title: Water on Mars

text: Over 60 meteorites have been found that came from Mars. Some of them contain evidence that they were exposed to water when on Mars. Some Martian meteorites called basaltic shergottites, appear (from the presence of hydrated carbonates and sulfates) to have been exposed to liquid water prior to ejection into space. It has been shown that another class of meteorites, the nakhlites, were suffused with liquid water around 620 million years ago and that they were ejected from Mars around 10.75 million years ago by an asteroid impact. They fell to Earth within the last 10,000 years. Martian meteorite NWA 7034 has one order of magnitude more water than most other Martian meteorites. It is similar to the basalts studied by rover missions, and it was formed in the early Amazonian epoch.


title: Water on Mars

text: In 1996, a group of scientists reported the possible presence of microfossils in the Allan Hills 84001, a meteorite from Mars. Many studies disputed the validity of their interpretation mainly based on the shape of these presumed fossils. It was found that most of the organic matter in the meteorite was of terrestrial origin. In addition, the scientific consensus is that "morphology alone cannot be used unambiguously as a tool for primitive life detection". Interpretation of morphology is notoriously subjective, and its use alone has led to numerous errors of interpretation.


title: Water on Mars

text: The 1971 Mariner 9 spacecraft caused a revolution in our ideas about water on Mars. Huge river valleys were found in many areas. Images showed that floods of water broke through dams, carved deep valleys, eroded grooves into bedrock, and traveled thousands of kilometers. Areas of branched streams, in the southern hemisphere, suggested that rain once fell. The numbers of recognised valleys has increased through time. Research published in June 2010 mapped 40,000 river valleys on Mars, roughly quadrupling the number of river valleys that had previously been identified. Martian water-worn features can be classified into two distinct classes: 1) dendritic (branched), terrestrial-scale, widely distributed, Noachian-age valley networks and 2) exceptionally large, long, single-thread, isolated, Hesperian-age outflow channels. Recent work suggests that there may also be a class of currently enigmatic, smaller, younger (Hesperian to Amazonian) channels in the mid-latitudes, perhaps associated with the occasional local melting of ice deposits.


title: Water on Mars

text: Some parts of Mars show inverted relief. This occurs when sediments are deposited on the floor of a stream and then become resistant to erosion, perhaps by cementation. Later the area may be buried. Eventually, erosion removes the covering layer and the former streams become visible since they are resistant to erosion. Mars Global Surveyor found several examples of this process. Many inverted streams have been discovered in various regions of Mars, especially in the Medusae Fossae Formation, Miyamoto Crater, Saheki Crater, and the Juventae Plateau.


title: Water on Mars

text: A variety of lake basins have been discovered on Mars. Some are comparable in size to the largest lakes on Earth, such as the Caspian Sea, Black Sea, and Lake Baikal. Lakes that were fed by valley networks are found in the southern highlands. There are places that are closed depressions with river valleys leading into them. These areas are thought to have once contained lakes; one is in Terra Sirenum that had its overflow move through Ma'adim Vallis into Gusev Crater, explored by the Mars Exploration Rover Spirit. Another is near Parana Valles and Loire Vallis. Some lakes are thought to have formed by precipitation, while others were formed from groundwater. Lakes are estimated to have existed in the Argyre basin, the Hellas basin, and maybe in Valles Marineris. It is likely that at times in the Noachian, many craters hosted lakes. These lakes are consistent with a cold, dry (by Earth standards) hydrological environment somewhat like that of the Great Basin of the western USA during the Last Glacial Maximum.


title: Water on Mars

text: Research from 2010 suggests that Mars also had lakes along parts of the equator. Although earlier research had showed that Mars had a warm and wet early history that has long since dried up, these lakes existed in the Hesperian Epoch, a much later period. Using detailed images from NASA's Mars Reconnaissance Orbiter, the researchers speculate that there may have been increased volcanic activity, meteorite impacts or shifts in Mars' orbit during this period to warm Mars' atmosphere enough to melt the abundant ice present in the ground. Volcanoes would have released gases that thickened the atmosphere for a temporary period, trapping more sunlight and making it warm enough for liquid water to exist. In this study, channels were discovered that connected lake basins near Ares Vallis. When one lake filled up, its waters overflowed the banks and carved the channels to a lower area where another lake would form. These dry lakes would be targets to look for evidence (biosignatures) of past life.


title: Water on Mars

text: On September 27, 2012, NASA scientists announced that the "Curiosity" rover found direct evidence for an ancient streambed in Gale Crater, suggesting an ancient "vigorous flow" of water on Mars. In particular, analysis of the now dry streambed indicated that the water ran at , possibly at hip-depth. Proof of running water came in the form of rounded pebbles and gravel fragments that could have only been weathered by strong liquid currents. Their shape and orientation suggests long-distance transport from above the rim of the crater, where a channel named Peace Vallis feeds into the alluvial fan.


title: Water on Mars

text: Eridania Lake is a theorized ancient lake with a surface area of roughly 1.1 million square kilometers. Its maximum depth is 2,400 meters and its volume is 562,000 km. It was larger than the largest landlocked sea on Earth, the Caspian Sea, and contained more water than all the other Martian lakes together. The Eridania sea held more than nine times as much water as all of North America's Great Lakes. The upper surface of the lake was assumed to be at the elevation of valley networks that surround the lake; they all end at the same elevation, suggesting that they emptied into a lake.


title: Water on Mars

text: Research with CRISM found thick deposits, greater than 400 meters thick, that contained the minerals saponite, talc-saponite, Fe-rich mica (for example, glauconite-nontronite), Fe- and Mg-serpentine, Mg-Fe-Ca-carbonate and probable Fe-sulfide. The Fe-sulfide probably formed in deep water from water heated by volcanoes. Such a process, classified as hydrothermal may have been a place where life on Earth began.


title: Water on Mars

text: Researchers have found a number of examples of deltas that formed in Martian lakes. Finding deltas is a major sign that Mars once had a lot of liquid water. Deltas usually require deep water over a long period of time to form. Also, the water level needs to be stable to keep sediment from washing away. Deltas have been found over a wide geographical range, though there is some indication that deltas may be concentrated around the edges of the putative former northern ocean of Mars.


title: Water on Mars

text: By 1979 it was thought that outflow channels formed in single, catastrophic ruptures of subsurface water reservoirs, possibly sealed by ice, discharging colossal quantities of water across an otherwise arid Mars surface. In addition, evidence in favor of heavy or even catastrophic flooding is found in the giant ripples in the Athabasca Vallis. Many outflow channels begin at Chaos or Chasma features, providing evidence for the rupture that could have breached a subsurface ice seal.


title: Water on Mars

text: The branching valley networks of Mars are not consistent with formation by sudden catastrophic release of groundwater, both in terms of their dendritic shapes that do not come from a single outflow point, and in terms of the discharges that apparently flowed along them. Instead, some authors have argued that they were formed by slow seepage of groundwater from the subsurface essentially as springs. In support of this interpretation, the upstream ends of many valleys in such networks begin with box canyon or "amphitheater" heads, which on Earth are typically associated with groundwater seepage. There is also little evidence of finer scale channels or valleys at the tips of the channels, which some authors have interpreted as showing the flow appeared suddenly from the subsurface with appreciable discharge, rather than accumulating gradually across the surface. Others have disputed the link between amphitheater heads of valleys and formation by groundwater for terrestrial examples, and have argued that the lack of fine scale heads to valley networks is due to their removal by weathering or impact gardening. Most authors accept that most valley networks were at least partly influenced and shaped by groundwater seep processes.


title: Water on Mars

text: Groundwater also played a vital role in controlling broad scale sedimentation patterns and processes on Mars. According to this hypothesis, groundwater with dissolved minerals came to the surface, in and around craters, and helped to form layers by adding minerals—especially sulfate—and cementing sediments. In other words, some layers may have been formed by groundwater rising up depositing minerals and cementing existing, loose, aeolian sediments. The hardened layers are consequently more protected from erosion. A study published in 2011 using data from the Mars Reconnaissance Orbiter, show that the same kinds of sediments exist in a large area that includes Arabia Terra. It has been argued that areas that are rich in sedimentary rocks are also those areas that most likely experienced groundwater upwelling on a regional scale.


title: Water on Mars

text: In February 2019, European scientists published geological evidence of an ancient planet-wide groundwater system that was, arguably, connected to a putative vast ocean. In September 2019, researchers reported that the "InSight" lander uncovered unexplained magnetic pulses, and magnetic oscillations consistent with a planet-wide reservoir of liquid water deep underground.


title: Water on Mars

text: The Mars ocean hypothesis proposes that the Vastitas Borealis basin was the site of an ocean of liquid water at least once, and presents evidence that nearly a third of the surface of Mars was covered by a liquid ocean early in the planet's geologic history. This ocean, dubbed Oceanus Borealis, would have filled the Vastitas Borealis basin in the northern hemisphere, a region that lies below the mean planetary elevation. Two major putative shorelines have been suggested: a higher one, dating to a time period of approximately 3.8 billion years ago and concurrent with the formation of the valley networks in the Highlands, and a lower one, perhaps correlated with the younger outflow channels. The higher one, the 'Arabia shoreline', can be traced all around Mars except through the Tharsis volcanic region. The lower, the 'Deuteronilus', follows the Vastitas Borealis formation.


title: Water on Mars

text: A study in June 2010 concluded that the more ancient ocean would have covered 36% of Mars. Data from the Mars Orbiter Laser Altimeter (MOLA), which measures the altitude of all terrain on Mars, was used in 1999 to determine that the watershed for such an ocean would have covered about 75% of the planet. Early Mars would have required a warmer climate and denser atmosphere to allow liquid water to exist at the surface. In addition, the large number of valley networks strongly supports the possibility of a hydrological cycle on the planet in the past.


title: Water on Mars

text: The existence of a primordial Martian ocean remains controversial among scientists, and the interpretations of some features as 'ancient shorelines' has been challenged. One problem with the conjectured 2-billion-year-old (2 Ga) shoreline is that it is not flat—i.e., does not follow a line of constant gravitational potential. This could be due to a change in distribution in Mars' mass, perhaps due to volcanic eruption or meteor impact; the Elysium volcanic province or the massive Utopia basin that is buried beneath the northern plains have been put forward as the most likely causes.


title: Water on Mars

text: In March 2015, scientists stated that evidence exists for an ancient Martian ocean, likely in the planet's northern hemisphere and about the size of Earth's Arctic Ocean, or approximately 19% of the Martian surface. This finding was derived from the ratio of water and deuterium in the modern Martian atmosphere compared to the ratio found on Earth. Eight times as much deuterium was found at Mars than exists on Earth, suggesting that ancient Mars had significantly higher levels of water. Results from the "Curiosity" rover had previously found a high ratio of deuterium in Gale Crater, though not significantly high enough to suggest the presence of an ocean. Other scientists caution that this new study has not been confirmed, and point out that Martian climate models have not yet shown that the planet was warm enough in the past to support bodies of liquid water.


title: Water on Mars

text: Additional evidence for a northern ocean was published in May 2016, describing how some of the surface in Ismenius Lacus quadrangle was altered by two tsunamis. The tsunamis were caused by asteroids striking the ocean. Both were thought to have been strong enough to create 30 km diameter craters. The first tsunami picked up and carried boulders the size of cars or small houses. The backwash from the wave formed channels by rearranging the boulders. The second came in when the ocean was 300 m lower. The second carried a great deal of ice which was dropped in valleys. Calculations show that the average height of the waves would have been 50 m, but the heights would vary from 10 m to 120 m. Numerical simulations show that in this particular part of the ocean two impact craters of the size of 30 km in diameter would form every 30 million years. The implication here is that a great northern ocean may have existed for millions of years. One argument against an ocean has been the lack of shoreline features. These features may have been washed away by these tsunami events. The parts of Mars studied in this research are Chryse Planitia and northwestern Arabia Terra. These tsunamis affected some surfaces in the Ismenius Lacus quadrangle and in the Mare Acidalium quadrangle.


title: Water on Mars

text: In July 2019, support was reported for an ancient ocean on Mars that may have been formed by a possible mega-tsunami source resulting from a meteorite impact creating Lomonosov crater.


title: Water on Mars

text: In January 2022, a study about the climate 3 Gy ago on Mars shows that an ocean is stable with a water cycle that is closed. They estimate a return water flow, in form of ice in glacier, from the icy highlands to the ocean is in magnitude less than the Earth at the last glacial maximum. This simulation includes for the first time a circulatin of the ocean. They demonstrate that the ocean's circulation prevent the ocean to freeze. These also shows that simulations are in agreement with observed geomorphological features identified as ancient glacial valleys.


title: Water on Mars

text: Pure liquid water cannot exist in a stable form on the surface of Mars with its present low atmospheric pressure and low temperature, except at the lowest elevations for a few hours. So, a geological mystery commenced in 2006 when observations from NASA's "Mars Reconnaissance Orbiter" revealed gully deposits that were not there ten years prior, possibly caused by flowing liquid brine during the warmest months on Mars. The images were of two craters in Terra Sirenum and Centauri Montes that appear to show the presence of flows (wet or dry) on Mars at some point between 1999 and 2001.


title: Water on Mars

text: There is disagreement in the scientific community as to whether or not gullies are formed by liquid water. It is also possible that the flows that carve gullies are dry grains, or perhaps lubricated by carbon dioxide. Some studies attest that gullies forming in the southern highlands could not be formed by water due to improper conditions. The low pressure, non-geothermal, colder regions would not give way to liquid water at any point in the year but would be ideal for solid carbon dioxide. The carbon dioxide melting in the warmer summer would yield liquid carbon dioxide which would then form the gullies. Even if gullies are carved by flowing water at the surface, the exact source of the water and the mechanisms behind its motion are not understood.


title: Water on Mars

text: The dry gullies are deep grooves etched into the slopes that persist year-round. There are many other features on Mars, and some of them change seasonally.


title: Water on Mars

text: In August 2011, NASA announced the discovery by undergraduate student Lujendra Ojha of current seasonal changes on steep slopes below rocky outcrops near crater rims in the Southern hemisphere. These dark streaks, now called recurrent slope lineae (RSL), were seen to grow downslope during the warmest part of the Martian Summer, then to gradually fade through the rest of the year, recurring cyclically between years. The researchers suggested these marks were consistent with salty water (brines) flowing downslope and then evaporating, possibly leaving some sort of residue. The CRISM spectroscopic instrument has since made direct observations of hydrous salts appearing at the same time that these recurrent slope lineae form, confirming in 2015 that these lineae are produced by the flow of liquid brines through shallow soils. The lineae contain hydrated chlorate and perchlorate salts (), which contain liquid water molecules. The lineae flow downhill in Martian summer, when the temperature is above . However, the source of the water remains unknown. However, neutron spectrometer data by the "Mars Odyssey" orbiter obtained over one decade, was published in December 2017, and shows no evidence of water (hydrogenated regolith) at the active sites, so its authors also support the hypotheses of either short-lived atmospheric water vapour deliquescence, or dry granular flows. They conclude that liquid water on today's Mars may be limited to traces of dissolved moisture from the atmosphere and thin films, which are challenging environments for life as it is currently known.


title: Water on Mars

text: An alternative scenario is a Knudsen pump effect, from photophoretic when shadows occurs in a granular material. The authors demonstrated that the RSLs stopped at an angle of 28° in Garni crater, in agreement with dry granular avalanche. In addition, the authors pointed out several limitations of the wet hypothesis, such as the fact that the detection of water was only indirect (salt detection but not water).


title: Water on Mars

text: A significant amount of surface hydrogen has been observed globally by the Mars Odyssey neutron spectrometer and gamma ray spectrometer and the Mars Express High Resolution Stereo Camera (HRSC). This hydrogen is thought to be incorporated into the molecular structure of ice, and through stoichiometric calculations the observed fluxes have been converted into concentrations of water ice in the upper meter of the Martian surface. This process has revealed that ice is both widespread and abundant on the present surface. Below 60 degrees of latitude, ice is concentrated in several regions, particularly around the Elysium volcanoes, Terra Sabaea, and northwest of Terra Sirenum, and exists in concentrations up to 18% ice in the subsurface. Above 60 degrees latitude, ice is highly abundant. Polewards on 70 degrees of latitude, ice concentrations exceed 25% almost everywhere, and approach 100% at the poles. The SHARAD and MARSIS radar sounding instruments have also confirmed that individual surface features are ice rich. Due to the known instability of ice at current Martian surface conditions, it is thought that almost all of this ice is covered by a thin layer of rocky or dusty material.


title: Water on Mars

text: The Mars Odyssey neutron spectrometer observations indicate that if all the ice in the top meter of the Martian surface were spread evenly, it would give a Water Equivalent Global layer (WEG) of at least ≈—in other words, the globally averaged Martian surface is approximately 14% water. The water ice currently locked in both Martian poles corresponds to a WEG of , and geomorphic evidence favors significantly larger quantities of surface water over geologic history, with WEG as deep as . It is thought that part of this past water has been lost to the deep subsurface, and part to space, although the detailed mass balance of these processes remains poorly understood. The current atmospheric reservoir of water is important as a conduit allowing gradual migration of ice from one part of the surface to another on both seasonal and longer timescales, but it is insignificant in volume, with a WEG of no more than .


title: Water on Mars

text: It is possible that liquid water could also exist on the surface of Mars through the formation of brines suggested by the abundance of hydrated salts. Brines are significant on Mars because they can stabilize liquid water at lower temperatures than pure water on its own. Pure liquid water is unstable on the surface of the planet, as it is subjected to freezing, evaporation, and boiling. Similar to how salt is applied to roads on Earth to prevent them from icing over, briny mixtures of water and salt on Mars may have low enough freezing points to lead to stable liquid at the surface. Given the complex nature of the Martian regolith, mixtures of salts are known to change the stability of brines. Modeling the deliquescence of salt mixtures can be used to test for brine stability and can help us determine if liquid brines are present on the surface of Mars. The composition of the Martian regolith, determined by the Phoenix lander, can be used to constrain these models and give an accurate representation of how brines may actually form on the planet. Results of these models give water activity values for various salts at different temperatures, where the lower the water activity, the more stable the brine. At temperatures between 208 K and 253 K, chlorate salts exhibit the lowest water activity values, and below 208 K chloride salts exhibit the lowest values. Results of modeling show that the aforementioned complex mixtures of salts do not significantly increase the stability of brines, indicating that brines may not be a significant source of liquid water at the surface of Mars.


title: Water on Mars

text: The existence of ice in the Martian northern (Planum Boreum) and southern (Planum Australe) polar caps has been known since the time of Mariner 9 orbiter. However, the amount and purity of this ice were not known until the early 2000s. In 2004, the MARSIS radar sounder on the European "Mars Express" satellite confirmed the existence of relatively clean ice in the south polar ice cap that extends to a depth of below the surface. Similarly, the SHARAD radar sounder on board the "Mars Reconnaissance Orbiter" observed the base of the north polar cap 1.5 – 2 km beneath the surface. Together, the volume of ice present in the Martian north and south polar ice caps is similar to that of the Greenland ice sheet.


title: Water on Mars

text: An even larger ice sheet on south polar region sheet is suspected to have retreated in ancient times (Hesperian period), that may have contained 20 million km of water ice, which is equivalent to a layer 137 m deep over the entire planet.


title: Water on Mars

text: Both polar caps reveal abundant internal layers of ice and dust when examined with images of the spiral-shaped troughs that cut through their volume, and the subsurface radar measurements showed that these layers extend continuously across the ice sheets. This layering contains a record of past climates on Mars, just how Earth's ice sheets have a record for Earth's climate. Reading this record is not straightforward however, so, many researchers have studied this layering not only to understand the structure, history, and flow properties of the caps, but also to understand the evolution of climate on Mars.


title: Water on Mars

text: Surrounding the polar caps are many smaller ice sheets inside craters, some of which lie under thick deposits of sand or martian dust. Particularly, the wide Korolev Crater, is estimated to contain approximately of water ice exposed to the surface. Korolev's floor lies about below the rim, and is covered by a deep central mound of permanent water ice, up to in diameter.


title: Water on Mars

text: The existence of subglacial lakes on Mars was hypothesised when modelling of Lake Vostok in Antarctica showed that this lake could have existed before the Antarctic glaciation, and that a similar scenario could potentially have occurred on Mars. In July 2018, scientists from the Italian Space Agency reported the detection of such a subglacial lake on Mars, below the southern polar ice cap, and spanning horizontally, the first evidence for a stable body of liquid water on the planet. The evidence for this Martian lake was deduced from a bright spot in the radar echo sounding data of the MARSIS radar on board the European "Mars Express" orbiter, collected between May 2012 and December 2015. The detected lake is centred at 193°E, 81°S, a flat area that does not exhibit any peculiar topographic characteristics but is surrounded by higher ground, except on its eastern side where there is a depression. The SHARAD radar on board NASA's "Mars Reconnaissance Orbiter" has seen no sign of the lake. The operating frequencies of SHARAD are designed for higher resolution, but lower penetration depth, so if the overlying ice contains a significant amount of silicates, it is unlikely that SHARAD will be able to detect the putative lake.


title: Water on Mars

text: On 28 September 2020, the MARSIS discovery was confirmed, using new data, and reanalysing all the data with a new technique. These new radar studies report three more subglacial lakes on Mars. All are below the southern polar ice cap. The size of the first lake found, and the largest, has been corrected to wide. It is surrounded by 3 smaller lakes, each a few kilometres wide.


title: Water on Mars

text: Because the temperature at the base of the polar cap is estimated to be , scientists assume that the water may remain liquid through the antifreeze effect of magnesium and calcium perchlorates. The ice layer covering the lake is composed of water ice with 10 to 20% admixed dust, and seasonally covered by a -thick layer of ice. Since the raw-data coverage of the south polar ice cap is limited, the discoverers stated that "there is no reason to conclude that the presence of subsurface water on Mars is limited to a single location."


title: Water on Mars

text: In 2019, a study was published that explored the physical conditions necessary for such a lake to exist. The study calculated the amount of geothermal heat necessary to reach temperatures under which a liquid water and perchlorate mix would be stable under the ice. The authors concluded that "even if there are local concentrations of large amounts of perchlorate salts at the base of the south polar ice, typical Martian conditions are too cold to melt the ice...a local heat source within the crust is needed to increase the temperatures, and a magma chamber within 10 km of the ice could provide such a heat source. This result suggests that if the liquid water interpretation of the observations is correct, magmatism on Mars may have been active extremely recently."


title: Water on Mars

text: If a liquid lake does indeed exist, its salty water may also be mixed with soil to form a sludge. The lake's high levels of salt would present difficulties for most lifeforms. On Earth, organisms called halophiles exist that thrive in extremely salty conditions, though not in dark, cold, concentrated perchlorate solutions. Nevertheless, halotolerant organisms might be able to cope with enhanced perchlorate concentrations by drawing on physiological adaptations similar to those observed in the yeast "Debaryomyces hansenii" exposed in lab experiments to increasing NaClO concentrations.


title: Water on Mars

text: For many years, various scientists have suggested that some Martian surfaces look like periglacial regions on Earth. By analogy with these terrestrial features, it has been argued for many years that these may be regions of permafrost. This would suggest that frozen water lies right beneath the surface. A common feature in the higher latitudes, patterned ground, can occur in a number of shapes, including stripes and polygons. On the Earth, these shapes are caused by the freezing and thawing of soil. There are other types of evidence for large amounts of frozen water under the surface of Mars, such as terrain softening, which rounds sharp topographical features. Evidence from Mars Odyssey's gamma ray spectrometer and direct measurements with the Phoenix lander have corroborated that many of these features are intimately associated with the presence of ground ice.


title: Water on Mars

text: In 2017, using the HiRISE camera on board the Mars Reconnaissance Orbiter (MRO), researchers found at least eight eroding slopes showing exposed water ice sheets as thick as 100 meters, covered by a layer of about 1 or 2 meters thick of soil. The sites are at latitudes from about 55 to 58 degrees, suggesting that there is shallow ground ice under roughly a third of the Martian surface. This image confirms what was previously detected with the spectrometer on 2001 Mars Odyssey, the ground-penetrating radars on MRO and on Mars Express, and by the "Phoenix" lander "in situ" excavation. These ice layers hold easily accessible clues about Mars' climate history and make frozen water accessible to future robotic or human explorers. Some researchers suggested these deposits could be the remnants of glaciers that existed millions of years ago when the planet's spin axis and orbit were different. (See section Mars' Ice ages below.) A more detailed study published in 2019 discovered that water ice exists at latitudes north of 35°N and south of 45°S, with some ice patches only a few centimeters from the surface covered by dust. Extraction of water ice at these conditions would not require complex equipment.


title: Water on Mars

text: Certain regions of Mars display scalloped-shaped depressions. The depressions are suspected to be the remains of a degrading ice-rich mantle deposit. Scallops are caused by ice sublimating from frozen soil. The landforms of scalloped topography can be formed by the subsurface loss of water ice by sublimation under current Martian climate conditions. A model predicts similar shapes when the ground has large amounts of pure ice, up to many tens of meters in depth. This mantle material was probably deposited from the atmosphere as ice formed on dust when the climate was different due to changes in the tilt of the Mars pole (see "Ice ages", below). The scallops are typically tens of meters deep and from a few hundred to a few thousand meters across. They can be almost circular or elongated. Some appear to have coalesced causing a large heavily pitted terrain to form. The process of forming the terrain may begin with sublimation from a crack. There are often polygonal cracks where scallops form, and the presence of scalloped topography seems to be an indication of frozen ground.


title: Water on Mars

text: On November 22, 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior.


title: Water on Mars

text: The volume of water ice in the region were based on measurements from the ground-penetrating radar instrument on Mars Reconnaissance Orbiter, called SHARAD. From the data obtained from SHARAD, “dielectric permittivity”, or the dielectric constant was determined. The dielectric constant value was consistent with a large concentration of water ice.


title: Water on Mars

text: These scalloped features are superficially similar to Swiss cheese features, found around the south polar cap. Swiss cheese features are thought to be due to cavities forming in a surface layer of solid carbon dioxide, rather than water ice—although the floors of these holes are probably HO-rich.


title: Water on Mars

text: On July 28, 2005, the European Space Agency announced the existence of a crater partially filled with frozen water; some then interpreted the discovery as an "ice lake". Images of the crater, taken by the High Resolution Stereo Camera on board the European Space Agency's Mars Express orbiter, clearly show a broad sheet of ice in the bottom of an unnamed crater located on Vastitas Borealis, a broad plain that covers much of Mars' far northern latitudes, at approximately 70.5° North and 103° East. The crater is wide and about deep. The height difference between the crater floor and the surface of the water ice is about . ESA scientists have attributed most of this height difference to sand dunes beneath the water ice, which are partially visible. While scientists do not refer to the patch as a "lake", the water ice patch is remarkable for its size and for being present throughout the year. Deposits of water ice and layers of frost have been found in many different locations on the planet.


title: Water on Mars

text: As more and more of the surface of Mars has been imaged by the modern generation of orbiters, it has become gradually more apparent that there are probably many more patches of ice scattered across the Martian surface. Many of these putative patches of ice are concentrated in the Martian mid-latitudes (≈30–60° N/S of the equator). For example, many scientists think that the widespread features in those latitude bands variously described as "latitude dependent mantle" or "pasted-on terrain" consist of dust- or debris-covered ice patches, which are slowly degrading. A cover of debris is required both to explain the dull surfaces seen in the images that do not reflect like ice, and also to allow the patches to exist for an extended period of time without subliming away completely. These patches have been suggested as possible water sources for some of the enigmatic channelized flow features like gullies also seen in those latitudes.


title: Water on Mars

text: Surface features consistent with existing pack ice have been discovered in the southern Elysium Planitia. What appear to be plates, ranging in size from to , are found in channels leading to a large flooded area. The plates show signs of break up and rotation that clearly distinguish them from lava plates elsewhere on the surface of Mars. The source for the flood is thought to be the nearby geological fault Cerberus Fossae that spewed water as well as lava aged some 2 to 10 million years. It was suggested that the water exited the Cerberus Fossae then pooled and froze in the low, level plains and that such frozen lakes may still exist.


title: Water on Mars

text: Many large areas of Mars either appear to host glaciers, or carry evidence that they used to be present. Much of the areas in high latitudes, especially the Ismenius Lacus quadrangle, are suspected to still contain enormous amounts of water ice. Recent evidence has led many planetary scientists to conclude that water ice still exists as glaciers across much of the Martian mid- and high latitudes, protected from sublimation by thin coverings of insulating rock and/or dust. An example of this are the glacier-like features called lobate debris aprons in an area called Deuteronilus Mensae, which display widespread evidence of ice lying beneath a few meters of rock debris. Glaciers are associated with fretted terrain, and many volcanoes. Researchers have described glacial deposits on Hecates Tholus, Arsia Mons, Pavonis Mons, and Olympus Mons. Glaciers have also been reported in a number of larger Martian craters in the mid-latitudes and above.


title: Water on Mars

text: Glacier-like features on Mars are known variously as viscous flow features, Martian flow features, lobate debris aprons, or lineated valley fill, depending on the form of the feature, its location, the landforms it is associated with, and the author describing it. Many, but not all, small glaciers seem to be associated with gullies on the walls of craters and mantling material. The lineated deposits known as lineated valley fill are probably rock-covered glaciers that are found on the floors most channels within the fretted terrain found around Arabia Terra in the northern hemisphere. Their surfaces have ridged and grooved materials that deflect around obstacles. Lineated floor deposits may be related to lobate debris aprons, which have been proven to contain large amounts of ice by orbiting radar. For many years, researchers interpreted that features called 'lobate debris aprons' were glacial flows and it was thought that ice existed under a layer of insulating rocks. With new instrument readings, it has been confirmed that lobate debris aprons contain almost pure ice that is covered with a layer of rocks.


title: Water on Mars

text: Moving ice carries rock material, then drops it as the ice disappears. This typically happens at the snout or edges of the glacier. On Earth, such features would be called moraines, but on Mars they are typically known as "moraine-like ridges", "concentric ridges", or "arcuate ridges". Because ice tends to sublime rather than melt on Mars, and because Mars's low temperatures tend to make glaciers "cold based" (frozen down to their beds, and unable to slide), the remains of these glaciers and the ridges they leave do not appear the exactly same as normal glaciers on Earth. In particular, Martian moraines tend to be deposited without being deflected by the underlying topography, which is thought to reflect the fact that the ice in Martian glaciers is normally frozen down and cannot slide. Ridges of debris on the surface of the glaciers indicate the direction of ice movement. The surface of some glaciers have rough textures due to sublimation of buried ice. The ice evaporates without melting and leaves behind an empty space. Overlying material then collapses into the void. Sometimes chunks of ice fall from the glacier and get buried in the land surface. When they melt, a more or less round hole remains. Many of these "kettle holes" have been identified on Mars.


title: Water on Mars

text: Despite strong evidence for glacial flow on Mars, there is little convincing evidence for landforms carved by glacial erosion, e.g., U-shaped valleys, crag and tail hills, arêtes, drumlins. Such features are abundant in glaciated regions on Earth, so their absence on Mars has proven puzzling. The lack of these landforms is thought to be related to the cold-based nature of the ice in most recent glaciers on Mars. Because the solar insolation reaching the planet, the temperature and density of the atmosphere, and the geothermal heat flux are all lower on Mars than they are on Earth, modelling suggests the temperature of the interface between a glacier and its bed stays below freezing and the ice is literally frozen down to the ground. This prevents it from sliding across the bed, which is thought to inhibit the ice's ability to erode the surface.


title: Water on Mars

text: The variation in Mars's surface water content is strongly coupled to the evolution of its atmosphere and may have been marked by several key stages.


title: Water on Mars

text: The early Noachian era was characterized by atmospheric loss to space from heavy meteoritic bombardment and hydrodynamic escape. Ejection by meteorites may have removed ~60% of the early atmosphere. Significant quantities of phyllosilicates may have formed during this period requiring a sufficiently dense atmosphere to sustain surface water, as the spectrally dominant phyllosilicate group, smectite, suggests moderate water-to-rock ratios. However, the pH-pCO between smectite and carbonate show that the precipitation of smectite would constrain pCO to a value not more than . As a result, the dominant component of a dense atmosphere on early Mars becomes uncertain, if the clays formed in contact with the Martian atmosphere, particularly given the lack of evidence for carbonate deposits. An additional complication is that the ~25% lower brightness of the young Sun would have required an ancient atmosphere with a significant greenhouse effect to raise surface temperatures to sustain liquid water. Higher CO content alone would have been insufficient, as CO precipitates at partial pressures exceeding , reducing its effectiveness as a greenhouse gas.


title: Water on Mars

text: During the middle to late Noachean era, Mars underwent potential formation of a secondary atmosphere by outgassing dominated by the Tharsis volcanoes, including significant quantities of HO, CO, and SO. Martian valley networks date to this period, indicating globally widespread and temporally sustained surface water as opposed to catastrophic floods. The end of this period coincides with the termination of the internal magnetic field and a spike in meteoritic bombardment. The cessation of the internal magnetic field and subsequent weakening of any local magnetic fields allowed unimpeded atmospheric stripping by the solar wind. For example, when compared with their terrestrial counterparts, Ar/Ar, N/N, and C/C ratios of the Martian atmosphere are consistent with ~60% loss of Ar, N, and CO by solar wind stripping of an upper atmosphere enriched in the lighter isotopes via Rayleigh fractionation. Supplementing the solar wind activity, impacts would have ejected atmospheric components in bulk without isotopic fractionation. Nevertheless, cometary impacts in particular may have contributed volatiles to the planet.


title: Water on Mars

text: Atmospheric enhancement by sporadic outgassing events were countered by solar wind stripping of the atmosphere, albeit less intensely than by the young Sun. Catastrophic floods date to this period, favoring sudden subterranean release of volatiles, as opposed to sustained surface flows. While the earlier portion of this era may have been marked by aqueous acidic environments and Tharsis-centric groundwater discharge dating to the late Noachian, much of the surface alteration processes during the latter portion is marked by oxidative processes including the formation of Fe oxides that impart a reddish hue to the Martian surface. Such oxidation of primary mineral phases can be achieved by low-pH (and possibly high temperature) processes related to the formation of palagonitic tephra, by the action of HO that forms photochemically in the Martian atmosphere, and by the action of water, none of which require free O. The action of HO may have dominated temporally given the drastic reduction in aqueous and igneous activity in this recent era, making the observed Fe oxides volumetrically small, though pervasive and spectrally dominant. Nevertheless, aquifers may have driven sustained, but highly localized surface water in recent geologic history, as evident in the geomorphology of craters such as Mojave. Furthermore, the Lafayette Martian meteorite shows evidence of aqueous alteration as recently as 650 Ma.


title: Water on Mars

text: In 2020 scientists reported that Mars' current loss of atomic hydrogen from water is largely driven by seasonal processes and dust storms that transport water directly to the upper atmosphere and that this has influenced the planet's climate likely during the last 1 Ga. More recent studies have suggested that upward propagating atmospheric gravity waves can play an important role during global dust storms in modulating water escape.


title: Water on Mars

text: Mars has experienced about 40 large scale changes in the amount and distribution of ice on its surface over the past five million years, with the most recent happening about 2.1 to 0.4 Myr ago, during the Late Amazonian glaciation at the dichotomy boundary. These changes are known as ice ages. Ice ages on Mars are very different from the ones that the Earth experiences. Ice ages are driven by changes in Mars's orbit and tilt —also known as obliquity. Orbital calculations show that Mars wobbles on its axis far more than Earth does. The Earth is stabilized by its proportionally large moon, so it only wobbles a few degrees. Mars may change its tilt by many tens of degrees. When this obliquity is high, its poles get much more direct sunlight and heat; this causes the ice caps to warm and become smaller as ice sublimes. Adding to the variability of the climate, the eccentricity of the orbit of Mars changes twice as much as Earth's eccentricity. As the poles sublime, the ice is redeposited closer to the equator, which receive somewhat less solar insolation at these high obliquities. Computer simulations have shown that a 45° tilt of the Martian axis would result in ice accumulation in areas that display glacial landforms.


title: Water on Mars

text: The moisture from the ice caps travels to lower latitudes in the form of deposits of frost or snow mixed with dust. The atmosphere of Mars contains a great deal of fine dust particles, the water vapor condenses on these particles that then fall down to the ground due to the additional weight of the water coating. When ice at the top of the mantling layer returns to the atmosphere, it leaves behind dust that serves to insulate the remaining ice. The total volume of water removed is a few percent of the ice caps, or enough to cover the entire surface of the planet under one meter of water. Much of this moisture from the ice caps results in a thick smooth mantle with a mixture of ice and dust. This ice-rich mantle, that can be 100 meters thick at mid-latitudes, smoothes the land at lower latitudes, but in places it displays a bumpy texture or patterns that give away the presence of former water ice underneath.


title: Water on Mars

text: Since the "Viking" landers that searched for current microbial life in 1976, NASA has pursued a "follow the water" strategy on Mars. However, liquid water is a necessary but not sufficient condition for life as we know it because habitability is a function of a multitude of environmental parameters. 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.


title: Water on Mars

text: Habitable environments need not be inhabited, and for purposes of planetary protection, scientists are trying to identify potential habitats where stowaway bacteria from Earth on spacecraft could contaminate Mars. If life exists —or existed— on Mars, evidence or biosignatures could be found in the subsurface, away from present-day harsh surface conditions such as perchlorates, ionizing radiation, desiccation and freezing. Habitable locations could occur kilometers below the surface in a hypothetical hydrosphere, or it could occur near the sub-surface in contact with permafrost.


title: Water on Mars

text: The "Curiosity" rover is assessing Mars' past and present habitability potential. The European-Russian ExoMars programme is an astrobiology project dedicated to the search for and identification of biosignatures on Mars. It includes the ExoMars Trace Gas Orbiter that started mapping the atmospheric methane in April 2018, and the 2022 ExoMars rover that will drill and analyze subsurface samples 2 meters deep. NASA's Mars 2020 rover will cache dozens of drilled core samples for their potential transport to Earth laboratories in the late 2020s or 2030s.


title: Water on Mars

text: The images acquired by the Mariner 9 Mars orbiter, launched in 1971, revealed the first direct evidence of past water in the form of dry river beds, canyons (including the Valles Marineris, a system of canyons over about long), evidence of water erosion and deposition, weather fronts, fogs, and more. The findings from the Mariner 9 missions underpinned the later Viking program. The enormous Valles Marineris canyon system is named after Mariner 9 in honor of its achievements.


title: Water on Mars

text: By discovering many geological forms that are typically formed from large amounts of water, the two Viking orbiters and the two landers caused a revolution in our knowledge about water on Mars. Huge outflow channels were found in many areas. They showed that floods of water broke through dams, carved deep valleys, eroded grooves into bedrock, and traveled thousands of kilometers. Large areas in the southern hemisphere contained branched valley networks, suggesting that rain once fell. Many craters look as if the impactor fell into mud. When they were formed, ice in the soil may have melted, turned the ground into mud, then the mud flowed across the surface. Regions, called "Chaotic Terrain," seemed to have quickly lost great volumes of water that caused large channels to form downstream. Estimates for some channel flows run to ten thousand times the flow of the Mississippi River. Underground volcanism may have melted frozen ice; the water then flowed away and the ground collapsed to leave chaotic terrain. Also, general chemical analysis by the two Viking landers suggested the surface has been either exposed to or submerged in water in the past.


title: Water on Mars

text: The Mars Global Surveyor's Thermal Emission Spectrometer (TES) is an instrument able to determine the mineral composition on the surface of Mars. Mineral composition gives information on the presence or absence of water in ancient times. TES identified a large () area in the Nili Fossae formation that contains the mineral olivine. It is thought that the ancient asteroid impact that created the Isidis basin resulted in faults that exposed the olivine. The discovery of olivine is strong evidence that parts of Mars have been extremely dry for a long time. Olivine was also discovered in many other small outcrops within 60 degrees north and south of the equator. The probe has imaged several channels that suggest past sustained liquid flows, two of them are found in Nanedi Valles and in Nirgal Vallis.


title: Water on Mars

text: The Pathfinder lander recorded the variation of diurnal temperature cycle. It was coldest just before sunrise, about , and warmest just after Mars noon, about . At this location, the highest temperature never reached the freezing point of water (), too cold for pure liquid water to exist on the surface.


title: Water on Mars

text: The atmospheric pressure measured by the Pathfinder on Mars is very low —about 0.6% of Earth's, and it would not permit pure liquid water to exist on the surface.


title: Water on Mars

text: Other observations were consistent with water being present in the past. Some of the rocks at the Mars Pathfinder site leaned against each other in a manner geologists term imbricated. It is suspected that strong flood waters in the past pushed the rocks around until they faced away from the flow. Some pebbles were rounded, perhaps from being tumbled in a stream. Parts of the ground are crusty, maybe due to cementing by a fluid containing minerals. There was evidence of clouds and maybe fog.


title: Water on Mars

text: The 2001 Mars Odyssey found much evidence for water on Mars in the form of images, and with its neutron spectrometer, it proved that much of the ground is loaded with water ice. Mars has enough ice just beneath the surface to fill Lake Michigan twice. In both hemispheres, from 55° latitude to the poles, Mars has a high density of ice just under the surface; one kilogram of soil contains about of water ice. But close to the equator, there is only 2% to 10% of water in the soil. Scientists think that much of this water is also locked up in the chemical structure of minerals, such as clay and sulfates. Although the upper surface contains a few percent of chemically-bound water, ice lies just a few meters deeper, as it has been shown in Arabia Terra, Amazonis quadrangle, and Elysium quadrangle that contain large amounts of water ice. The orbiter also discovered vast deposits of bulk water ice near the surface of equatorial regions. Evidence for equatorial hydration is both morphological and compositional and is seen at both the Medusae Fossae formation and the Tharsis Montes. Analysis of the data suggests that the southern hemisphere may have a layered structure, suggestive of stratified deposits beneath a now extinct large water mass.


title: Water on Mars

text: The instruments aboard the "Mars Odyssey" are able to study the top meter of soil. In 2002, available data were used to calculate that if all soil surfaces were covered by an even layer of water, this would correspond to a global layer of water (GLW) .


title: Water on Mars

text: Thousands of images returned from "Odyssey" orbiter also support the idea that Mars once had great amounts of water flowing across its surface. Some images show patterns of branching valleys; others show layers that may have been formed under lakes; even river and lake deltas have been identified.


title: Water on Mars

text: For many years researchers suspected that glaciers exist under a layer of insulating rocks. Lineated valley fill is one example of these rock-covered glaciers. They are found on the floors of some channels. Their surfaces have ridged and grooved materials that deflect around obstacles. Lineated floor deposits may be related to lobate debris aprons, which have been shown by orbiting radar to contain large amounts of ice.


title: Water on Mars

text: The "Phoenix" lander also confirmed the existence of large amounts of water ice in the northern region of Mars. This finding was predicted by previous orbital data and theory, and was measured from orbit by the Mars Odyssey instruments. On June 19, 2008, NASA announced that dice-sized clumps of bright material in the "Dodo-Goldilocks" trench, dug by the robotic arm, had vaporized over the course of four days, strongly indicating that the bright clumps were composed of water ice that sublimes following exposure. Recent radiative transfer modeling has shown that this water ice was snow with a grain size of ~350 µm with 0.015% dust. Even though CO (dry ice) also sublimes under the conditions present, it would do so at a rate much faster than observed. On July 31, 2008, NASA announced that "Phoenix" further confirmed the presence of water ice at its landing site. During the initial heating cycle of a sample, the mass spectrometer detected water vapor when the sample temperature reached . Liquid water cannot exist on the surface of Mars with its present low atmospheric pressure and temperature, except at the lowest elevations for short periods.


title: Water on Mars

text: The presence of the perchlorate (ClO) anion, a strong oxidizer, in the martian soil was confirmed. This salt can considerably lower the water freezing point.


title: Water on Mars

text: When "Phoenix" landed, the retrorockets splashed soil and melted ice onto the vehicle. Photographs showed the landing had left blobs of material stuck to the landing struts. The blobs expanded at a rate consistent with deliquescence, darkened before disappearing (consistent with liquefaction followed by dripping), and appeared to merge. These observations, combined with thermodynamic evidence, indicated that the blobs were likely liquid brine droplets. Other researchers suggested the blobs could be "clumps of frost." In 2015 it was confirmed that perchlorate plays a role in forming recurring slope lineae on steep gullies.


title: Water on Mars

text: For about as far as the camera can see, the landing site is flat, but shaped into polygons between in diameter which are bounded by troughs that are deep. These shapes are due to ice in the soil expanding and contracting due to major temperature changes. The microscope showed that the soil on top of the polygons is composed of rounded particles and flat particles, probably a type of clay. Ice is present a few inches below the surface in the middle of the polygons, and along its edges, the ice is at least deep.


title: Water on Mars

text: Snow was observed to fall from cirrus clouds. The clouds formed at a level in the atmosphere that was around , so the clouds would have to be composed of water-ice, rather than carbon dioxide-ice (CO or dry ice), because the temperature for forming carbon dioxide ice is much lower than . As a result of mission observations, it is now suspected that water ice (snow) would have accumulated later in the year at this location. The highest temperature measured during the mission, which took place during the Martian summer, was , while the coldest was . So, in this region the temperature remained far below the freezing point () of water.


title: Water on Mars

text: The Mars Exploration Rovers, "Spirit" and "Opportunity" found a great deal of evidence for past water on Mars. The Spirit rover landed in what was thought to be a large lake bed. The lake bed had been covered over with lava flows, so evidence of past water was initially hard to detect. On March 5, 2004, NASA announced that "Spirit" had found hints of water history on Mars in a rock dubbed "Humphrey".


title: Water on Mars

text: As "Spirit" traveled in reverse in December 2007, pulling a seized wheel behind, the wheel scraped off the upper layer of soil, uncovering a patch of white ground rich in silica. Scientists think that it must have been produced in one of two ways. One: hot spring deposits produced when water dissolved silica at one location and then carried it to another (i.e. a geyser). Two: acidic steam rising through cracks in rocks stripped them of their mineral components, leaving silica behind. The "Spirit" rover also found evidence for water in the Columbia Hills of Gusev crater. In the Clovis group of rocks the Mössbauer spectrometer (MB) detected goethite, that forms only in the presence of water, iron in the oxidized form Fe, carbonate-rich rocks, which means that regions of the planet once harbored water.


title: Water on Mars

text: The "Opportunity" rover was directed to a site that had displayed large amounts of hematite from orbit. Hematite often forms from water. The rover indeed found layered rocks and marble- or blueberry-like hematite concretions. Elsewhere on its traverse, "Opportunity" investigated aeolian dune stratigraphy in Burns Cliff in Endurance Crater. Its operators concluded that the preservation and cementation of these outcrops had been controlled by flow of shallow groundwater. In its years of continuous operation, "Opportunity" sent back evidence that this area on Mars was soaked in liquid water in the past.


title: Water on Mars

text: The MER rovers found evidence for ancient wet environments that were very acidic. In fact, what "Opportunity" found evidence of sulfuric acid, a harsh chemical for life. But on May 17, 2013, NASA announced that "Opportunity" found clay deposits that typically form in wet environments that are near neutral acidity. This find provides additional evidence about a wet ancient environment possibly favorable for life.


title: Water on Mars

text: The Mars Reconnaissance Orbiter's HiRISE instrument has taken many images that strongly suggest that Mars has had a rich history of water-related processes. A major discovery was finding evidence of ancient hot springs. If they have hosted microbial life, they may contain biosignatures. Research published in January 2010, described strong evidence for sustained precipitation in the area around Valles Marineris. The types of minerals there are associated with water. Also, the high density of small branching channels indicates a great deal of precipitation.


title: Water on Mars

text: Rocks on Mars have been found to frequently occur as layers, called strata, in many different places. Layers form by various ways, including volcanoes, wind, or water. Light-toned rocks on Mars have been associated with hydrated minerals like sulfates and clay.


title: Water on Mars

text: The orbiter helped scientists determine that much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust.


title: Water on Mars

text: The ice mantle under the shallow subsurface is thought to result from frequent, major climate changes. Changes in Mars' orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas. During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water returns to the ground at lower latitudes as deposits of frost or snow mixed generously with dust. The atmosphere of Mars contains a great deal of fine dust particles. Water vapor condenses on the particles, then they fall down to the ground due to the additional weight of the water coating. When ice at the top of the mantling layer goes back into the atmosphere, it leaves behind dust, which insulates the remaining ice.


title: Water on Mars

text: In 2008, research with the Shallow Radar on the Mars Reconnaissance Orbiter provided strong evidence that the lobate debris aprons (LDA) in Hellas Planitia and in mid northern latitudes are glaciers that are covered with a thin layer of rocks. Its radar also detected a strong reflection from the top and base of LDAs, meaning that pure water ice made up the bulk of the formation. The discovery of water ice in LDAs demonstrates that water is found at even lower latitudes.


title: Water on Mars

text: Research published in September 2009, demonstrated that some new craters on Mars show exposed, pure water ice. After a time, the ice disappears, evaporating into the atmosphere. The ice is only a few feet deep. The ice was confirmed with the Compact Imaging Spectrometer (CRISM) on board the Mars Reconnaissance Orbiter. Similar exposures of ice have been detected within the mid-latitude mantle (originally proposed to contain buried dusty snow covered with dust and regolith;) that drapes most pole-facing slopes in the mid-latitudes using spectral analysis of HiRISE images.


title: Water on Mars

text: Additional collaborating reports published in 2019 evaluated the amount of water ice located at the northern pole. One report used data from the MRO's SHARAD (SHAllow RADar sounder) probes. SHARAD has the capability scanning up to about below the surface at intervals. The analysis of past SHARAD runs showed evidence of strata of water ice and sand below the Planum Boreum, with as much as 60% to 88% of the volume being water ice. This supports the theory of the long-term global weather of Mars consisting of cycles of global warming and cooling; during cooling periods, water gathered at the poles to form the ice layers, and then as global warming occurred, the unthawed water ice was covered by dust and dirt from Mars' frequent dust storms. The total ice volume determine by this study indicated that there was approximately , or enough water, if melted, to fully cover the Mars surface with a layer of water. The work was corroborated by a separate study that used recorded gravity data to estimate the density of the Planum Boreum, indicating that on average, it contained up to 55% by volume of water ice.


title: Water on Mars

text: Many features that look like the pingos on the Earth were found in Utopia Planitia (~35-50° N; ~80-115° E) by examining photos from HiRISE. Pingos contain a core of ice.


title: Water on Mars

text: Very early in its ongoing mission, NASA's "Curiosity" rover discovered unambiguous fluvial sediments on Mars. The properties of the pebbles in these outcrops suggested former vigorous flow on a streambed, with flow between ankle- and waist-deep. These rocks were found at the foot of an alluvial fan system descending from the crater wall, which had previously been identified from orbit.


title: Water on Mars

text: In October 2012, the first X-ray diffraction analysis of a Martian soil was performed by "Curiosity". The results revealed the presence of several minerals, including feldspar, pyroxenes and olivine, and suggested that the Martian soil in the sample was similar to the weathered basaltic soils of Hawaiian volcanoes. The sample used is composed of dust distributed from global dust storms and local fine sand. So far, the materials "Curiosity" has analyzed are consistent with the initial ideas of deposits in Gale Crater recording a transition through time from a wet to dry environment.


title: Water on Mars

text: In December 2012, NASA reported that "Curiosity" performed its first extensive soil analysis, revealing the presence of water molecules, sulfur and chlorine in the Martian soil. And in March 2013, NASA reported evidence of mineral hydration, likely hydrated calcium sulfate, in several rock samples including the broken fragments of "Tintina" rock and "Sutton Inlier" rock as well as in veins and nodules in other rocks like "Knorr" rock and "Wernicke" rock. Analysis using the rover's DAN instrument provided evidence of subsurface water, amounting to as much as 4% water content, down to a depth of , in the rover's traverse from the "Bradbury Landing" site to the "Yellowknife Bay" area in the "Glenelg" terrain.


title: Water on Mars

text: On September 26, 2013, NASA scientists reported the Mars "Curiosity" rover detected abundant chemically-bound water (1.5 to 3 weight percent) in soil samples at the Rocknest region of Aeolis Palus in Gale Crater. In addition, NASA reported the rover found two principal soil types: a fine-grained mafic type and a locally derived, coarse-grained felsic type. The mafic type, similar to other martian soils and martian dust, was associated with hydration of the amorphous phases of the soil. Also, perchlorates, the presence of which may make detection of life-related organic molecules difficult, were found at the "Curiosity" rover landing site (and earlier at the more polar site of the Phoenix lander) suggesting a "global distribution of these salts". NASA also reported that Jake M rock, a rock encountered by "Curiosity" on the way to Glenelg, was a mugearite and very similar to terrestrial mugearite rocks.


title: Water on Mars

text: On December 9, 2013, NASA reported that Mars once had a large freshwater lake inside Gale Crater, that could have been a hospitable environment for microbial life.


title: Water on Mars

text: On December 16, 2014, NASA reported detecting an unusual increase, then decrease, in the amounts of methane in the atmosphere of the planet Mars; in addition, organic chemicals were detected in powder drilled from a rock by the "Curiosity" rover. Also, based on deuterium to hydrogen ratio studies, much of the water at Gale Crater on Mars was found to have been lost during ancient times, before the lake bed in the crater was formed; afterwards, large amounts of water continued to be lost.


title: Water on Mars

text: On April 13, 2015, "Nature" published an analysis of humidity and ground temperature data collected by "Curiosity", showing evidence that films of liquid brine water form in the upper 5 cm of Mars's subsurface at night. The water activity and temperature remain below the requirements for reproduction and metabolism of known terrestrial microorganisms.


title: Water on Mars

text: On October 8, 2015, NASA confirmed that lakes and streams existed in Gale crater 3.3 – 3.8 billion years ago delivering sediments to build up the lower layers of Mount Sharp.


title: Water on Mars

text: On November 4, 2018, geologists presented evidence, based on studies in Gale Crater by the "Curiosity" rover, that there was plenty of water on early Mars.


title: Water on Mars

text: The "Mars Express Orbiter", launched by the European Space Agency, has been mapping the surface of Mars and using radar equipment to look for evidence of sub-surface water. Between 2012 and 2015, the "Orbiter" scanned the area beneath the ice caps on the Planum Australe. Scientists determined by 2018 that the readings indicated a sub-surface lake bearing water about wide. The top of the lake is located under the planet's surface; how much deeper the liquid water extends remains unknown.


title: Levi Stubbs

text: Levi Stubbs (born Levi Stubbles, June 6, 1936 – October 17, 2008) was an American baritone singer, best known as the lead vocalist of the R&B group the Four Tops, who released a variety of Motown hit records during the 1960s and 1970s. He has been noted for his powerful, emotional, dramatic style of singing. In 1990, he was inducted into the Rock and Roll Hall of Fame as a member of the Four Tops.


title: Levi Stubbs

text: Stubbs was also a voice artist in film and television, and provided the voice of "Audrey II", the alien plant in the 1986 musical horror comedy film "Little Shop of Horrors" (an adaption of the stage musical of the same name), as well as Mother Brain in the 1989 TV series "". Stubbs was admired by his peers for his impressive vocal range, and influenced many later pop and soul artists, such as Daryl Hall of Hall and Oates.


title: Levi Stubbs

text: Stubbs was born and spent much of his life in Detroit, Michigan. He had five children with his wife Clineice Stubbs, to whom he was married for almost 50 years. His last performance was at the Four Tops' "50th Anniversary Concert" on July 28, 2004, at the Detroit Opera House.


title: Levi Stubbs

text: Born in 1936 in Detroit, Stubbs had a brother, Joe, who later became a member of 100 Proof (Aged in Soul), The Falcons, The Contours and The Originals. His cousin was Jackie Wilson. Stubbs attended Detroit Pershing High School, where he met Abdul "Duke" Fakir. He began his professional singing career with friends Fakir, Renaldo "Obie" Benson and Lawrence Payton, forming a singing group called the Four Aims in 1954.


title: Levi Stubbs

text: Two years later, after signing with Chess Records, the group changed their name to the Four Tops. The name change was meant to avoid confusion with the then-popular Ames Brothers. The Four Tops began as a supper-club act before signing to Motown Records in 1963. By the end of the decade, they had over a dozen hits. The most popular of their hits (all of which featured Stubbs on lead vocals) include "Ask the Lonely", "Baby I Need Your Loving", "I Can't Help Myself (Sugar Pie, Honey Bunch)", "It's the Same Old Song", "I'll Turn to Stone", "Reach Out I'll Be There", "Standing in the Shadows of Love", "Bernadette", "Still Water (Love)", "Ain't No Woman (Like the One I've Got)", as well as the late hit "Loco In Acapulco".


title: Levi Stubbs

text: Although Stubbs was a natural baritone, most Four Tops' hits were written in a tenor range to give the lead vocals a sense of urgency.


title: Levi Stubbs

text: Despite being the most prominent member of the group, Stubbs refused to have separate billing (in contrast to other Motown acts such as Smokey Robinson and the Miracles and Diana Ross and the Supremes), and he also turned down several offers for a solo career, out of loyalty to his bandmates. Stubbs and the other Tops remained a team until Lawrence Payton died in 1997, at which point Theo Peoples took his place. The Four Tops were inducted into the Rock and Roll Hall of Fame in 1990 and the Rhythm and Blues Music Hall of Fame in 2013. They have sold over 50 million records worldwide.


title: Levi Stubbs

text: During the band's long career it was signed to the Motown, ABC Dunhill, Arista and Casablanca record labels, and Stubbs' vocals influenced many later pop and soul artists, such as Daryl Hall of Hall and Oates. Hall has remarked that Stubbs' "unique" style rendered the Four Tops' material "timeless". Other musical peers expressing admiration for the Four Tops' work include Lonnie Jordan of War and Smokey Robinson of The Miracles, among many others.


title: Levi Stubbs

text: In 2000, Theo Peoples replaced Stubbs as lead singer after Stubbs suffered a stroke, with Ronnie McNeir taking the place that Lawrence Payton originally held. Renaldo Benson died on July 1, 2005, leaving Duke Fakir as the only surviving member of the Four Tops' original lineup. Stubb's final performance with the Four Tops was at the group's "50th Anniversary Concert" on July 28, 2004 at the Detroit Opera House.


title: Levi Stubbs

text: Stubbs provided the voice of the carnivorous plant Audrey II in the 1986 film version of the musical "Little Shop of Horrors", in which he sang the Oscar-nominated "Mean Green Mother from Outer Space". He also was the voice of Mother Brain in the animated TV series "" (1989).


title: Levi Stubbs

text: Stubbs also guest-starred in a number of TV shows as himself. Berry Gordy offered him the role of Louis McKay in the 1972 film "Lady Sings the Blues", which would have starred him opposite Diana Ross as Billie Holiday. Stubbs turned the role down, however, once again not wishing to overshadow the other members of the Four Tops.


title: Levi Stubbs

text: Stubbs has been regarded by some as one of the quintessential male soul singers. According to AllMusic's Ed Hogan, the vocalist had a "pleading urgency in his voice that perfectly captured the longing anxiousness of the songs written by the producing trio of Holland-Dozier-Holland". War band member Lonnie Jordan later told Billboard.com he felt "blessed" to meet Stubbs, and thought that the Four Tops singer's "voice was so good he was just, like, from another planet."


title: Levi Stubbs

text: Stubbs and his wife Clineice were married (for 48 years) from 1960 until his death in 2008. The couple had five children along with 11 grandchildren and 10 great-grandchildren.


title: Levi Stubbs

text: Stubbs was diagnosed with cancer in 1995, and after suffering a stroke in 2000, he was no longer able to tour with the Four Tops. He died in his sleep on October 17, 2008, at his home in Detroit. A memorial service for Stubbs was held at the Greater Grace Temple in Detroit on October 27. Many of Stubbs' friends from the music industry attended including Berry Gordy, Martha Reeves, Brian Holland, Ali-Ollie Woodson and Dennis Edwards. Detroit City Council member JoAnn Watson, along with Martha Reeves, presented a resolution naming Stubbs' birthday "Levi Stubbs Day" in Detroit. Stubbs is interred at Detroit's historic Woodlawn Cemetery.


title: Levi Stubbs

text: Stubbs features in Billy Bragg's 1986 song "Levi Stubbs' Tears", about a woman whose Four Tops cassette brings her comfort through difficult times.


title: 1992–93 FA Premier League

text: The 1992–93 FA Premier League was the inaugural season of the Premier League, the top division of English football. The season began on 15 August 1992 and ended on 11 May 1993. The league was made up of the 22 clubs that broke away from The Football League at the end of the 1991–92 season. The new league was backed up by a five-year, £305 million deal with Sky to televise Premier League matches. In concept, the Premier League was identical to the old First Division of the Football League, which was now reduced to three divisions.


title: 1992–93 FA Premier League

text: In May 1992–93, the breakaway league signed a broadcasting rights contract with Sky and the BBC valued at £304 million, the largest such agreement in the history of British sport. The league's executive committee was unable, however, to secure title sponsorship for the new competition after eight clubs blocked a proposed £13 million deal with brewers Bass. Nonetheless, clubs began to utilise their dramatically increased wealth to fund a series of high-profile transfers.


title: 1992–93 FA Premier League

text: Although the idea of a super league had been mentioned by football's governing bodies and evaluated by the media since the mid 1980s, plans for a new Premier League of 22 clubs were first unveiled by the Football Association in October 1990, and included in the Football Association's "Blueprint for the Future of Football", published in June 1991. The majority of First Division clubs, particularly long-established top clubs including Arsenal and Manchester United, were in favour of a breakaway from the Football League, although Football League president Bill Fox criticised the planned Premier League as an attempt by the Football Association to "hijack" the First Division.


title: 1992–93 FA Premier League

text: Shortly before the season began, newly promoted Blackburn Rovers signed Southampton's 21-year-old England international striker Alan Shearer for a new British record fee variously reported as £3.3 million, £3.4 million, or £3.6 million. Several other players moved for fees of £2 million or more, including Arsenal's David Rocastle, who joined Leeds United, Dean Saunders, who moved from Liverpool to Aston Villa, and Teddy Sheringham, who left Nottingham Forest for Tottenham Hotspur.


title: 1992–93 FA Premier League

text: The structure of the new league was identical to that of the previous season's Football League First Division, comprising 22 teams, with each playing the other 21 twice for a total of 42 matches. Ipswich Town and Middlesbrough had been promoted from the old Second Division as champions and runners-up respectively, and Blackburn Rovers took the third promotion place after winning the 1991–92 Second Division playoff.


title: 1992–93 FA Premier League

text: The first Premier League title went to Manchester United, the club's first title for 26 years. Their title was achieved with a 10-point lead over runners-up Aston Villa. Norwich City led the table for much of the season, but their challenge faded in the final weeks of the season and were out of contention three games before the season was over after they lost 3–1 to Ipswich Town. Norwich did however finish in third place, achieving European qualification in Mike Walker's debut season as manager; with a goal difference of −4, this is the highest Premier League finish by a team with a negative goal difference. Blackburn, in the top division for the first time in almost 30 years, finished in fourth place. They briefly led the league early in the season, but suffered a shortage of goals after Alan Shearer, who had scored 16 times before the turn of the year, suffered a torn cruciate ligament and missed the second half of the season. The title race was largely between the clubs who finished in the top four after early challenges from the likes of Arsenal, Coventry City, and Queens Park Rangers were not sustained.


title: 1992–93 FA Premier League

text: Nottingham Forest's league form had suffered through the sale of key players like Des Walker and Teddy Sheringham, and they were bottom of the Premier League for much of the 1992–93 season. Their relegation was confirmed in early May when they lost to Sheffield United, and manager Brian Clough announced his retirement after 18 years as manager, which had yielded one league title, two European Cups and four League Cups. Next to go were newly promoted Middlesbrough, who fell from mid-table at Christmas to go down in second from bottom place. Last to go down were Crystal Palace, who failed to win their final game of the season which would have instead consigned Oldham Athletic to the final relegation place - Oldham's survival was secured with a thrilling 4–3 win over Southampton.


title: 1992–93 FA Premier League

text: Title holders Leeds United finished 17th, which was the lowest finish from a defending league champion since Ipswich Town finished 17th in 1962–63 after having won the title in 1961–62, and the lowest any top tier champions have so far finished in the Premier League. Leeds failed to win an away game in the league. The lowest a defending champion has finished since then has been 12th (Leicester City in 2016–17, having won the title in 2015–16).


title: 1992–93 FA Premier League

text: The top scorer in the new Premier League was Teddy Sheringham, who found the net for Nottingham Forest in their opening game of the season before being sold to Tottenham Hotspur, scoring a further 21 goals for the North London side in the league. PFA Player of the Year was Paul McGrath of Aston Villa. FWA Player of the Year was Chris Waddle, who helped Sheffield Wednesday achieve runners-up spot in both of the cups after ending his three-year spell in France. PFA Young Player of the Year was Ryan Giggs, who won the award for the second year running, and also picked up a league title medal with Manchester United.


title: 1992–93 FA Premier League

text: Twenty-two teams competed in the league – the top nineteen teams from the First Division and the three teams promoted from the Second Division. The promoted teams were Ipswich Town, Middlesbrough and Blackburn Rovers, returning to the top flight after an absence of six, three and twenty-six years respectively. They replaced Luton Town, Notts County and West Ham United, ending Luton Town's ten-year spell in the top flight, whilst both Notts County and West Ham United were relegated after only one year in the top flight.


title: 1992–93 FA Premier League

text: The top goalscorer in the Premier League's inaugural season was Teddy Sheringham, who scored one goal for Nottingham Forest before his early-season transfer followed by 21 for Tottenham Hotspur for a total of 22. Alan Shearer had scored 16 goals by Christmas before suffering a season-ending injury.


title: 1992–93 FA Premier League

text: The Professional Footballers' Association (PFA) presented its annual Players' Player of the Year award to Paul McGrath, a veteran central defender who contributed to Aston Villa's second-place finish in the Premier League. Manchester United's Paul Ince came second and Blackburn's Alan Shearer third. The Young Player of the Year award was given to Ryan Giggs, the 19-year-old Manchester United left winger who had also won the award in the previous season. Giggs, who finished ahead of Tottenham's Nick Barmby and Nottingham Forest's Roy Keane, became the first player to win the award more than once.


title: 1992–93 FA Premier League

text: The Football Writers' Association (the FWA) chose Chris Waddle as its Footballer of the Year. Waddle, who made his return to English football with Sheffield Wednesday after three years in France with Olympique Marseille, became the first Wednesday player to win the award in its 45-year history. McGrath and Giggs finished in second and joint third place respectively in the writers' poll.


title: 1992–93 FA Premier League

text: The PFA also selected eleven players to form its Team of the Year. The team included four Manchester United players (Giggs, Ince, Peter Schmeichel and Gary Pallister) and two from Leeds United (Tony Dorigo and Gary Speed). The other members of the team were McGrath, Keane, Shearer, David Bardsley (Queens Park Rangers) and Ian Wright (Arsenal). The Manager of the Year award, chosen by a panel representing football's governing body, the media, and fans, was given to Manchester United manager Alex Ferguson. The newly formed League Managers Association also presented its own Manager of the Year award for the first time, specifically designed to recognise "the manager who made best use of the resources available to him". This award went to Dave Bassett of Sheffield United.


title: Carbon credit

text: A carbon credit is a generic term for any tradable certificate or permit representing the right to emit a set amount of carbon dioxide or the equivalent amount of a different greenhouse gas (tCOe).


title: Carbon credit

text: Carbon credits and carbon markets are a component of national and international attempts to mitigate the growth in concentrations of greenhouse gases (GHGs). One carbon credit is equal to one tonne of carbon dioxide, or in some markets, carbon dioxide equivalent gases. Carbon trading is an application of an emissions trading approach. Greenhouse gas emissions are capped and then markets are used to allocate the emissions among the group of regulated sources.


title: Carbon credit

text: The goal is to allow market mechanisms to drive industrial and commercial processes in the direction of low emissions or less carbon intensive approaches than those used when there is no cost to emitting carbon dioxide and other GHGs into the atmosphere. Since GHG mitigation projects generate credits, this approach can be used to finance carbon reduction schemes between trading partners around the world.


title: Carbon credit

text: There are also many companies that sell carbon credits to commercial and individual customers who are interested in lowering their carbon footprint on a voluntary basis. These carbon offsetters purchase the credits from an investment fund or a carbon development company that has aggregated the credits from individual projects. Buyers and sellers can also use an exchange platform to trade, which is like a stock exchange for carbon credits. The quality of the credits is based in part on the validation process and sophistication of the fund or development company that acted as the sponsor to the carbon project. This is reflected in their price; voluntary units typically have less value than the units sold through the rigorously validated Clean Development Mechanism. The European Union's carbon credits traded from $7.78 to $25.19 averaging $16.21 per tonne in 2018. Although it remains in development, it is anticipated that the value and trading of carbon credits will continue to grow particularly as several governments have committed to "green recoveries" following the COVID-19 pandemic recession.


title: Carbon credit

text: The Collins English Dictionary defines a carbon credit as “"a certificate showing that a government or company has paid to have a certain amount of carbon dioxide removed from the environment"”.


title: Carbon credit

text: The Environment Protection Authority of Victoria defines a carbon credit as a “"generic term to assign a value to a reduction or offset of greenhouse gas emissions.. usually equivalent to one tonne of carbon dioxide equivalent (-e)."”


title: Carbon credit

text: The Investopedia Inc investment dictionary defines a carbon credit as a “"permit that allows the holder to emit one ton of carbon dioxide"”..which “"can be traded in the international market at their current market price"”.


title: Carbon credit

text: There are two types of credits. Voluntary emissions reduction (VER) is a carbon offset that is exchanged in the over-the-counter or voluntary market for credits. Certified emissions reduction (CER) relies on emission units (or credits) created through a regulatory framework with the purpose of offsetting a project's emissions.


title: Carbon credit

text: The burning of fossil fuels is a major source of greenhouse gas emissions, especially for power, cement, steel, textile, fertilizer and many other industries which rely on fossil fuels (coal, electricity derived from coal, natural gas and oil). The major greenhouse gases emitted by these industries are carbon dioxide, methane, nitrous oxide, hydrofluorocarbons (HFCs), etc., all of which increase the atmosphere's ability to trap infrared energy and thus affect the climate.


title: Carbon credit

text: The concept of carbon credits came into existence as a result of increasing awareness of the need for controlling emissions. The IPCC (Intergovernmental Panel on Climate Change) has observed


title: Carbon credit

text: "Policies that provide a real or implicit price of carbon could create incentives for producers and consumers to significantly invest in low-GHG products, technologies and processes. Such policies could include economic instruments, government funding and regulation",


title: Carbon credit

text: while noting that a tradable permit system is one of the policy instruments that has been shown to be environmentally effective in the industrial sector, as long as there are reasonable levels of predictability over the initial allocation mechanism and long-term price.


title: Carbon credit

text: The mechanism was formalized in the Kyoto Protocol, an international agreement between more than 170 countries, and the market mechanisms were agreed through the subsequent Marrakesh Accords.


title: Carbon credit

text: The mechanism adopted was similar to the successful US Acid Rain Program to reduce some industrial pollutants.


title: Carbon credit

text: Under the Kyoto Protocol, the 'caps' or quotas for Greenhouse gases for the developed Annex 1 countries are known as Assigned Amounts and are listed in Annex B. The quantity of the initial assigned amount is denominated in individual units, called Assigned amount units (AAUs), each of which represents an allowance to emit one tonne of carbon dioxide equivalent, and these are entered into the country's national registry.


title: Carbon credit

text: In turn, these countries set quotas on the emissions of installations run by local business and other organizations, generically termed 'operators'. Countries manage this through their national registries, which are required to be validated and monitored for compliance by the UNFCCC. Each operator has an allowance of credits, where each unit gives the owner the right to emit one tonne of carbon dioxide or other equivalent greenhouse gas. Operators that have not used up their quotas can sell their unused allowances as carbon credits, while businesses that are about to exceed their quotas can buy the extra allowances as credits, privately or on the open market.


title: Carbon credit

text: As demand for energy grows over time, the total emissions must still stay within the cap, but it allows industry some flexibility and predictability in its planning to accommodate this.


title: Carbon credit

text: Since 2005, the Kyoto mechanism has been adopted for CO trading by all the countries within the European Union under its European Trading Scheme (EU ETS) with the European Commission as its validating authority. From 2008, EU participants must link with the other developed countries who ratified Annex I of the protocol, and trade the six most significant anthropogenic greenhouse gases. In the United States, which has not ratified Kyoto, and Australia, whose ratification came into force in March 2008, similar schemes are being considered.


title: Carbon credit

text: By permitting allowances to be bought and sold, an operator can seek out the most cost-effective way of reducing its emissions, either by investing in 'cleaner' machinery and practices or by purchasing emissions from another operator who already has excess 'capacity'. Through ETSs, the price of carbon is driven by emissions limits and the number of carbon allowances in circulation. These markets create a price for the impact of carbon emissions. ETS markets are regulated by governmental organizations and trading in these markets is tracked by the IHS Markit's Global Carbon Index, which provides a benchmark that track carbon credits future contracts globally. Investors participate in these markets by buying shares in highly specialized funds that buy an assortment of contracts to track index like The KraneShares Global Carbon ETF (KRBN).


title: Carbon credit

text: A tradable credit can be an emissions allowance or an assigned amount unit which was originally allocated or auctioned by the national administrators of a Kyoto-compliant cap-and-trade scheme, or it can be an offset of emissions. Such offsetting and mitigating activities can occur in any developing country which has ratified the Kyoto Protocol, and has a national agreement in place to validate its carbon project through one of the UNFCCC's approved mechanisms. Once approved, these units are termed Certified Emission Reductions, or CERs. The Protocol allows these projects to be constructed and credited in advance of the Kyoto trading period.


title: Carbon credit

text: The Kyoto Protocol provides for three mechanisms that enable countries or operators in developed countries to acquire greenhouse gas reduction credits


title: Carbon credit

text: In reality, most of the transactions are not performed by national governments directly, but by operators who have been set quotas by their country.


title: Carbon credit

text: For trading purposes, one allowance or CER is considered equivalent to one metric ton of CO emissions. These allowances can be sold privately or in the international market at the prevailing market price. These trade and settle internationally and hence allow allowances to be transferred between countries. Each international transfer is validated by the UNFCCC. Each transfer of ownership within the European Union is additionally validated by the European Commission.


title: Carbon credit

text: Climate exchanges have been established to provide a spot market in allowances, as well as futures and options market to help discover a market price and maintain liquidity. Carbon prices are normally quoted in Euros per tonne of carbon dioxide or its equivalent (COe). Other greenhouse gasses can also be traded, but are quoted as standard multiples of carbon dioxide with respect to their global warming potential. These features reduce the quota's financial impact on business, while ensuring that the quotas are met at a national and international level.


title: Carbon credit

text: Currently there are five exchanges trading in carbon allowances: the European Climate Exchange, NASDAQ OMX Commodities Europe, PowerNext, Commodity Exchange Bratislava and the European Energy Exchange. NASDAQ OMX Commodities Europe listed a contract to trade offsets generated by a CDM carbon project called Certified Emission Reductions (CERs). Many companies now engage in emissions abatement, offsetting, and sequestration programs to generate credits that can be sold on one of the exchanges. At least one private electronic market has been established in 2008: CantorCO2e. Carbon credits at Commodity Exchange Bratislava are traded at special platform - Carbon place.


title: Carbon credit

text: Managing emissions is one of the fastest-growing segments in financial services in the City of London with a market estimated to be worth about €30 billion in 2007. Louis Redshaw, head of environmental markets at Barclays Capital predicts that "Carbon will be the world's biggest commodity market, and it could become the world's biggest market overall."


title: Carbon credit

text: Unchecked, energy use and hence emission levels are predicted to keep rising over time. Thus the number of companies needing to buy credits will increase, and the rules of supply and demand will push up the market price, encouraging more groups to undertake environmentally friendly activities that create carbon credits to sell.


title: Carbon credit

text: An individual allowance, such as an Assigned amount unit (AAU) or its near-equivalent European Union Allowance (EUA), may have a different market value to an offset such as a CER. This is due to the lack of a developed secondary market for CERs, a lack of homogeneity between projects which causes difficulty in pricing, as well as questions due to the principle of supplementarity and its lifetime. Additionally, offsets generated by a carbon project under the Clean Development Mechanism are potentially limited in value because operators in the EU ETS are restricted as to what percentage of their allowance can be met through these flexible mechanisms.


title: Carbon credit

text: Yale University economics professor William Nordhaus argues that the price of carbon needs to be high enough to motivate the changes in behavior and changes in economic production systems necessary to effectively limit emissions of greenhouse gases.


title: Carbon credit

text: Raising the price of carbon will achieve four goals. First, it will provide signals to consumers about what goods and services are high-carbon ones and should therefore be used more sparingly. Second, it will provide signals to producers about which inputs use more carbon (such as coal and oil) and which use less or none (such as natural gas or nuclear power), thereby inducing firms to substitute low-carbon inputs. Third, it will give market incentives for inventors and innovators to develop and introduce low-carbon products and processes that can replace the current generation of technologies. Fourth, and most important, a high carbon price will economize on the information that is required to do all three of these tasks. Through the market mechanism, a high carbon price will raise the price of products according to their carbon content. Ethical consumers today, hoping to minimize their “carbon footprint,” have little chance of making an accurate calculation of the relative carbon use in, say, driving 250 miles as compared with flying 250 miles. A harmonized carbon tax would raise the price of a good proportionately to exactly the amount of CO that is emitted in all the stages of production that are involved in producing that good. If 0.01 of a ton of carbon emissions results from the wheat growing and the milling and the trucking and the baking of a loaf of bread, then a tax of $30 per ton carbon will raise the price of bread by $0.30. The “carbon footprint” is automatically calculated by the price system. Consumers would still not know how much of the price is due to carbon emissions, but they could make their decisions confident that they are paying for the social cost of their carbon footprint.


title: Carbon credit

text: Nordhaus has suggested, based on the social cost of carbon emissions, that an optimal price of carbon is around $30(US) per ton and will need to increase with inflation.


title: Carbon credit

text: The social cost of carbon is the additional damage caused by an additional ton of carbon emissions. ... The optimal carbon price, or optimal carbon tax, is the market price (or carbon tax) on carbon emissions that balances the incremental costs of reducing carbon emissions with the incremental benefits of reducing climate damages. ... [I]f a country wished to impose a carbon tax of $30 per ton of carbon, this would involve a tax on gasoline of about 9 cents per gallon. Similarly, the tax on coal-generated electricity would be about 1 cent per kWh, or 10 percent of the current retail price. At current levels of carbon emissions in the United States, a tax of $30 per ton of carbon would generate $50 billion of revenue per year.


title: Carbon credit

text: Carbon credits create a market for reducing greenhouse emissions by giving a monetary value to the cost of polluting the air. Emissions become an internal cost of doing business and are visible on the balance sheet alongside raw materials and other liabilities or assets.