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In 1277, the Bishop of Paris, Étienne Tempier, did overturn Aristotle on one point: Godcould have created more than one world (given His omnipotence). Taking a further step, and arguing that aliens actually existed, remained rare. Notably, Cardinal Nicholas of Kues speculated about aliens on the Moon and Sun.[133] William Vorilong also speculated about the existence of humans on alien worlds, DELL DFS541305MH0T Laptop CPU Cooling Fan

but he came to the conclusion that God, although empowered to create them, would choose to not do so.

There was a dramatic shift in thinking initiated by the invention of the telescope and the Copernican assault on geocentric cosmology. Once it became clear that the Earth was merely one planet amongst countless bodies in the universe, the theory of extraterrestrial life started to become a topic in the scientific community. HP G62-341NR Laptop CPU Cooling Fan

The best known early-modern proponent of such ideas was the Italian philosopher Giordano Bruno, who argued in the 16th century for an infinite Universe in which every star is surrounded by its own planetary system. Bruno wrote that other worlds "have no less virtue nor a nature different to that of our earth" and, like Earth, "contain animals and inhabitants".[134] HP Pavilion dv6648el Laptop CPU Cooling Fan

In the early 17th century, the Czech astronomer Anton Maria Schyrleus of Rheita mused that "if Jupiter has (...) inhabitants (...) they must be larger and more beautiful than the inhabitants of the Earth, in proportion to the [characteristics] of the two spheres".[135]

In Baroque literature such as The Other World: The Societies and Governments of the Moon by Cyrano de Bergerac, HP Pavilion dv7-6151ed Laptop CPU Cooling Fan

extraterrestrial societies are presented as humoristic or ironic parodies of earthly society. The didactic poet Henry Moretook up the classical theme of the Greek Democritus in "Democritus Platonissans, or an Essay Upon the Infinity of Worlds" (1647). In "The Creation: a Philosophical Poem in Seven Books" (1712), Sir Richard Blackmore observed: "We may pronounce each orb sustains a race / Of living things adapted to the place". Toshiba Satellite P100-386 Laptop CPU Cooling Fan

With the new relative viewpoint that the Copernican revolution had wrought, he suggested "our world's sunne / Becomes a starre elsewhere". Fontanelle's "Conversations on the Plurality of Worlds" (translated into English in 1686) offered similar excursions on the possibility of extraterrestrial life, expanding, rather than denying, the creative sphere of a Maker.  HP G42-380LA Laptop CPU Cooling Fan

The possibility of extraterrestrials remained a widespread speculation as scientific discovery accelerated. William Herschel, the discoverer of Uranus, was one of many 18th–19th-century astronomers convinced that the Solar System, and perhaps others, would be well populated by alien life. Other luminaries of the period who championed "cosmic pluralism" included Immanuel Kant and Benjamin Franklin.  HP G60-230us Laptop CPU Cooling Fan

At the height of the Enlightenment, even the Sun and Moon were considered candidates for extraterrestrial inhabitants.

Since the 1830s, Mormons have believed that God has created and will create many Earth-like planets on which humans live.[136] HP KSB06105HA Laptop CPU Cooling Fan

They believe that all of these people are children of God. Joseph Smith, the founder of The Church of Jesus Christ of Latter-day Saints, taught that God revealed this information to Moses and that the Creation account written by Moses corresponded only to "our" earth.[137] There is no official doctrine relating to the location or commonality of these inhabited planets.[138] SONY Vaio VPC-EB1E0E Laptop CPU Cooling FanSpeculation about life on Mars increased in the late 19th century, following telescopic observation by some observers of apparent Martian canals — which were however soon found to be optical illusions. Despite this, in 1895, American astronomer Percival Lowell published his book Mars, followed by Mars and its Canalsin 1906, proposing that the canals were the work of a long-gone civilization.[139]  Compaq Presario CQ70-220EO Laptop CPU Cooling Fan

This idea led British writer H. G. Wells to write The War of the Worlds in 1897, telling of an invasion by aliens from Mars who were fleeing the planet's desiccation.

Spectroscopic analysis of Mars' atmosphere began in earnest in 1894, when U.S. astronomer William Wallace Campbell showed that neither water nor oxygen was present in the Martian atmosphere.[140] HP Pavilion dv7-3060sb Laptop CPU Cooling Fan

By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.

The science fiction genre, although not so named during the time, develops during the late 19th century. Jules Verne's Around the Moon (1870) features a discussion of the possibility of life on the Moon, but with the conclusion that it is barren. ACER Aspire 7720 Series Laptop CPU Cooling Fan

Stories involving extraterrestrials are found in e.g. Garrett P. Serviss's Edison's Conquest of Mars (1897). The War of the Worlds by H. G. Wells was published in 1898 and stands at the beginning of the popular idea of the "Martian invasion" of Earth prominent in 20th-century pop culture.

A radio drama version of Wells' novel broadcast in 1938 over the CBS Radio Network led to outrage because it supposedly suggested to many listeners that an actual alien invasion by Martians was in progress. SONY UDQF2PH52CF0 Laptop CPU Cooling Fan

In the wake of the Roswell UFO incident in 1947, conspiracy theories on the presence of extraterrestrials became a widespread phenomenon in the United States during the 1940s and the beginning Space Age during the 1950s, accompanied by a surge of UFO reports. The term UFO itself was coined in 1952 in the context of the enormous popularity of the concept of "flying saucers" in the wake of the Kenneth Arnold UFO sightingin 1947. Compaq Presario CQ61-216TU Laptop CPU Cooling Fan

The Majestic 12 documents published in 1982 suggest that there was genuine interest in UFO conspiracy theories in the US government during the 1940s.

The trend to assume that celestial bodies were populated almost by default was tempered as actual probes visited potential alien abodes in the Solar System beginning in the second half of the 20th century, Toshiba Satellite A215-S5802 Laptop CPU Cooling Fan

and by the 1970s belief in UFOs had become part of the fringe beliefs associated with the paranormal, New Age, Earth mysteries, Forteana etc. A number of UFO religions developed during the surge in UFO belief during the 1950s to 1970s period, and some, such as Scientology (founded 1953) and Raëlism (founded 1974) remain active into the present. Toshiba Satellite A210-1BC Laptop CPU Cooling Fan

The idea of "paleocontact", supposing that extraterrestrials ("ancient astronauts") have visited the Earth in the remote past and left traces in ancient cultures, appears in early-20th-century fiction such as The Call of Cthulhu (1926) and the idea came to be established as a notable aspect of the Ufology subculture in the wake of Erich von Däniken's Chariots of the Gods? (1968). DELL Inspiron 630m Laptop CPU Cooling Fan

Alien abduction claims were widespread during the 1960s and 1970s in the United States.

On the scientific side, the possibility of extraterrestrial life on the Moon was decisively ruled out by the 1960s, and during the 1970s it became clear that most of the other bodies of the Solar System do not harbour highly developed life, although the question of primitive life on bodies in the Solar System remains an open question. ACER Travelmate 4152nlci Laptop CPU Cooling Fan

Carl Sagan, Bruce Murray, and Louis Friedman founded the U.S. Planetary Society, partly as a vehicle for SETI studies in 1980, and since the 1990s, systematic search for radio signals attributable to intelligent extraterrestrial life has been ongoing.

In the early 1990s, NASA was set to join in on SETI research with a planned targeted search and all-sky survey. HP Pavilion dv6-3034tx Laptop CPU Cooling Fan

However, Senator Richard Bryan of Nevada cut funding for the project, and no comparable search has taken place since.

The failure so far of the SETI program to detect an intelligent radio signal after decades of effort, has at least partially dimmed the prevailing optimism of the beginning of the space ageHP G62-107SA Laptop CPU Cooling Fan

. Notwithstanding, the belief in extraterrestrial beings continues to be voiced inpseudoscience, conspiracy theories, and in popular folklore, notably "Area 51" and legends. It has become a pop culture trope given less-than-serious treatment in popular entertainment with e.g. the ALF TV series (1986–1990), The X-Files (1993–2002), etc.  HP G62-455TX Laptop CPU Cooling Fan

The SETI program is not the result of a continuous, dedicated search, but instead utilizes what resources and manpower it can, when it can. Furthermore, the SETI program only searches a limited range of frequencies at any one time.[142]

In the words of SETI's Frank Drake, "All we know for sure is that the sky is not littered with powerful microwave transmitters".[143] HP 532617-001 Laptop CPU Cooling Fan

Drake noted that it is entirely possible that advanced technology results in communication being carried out in some way other than conventional radio transmission. At the same time, the data returned by space probes, and giant strides in detection methods, have allowed science to begin delineating habitability criteria on other worlds, and to confirm that at least other planets are plentiful, though aliens remain a question mark. HP Pavilion dv6-1101au CPU Fan

The Wow! signal, detected in 1977 by a SETI project, remains a subject of speculative debate.

In 2000, geologist and paleontologist Peter Ward and astrobiologist Donald Brownlee published a book entitled Rare Earth: Why Complex Life is Uncommon in the Universe.[144] In it, they discussed the Rare Earth hypothesis, in which they claim that Earth-like life is rare in the Universe, while microbial life is common. HP Pavilion dv7-3190ev CPU Fan

Ward and Brownlee are open to the idea of evolution on other planets which is not based on essential Earth-like characteristics (such as DNA and carbon).The possible existence of primitive (microbial) life outside of Earth is much less controversial to mainstream scientists, although, at present, no direct evidence of such life has been found. Indirect evidence has been offered for the current existence of primitive life on Mars. HP Pavilion dv7-1157cl CPU Fan

However, the conclusions that should be drawn from such evidence remain in debate.

The Catholic Church has not made a formal ruling on the existence of extraterrestrials. However, writing in the Vatican newspaper, the astronomer, Father José Gabriel Funes, director of the Vatican Observatory near Rome, said in 2008 that intelligent beings created by God could exist in outer space.[ HP COMPAQ NX9420 CPU Fan

In September 2010, it was reported that the U.N. General Assembly had appointed Mazlan Othman as their official extraterrestrial liaison by the UK paper The Sunday Times.[147] This claim was later refuted.[148]

Theoretical physicist Stephen Hawking in 2010 warned that humans should not try to contact alien life forms. He warned that aliens might pillage Earth for resources. "HP Mini 110-1110ET CPU Fan

If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans", he said.[149]Jared Diamond has expressed similar concerns.[150] Scientists at NASA and Penn State University published a paper in April 2011 addressing the question "Would contact with extraterrestrials benefit or harm humanity?" The paper describes positive, negative and neutral scenarios.[151] HP Pavilion dv7-1157cl CPU Fan

In 2011, Richard Hoover, an astrobiologist at the U.S. Space Flight Center in Alabama, claimed that filaments and other structures in rare meteorites appear to be microscopic fossils of extraterrestrial beings that resemble cyanobacteria—a phylum of photosynthetic bacteria.[152]

On May 9, 2013, a congressional hearing by two U. S. House of Representatives subcommittees discussed "Exoplanet Discoveries:HP Pavilion dv6-3163eo CPU Fan

Have We Found Other Earths?", prompted by the discovery of exoplanet Kepler-62f, along with Kepler-62e and Kepler-62c. A related special issue of the journal Science, published earlier, described the discovery of the exoplanets.

For centuries people have speculated about the possibility of life on Mars due to the planet's proximity and similarity toEarth.HP Pavilion dv9740us CPU Fan

Serious searches for evidence of life began in the 19th century, and continue via telescopic investigations and landed missions. While early work focused on phenomenology and bordered on fantasy, modern scientific inquiry has emphasized the search for water, chemical biosignatures in the soil and rocks at the planet's surface, and the search for biomarker gases in the atmosphere.[1] ACER Aspire 4743 CPU Fan

Mars is of particular interest for the study of the origins of life, because of its similarity to the early Earth. This is especially so as Mars has a cold climate and lacks plate tectonics or continental drift, and has remained almost unchanged since the end of the Hesperian period. At least two thirds of Mars' surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to abiogenesis, even if life does not or has never existed there.[2][3] It remains an open question whether life currently exists on Mars, or has existed there in the past, and fictional Martians have been a recurring feature of popular entertainment of the 20th and 21st centuries. HP Pavilion dv6-2170us CPU Fan

On January 24, 2014, NASA reported that current studies on the planet Mars by the Curiosity and Opportunity rovers will now be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic and/orchemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable.[ Toshiba Satellite L675-S7018 CPU Fan

The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on the planet Mars is now a primary NASA objective.

Mars' polar ice caps were observed as early as the mid-17th century, and they were first proven to grow and shrink alternately, in the summer and winter of each hemisphere, byWilliam Herschel in the latter part of the 18th century. ASUS F80Q CPU Fan

By the mid-19th century, astronomers knew that Mars had certain other similarities to Earth, for example that thelength of a day on Mars was almost the same as a day on Earth. They also knew that its axial tilt was similar to Earth's, which meant it experienced seasons just as Earth does — but of nearly double the length owing to its much longer year. ACER TravelMate 4200 CPU Fan

These observations led to the increase in speculation that the darker albedo features were water, and brighter ones were land. It was therefore natural to suppose that Mars may be inhabited by some form of life.

In 1854, William Whewell, a fellow of Trinity College, Cambridge, who popularized the wordscientist, theorized that Mars had seas, land and possibly life forms. HP 434678-001 CPU Fan

Speculation about life on Mars exploded in the late 19th century, following telescopic observation by some observers of apparent Martian canals — which were later found to be optical illusions. Despite this, in 1895, American astronomer Percival Lowell published his book Mars, followed by Mars and its Canals in 1906, proposing that the canals were the work of a long-gone civilization.[8] HP G70-120EA CPU Fan

This idea led British writer H. G. Wells to write The War of the Worlds in 1897, telling of an invasion by aliens from Mars who were fleeing the planet’s desiccation.

Spectroscopic analysis of Mars' atmosphere began in earnest in 1894, when U.S. astronomer William Wallace Campbell showed that neither water nor oxygen were present in the Martian atmosphere.[9] Toshiba Satellite A300-034 CPU Fan

By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.

Chemical, physical, geological and geographic attributes shape the environments on Mars. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential.[10] HP 606609-001 CPU Fan

The two current ecological approaches for predicting the potential habitability of the Martian surface use 19 or 20 environmental factors, with emphasis on water availability, temperature, presence of nutrients, an energy source, and protection from Solar ultraviolet and galactic cosmic radiation.[11][12]

Scientists do not know the minimum number of parameters for determination of habitability potential, but they are certain it is greater than one or two of the factors in the table below.[10] Compaq Presario CQ60-301sl CPU Fan

Similarly, for each group of parameters, the habitability threshold for each is to be determined.[10] Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.[13] There are no full-Mars simulations published yet that include all of the biocidal factors combined. TOSHIBA Satellite L300 CPU Fan

The loss of the Martian magnetic field strongly affected surface environments through atmospheric loss and increased radiation; this change significantly degraded surface habitability.[14] When there was a magnetic field, the atmosphere would have been protected from erosion by solar wind, which would ensure the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars.[15] ASUS Eee PC 701 CPU Fan

Soil and rock samples studied in 2013 by NASA's Curiosity rover's onboard instruments brought about additional information on several habitability factors.[16]The rover team identified some of the key chemical ingredients for life in this soil, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and possibly carbon, as well as clay minerals, suggesting a long-ago aqueous environment — perhaps a lake or an ancient streambed — that was neutral and not too salty.[16] Compaq Presario CQ60-305sa CPU Fan

On December 9, 2013, NASA reported that, based on evidence from Curiosity studying Aeolis Palus, Gale Crater contained an ancient freshwater lake which could have been a hospitable environment for microbial life.[17][18] The confirmation that liquid water once flowed on Mars, the existence of nutrients, and the previous discovery of a past magnetic field that protected the planet from cosmic and Solar radiation,[1HP 637607-001 CPU Fan

9][20] together strongly suggest that Mars could have had the environmental factors to support life.[21] However, the assessment of past habitability is not in itself evidence that Martian life has ever actually existed. If it did, it was probably microbial, existing communally in fluids or on sediments, either free-living or as biofilms, respectively. HP Pavilion dv7-3067nr CPU Fan

No definitive evidence for biosignatures or organics of Martian origin has been identified, and assessment will continue not only through the Martian seasons, but also back in time as the Curiosity rover studies what is recorded in the depositional history of the rocks in Gale Crater.[10] While scientists have not identified the minimum number of parameters for determination of habitability potential, some teams have proposed hypotheses based on simulations. HP Pavilion dv5-1210ez CPU Fan

Although Mars soils are likely not to be overtly toxic to terrestrial microorganisms,[10] life on the surface of Mars is extremely unlikely because it is bathed in radiation and it is completely frozen. Therefore, the best potential locations for discovering life on Mars may be at subsurface environments that have not been studied yet. Compaq Presario CQ50-211nr CPU Fan

The extensive volcanism in the past possibly created subsurface cracks and caves within different strata where liquid water could have been stored, forming large aquifers with deposits of saline liquid water, minerals, organic molecules, andgeothermal heat – potentially providing a habitable environment away from the harsh surface conditions.

Although liquid water does not appear at the surface of Mars, HP G56-114SA CPU Fan

several modeling studies suggest that potential locations on Mars could include regions where thin films of salty liquid brine or perchlorate may form near the surface[36][36][37] that may provide a potential location for terrestrial salt and cold-loving microorganisms (halophile psychrophilic).[38] Various salts present in the Martian soil may act as an antifreeze and could keep water liquid well below its normal freezing point, if water was present at certain favorable locations.[36SONY Vaio VGN-CR21Z/N CPU Fan

] Astrobiologists are keen to find out more, as not much is known about these brines at the moment. The briny water may or may not be habitable to microbes from Earth or Mars.[41] Another researcher argues that although chemically important, thin films of transient liquid water are not likely to provide suitable sites for life.[39] In addition, an astrobiology team asserted that theactivity of water on salty films, HP Pavilion dv7-4060eo CPU Fan

the temperature, or both are less than the biological thresholds across the entire Martian surface and shallow subsurface.[12]

The damaging effect of ionizing radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats.[25 ] Even at a depth of 2 meters beneath the surface, any microbes would probably be dormant, Toshiba Satellite M70-252 CPU Fan

cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs.[26] Also, solar ultraviolet (UV) radiation proved particularly devastating for the survival of cold-resistant microbes under simulated surface conditions on Mars, as UV radiation was readily and easily able to penetrate the salt-organic matrix that the bacterial cells were embedded in.[43] Toshiba Satellite A100-455 CPU Fan

In addition, NASA's Mars Exploration Program states that life on the surface of Mars is unlikely, given the presence of superoxides that break down organic (carbon-based) molecules on which life is based

In 1965, the Mariner 4 probe discovered that Mars had no global magnetic field that would protect the planet from potentially life-threatening cosmic radiationand solar radiation; HP Pavilion dv5-2112br CPU Fan

observations made in the late 1990s by the Mars Global Surveyor confirmed this discovery.[45] Scientists speculate that the lack of magnetic shielding helped the solar wind blow away much of Mars's atmosphere over the course of several billion years.[46] As a result, the planet has been vulnerable to radiation from space for about 4 billion years.[47] DELL BFB0505HA CPU Fan

Currently, ionizing radiation on Mars is typically two orders of magnitude (or 100 times) higher than on Earth.[48] Even the hardiest cells known could not possibly survive the cosmic radiation near the surface of Mars for that long.[22][49] After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several meters of the planet's surface would be killed by lethal doses of cosmic radiation.[22][23][24HP Pavilion dv6-3299en CPU Fan

] The team calculated that the cumulative damage to DNA and RNA by cosmic radiation would limit retrieving viable dormant cells on Mars to depths greater than 7.5 metres below the planet's surface.Even the most radiation-tolerant Earthly bacteria would survive in dormant spore state only 18,000 years at the surface; at 2 meters —the greatest depth at which the ExoMars rover will be capable of reaching— survival time would be 90,000 to half million years, depending on the type of rock.[24] SONY Vaio VGN-NW11Z/T CPU Fan

The Radiation assessment detector (RAD) on board the Curiosity rover is currently quantifying the flux of biologically hazardous radiation at the surface of Mars today, and will help determine how these fluxes vary on diurnal, seasonal, solar cycle and episodic (flare, storm) timescales. These measurements will allow calculations of the depth in rock or soil to which this flux,Toshiba Satellite L550-20W CPU Fan

when integrated over long timescales, provides a lethal dose for known terrestrial organisms.[50]

Research published in January 2014 of data collected by the RAD instrument, revealed that the actual absorbed dose measured is 76 mGy/year at the surface,[51]and that "ionizing radiation strongly influences chemical compositions and structures, especially for water, salts, and redox-sensitive components such as organic matter."[51] HP Pavilion dv7-4183sf CPU Fan

Regardless of the source of Martian organic matter (meteoritic, geological, or biological), its carbon bonds are susceptible to breaking and reconfigurating with surrounding elements by ionizing charged particle radiation.[51] These improved subsurface radiation estimates give insight into the potential for the preservation of possible organic biosignatures as a function of depth as well as survival times of possible microbial or bacterial life forms left dormant beneath the surface.[51] HP Pavilion dv7-3190ev CPU Fan

The report concludes that the in situ "surface measurements —and subsurface estimates— constrain the preservation window for Martian organic matter following exhumation and exposure to ionizing radiation in the top few meters of the Martian surface."

After carbon, nitrogen is arguably the most important element needed for life. HP KSB06105HA CPU Fan

Thus, measurements of nitrate over the range of 0.1% to 5% are required to address the question of its occurrence and distribution. There is nitrogen (as N2) in the atmosphere at low levels, but this is not adequate to support nitrogen fixation for biological incorporation.[52] Nitrogen in the form of nitrate, if present, could be a resource for human exploration both as a nutrient for plant growth and for use in chemical processes. HP G62-244CA CPU Fan

On Earth, nitrates correlate with perchlorates in desert environments, and this may also be true on Mars. Nitrate is expected to be stable on Mars and to have formed in shock and electrical processes. Currently there is no data on its availability.Further complicating estimates of the habitability of the Martian surface is the fact that very little is known on the growth of microorganisms at pressures close to the conditions found on the surface of Mars. HP Pavilion dv7-3190ei CPU Fan

Some teams determined that some bacteria may be capable of cellular replication down to 25 mbar, but that is still above the atmospheric pressures found on Mars (range 1–14 mbar).[53] In another study, twenty-six strains of bacteria were chosen based on their recovery from spacecraft assembly facilities, and only Serratia liquefaciens strain ATCC 27592 exhibited growth at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres. HP G62-244CA CPU Fan

Liquid water, necessary for life as we know it, cannot exist on the surface of Mars except at the lowest elevations for minutes or hours.[54][55] Liquid water does not appear at the surface itself,[56] but it could form in minuscule amounts around dust particles in snow heated by the Sun.[57][57][58][58] Also, the ancient equatorial ice sheets beneath the ground may slowly sublimate or melt, accessible from the surface via caves.[ ASUS A6000R CPU Fan

Water on Mars exists almost exclusively as water ice, located in the Martian polar ice caps and under the shallow Martian surface even at more temperate latitudes.A small amount of water vapor is present in the atmosphere. There are no bodies of liquid water on the Martian surface because its atmospheric pressure at the surface averages 600 pascals (0.087 psi)—about 0.6% of Earth's mean sea level pressure—and because the temperature is far too low, HP Pavilion dv7-6011sg CPU Fan

(210 K (−63 °C)) leading to immediate freezing. Despite this, about 3.8 billion years ago, there was a denser atmosphere, higher temperature, and vast amounts of liquid water flowed on the surface, including large oceans.It has been estimated that the primordial oceans on Mars would have covered between 36% and 75% of the planet. Toshiba Satellite L300D-01P CPU Fan

Analysis of Martian sandstones, using data obtained from orbital spectrometry, suggests that the waters that previously existed on the surface of Mars would have had too high a salinity to support most Earth-like life. Tosca et al. found that the Martian water in the locations they studied all had water activity, aw ≤ 0.78 to 0.86—a level fatal to most Terrestrial life.[78] Compaq Presario CQ60-409CA CPU Fan

Haloarchaea, however, are able to live in hypersaline solutions, up to the saturation point.[79]

In June 2000, possible evidence for current liquid water flowing at the surface of Mars was discovered in the form of flood-like gullies.[80][81] Additional similar images were published in 2006, taken by the Mars Global Surveyor, that suggested that water occasionally flows on the surface of Mars. HP Mini 110-3010sf CPU Fan

The images did not actually show flowing water. Rather, they showed changes in steep crater walls and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago.

There is disagreement in the scientific community as to whether or not the recent gully streaks were formed by liquid water. Some suggest the flows were merely dry sand flows.[ Toshiba Satellite L645D-S4056 CPU Fan

Others suggest it may be liquid brine near the surface, but the exact source of the water and the mechanism behind its motion are not understood.

In May 2007, the Spirit rover disturbed a patch of ground with its inoperative wheel, uncovering an area extremely rich insilica (90%).[90] The feature is reminiscent of the effect of hot spring water or steam coming into contact with volcanic rocks.Toshiba Satellite M70-142 CPU Fan

Scientists consider this as evidence of a past environment that may have been favorable for microbial life, and theorize that one possible origin for the silica may have been produced by the interaction of soil with acid vapors produced by volcanic activity in the presence of water.[91]

Based on Earth analogs, hydrothermal systems on Mars would be highly attractive for their potential for preserving organicand inorganic biosignatures.[ DELL Inspiron E1505 CPU Fan

For this reason, hydrothermal deposits are regarded as important targets in the exploration for fossil evidence of ancient Martian life.

Trace amounts of methane in the atmosphere of Mars were discovered in 2003 and verified in 2004.As methane is an unstable gas, its presence indicates that there must be an active source on the planet in order to keep such levels in the atmosphere. It is estimated that Mars must produce 270 ton/year of methane,[104][105] HP 532613-001 CPU Fan

but asteroid impacts account for only 0.8% of the total methane production. Although geologic sources of methane such as serpentinization are possible, the lack of current volcanism, hydrothermal activity or hotspots[106] are not favorable for geologic methane. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. HP Envy 14-1080eo CPU Fan

Although research published in December 2009 ruled out this possibility,[107] research published in 2012 suggest that a source may be organic compounds on meteorites that are converted to methane by ultraviolet radiation.

The existence of life in the form of microorganisms such as methanogens is among possible, but as yet unproven sources. ACER TravelMate 5230 CPU Fan

If microscopic Martian life is producing the methane, it probably resides far below the surface, where it is still warm enough for liquid water to exist.[28]

Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and in vitroexperiments testing growth of methanogenic bacteria on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0wt% perchlorate salt.[109] Lenovo 3000 G430 CPU Fan

The results reported indicate that the perchlorates discovered by the Phoenix Lander would not rule out the possible presence of methanogens on Mars.[109][110]

A team led by Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.[110][111] ASUS EEE PC 1215N CPU Fan

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.[112][113] According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."[112] Other scientists have recently reported methods of detecting hydrogen and methane inextraterrestrial atmospheres.[114][115] Dell Vostro 3750 CPU Fan

In contrast to the findings described above, studies by Kevin Zahnle, a planetary scientist at NASA's Ames Research Center, and two colleagues, conclude that "there is as yet no compelling evidence for methane on Mars". They argue that the strongest reported observations of the gas to date have been taken at frequencies where interference from methane in Earth's atmosphere is particularly difficult to remove, and are thus unreliable. Toshiba Satellite L500-018 CPU Fan

Additionally, they claim that the published observations most favorable to interpretation as indicative of Martian methane are also consistent with no methane being present on Mars.[116][117][118]

The Curiosity rover, which landed on Mars in August 2012, is able to make measurements that distinguish between different isotopologues of methane;[119] COMPAQ Presario CQ42-116TU CPU Fan

but even if the mission is to determine that microscopic Martian life is the seasonal source of the methane, the life forms probably reside far below the surface, outside of the rover's reach.[120] The first measurements with the Tunable Laser Spectrometer (TLS) in the Curiosity rover indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement.On July 19, 2013, HP Pavilion dv6-2115eg CPU Fan

NASA scientists published the results of a new analysis of the atmosphere of Mars, reporting a lack of methane around the landing site of the Curiosity rover. On September 19, 2013, NASA again reported no detection of atmospheric methane with a measured value of 0.18±0.67 ppbv corresponding to an upper limit of only 1.3 ppbv (95% confidence limit) and, as a result, conclude that the probability of current methanogenic microbial activity on Mars is reduced. Toshiba Satellite L645D-S4056 CPU Fan

India's Mars Orbiter Mission, launched on November 5, 2013, will search for methane in the atmosphere of Mars using its Methane Sensor for Mars (MSM). The orbiter is scheduled to arrive at Mars on September 24, 2014. The Mars Trace Gas Mission orbiter planned to launch in 2016 would further study the methane, if present,[131][132] as well as its decomposition products such as formaldehyde and methanol. HP 646578-001 CPU Fan

In February 2005, it was announced that the Planetary Fourier Spectrometer (PFS) on the European Space Agency's Mars Express Orbiter had detected traces offormaldehyde in the atmosphere of Mars. Vittorio Formisano, the director of the PFS, has speculated that the formaldehyde could be the byproduct of the oxidation of methane and, according to him, SONY VAIO PCG-6L2L CPU Fan

would provide evidence that Mars is either extremely geologically active or harbouring colonies of microbial life.[133][134] NASA scientists consider the preliminary findings well worth a follow-up, but have also rejected the claims of life.

NASA maintains a catalog of 34 Mars meteorites.[137] These assets are highly valuable since they are the only physical samples available of Mars. Toshiba Satellite X205-S9349 CPU Fan

Studies conducted by NASA's Johnson Space Center show that at least three of the meteorites contain potential evidence of past life on Mars, in the form of microscopic structures resembling fossilized bacteria (so-called biomorphs). Although the scientific evidence collected is reliable, its interpretation varies. To date, none of the original lines of scientific evidence for the hypothesis that the biomorphs are of exobiological origin  DELL yy529 CPU Fan

(the so-called biogenic hypothesis) have been either discredited or positively ascribed to non-biological explanations.

The ALH84001 meteorite was found in December 1984 in Antarctica, by members of the ANSMET project; the meteorite weighs 1.93 kilograms (4.3 lb).[139] The sample was ejected from Mars about 17 million years ago and spent 11,000 years in or on the Antarctic ice sheets. HP Pavilion dv7-3020es CPU Fan

Composition analysis by NASA revealed a kind of magnetite that on Earth, is only found in association with certain microorganisms.[138] Then, in August 2002, another NASA team led by Thomas-Keptra published a study indicating that 25% of the magnetite in ALH 84001 occurs as small, uniform-sized crystals that, on Earth, is associated only with biologic activity, and that the remainder of the material appears to be normal inorganic magnetite. HP G62-369TX CPU Fan

The extraction technique did not permit determination as to whether the possibly biological magnetite was organized into chains as would be expected. The meteorite displays indication of relatively low temperature secondary mineralization by water and shows evidence of preterrestrial aqueous alteration. Evidence of polycyclic aromatic hydrocarbons (PAHs) have been identified with the levels increasing away from the surface. HP 13.V1.BJ195.F.GN CPU Fan

Some structures resembling the mineralized casts of terrestrial bacteria and their appendages (fibrils) or by-products (extracellular polymeric substances) occur in the rims of carbonate globules and preterrestrial aqueous alteration regions.[140][141] The size and shape of the objects is consistent with Earthly fossilized nanobacteria, but the existence of nanobacteria itself is controversial. Toshiba Satellite L675D-S7016 CPU Fan

In November 2009, NASA scientists reported after more detailed analyses, that a biogenic explanation is a more viable hypothesis for the origin of themagnetites in the meteorite.

The Nakhla meteorite fell on Earth on June 28, 1911 on the locality of Nakhla, Alexandria, Egypt.[144][145]

In 1998, a team from NASA's Johnson Space Center obtained a small sample for analysis. HP Pavilion dv7-1451nr CPU Fan

Researchers found preterrestrial aqueous alteration phases and objects[146] of the size and shape consistent with Earthly fossilized nanobacteria, but the existence of nanobacteria itself is controversial. Analysis with gas chromatography and mass spectrometry (GC-MS) studied its high molecular weight polycyclic aromatic hydrocarbons in 2000,HP G62-a57SG CPU Fan

and NASA scientists concluded that as much as 75% of the organic matter in Nakhla "may not be recent terrestrial contamination".[138][147]

This caused additional interest in this meteorite, so in 2006, NASA managed to obtain an additional and larger sample from the London Natural History Museum. On this second sample, a large dendritic carbon content was observed. SONY Vaio VGN-NR31S/S CPU Fan

When the results and evidence were published on 2006, some independent researchers claimed that the carbon deposits are of biologic origin. However, it was remarked that since carbon is the fourth most abundant element in the Universe, finding it in curious patterns is not indicative or suggestive of biologica origin.

he Shergotty meteorite, a 4 kg Martian meteorite, fell on Earth on Shergotty, India on August 25, 1865 and was retrieved by witnesses almost immediately.[150IBM 91P9252 CPU Fan

]This meteorite is relatively young, calculated to have been formed on Mars only 165 million years ago from volcanic origin. It is composed mostly of pyroxeneand thought to have undergone preterrestrial aqueous alteration for several centuries. Certain features in its interior suggest remnants of a biofilm and its associated microbial communities.[138] Work is in progress on searching for magnetites within alteration phases. Toshiba Satellite M70-122 CPU Fan,SONY UDQFWPH22FQU CPU Fan,HP Pavilion dv6-2150ei CPU Fan,HP G42-367TU CPU Fan

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