although it is not their main motivation, this approach of course also eliminates back contamination risks.

Some of these exobiologists advocate more in situ studies followed by a sample-return in the near future. Others go as far as to advocate in situ study instead of a sample-return at the present state of understanding of Mars.<ref name=JeffreyBada>Jeffrey L. Bada, Andrew D. Aubrey, Frank J. Grunthaner, Michael Hecht, Richard Quinn, Richard Mathies, Aaron Zent, John H. Chalmers [https://archive.org/details/JeffreyLBada Seeking signs of life on mars: in situ investigations as prerequisites to sample return missions] Independent Contribution to the Mars Decadal Survey Panel</ref><ref name=paige>[http://www.lpi.usra.edu/meetings/robomars/pdf/6199.pdf Mars Exploration Strategies: Forget About Sample Return] D. A. Paige, Dept. of Earth and Space Sciences, UCLA,
Los Angeles, CA 90095</ref><ref>[http://www.space.com/18322-mars-sample-return-humans-robots.html Future Mars Missions: Can Humans Trump Robots?]</ref>

Their reasoning is that life on Mars is likely to be hard to find. Any present day life is likely to be sparse and occur in only a few niche habitats. Past life is likely to be degraded by cosmic radiation over geological time periods if exposed in the top few meters of the Mars surface. Also, only certain special deposits of salts or clays on Mars would have the capability to preserve organics for billions of years. So, they argue, there is a high risk that a Mars sample-return at our current stage of understanding would return samples that are no more conclusive about the origins of life on Mars or present day life than the Martian meteorite samples we already have.

Another consideration is the difficulty of keeping the sample completely free from Earth life contamination during the return journey and during handling procedures on Earth. This might make it hard to show conclusively that any biosignatures detected does not result from contamination of the samples.

Instead they advocate sending more sensitive instruments on Mars surface rovers. These could examine many different rocks and soil types, and search for biosignatures on the surface and so examine a wide range of materials which could not all be returned to Earth with current technology at reasonable cost.

A sample-return to Earth would then be considered at a later stage, once we have a reasonably thorough understanding of conditions on Mars, and possibly have already detected life there, either current or past life, through biosignatures and other ''in situ'' analyses.

==== Instruments under development for ''in situ'' analyses ====

* NASA Marshall Space Flight Center is leading a research effort to develop a Miniaturized Variable Pressure Scanning Electron Microscope (MVP-SEM) for future lunar and Martian missions.<ref>Gaskin, J.A.; Jerman, G.; Gregory, D.; Sampson, A.R., [http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6187064&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F6178851%2F6186985%2F06187064.pdf%3Farnumber%3D6187064 Miniature Variable Pressure Scanning Electron Microscope for in-situ imaging & chemical analysis] Aerospace Conference, 2012 IEEE, vol., no., pp.1,10, 3–10 March 2012
doi: 10.1109/AERO.2012.6187064</ref>

* Several teams, including Jonathan Rothberg, and J. Craig Venter, are separately developing solutions for sequencing alien DNA directly on the Martian surface itself.<ref>[http://www.zmescience.com/science/martian-dna-sequencer-aline-life-041431/ Mars Sample Return Mission? Naaah… Just Beam Back Martian DNA]</ref><ref>Biomedicine News [http://www.zmescience.com/science/martian-dna-sequencer-aline-life-041431/ Genome Hunters Go After Martian DNA]</ref><ref>[http://scitechdaily.com/researchers-design-a-dna-sequencing-microchip-for-detecting-life-on-mars/ Researchers Design a DNA Sequencing Microchip for Detecting Life on Mars] Science Tech Daily, July 9, 2013</ref><ref>[http://online.liebertpub.com/doi/abs/10.1089/ast.2012.0923 Radiation Resistance of Sequencing Chips for in situ Life Detection] Christopher E. Carr, Holli Rowedder, Clarissa S. Lui, Ilya Zlatkovsky, Chris W. Papalias, Jarie Bolander, Jason W. Myers, James Bustillo, Jonathan M. Rothberg, Maria T. Zuber, and Gary Ruvkun. Astrobiology. June 2013, 13(6)  560-569. {{doi|10.1089/ast.2012.0923}}</ref>
* Levin is working on updated versions of the Labeled release instrument flown on Viking. For instance versions that rely on detecting chirality. This is of special interest because it can enable detection of life even if it is not based on standard life chemistry.<ref>{{cite conference|first1= A. D.|last1= Anbar|first2= G. V.|last2= Levin|url = http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4319.pdf |title =A Chiral Labeled Release Instrument for In Situ Detection of Extant Life|conference= Concepts and Approaches for Mars Exploration |date = June 12–14, 2012|location = Houston, TX}}</ref>
* The Urey Mars Organic and Oxidant Detector instrument for detection of biosignatures has been descoped, but was due to be flown on [[ExoMars]] in 2018. It is designed with much higher levels of sensitivity for biosignatures than any previous instruments<ref name=JeffreyBada /><ref>Andrew D. Aubrey,
John H. Chalmers, Jeffrey L. Bada, Frank J. Grunthaner, Xenia Amashukeli, Peter Willis, Alison M. Skelley,
Richard A. Mathies, Richard C. Quinn, Aaron P. Zent, Pascale Ehrenfreund, Ron Amundson, Daniel P. Glavin,
Oliver Botta, Laurence Barron, [[Diana Blaney|Diana L. Blaney]], Benton C. Clark, Max Coleman, Beda A. Hofmann, Jean-Luc Josset,
Petra Rettberg, Sally Ride, François Robert, Mark A. Sephton, and Albert Yen.  [http://astrobiology.berkeley.edu/PDFs_articles/08UreyAstrobio.pdf The Urey Instrument: An Advanced In Situ Organic and Oxidant Detector for Mars Exploration] ''Astrobiology''.
Volume 8, Number 3, 2008</ref><ref>J.L. Bada, P. Ehrenfreund F. Grunthaner, [[Diana Blaney|D. Blaney]], M. Coleman, 
A. Farrington, A. Yen, R. Mathies, R. Amudson, R. Quinn, A. Zen, S. Ride, L. Barron, O. Botta, B. Clark, D. Glavin, B. Hofmann, J.L. Josse, P. Rettberg, F. Robert, M. Sephton. [http://www.geology.wisc.edu/~astrobio/docs/Bada_et_al_2008_Space_Sci_Rev.pdf Urey: Mars Organic and Oxidant Detector] Space Sci Rev (2008) 135: 269–279</ref>

==== Study and analyses from orbit ====

During the “Exploration Telerobotics Symposium" in 2012 experts on telerobotics from industry, NASA and academics met to discuss telerobotics, and its applications to space exploration. Amongst other issues, particular attention was given to Mars missions and a Mars sample-return.

They came to the conclusion that telerobotic approaches could permit direct study of the samples on the Mars surface via telepresence from Mars orbit, permitting rapid exploration and use of human cognition to take advantage of chance discoveries and feedback from the results obtained so far.<ref name="lpi.usra.edu">[http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4214.pdf LOW-LATENCY TELEROBOTICS FROM MARS ORBIT: THE CASE FOR SYNERGY BETWEEN SCIENCE AND HUMAN EXPLORATION], Concepts and Approaches for Mars Exploration (2012)</ref>

They found that telepresence exploration of Mars has many advantages. The astronauts have near real-time control of the robots, and can respond immediately to discoveries. It also prevents contamination both ways and has mobility benefits as well.<ref>[http://telerobotics.gsfc.nasa.gov/papers/TelepresenceSymposiumfinal.pdf Space Exploration Enabled by Telepresence: Combining Science and Human Exploration] {{webarchive|url=https://web.archive.org/web/20130217143104/http://telerobotics.gsfc.nasa.gov/papers/TelepresenceSymposiumfinal.pdf |date=2013-02-17 }} Based on Findings from: "Exploration Telerobotics Symposium". May 2–3, 2012 NASA Goddard Space Flight Center</ref>

Return of the sample to orbit has the advantage that it permits analysis of the sample without delay, to detect volatiles that may be lost during a voyage home. This was the conclusion of a meeting of researchers at the NASA Goddard Space Flight Center in 2012.<ref name="lpi.usra.edu" /><ref>[http://telerobotics.gsfc.nasa.gov/papers/SymposiumReport-ExtendedVersion29Oct.pdf Space Exploration Via Telepresence: The Case for Synergy Between Science and Human Exploration, Findings and Observations from: "Exploration Telerobotics Symposium". May 2-3, 2012. NASA Goddard Space Flight Center] {{webarchive|url=https://web.archive.org/web/20130217143111/http://telerobotics.gsfc.nasa.gov/papers/SymposiumReport-ExtendedVersion29Oct.pdf |date=2013-02-17 }}</ref>
[[File:Telerobotics image1 large.jpg|thumb|Telerobotics exploration of Mars]]

Similar methods could be used to directly explore other biologically sensitive moons such as [[Europa (moon)|Europa]], [[Titan (moon)|Titan]], or [[Enceladus]], once the human presence in the vicinity becomes possible.

==Forward contamination==

===The 2019 ''Beresheet'' incident===

{{Main article|Tardigrades on the Moon}}

In August 2019, scientists reported that a capsule containing [[tardigrades]] (a resilient microbial animal) in a [[cryptobiotic state]] may have survived for a while on the Moon after the April 2019 crash landing of ''[[Beresheet]]'', a failed Israeli [[lunar lander]].<ref>{{cite magazine|url=https://www.wired.com/story/a-crashed-israeli-lunar-lander-spilled-tardigrades-on-the-moon/|title=A Crashed Israeli Lunar Lander Spilled Tardigrades On The Moon|last=Oberhaus|first=Daniel|date=5 August 2019|magazine=[[wired (magazine)|Wired]]|access-date=6 August 2019}}</ref><ref>{{cite news|url=https://www.vox.com/science-and-health/2019/8/6/20756844/tardigrade-moon-beresheet-arch-mission|title=Tardigrades, the toughest animals on Earth, have crash-landed on the moon – The tardigrade conquest of the solar system has begun|last=Resnick|first=Brian|date=6 August 2019|work=[[Vox (website)|Vox]]|access-date=6 August 2019}}</ref>

==See also==
{{Columns-list|

* {{annotated link|Astrobiology}}
* {{annotated link|Directed panspermia}}
* {{annotated link|Ethics of terraforming}} 
* {{annotated link|Extremophile|Extremophiles}}
* {{annotated link|Glossary of invasion biology terms}} 
* [[List of microorganisms tested in outer space]]
* {{annotated link|Panspermia}}
* {{annotated link|Planetary protection}}
* {{annotated link|Space debris}}
* {{section link|Terraforming|Other possibilities}}
}}

==References==
{{Reflist|33em}}

{{Doomsday}}

[[Category:Astrobiology]]
[[Category:Biological contamination]]
[[Category:Biological invasions]]
[[Category:Cosmic doomsday]]
[[Category:Extraterrestrial life]]
[[Category:Space debris]]
[[Category:Spaceflight]]