Astrobiologists are concerned with the possibility of life on Mars because of its proximity and resemblance to Earth. There has been no accepted evidence of life on Mars in the past or the present. However, habitable conditions do not necessarily imply life, even though evidence suggests that Mars' surface had liquid water during the ancient Noachian period and may have been suitable for microorganisms.
Telescopic studies and deployed probes were first used in the nineteenth century and are still being used today in the quest for proof of life on other planets. Modern scientific investigation has focused on searching for water, chemical biosignatures in soil and rocks on the surface, and biomarker gases, as opposed to earlier work that was phenomenological and bordered on fantasy.
In the study of the origins of life, Mars is of particular interest because of its resemblance to the early Earth. For this reason, Mars' climate has remained largely unchanged since the end of the Hesperian period due to its cold climate and lack of plate tectonics or continental drift. Even if life has never existed on Mars, the planet's surface is at least 3.5 billion years old, making it the best place to study the prebiotic conditions that led to life, even if life never existed there.
The Curiosity, Perseverance, and Opportunity rovers began searching for evidence of past life after discovering liquid water on the surface, including a past biosphere made up of autotrophic, chemotrophic, or chemolithoautotrophic microorganisms, as well as ancient water, including potentially habitable fluvio-lacustrine environments (plains associated with ancient rivers and lakes). Evidence of life, taphonomy (the study of fossils), and organic compounds on Mars are now primary goals for NASA and the European Space Agency (ESA).
The discovery of organic compounds in sedimentary rocks and of boron on Mars is significant because these are precursors to prebiotic chemistry in the universe. These findings, along with other findings showing that liquid water was present on ancient Mars, add credence to the idea that Gale Crater on Mars might have been habitable in its early days. Toxic perchlorates in the Martian soil make it impossible for microorganisms to thrive on the red planet's surface. As a result, scientists agree that life, if it exists or ever did exist on Mars, is most likely to be found or preserved below the planet's surface, far from the planet's current harsh environmental conditions.
NASA announced in June 2018 that seasonal variations in Mars' methane levels had been discovered. Microorganisms or geological processes could produce methane. NASA Mars 2020 rover Perseverance, having successfully landed, will store dozens of drill samples for eventual return to Earth for analysis in the late 2020s or 2030s. The European ExoMars Trace Gas Orbiter began mapping atmospheric methane in April 2018, and the 2022 ExoMars Rosalind Franklin will conduct subsurface sampling and analysis. There has been an updated status report on the studies looking into the possibility of finding life on Venus and Mars via phosphine and methane.
In the mid-17th century, the polar ice caps of Mars were discovered. During the late 18th century, William Herschel proved that they grow and shrink in the summer and winter of each hemisphere, depending on the season. Astronomers were aware of other similarities between Mars and Earth by the mid-19th century, such as the length of a day being nearly identical to the length of a day on Earth. Because its axial tilt was similar to that of Earth, it had seasons just like ours, but they lasted nearly twice as long because of its much longer year. As a result of these findings, scientists began to wonder if water or land could be hiding beneath the brighter albedo features on Mars. This sparked further speculation about the possibility that life could exist on Mars.
A fellow at Cambridge's Trinity College, William Whewell, proposed in 1854 that there could be life on Mars. After some observers, using telescopic lenses, observed what appeared to be Martian canals—which were later determined to be optical illusions—speculation about life on Mars erupted in the late 1800s. However, American astronomer Percival Lowell published his book Mars in 1895 and Mars and its Canals in 1906, claiming that the canals were the work of a long-dead civilization. Wells, a British author, wrote The War of the Worlds in 1897, which depicted an invasion by aliens from Mars who had escaped from their desiccated planet and were looking for a new home.
Beginning in 1894, when American astronomer William Wallace Campbell discovered that water and oxygen were absent from Mars' atmosphere, spectroscopy of the Red Planet's atmosphere got underway. After influential observers such as Eugène Antoniadi, who observed Mars from Meudon Observatory's 83-cm (32.6-inch) aperture telescope in 1909 and found no canals, and after stunning images of Mars from Pic du Midi Observatory's new Baillaud dome in the same year, the canals theory started to lose favor.
Mars' ecosystems are shaped by a combination of chemistry, physics, geology, and geography. The aggregate of these criteria may not be sufficient to determine whether an area is habitable, but the sum of these elements can assist in anticipating sites with greater or lower habitability potential. Environmental factors such as water availability, temperature, nutrients, a power source, and protection from solar ultraviolet and galactic cosmic radiation are all important in the two ecological approaches currently being used to estimate whether the Martian surface will be habitable in the future or not.
No one knows how many parameters are needed to determine a planet's habitability. The habitability threshold for each parameter set must be computed in the same way. Survivability rates drop precipitously in laboratory simulations when numerous deadly variables are present at the same time. There haven't been any simulations of Mars that take into account all of the biocidal elements. Furthermore, it's still unclear whether or not life on Mars would have radically different biochemistry and habitat requirements than life on Earth.
Even with a thick CO2 atmosphere, early Mars was colder than Earth has ever been, according to recent models. Even though global circumstances in the mid-late Noachian were probably frigid, localized warm conditions connected to impacts or volcanism could have created favorable conditions for the creation of the late Noachian valley networks. Water flowing on the surface of Mars should have occurred often, even though volcanism and impacts would have caused local warming. From the mid-Hesperian onward, there is evidence of a decline in habitability based on both mineralogical and morphological evidence. Impact erosion and/or loss of early atmosphere are two possible causes; however, no one knows for sure at this time.
As a result of atmosphere depletion and increased radiation due to the disappearance of Mars' magnetic field, the planet's surface became uninhabitable. Having a magnetic field would have prevented solar wind erosion, allowing Mars' atmosphere to remain dense enough to support the presence of liquid water at its surface. Temperatures fell as a result of the atmosphere's depletion. Permafrost, a subsurface ice layer, was formed when some of the liquid water inventory evaporated and was transferred to the poles.
Crater-forming impacts can create long-lasting hydrothermal systems when ice is present in the crust, according to observations and computer simulations. An active hydrothermal system in a 130 km wide crater, for example, may last up to 2 million years, long enough for microscopic life to arise but not far enough along the evolutionary path to have advanced.
In 2013, NASA's Curiosity rover's onboard equipment investigated soil and rock samples to learn more about many aspects of habitability. In addition to sulfur, nitrogen, hydrogen, oxygen, and phosphorus, the rover team found clay minerals that imply this soil was once part of a wetland, probably a lake or an ancient streambed with a neutral acidity and low salinity. Using data from Curiosity's investigation of Aeolis Palus, NASA announced on December 9, 2013, that Gale Crater may have once held a freshwater lake that might have been a favorable habitat for microbial life to flourish. Evidence that Mars formerly possessed a magnetic field that shielded it from cosmic and solar radiation, as well as evidence that liquid water once flowed on the planet, strongly suggests that Mars might have supported life. There is no confirmed proof that life ever existed on Mars based only on the assessment of the planet's previous habitability. In the event it happened, it is likely that it was a microbial community living together in fluids or sediments, either free-living or as biofilms. A look at how and where to look for indications of life on Mars is aided by studying terrestrial analogs.
If life ever existed on Mars in the past, it may have been preserved in the impactite, which has been proven to do so on Earth. According to NASA, the Curiosity rover identified organic compounds in sedimentary rocks that are three billion years old on June 7, 2018. Some of the basic chemical components needed for life have been found in rocks, as evidenced by the presence of organic compounds.
If there is life on Mars, evidence of it may be best kept in the subsurface, away from the severe circumstances on the surface. Current life on Mars, or its biosignatures, may exist in depths ranging from a few meters to several kilometers beneath the planet's surface. Only a few centimeters beneath the surface of Mars' permafrost do salty brines begin to flow freely, but this isn't very far. Unless there is a sudden release of subsurface water, the Hellas basin's water will not be able to remain liquid on the surface of Mars in its current state.
Since the Viking missions, NASA has focused on following the water on Mars and has not directly searched for biosignatures for life. For now, astrobiologists agree that exploring the Martian subsurface may be necessary to locate potentially livable regions.
It was revealed in 1965 by the Mariner 4 mission that Mars does not have a worldwide magnetic field that would shield the planet from potentially life-threatening cosmic radiation and solar radiation. In the course of several billion years, the solar wind may have been aided by the absence of magnetic shielding on Mars. Thus, Earth has been exposed to radiation from the cosmos for around 4 billion years.
Ionizing radiation from galactic cosmic rays and solar particle events may not be a limiting factor in habitability assessments for current surface life on Mars, according to recent in-situ data from the Curiosity rover. Curiosity's reading of 76 mGy per year is comparable to the radiation levels on the International Space Station.
Ionizing radiation levels were found to be 76 mGy per year by Curiosity's rover. Dormant life on Mars would be wiped off by this intensity of ionizing radiation. Based on its orbital eccentricity and tilt, it has a very different ability to support life than other planets. Estimates suggest that Mars rovers could detect dormant but still functional life at a depth of one meter below the surface if surface life was reactivated as recently as 450,000 years ago. Since Mars lost its atmosphere and magnetosphere, even the toughest cells on Earth could not withstand the radiation on Mars' surface. Researchers on Mars have concluded that the lethal dosages of cosmic radiation will eventually kill any life within the first few meters of the planet's surface after mapping the amounts of cosmic radiation at various depths on the planet. To avoid irreparable damage to DNA and RNA, scientists calculated that retrieving viable dormant cells on Mars would necessitate going deeper than 7.5 meters below the surface. ExoMars rover will be able to reach a maximum depth of 2 meters, which would allow even the most radiation-resistant terrestrial microorganisms to survive in a latent spore condition for 90,000 to 0.5 million years, depending on the type of rock.
It was discovered that "ionizing radiation considerably alters chemical compositions and structures, especially for water, salts and redox-sensitive components like as organic compounds," according to data acquired by the Radiation assessment detector (RAD) instrument on the Curiosity rover. Carbon bonds in Martian organic molecules can be broken and reconfigured with surrounding elements by ionizing charged particle radiation, regardless of their origin (meteoric, geological, or biological). New subsurface radiation estimations shed light on how long latent microorganisms or bacteria can survive at varying depths to preserve whatever organic biosignatures they may contain.
Solar storms in September 2017 temporarily increased radiation on the surface of Mars and caused an aurora 25 times brighter than any previously witnessed on the red planet, according to NASA.
UV radiation is fast fatal to unshielded bacteria on Mars. However, it can be mitigated by global dust storms and shielded completely with less than 1 millimeter of regolith or other creatures. UV irradiated perchlorates, on the other hand, caused a 10.8-fold increase in cell death compared to UV radiation exposure after 60 seconds in a laboratory study published in July 2017. Sunlight rays penetrate soils at the sub-millimeter to millimeter level, depending on the soil's physical qualities.
In the Martian regolith, perchlorate (ClO4) is known to be toxic to most living organisms, but because they drastically lower the freezing point of water and a few extremophiles can use it as an energy source, it has prompted speculation about what their influence on habitability would be.
Perchlorates become much more harmful to bacteria when exposed to a simulated Martian UV flux, according to research published in July 2017. (bactericide). Within minutes, even dormant spores were no longer viable. Perchlorates blasted with UV radiation induce a 10.8-fold greater increase in cell mortality than cells exposed to iron oxides and hydrogen peroxide on the Martian surface after 60 seconds of exposure. Toxic reactive oxygen species can be formed by abrading silicates (such as quartz and basalt). According to the researchers, "the surface of Mars is fatal to vegetative cells, which makes much of the surface and near-surface regions inhospitable," the present-day surface is more inhospitable than previously anticipated, and radiation levels should be checked at least a few meters below the surface is reinforced by this study.
However, a paleolake in Pilot Valley, Great Salt Lake Desert, Utah, was found to contain perchlorates and perchlorates-reducing bacteria for the first time in an analog setting. Having studied the biosignature of these bacteria, she hopes that the Mars Perseverance rover will uncover biosignature matches in its Jezero Crater location.
Temperatures above the melting point of ice cause the formation of recurrent slope lineae (RSL) characteristics on sun-facing slopes. There is a gradual increase of streaks in spring, which widens in late summer, and then fades away in autumn. Although the streaks themselves are regarded to be secondary effects and not directly indicative of the wetness of the regolith, it is difficult to represent this in any other way than as requiring liquid water in some form. Because of this, it is still possible that the water is either too cold or too salty to support life. Currently, they are considered "Uncertain Regions, to be classified as Special Regions.") Flowing brines were suspected at the time.
Brine ionic strength appears to be a major barrier to the habitability of Mars because of the limited thermodynamic availability of water (water activity) on Earth, particularly in hypersaline conditions. On Mars, divalent ions are so prevalent that they "make certain ecosystems inhospitable even in the presence of physiologically accessible water," according to an experiment.
It's hard to argue that nitrogen is the most crucial element for life after carbon. As a result, nitrate concentrations ranging from 0.1 to 5 percent must be measured to determine its prevalence and dispersion. Nitrogen (in the form of N2) is present in the atmosphere, but the concentrations are too low to sustain biological nitrogen-fixing. Nitrogen in nitrate form is a potential source of both plant nutrients and chemical processes for human research. Desert ecosystems on Earth have nitrates and perchlorates in common; the same may be true on Mars. An impact or volcanic plume of lightning may have caused the formation of nitrate on ancient Mars.
Nitrates were identified by heating surface sediments on Curiosity on March 24, 2015, according to NASA. "Fixed" means that the nitrogen is in an oxidized condition and may be utilized by living organisms. The finding lends support to the idea that life once flourished on Mars' ancient surface. There is a strong possibility that all of the nitrates on Mars are a byproduct of the planet's geological history. Since late 2017, nitrate concentrations have ranged from zero to 681 304 mg/kg in the samples tested. The condensed water coatings on the surface may transfer nitrates to lower depths (less than 10 meters), where subterranean microbes may thrive, according to modeling.
It's also abundant on Mars, phosphate, one of the chemical ingredients thought to be required for life.
The lack of knowledge on the growth of microbes at pressures close to those on the surface of Mars complicates estimates of the habitability of the Martian surface. Even if some bacteria can replicate at 25 mbar, it is still above the atmospheric pressures found on Mars (ranging from 1–14 mbar). In another investigation, only Serratia liquefaciens strain ATCC 27592 grew at 7 mbar, 0 °C, and CO2-enriched anoxic atmospheres out of 26 bacterial strains recovered from satellite assembly facilities.
The development of life as we know it requires the presence of liquid water, yet this is not sufficient because habitability depends on a wide range of environmental factors. On Mars' surface, liquid water can only last for a few minutes or hours at the lowest elevations. When the snow is heated by the Sun, small amounts of liquid water may form around the heated dust particles in the snow. Another possibility is that old ice sheets under the ground, which can be accessed from the surface via caves, may progressively sublimate or melt.
On Mars, the vast majority of the planet's water is in the form of water ice, which can be found in the Martian polar ice caps as well as beneath the surface of the planet. The atmosphere contains a trace amount of water vapor. 210 K (63 °C) temperature and 600 pascals (0.087 psi) atmospheric pressure at the surface means that there is no liquid water on the Martian surface, which is 0.6 percent of Earth's mean sea level pressure. Despite this, the atmosphere was denser, the temperature was higher, and massive quantities of liquid water flowed on the surface, including large seas, some 3.8 billion years ago.
Between 36% and 75% of the planet's surface may have been covered by the planet's primordial waters. According to NASA, the Utopia Planitia region of Mars contains a substantial amount of subterranean ice. The observed water is similar in volume to Lake Superior, according to the best estimates. For most Earth-like life to have flourished once Mars' surface waters were too salty, an analysis of Martian sediments using data from orbital spectrometry has revealed. Water activity (aw) ranged from 0.78 to 0.86, which is too high for most terrestrial life forms to survive in the Martian water tested by Tosca et al. While most microorganisms cannot survive in hypersaline solutions, haloarchaea can.
In June 2000, gullies resembling floods were discovered on the surface of Mars, indicating that there may be current liquid water moving there. Images acquired by the Mars Global Surveyor in 2006 show that water runs over the red planet's surface at times. As a result of these photographs, scientists now have conclusive proof that water once flowed through steep crater walls and sediment layers.
The scientific community is uncertain whether or not liquid water caused the recent gully streaks. Dry sand may have flowed down the slopes, according to some. Others have suggested that liquid brine may be near the surface, but the actual source of the water and the process underlying its movement are still unknown.
In July of this year, researchers announced the finding of the planet's first stable body of water, a 1.5-kilometer (0.93-mile)-deep subglacial lake beneath the southern polar ice sheet. The MARSIS radar aboard the Mars Express spacecraft detected the lake, and a series of profile images were taken between May 2012 and December 2015. In the vicinity of 193°E, 81°S, the lake's center is surrounded by higher ground, except for a depression on the lake's eastern side.
With its inoperative wheel in May 2007, the Spirit rover exposed an area rich in silica 90 percent of the time. When hot spring water or steam comes into contact with volcanic rocks, this result is reminiscent. Evidence of a formerly suitable environment for microbial life has been found in the form of silica, which scientists believe was formed by soil and acid fumes from volcanic activity in the presence of water.
Because of their ability to preserve organic and inorganic biosignatures, hydrothermal systems on Mars have a lot of appeal based on Earth analogs. In the search for fossil evidence of early Martian life, hydrothermal deposits are seen as important candidates.
3.48 billion-year-old geyserite and other related mineral deposits (typically found surrounding hot springs and geysers) were uncovered in Western Australia's Pilbara Craton in May 2017 as evidence of Earth's earliest known life on land. These findings may help select where best to seek early indications of life on the planet Mars.
Methane (CH4) is chemically unstable in the modern oxidizing atmosphere of Mars. Ultraviolet radiation from the Sun and reactions with other gases would cause it to quickly degrade. Therefore, a constant presence of methane in the atmosphere may imply the existence of a source to continually replenish the gas.
Trace levels of methane, at the level of a few parts per billion (ppb), were initially found in Mars's atmosphere by a team at the NASA Goddard Space Flight Center in 2003. Large changes in the abundances were recorded between measurements performed in 2003 and 2006, which revealed that the methane was locally concentrated and presumably seasonal. Mars' methane levels have been found to vary seasonally, according to a NASA announcement made on June 7, 2018.
The ExoMars Trace Gas Orbiter (TGO), sent to Mars in March 2016, began collecting data on April 21, 2018, to map the levels and sources of methane in the atmosphere, as well as its breakdown of chemicals such as formaldehyde and methanol. Since May 2019, the Trace Gas Orbiter indicated that the concentration of methane is under detectable level (< 0.05 ppbv).
Methane concentrations in the atmosphere were found to fluctuate seasonally, as discovered by Curiosity. The primary theories for the origin of Mars's methane include non-biological processes like radiolysis of water, water-rock reactions, and pyrite formation. These reactions all produce H2 that might later make methane and other hydrocarbons via Fischer–Tropsch synthesis with CO and CO2. Water, CO2, and the mineral olivine, which is found in abundance on Mars, have been demonstrated to work together to make methane. Other sources, like geologic methane produced through serpentinization, are plausible, but the lack of present volcanism, hydrothermal activity, or hotspots is not suitable for geologic methane.
An additional potential source is the presence of living microbes, such as methanogens, but until the Curiosity rover discovered methane in June 2019, there was no proof that these organisms existed on Mars. Methanogens do not require oxygen or organic foods, are non-photosynthetic, and use hydrogen for energy and CO2 as their carbon supply. Therefore they might exist in underground settings on Mars. If the methane is being produced by tiny life on Mars, it is most likely found deep below the planet's surface, where temperatures are still warm enough to support liquid water.
After finding methane in the atmosphere, some researchers have been working on in vitro experiments to see if methanogenic bacteria can grow on simulated Martian soil. They found that even when exposed to 1.0wt percent perchlorate salt, all four tested methanogen strains produced significant amounts of methane. Both the creation and degradation of methane might be explained by an ecosystem of microbes that produce and consume methane, according to research led by Levin.
Research from the University of Arkansas presented in June 2015 revealed that some methanogens could thrive in Mars's low-pressure environment. Previously, four species of methanogens have been found to survive in low-pressure circumstances that were equivalent to a deep liquid aquifer on Mars. The four species tested were Methanothermobacter wolfeii, Methanobacterium formicicum, Methanosarcina barkeri, and Methanococcus maripaludis. In June 2012, scientists reported that analyzing the ratio of hydrogen and methane levels on Mars may assist evaluate the likelihood of life on Mars. The detected ratios in the lower Martian atmosphere were roughly ten times higher, suggesting that biological activities may not be responsible for the reported CH4. A more precise estimate might be made by monitoring the H2 and CH4 flux on the Martian surface. Other scientists have lately developed methods of detecting hydrogen and methane in extraterrestrial atmospheres. Even if rover missions confirm that microscopic Martian life is the seasonal source of the methane, the living forms probably remain far below the surface, outside of the rover's grasp.
In February 2005, it was revealed that the Planetary Fourier Spectrometer (PFS) aboard the European Space Agency's Mars Express Orbiter had identified evidence of formaldehyde in the atmosphere of Mars. He believes that formaldehyde could be a result of methane oxidation and that this would indicate that Mars is either incredibly active geologically or harbors microbial life colonies, according to PFS director Vittorio Formisano. NASA scientists deem the preliminary findings well worth a follow-up but have also denied the claims of life.
The Viking mission of the 1970s sent two identical rovers to Mars' surface to search for signs of microbial life. Only the 'Labeled Release' (LR) experiment, which was carried out by each Viking lander, detected organic chemicals, as opposed to the other three. In light of this, the LR was judged inconclusive because it only tested a single, narrowly specified component of the notion that life could exist on Mars.
No Mars lander mission has identified meaningful signs of biomolecules or biosignatures. There are claims that Viking LR experiments found evidence of extant microbial life on Mars that are based on data from the Viking landers that have been reinterpreted as sufficient evidence of life, primarily by Gilbert Levin, Joseph D. Miller, Navarro and Giorgio Bianciardi, and Patricia Ann Straat.
Assessments reported in December 2010 by Rafael Navarro-Gonzáles show that organic molecules "may have been present" in the soil sampled by both Viking 1 and 2. The study found that perchlorate—discovered in 2008 by the Phoenix lander—can degrade organic compounds when heated and create chloromethane and dichloromethane as a byproduct, the exact chlorine chemicals discovered by both Viking landers when they did the same tests on Mars. Viking's search for organic compounds on Mars remains an unanswered subject due to perchlorate's ability to degrade any Martian organics.
There have been upwards of 224 known Martian meteorites discovered on Earth (some of which were recovered in numerous chunks) (some of which were found in several fragments). These are important because they are the only Martian samples that can be obtained by laboratories that are not on Mars' surface. Some scholars have proposed that microscopic morphological features identified in ALH84001 are biomorphs. However, this interpretation has been very controversial and is not endorsed by the majority of academics in the field.
For the detection of ancient life in terrestrial geologic rocks, a set of seven criteria has been developed. Those conditions are:
1. Is the geologic context of the sample compatible with past life?
2. Is the age of the sample and its stratigraphic location compatible with possible life?
3. Is there any evidence of cell shape and colonies in the sample?
4. Is there any evidence of biominerals showing chemical or mineral disequilibria?
5. Is there any evidence of stable isotope patterns unique to biology?
6. Are there any organic biomarkers present?
7. Are the features indigenous to the sample?
Most of these conditions must be met before previous life in a geologic sample may be accepted as a fact. No Martian sample has met all seven criteria.
In 1996, the Martian meteorite ALH84001 received considerable attention when a team of NASA scientists led by David S. McKay reported microscopic features and geochemical anomalies that they considered to be best explained by the rock having hosted Martian bacteria in the distant past. Aside from the fact that they were considerably smaller than any known living form, some of these traits matched those of terrestrial bacteria. Despite the heated debate that ensued, the data that McKay's team offered as proof of life was ultimately revealed to be non-biological. The debate over whether ALH 84001 includes evidence of ancient Martian life is now recognized as an important point in the development of exobiology, even if the scientific community has largely dismissed the hypothesis.
The Nakhla meteorite impacted Earth on June 28, 1911, in Nakhla, Alexandria, Egypt.
In 1998, a group from NASA's Johnson Space Center obtained a small sample of the meteorite to study. According to the findings, items identified in preterrestrial aqueous alteration phases resemble fossilized Earthly nanobacteria in both size and morphology. Testing done with gas chromatography and mass spectrometry (GC-MS) revealed its high molecular weight polycyclic aromatic hydrocarbons in 2000, and NASA scientists estimated that as much as 75 percent of the organic molecules in Nakhla "may not be recent terrestrial pollution."
This prompted more interest in this meteorite, so in 2006, NASA succeeded in getting another, larger sample from the London Natural History Museum. In this second sample, substantial dendritic carbon content was found. When the data and proof were presented in 2006, some independent researchers asserted that the carbon deposits are of biological origin. It was stated that as carbon is the fourth most prevalent element in the universe, finding it in odd patterns is not diagnostic or suggestive of biological genesis.
The Shergotty meteorite was a 4 kilograms (8.8 lb) Martian meteorite that fell to Earth on Shergotty, India, on August 25, 1865, and was picked up by witnesses nearly immediately. It is made largely of pyroxene and is assumed to have experienced preterrestrial aqueous modification for numerous centuries. Specific features in its interior suggest remnants of a biofilm and its associated microbial populations.
Yamato 000593 is the second-largest meteorite from Mars found on Earth. According to research, the Martian meteorite was created from a lava flow on Mars some 1.3 billion years ago. A meteorite was expelled from Mars' surface into space approximately 12 million years ago due to a collision. The meteorite fell on Earth in Antarctica some 50,000 years ago. There is evidence of historical water flow in the meteorite, which weighs 13.7 kilograms (30 pounds). Carbon-rich spheres may be seen in the meteorite's microscopic composition, which contrasts sharply with the absence of such spheres in the surrounding area. The carbon-rich spheres may have been created by biotic activity, according to NASA.
Organism–substrate interactions and their products are crucial biosignatures on Earth as they represent direct proof of biological behavior. It was the discovery of fossilized products of life-substrate interactions (ichnofossils) that have shown biological activities in the Earth's early history, e.g., during the Proterozoic and Archean epochs. Two important ichnofossil-like structures have been recorded from Mars, specifically the stick-like structures from the Vera Rubin Ridge and the microtunnels found in Martian meteorites.
Observations at Vera Rubin Ridge made by the Mars Space Laboratory rover, Curiosity, show millimetric, elongate formations retained in sedimentary rocks produced in fluvio-lacustrine conditions within Gale Crater. Morphometric and topologic data found on Mars are similar to the stick-like structures among Martian geological features and reveal that ichnofossils are among the closest morphological parallels of these unique features. Despite this, there isn't enough evidence to rule out sedimentary cracking and evaporitic crystal formation as mechanisms for the emergence of the structures' genetic code.
Martian meteorites have left behind depictions of microtunnels. They consist of straight or curved microtunnels that may contain areas of increased carbon richness. The form of the curving microtunnels is similar to biogenic traces on Earth, including microbioerosion traces seen in basaltic glasses. To be sure, more research is required.
The periodic icing and defrosting of the southern ice cap leads to the creation of spider-like radial pathways cut on 1-meter thick ice by sunlight. Then, sublimed CO2 – and perhaps water – increases pressure in their interior, causing geyser-like eruptions of chilly fluids often associated with dark basaltic sand or mud. This process is quick, witnessed occurring in the period of a few days, weeks, or months, a growth rate relatively unique in geology - notably for Mars.
According to a group of Hungarian scientists, the geysers' black dune patches and spider tunnels could be the result of photosynthesis by photosynthetic Martian microorganisms, which hibernate beneath the ice cover throughout the winter and produce heat when the Sun returns to the pole in the early spring. A pocket of liquid water, which would ordinarily evaporate instantaneously in the thin Martian atmosphere, is retained around them by the surrounding ice. The microorganisms may be seen through the grey ice as it melts. The microorganisms quickly desiccate and turn black, surrounded by a grey aureole, once the coating has melted completely. In their opinion, even a complicated sublimation process cannot explain how the black dune areas emerge and change over time and space, according to Hungarian researchers. Since their discovery, fiction author Arthur C. Clarke championed these structures as worthwhile investigation from an astrobiological perspective.
According to a study by a multi-national European team, spiders' channels could have provided a niche for tiny living forms to retreat and adapt while protected from sun radiation if they contained liquid water throughout their yearly thaw cycle. A British team also explores the possibility that organic stuff, bacteria, or even basic plants might co-exist with these inorganic forms, especially if the mechanism incorporates liquid water and a geothermal energy source. They also highlight that the majority of geological structures may be accounted for without using any organic "life on Mars" theory. The Mars Geyser Hopper lander has been proposed for investigation of the geysers up-close.
Planetary protection of Mars tries to prevent biological contamination of the planet. Preventing human-caused microbial introductions, often known as forwarding contamination, is a crucial priority in preserving the planet's record of natural processes. There is much evidence as to what can happen when creatures from locations on Earth that have been separated from one another for significant periods are introduced into each other's habitat. Species that are limited in one environment might grow – frequently out of control – in another environment, much to the disadvantage of the original species that were present. In some ways, this dilemma could be worsened if life forms from one planet were placed into the utterly foreign biosphere of another globe.
Incomplete sterilization of some resilient terrestrial microbes (extremophiles) by spacecraft, despite the greatest attempts, is the primary cause of hardware contamination on Mars. Radiation-resistant bacteria such as Deinococcus radiodurans and the genera Brevundimonas, Rhodococcus, and Pseudomonas have been studied in simulated Martian circumstances, and the results have been promising. This experiment's findings, along with previous radiation modeling, suggest that Brevundimonases sp. MV.7, which was only buried 30 cm deep in Martian dust, could withstand cosmic radiation for up 100,000 years before suffering a 66% population decline. Deinococcus radiodurans cells were badly harmed by the diurnal, Mars-like fluctuations in temperature and relative humidity. In other simulations, Deinococcus radiodurans likewise failed to grow under low air pressure, under 0 °C, or in the absence of oxygen.
In 1962, the first mission to Mars, Mars-1, was launched but never reached its destination due to a communication failure. Mars-2 and Mars-3, launched in 1971–1972, collected data on the composition of the Martian surface rocks and soil, as well as its thermal conductivity and any thermal anomalies that may have occurred. A temperature of 110°C (166°F) was recorded on Mars' northern polar cap, and its atmosphere's water vapor level was found to be 5,096 times lower on Mars than on Earth. No indications of life were found.
Mariner 4 probe completed the first successful flyby of the planet Mars, producing the first photos of the Martian surface in 1965. The photos depicted a barren Mars without rivers, oceans, or any signs of life. The lack of plate tectonics and weathering over the last 4 billion years, as well as the presence of numerous craters on the surface, were also discovered by the mission. It was discovered that Mars lacks a worldwide magnetic field, which would have shielded the planet from harmful cosmic radiation. Mars, having only an atmospheric pressure of 0.6 kPa (as opposed to Earth's 101.3 kPa), cannot support liquid water on its surface, according to the probe's findings. Due to the harshness of the Martian environment, subsequent missions focused on detecting bacteria-like creatures rather than multicellular ones.
Because liquid water is required for known life and metabolism, the presence of water on Mars may have been decisive in supporting life. The Viking orbiters revealed evidence of probable river valleys in numerous regions, erosion, and, in the southern hemisphere, branched streams.
The primary goal of the Viking probes of the mid-1970s was to carry out studies targeted at discovering microbes in Martian soil because the optimal conditions for the evolution of multicellular creatures ceased approximately four billion years ago on Mars. The tests were devised to look for microbial life similar to that seen on Earth. Of the four tests, only the Labeled Release (LR) experiment gave a favorable result, showing increased 14CO2 generation on first exposure of soil to water and nutrients. Two things about the Viking missions are universally agreed upon: that the Labeled Release experiment evolved radiolabeled 14CO2 and that the GCMS found no organic compounds. There are drastically differing interpretations of what the data imply: A 2011 astrobiology textbook adds that the GCMS was the critical reason which "For the majority of the Viking scientists, the final conclusion was that the Viking missions failed to identify life in the Martian soil."
Norman Horowitz, the chief of the Jet Propulsion Laboratory bioscience branch for the Mariner and Viking missions from 1965 to 1976, considered that the immense adaptability of the carbon atom made it the element most likely to supply solutions, even unusual solutions, to the difficulties of survival of life on other worlds. However, he also considered that the circumstances discovered on Mars were incompatible with carbon-based life.
One of the creators of the Labeled Release experiment, Gilbert Levin, feels his discoveries offer a definitive diagnosis for life on Mars. Many scientists disagree with Levin's interpretation. It has been reported in an astrobiology textbook of 2006, "It would, however, release more radioactive gas if additional nutrients were added to unsterilized Terrestrial samples after initial incubation because latent bacteria leaped into activity to consume the additional amount of food. Second and third nutrition injections on Mars failed to induce any more gas release, unlike on Earth." Other scientists suggest that superoxides in the soil may have created this impact without life being present. Because the gas chromatograph and mass spectrometer, intended to identify natural organic materials, did not find organic molecules, the Labeled Release data were almost universally disregarded as proof of life. The Curiosity rover has discovered large concentrations of organic compounds, particularly chlorobenzene, in powder taken from the "Cumberland" rock and studied by the rover. The conclusions of the Viking mission concerning life are deemed by the global expert community as inconclusive.
In 2007, during a Seminar at the Geophysical Laboratory of the Carnegie Institution (Washington, DC, US), Gilbert Levin's work was assessed once more. Levin still maintains that his original data were correct, as the positive and negative control experiments were in order. Moreover, Levin's team, on April 12, 2012, released statistical speculation based on old data—reinterpreted statistically through cluster analysis—of the Labeled Release experiments that may reveal evidence of "extant microbial life on Mars ."Critics reply that the method has not yet been shown useful for differentiating between biological and non-biological processes on Earth; hence it is premature to draw any conclusions.
The GCMS technology (TV-GC-MS) employed by the Viking program to hunt for organic compounds may not be sensitive enough to identify low amounts of organics, according to a team led by Rafael Navarro-González from the National Autonomous University of Mexico. Klaus Biemann, the lead scientist of the GCMS experiment aboard Viking, issued a reply. Because of the convenience of sample handling, TV–GC–MS is currently regarded as the standard approach for organic detection on future Mars missions. Hence Navarro-González advises that the design of future organic instruments for Mars should incorporate additional ways of detection.
After the finding of perchlorates on Mars by the Phoenix lander, nearly the same team of Navarro-González submitted a study alleging that the Viking GCMS results were affected by the presence of perchlorates. A 2011 astrobiology textbook states that "although perchlorate is too weak an oxidant to recreate the LR results (under the settings of that experiment perchlorate does not oxidize organics), it does oxidize, and so destroy, organics at the higher temperatures utilized in the Viking GCMS experiment." Biemann has produced a commentary critical of this Navarro-González study as well, to which the latter have answered; the discussion was published in December 2011.
The Phoenix project landed a robotic spacecraft in the polar region of Mars on May 25, 2008, and it worked until November 10, 2008. Both the hunt for a "habitable zone" in the Martian regolith and the study of the geological history of water on Mars were important objectives of this mission. The robotic arm of the lander, which extends to a length of 2.5 meters, was designed to dig shallow trenches in the regolith. Electrochemistry was used to determine how many and what kinds of antioxidants were present in the Martian regolith during the experiment. The Viking program data suggest that oxidants on Mars may vary with latitude. During the data collection portion of that mission, Viking 2 saw fewer oxidants than Viking 1 in its more northerly position. Phoenix landed further north still. Phoenix's preliminary findings revealed that Mars soil includes perchlorate and hence may not be as life-friendly as anticipated earlier. The pH and salinity levels were deemed innocuous from the standpoint of biology. The analyzers also detected the presence of bound water and CO2. A recent examination of Martian meteorite EETA79001 discovered 0.6 ppm ClO4−, 1.4 ppm ClO3−, and 16 ppm NO3−, likely of Martian origin. The ClO3− suggests the presence of other strongly oxidizing oxychlorines such as ClO2− or ClO, formed both by UV oxidation of Cl and X-ray radiolysis of ClO4−. This would suggest only highly refractory and/or well-protected (sub-surface) organics are likely to survive in a Martian environment. In addition, recent research of the Phoenix WCL found that the Ca(ClO4)2 in the Phoenix soil had not interacted with liquid water of any type, maybe for as long as 600 million years. If it had been in contact with water, the highly soluble Ca(ClO4)2 in contact would have produced CaSO4 solely. This represents a highly arid environment, with minimum or no liquid water contact.
The MSL mission is a NASA project that launched on November 26, 2011, with the Curiosity rover, a nuclear-powered robotic vehicle, as its flagship probe, holding sensors meant to assess past and present habitability conditions on Mars. The Curiosity rover landed on Mars on Aeolis Palus in Gale Crater, near Aeolis Mons (a.k.a. Mount Sharp), on August 6, 2012.
On December 16, 2014, NASA said the Curiosity rover discovered a "tenfold spike," possibly localized, in the amount of detectable methane in the Martian atmosphere. Methane levels in the atmosphere rose by an average of 7 parts per billion (ppb) between late 2013 and early 2014, according to measurements performed "a dozen times over 20 months." Until then, readings were only a fraction of what they are now. In addition, modest quantities of chlorobenzene (C6H5Cl) were discovered in powder excavated from one of the rocks, dubbed "Cumberland," studied by the Curiosity rover.
NASA's Mars 2020 rover project is set to launch on July 30, 2020. It is designed to explore an astrobiologically relevant ancient habitat on Mars and investigate its geochemical processes and history, including the ascertainment of its previous habitability and potential for retention of biosignatures within accessible geological elements.
ExoMars is a European-led multi-spacecraft initiative currently under production by the European Space Agency (ESA) and the Russian Federal Space Agency (Roscosmos) for launch in 2016 and 2020. Its major objective will be to look for any evidence of life on Mars, ancient or modern. A rover with a 2 m (6.6 ft) core drill will be utilized to investigate various depths below the surface where liquid water may be discovered and where microbes or organic biosignatures might survive cosmic radiation. Mars sample-return mission – A Mars soil sample investigation on Earth is the most promising attempt to find signs of life. However, the problem of supplying and maintaining life support for the months of passage from Mars to Earth remains to be solved. This was a big task. Thus it was decided that instead of relying on culture-based methods, "investigating carbon-based organic molecules would be one of the more fruitful approaches for detecting potential signals of life in returning samples."