ars' polar ice caps were observed

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, a_w ≤ 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