Theory Some Data and Concepts About Mars

Mars as seen by the Hubble Space Telescope during the Red Planet closest proximity in 59,619 years, by Aug. 26, 2003, showing Hellas Basin. picture courtesy NASA

Mars recently is the planet of the solar system which was the most studied in terms of astronomy. That interest likely is due to that one thinks that it might harbor life, or that its seemingly proximity could allow for some manned flights in a near future

Seasons Water Life

Atmosphere More About Mars' Geology Mars' Moons

Seasons

As Mars, just like at Earth, seasons are due to the planet's axis tilt. On the other hand, Mars orbit's larger eccentricity is playing a role too. Mars' axis is tilted by 25.19°, that is barely more than Earth's. Hence northern and southern hemisphere are alternately tilted toward the Sun. Sun rays either graze or hit vertically the surface, defining winter and summer. Mars' orbit eccentricity is more accentuated than Earth's however and seasonal changes are sharper on Mars than on Earth. When Mars is at its perihelion (nearest to the Sun) it is 128,400,000 miles (1.36 AU) from the Sun, as at its aphelion (farthest from Sun) distance is 154,900,000 miles (1.64 AU). Like on Earth, northern summers are taking place at the aphelion as northern winters at the perihelion. From this, Southern summers are warmer. Like at Earth, seasons are termed solstices (summer and winter) and vernal and autumnal equinoxes (spring and fall). Mars has two polar caps which form and shrink according to the seasons. Mars' polar caps are made up of a mix of water ice and frozen carbon dioxide. One particularly prominent feature is a 311-mile (500 kilometers) long, 1-mile (2 kilometers) deep trench that almost cuts the cap in two. Mars' north polar cap is geologically young at about five million years old as it contains unequally spaced layers of dust and ice that are apparently related to cyclical changes in the planet’s tilt. Seasonal surface changes at mid to high latitudes appear related to freezing and thawing of carbon dioxide. The ice cap is made up of many individual layers of ice and dust extending to a depth of around 1 mile. Polar caps at Mars are a seasonal cover of carbon-dioxide ice and snow as at their lowest during summertime in the planet's North, the remaining northern polar cap is all water ice as the southern one is water ice as well but also covered by a relatively thin layer of carbon dioxide ice. Mars' polar caps, generally, are composed primarily of water ice and were deposited in layers that contain varying amounts of dust, as that is referred to as the Martian Polar Layered Deposits (PLD). A gravity study of Mars in 2016 determined that when one hemisphere experiences winter, approximately 3 trillion to 4 trillion tons of carbon dioxide freezes out of the atmosphere onto the northern and southern polar caps, respectively, or about 12 to 16 percent of the mass of the entire Martian atmosphere. Due to difference in revolutions (Mars orbits in 687 days, Earth in 365), seasons are longer than Earth's by nearly an average of 100 per cent more. Spring is 93 days on Earth, 171 on Mars, Summer, 94 and 199, Autumn 89 and 171, Winter 89 and 146. The more-elliptical orbit of Mars exaggerates the southern-hemisphere seasons, making them dominant even for locations close to the equator. Northern winters are shorter and warmer than southern winters. Southern hemisphere spring and summer on Mars are much warmer than northern spring and summer, because the eccentricity of Mars' orbit puts the planet closest to the sun near the end of southern spring. There is a larger disparity between martian summer and winter due to the eccentricity of the orbit too. Seasons on Mars also induce carbon dioxide (CO2), which is the main component of martian atmosphere, to freeze into polar caps during winter and to vaporize during summer. When the southern polar cap thaws, it's liberating more CO2 than the northern one due to the warmer southern summers. This is leading to variations in Mars' atmospheric pressure as more gas is liberated at this period. When spring further, is reaching the scarps at the polar caps of Mars, frost avalanches are common. Each year the atmosphere grows and shrinks by about 30 percent due to this effect. Clouds exist at Mars, although less numerous than at the Earth. Dust clouds appear low in the atmosphere, as water clouds from near the surface up to about 12 miles (20 kilometers). Carbon dioxide clouds are seen at very high altitudes. It is likely that high altitude clouds are composed of crystals of water ice that condense out onto dust grains where it is cold in the atmosphere as wisps are created as those crystals fall and evaporate in patterns known as 'fall streaks' or 'mare's tails.' Clouds made of ice crystals appear blue because the cloud particles scatter blue light more strongly than other colors. High water-ice clouds at Mars look like they are dependent from the hour of the day as they are present at sunrise and early afternoon, when temperatures are lower, allowing water-ice to condense, and when later in the day they disappear, as sunlight increases and water-ice evaporates. Temperature variability and water vapour content according to the season, as well as atmospheric dynamics, are also a factor. The tilt of Mars' spin axis (obliquity) varies cyclically over hundreds of thousands of years

Mars axis tilt is enduring variation, like for the Earth. The cycle duration of that variation however is shorter than on the Earth bringing, for example, that Mars endured a warm age some 500,000 years ago, then an ice age as, currently the Red Planet is issuing from the latter. At Earth such variable phases are called Milankovitch cycles. The Martian climate undergoes larger changes over time than that of the Earth. A record of the most recent Martian ice age was recorded in the planet's north polar ice cap, agreeing with previous models that indicate a glacial period ended about 400,000 years ago as the poles began to cool relative to the equator. Models suggest that since then, the polar deposits would have thickened by about 980 feet (300 meters). On Earth, ice ages take hold when the polar regions and high latitudes become cooler than average for thousands of years, causing glaciers to grow toward the mid-latitudes. In contrast, the Martian variety occurs when -as a result of the planet's increased tilt- its poles become warmer than lower latitudes. During these periods, the polar caps retreat and water vapor migrates toward the equator, forming ground ice and glaciers at mid-latitudes. As the warm polar period ends, polar ice begins accumulating again, while ice is lost from mid-latitudes. A duration of 120,000 years is the average one for the cycle of variation of the axis' tilt, heating the poles and driving ice away to middle latitudes

A newly found, buried deposit of frozen carbon dioxide near the south pole of Mars contains about 30 times more carbon dioxide than previously estimated. The deposit holds up to 80 percent as much carbon dioxide as today's Martian atmosphere. Collapse pits caused by dry ice sublimation and other clues suggest the deposit is in a dissipating phase, adding gas to the atmosphere each year. Mars' atmosphere is usually about 95 percent carbon dioxide as with that buried deposit, Martian carbon dioxide right now is roughly half frozen and half in the atmosphere, but at other times, varying with the planet axis tilt, it can be nearly all frozen or nearly all in the atmosphere. An occasional increase in the atmosphere would strengthen winds, leading to more frequent and more intense dust storms. Modeling based on known variation in the tilt of Mars' axis suggests several-fold changes in the total mass of the planet's atmosphere can happen on time frames of 100,000 years or less. With the discovery input into Mars climate models it shows, for the period when Mars' tilt and orbital properties maximize the amount of summer sunshine hitting the south pole, the year-round average air pressure is approximately 75 percent greater than the current level. A tilted Mars with a thicker carbon-dioxide atmosphere causes a greenhouse effect that tries to warm the Martian surface, while thicker and longer-lived polar ice caps try to cool it, albeit it has to be noticed that the polar caps cool more than the greenhouse warms as Mars atmosphere, even when its carbon-dioxide content doubles, keeps too thin and dry to really allow to a greenhouse effect

Water

A simplistic view of Mars going from wet to dry might have to let room to a more complicated water story, with evolutions. Astronomers found, generally, that there is a diversity of ancient water-related environments at Mars, many apparently habitable, with reservoirs of buried water ice that are remnants of past climates, including buried glaciers. Much of the water Mars once held was lost over time due to ultraviolet light from the Sun breaking apart water molecules as now most of the water on Mars is locked up in ice (some liquid water could exist also in underground aquifers). Since September 2015, one is certain that water, in a liquid form, exists at Mars. It is found at slopes where streaks or 'gullies,' or 'recurring slope lineae' (RSL), which had been observed since long, are flowing. Such darkish streaks appeared to ebb and flow over time, darkening and flowing down steep slopes during warm seasons (at above minus 10 degrees Fahrenheit (minus 23 Celsius)), and then fade in cooler seasons. Flows also exist sometimes at the same locations than RSLs. The source of the ice at the origin of gullies is unclear, but there is some thought that it was deposited from the atmosphere during periods of high obliquity at Mars. Flowing water likely occurs like a shallow subsurface flow, with enough water wicking to the surface to explain the darkening. Streaks are up to a few hundred yards (meters) in length. Hydrated salts are likely a mixture of magnesium perchlorate, magnesium chlorate and sodium perchlorate. Latest data brought by mid-2016, are showing that gullies are likely not being formed by flowing liquid water but other processes like carbon dioxyde frost for example, instead, as gullies now are considered distinct from RSLs. Further, RSLs' salts could also become hydrated by pulling water vapor from the atmosphere, with no need for any underground source, as totally dry mechanisms for explaining RSL should not be ruled out. RSLs have been identified at dozens of sites on Mars. Linear gullies are found associated with dunes, and thought to be the result of CO2 ice breaking apart into blocks, which then slide or roll down warmer sandy slopes, sublimating and carving as they go, which determines a exceptional sinuosity due to repeated movement of dry ice blocks in the same path, possibly in combination with different hardness or flow resistance of the sand within the dune slopes. 'Slope streaks,' on the other hand, are when dry dust avalanches leave behind dark swaths on dusty Martian hills

->Water No More at The RSLs!
By late 2017 'recurring slope lineae' at Mars were thought more like what to expect for dry sand flows as until now they had spectacularly be linked to water and even life-prone conditions. Most slopes are steeper than 27 degrees and each flow ends on a slope that matches the dynamic 'angle of repose' seen in the slumping dry sand of dunes on Mars and Earth. RSL were discovered since 2011 as many thousands of these Martian features have been identified in more than 50 rocky-slope areas, from the equator to about halfway to the poles. Such a granular-flow explanation for RSL fits with the earlier understanding that the surface of modern Mars, exposed to a cold, thin atmosphere, lacks flowing water. However, RSL remain puzzling as they probably form by some mechanism that is unique to the environment of Mars, and a full explanation of how these enigmatic features darken and fade still eludes us

recurring slope lineae' (RSL) seen on the slopes of Horowitz Crater (left) and Garni Crater (right) at Mars. site 'Amateur Astronomy' based upon pictures NASA

A primitive ocean on Mars held more water than Earth’s Arctic Ocean in the past according to a study in 2015. Perhaps about 4.3 billion years ago, Mars would have had enough water to cover its entire surface in a liquid layer about 450 feet (137 meters) of average depth. Researchers estimate an age of about 3.7 billion years for the Martian deposits attributed to seafloor hydrothermal activity. Such a ocean likely occupied Mars' Northern Plains, considered a good candidate because of the low-lying ground. Such a ancient ocean there would have covered 19 percent of the planet’s surface. By comparison, the Atlantic Ocean occupies 17 percent of Earth’s surface. Such a wet period might have made Mars life-hospitable longer than thought. At 3.4 billion years ago, several large aquifers catastrophically ruptured, carving large outflow channels and flooding Mars’ northern plains to form a ocean. Valleys younger than better-known ancient valley networks on Mars in the northern Arabia Terra region of Mars are showing how lakes and streams held water several hundred million years after better-known ancient lake environments on Mars. Some trouble arises about those views however, from that water at Mars in the past should go with a thicker, greenhouse carbon-dioxide atmosphere. But latest studies by NASA's rover Curiosity in Gale crater since 2012 have shown that Mars had far too little carbon dioxide about 3.5 billion years ago to provide for

click to a map of the concentration of water at Mars. Blue, at high latitudes north and south, indicates higher concentrations of water ice (deduced from detection of hydrogen); orange designates lowest concentrations. Some hydrogen, possibly in the form of bound water, is close to the surface even at middle latitudes. The white squares in the northern hemisphere mark locations of small fresh impact craters that exposed water ice close to the surface and validated the neutron spectrometer data. The red squares mark locations of putative deposits of chlorite based on observations Such salt deposits could have resulted from evaporation of salty water. The blue squares mark locations of a type of dark features appearing and incrementally growing down slopes during warm seasons. map courtesy NASA/JPL-Caltech/ASU/UA/LANL/MSSS

click to a map of neutrons at Mars, showing varying degrees of hydrogen in the Martian soil. The hydrogen is an indicator of the presence of water. That map was acquired by a orbiter in 2012 in preparation of the landing of the Curiosity rover. The redder, the more hydrogen. map courtesy NASA/JPL-Caltech/Russian Space Research Institute

In geologically relatively more recent times, water appears to have cycled as a gas between polar ice deposits and lower-latitude deposits of ice and snow. Extensive layering in ice or rock probably took at least hundreds of thousands, and possibly millions of years to form. Like ice ages on Earth, the layering is linked to cyclic changes in the tilt of the planet's rotation axis. A part of Mars' Utopia Planitia region, in the mid-northern latitudes, is holding a extensive subterranean deposit with a composition 50 to 85 percent water ice, mixed with dust or larger rocky particles. At the latitude of this deposit -- about halfway from the equator to the pole -- water ice cannot persist on the surface of Mars today. That deposit probably formed as snowfall accumulating into an ice sheet mixed with dust during a period in Mars history when the planet's axis was more tilted than it is today. Mars' current climate is also dynamic, with volatile carbon dioxide and summertime liquid water modifying gullies and forming new streaks. Mars thus nowadays is a partially frozen world, but not frozen in time, as change continues today. The water cycle at Mars has the water vapour content vary substantially in the atmosphere of Mars, both with the season and by geographical location. The question is to know where the water is coming from, and where it is going to. Water vapour in the atmosphere of Mars is a signature of water being transported around the planet. As the water at Mars is mostly found in the polar caps or the soil, it has first to evaporate or sublimate and get to the atmosphere, where it can transform into clouds (such clouds, on another hand, have a cooling effect on the Martian climate). It might, according to latest observations that Mars dried up significantly since the measures taken in the atmosphere by the Viking missions as there was then almost twice the quantity of water in the atmosphere over the north pole of Mars as there is now but that might be due too to that the spectroscopic database used to interpret the Viking results was incomplete leading to a over-estimated wetness of the atmosphere. A more stable Martian water cycle likely is the most reasonable solution. When the northern ice cap sublimates during summer, it reveals a layer of water ice beneath which can evaporate in turn. The southern ice cap however never completely evaporates and water remains trapped there thus leading to the thinking that Mars North Pole is the main contributor to the Martian water cycle!

->Mostly Freezing Water at Mars, With Volcanoes Active Until Several Million Years Ago!
The chemical signatures of isotopes present in the Martian atmosphere suggests that liquid water primarily existed at temperatures near freezing -and until in recent times- and that hydrothermal systems similar to Yellowstone's hot springs have been rare throughout the planet's past. Mars further has replenished its atmospheric carbon dioxide relatively recently with carbon dioxyde emitted from volcanoes, until into a recent past meaning that volcanism at Mars persisted unto about several million years ago

A stunning view: frost as seen by Viking 2 in 1979 at Utopia Planitia. Although frost is no more than one-thousandth of an inch, it leaves dust and water on the terrain when evaporating. Another cycle of water? Atmosphere water turning to frost on surface was further evidenced in 2015 picture courtesy NASA "Mars for Press"

As far as question of water is concerned, one school deems Mars always was a warm, dusty, and dry planet, with a thin and cold atmosphere which did not retain liquid water. Hence martian water stayed frozen in martian soil for billions years. Another school sticks to a more conventional vision, one of a planet scoured by floods of waters and even having had an ocean in its northern part. Hence a dynamic and hydrologically active Mars all along its history. Observations made at Mars are showing river-shaped channels at Mars surface. The idea of the existence of a early northern ocean at Mars, about 3.4 billion years ago, fed by enormous catastrophic floods posed a persistent problem as no definitive paleoshoreline had been observed. Studies in 2016 however in the circum-Chryse and northwestern Arabia Terra regions have shown evidence for two enormous tsunami events possibly triggered by bolide impacts, resulting in craters of about 19 miles (30 kilometers), and occurring perhaps a few million years apart. A colder global climatic regime occurred after the older tsunami event. The studies finally show that tsunamis played a major role in generating and resurfacing coastal terrains at the early Mars. But it seems that Mars quickly lost its atmosphere to the point of making the planet rapidly dry. Further, no limestone deposits -which would be a strong evidence of interaction between large amounts of water and atmosphere- have been found and olivine is abundant -that is a rock which does not last in the presence of water. Some explanations have been brought about such conflicting data. Water-shaped features would have been carved at an epoch dating back to what is called the "heavy bombardment period", when solar system formation leftovers heavily pondered newly formed planets. At Mars such impacts would have melt the underlying water-ice, sending it along with heated rocky material into the atmosphere. At such moments, Mars got warmer, more water-ice was vaporized, and a water-charged atmosphere triggered heavy localized rains. Each such period was followed by a back to a dry period. On the other hand, other processes may contribute to create watery related-looking relief features, such as volcanism, orbital and axis tilt variations (as they accentuate seasonal phenomenons), or even erosion by a mix of carbon dioxyn snow, dust, sand, and dry ice avalanching on carbon dioyin cushions. At last, some residual geological water-related processes are at work at Mars anyway, and are still nowaday. Most of Martian water is found about 18 inches deep as regions of long-lived hydrothermal activity exist where Martian magma is interacting with buried water-ice. This is generating limited water flows along million years, which have yielded those gullies seen at some crater's edges. Gullies are seen too at the top of sand dunes or commonly starting at a crest as most are seen on rockier slopes, such a the inner wall of craters, sometimes starting partway down the slope (ranging in size from about 50 yards or meters long to more than 2 miles (3 km) long). Gullies might also be linked to carbon dioxide mechanisms as before-and-after comparisons have shown changes when the winter season involved, and none with spring, summer and autumn. Mechanisms at work might consist into the sublimation of carbon dioxide when heat is back with gas lubricating a flow of dry sand or that sublimation erupt in puffs energetic enough to trigger slides as a pile of carbon-dioxide frost accumulating gets thick enough to avalanche down and drag other material with it). On Earth, similar features seen at places like Meteor Crater in Arizona are carved by liquid water. Bright objects seen in such gullies might be pieces of dry ice that have broken away from points higher on the slope as they might sublimate into pits downhill. Other seasonal features linked to C02 ice exist, like terrains near Mars' poles of the type spiders, or 'araneiform' under the form of multiple channels converging at a point. That is due to extensive sheets of ice thawing bottom-side first, with the ice warmed by the ground below it. Thawed carbon dioxide gas builds up pressure, and the gas escapes through vents in the overlying sheet of remaining ice, pulling dust with it. Such that process carves the araneiform channels. The dust propelled outwards is sculpted by local winds into hundreds of thousands of dark fans. Erosion-carved troughs growing and branching during numerous Martian years may be the infant versions of spiders. Spiders range in size from tens to hundreds of yards (or meters). Spiders might also occur in areas where the ground surface is made of ejecta of impact craters which blanketed older surface

->More About the Subsurface Structure and Ice Polar Layers at Mars!
New observations from NASA's Mars Reconnaissance Orbiter working in orbit At Mars indicate that the crust and upper mantle -or lithosphere- of Mars are stiffer and colder than previously thought. The thicker the lithosphere, the more gradually the temperatures increase, leading to that any aquifer below is now due to be found lower than thought. The discovery was made using the Shallow Radar instrument on the spacecraft, providing for views of the interior of Mars. The observations support too the idea that the north polar ice cap is geologically active and relatively young, at about 4 million years, with ice layers stretching up to 600 miles (1,000 kilometers) as previous studies had revealed that the thickness, in some places might reach 2,3 miles (3,7 km) -should such a material of ice melting, it would soak Mars under a water layer of 33 ft (11 meters). In-depth study of those layers also reveal four zones of finely spaced layers of ice and dust separated by thick layers of nearly pure ice, as such a pattern hints to cycles of climate change on Mars on a time scale of roughly one million years, caused by variations in the tilt of the planet's rotational axis and in the eccentricity of its orbit around the sun. The icy past of Mars too is linked to impact events

More frost at Mars, as seen by NASA's Phoenix Mars Lander in 2008 in the plains close to the north pole of the Red Planet! picture based on picture courtesy NASA/JPL-Caltech/University of Arizona/Texas A&M University

->A Lot of Water at Mars in the Ancient Times!
Results of observation in 2008 are showing that there really was a lot of water flowing at Mars, during what is called the 'Noachian' period of Mars geological history -4.6 billion to 3.8 billion years ago that is. Large amounts of clay matching that period have been observed at the Red Planet. Mars may have been covered too with a vast ocean about 3 billion years ago
Recentest studies still, by NASA's Mars Reconnaissance Orbiter (MRO), are adding to that, with opal or opaline (which geologically is hydrated silica, containing water) found in large areas of Mars. The mineral further is hinting to that large masses of water to have exist on the Red Planet until as recently than 2 billion years ago! With the opaline, it's now three types of hydrated minerals at Mars are hinting to a watery past on the planet. Clay-like hyllosilicates are igneous rocks which formed 3.5 billion years ago and came into a long-term contact with ancient water. Hydrated sulfates, which date back to between 3.5 and 3 billion years ago, formed then from the evaporation of salty and sometimes acidic water. Opaline formed less remotely in the past, where rocks emanating from volcanoes or meteorite impacts came into contact with water, like, for example, on the rims of the vast, famed Valles Marineris, that Martian canyon or along dry river chanels. Spirit, one of the Twin Rovers mission, also found opaline in the Gusev Crater. The discovery of opaline, dating back to less large amount of times is further showing that life-hospitable conditions occurred, or existed at Mars during a longer span of time than thought until now

->More Evidenced Water at Mars, and 10,000 Years Ago Only!
10,000 years ago only, before Mars got into a dryer area which is lasting until now, the water present there took refuge into the frost soil, where later, and until now, it's enduring the so-called 'frost heave' comportment, by which, like in the Arctic regions on Earth, thin films of liquid water around ice grains and soil grains migrate to form clear ice lenses on top of the ice table. Ice at Mars, thus, might well be 99 pure and, moreover, more extant than thought, as far as regions are concerned, and even by the equator! Despite the dryer period, ice has not retreated as fast as one could expect! That, further is evidencing that water was extant at Mars no longer than 10,000 years ago!

Some other data have been collected about water at Mars. There are evidences that deep underground Martian rocks are more water-rich than similar rocks at Earth. During Mars formation, melted magma, which contained important amounts of dissolved water (at least 3 percent) under great pression, had this water trapped when it cooled down. A combination of volcanism, tectonics, collapse and subsidence in some regions of Mars, generally, led to several massive groundwater releases, with flood. Most recent Mars Odyssey data are pointing too at Mars just coming out of an ice age. Hence underground water-ice would part into a deep, ice-rich layer -mark of the ice age, a middle layer with ice mixed to soil -that is the mark of a warmer era, and a dry soil layer topping both, as a result of dust left by as water ice vaporized. Finds by the Phoenix, polar lander, by 2008, have shown too that low-level, wispy ice clouds, similar to the cirrus clouds forming over the polar regions too at Earth, might yield there, when air temperatures are cool enough for water vapor in the atmosphere to condense and that the clouds become thicker, persistant, and lower to the ground, some snowfall, of the Earth's polar type, which however is small in quantity. Such snow might thus be another contributor to the water cycle at Mars! The most mainstream view, now, is that some relief features at Mars suggest that water was present, with water ponds ranging from seas to lakes, and rivers and gullies, as some evidence too suggest that Mars may have been permanently cold, with global temperatures well below the freezing point of pure water. A 2009 study showed that various concentrations of greenhouse gases in the Martian atmosphere could not efficiently have raised the surface temperature above freezing as, at the contrary the presence of silicon, iron, magnesium, calcium, chloride, sodium, potassium and aluminum could have allowed water at temperatures well below freezing. Further, minerals kept precipitating in such liquid solutions over time as they are similar to those still found today on the Red Planet. Salts likely added also. Highly perchlorated mud is likely existing, on the other hand, in the polar plains of Mars, during Martian winters, sustaining temperatures as low as minus 94° F (minus 34° C). Martian rocks containing sulfur and hydrogen might hint to hydrated calcium sulfates as such minerals could be gypsum or bassanite. On Earth, calcium sulfates like gypsum form frequently in veins when relatively dilute fluid circulates at low to moderate temperatures. Mars complex Martian history of climate change that produced a diversity of past watery environments over hundreds of millions of years. The same altitude of rivers delta 3.5 billion years ago in Mars' northern hemisphere suggest that they might have sat around a vast ancient ocean which would have covered one-third of the Red Planet, covering the northern lowlands. Such a observation is comforted by the fact that a set of craters in the Martian northern lowlands had exposed clay layers. Clay minerals that are signatures of a wet environment and had already been found at thousands of sites in the southern highlands of Mars, where rocks on or near the surface are about four billion years old. No sites with those minerals had been reported in the northern lowlands, where younger volcanic activity has buried the older surface more deeply. That suggest too that Mars was altered on a global scale by liquid water about four billion years ago as other types of evidence about liquid water in later epochs on Mars tend to point to shorter durations of wet conditions or water that was more acidic or salty. The wet period that may have been most favorable to life, likely occurred between the early giant impact which determined the shape of Mars' northern hemisphere, and the later time when younger sediments formed an overlying mantle. The impact would have eliminated any evidence for the surface environment in the North that preceded the impact. Latest evidence by 2011 suggests traces of water on Mars might be underestimated because a thin varnish of iron oxide, or rust might cover patches of carbonates, those minerals forming in large bodies of water. Such a varnish may also have extended temporarily the time that Mars was habitable, as the planet's surface slowly dried up protecting any living organism from deadly Sun's ultraviolet light. A giant mound of layers at the center of the Gale Crater confirmed in 2010, as seen by the MRO mission, how Mars' geology had evolved since billions of years. Clay-producing conditions were followed by sulfate-producing conditions, which in turn were followed by dry conditions. Clay minerals form under very wet conditions. Sulfate minerals are seen then intermixed with the clays, forming in wet conditions and deposited when the water in which they are, evaporates. Sulfates follow without detectable clays, eventually topped, in the Martian stratigraphy with layers bearing no detectable water-related minerals at all. Also a study released by November 2011 based upon years of mineral-mapping data by NASA and ESA orbiters states that, Martian environments with abundant liquid water on the surface existed only during short episodes. That is consistent with that the atmosphere not having been thick enough to provide warm, wet surface conditions for a prolonged period. These episodes occurred toward the end of hundreds of millions of years during which warm water interacted with subsurface rocks. Clay minerals found in the shallow subsurface are all over Mars as types formed on the surface are quite rare and in limited locations, hints to that water environment mostly occurred by subsurface and that hydrothermal places likely are the best candidates to have harboured life in the past. Conditions near the equator of Mars are favorable for small quantities of brine to form during some nights throughout the year, drying out again after sunrise. Conditions should be even more favorable at higher latitudes, where colder temperatures and more water vapor can result in higher relative humidity more often

A closeup view in the 'Murray Buttes' region of lower Mount Sharp, shows finely layered rocks, belonging to buttes and mesas rising above the surface and eroded remnants of ancient sandstone that originated when winds deposited sand after lower Mount Sharp had formed. Ancient sand dunes formed and were buried, chemically changed by groundwater, exhumed and eroded to form that current view picture based on a picture courtesy NASA

->Snow and Water at Mars's North Pole as Seen by the Phoenix Mission and Further
NASA's Phoenix mission, a mission which landed in May 2008 near the North Pole of Mars to study the soil and under-soil there, has uncovered snow falling between an altitude of 2.5 and 1.5 miles and is now to endeavour to watch whether such snow may reach ground! The lander, further, found in those polar regions -like the Twin Rovers are in other parts of Mars- rocks hinting to that they formed due to interaction with water (chalk, for example, that meaning too that Mars there could have had an ocean!). The Martian north pole in the past might have been more directly exposed to Sun due to the cyclic variation of the poles' axis tilt. All those evidences for water at Mars all go in the direction there likely was life at Mars in the past. The findings by the Twin Rovers however should bring to damper such assertions as that might be true for the Martian north pole only, with a lot of underground freezed water and possibly a lot of liquid water in the past, where life might have been harboured. Phoenix further found that the Martian soil was alcaline there and that it contains a lot of nutrients and minerals (which is not the case for the other regions of Mars). Brine also was observed on Phoenix legs. A orbiter by 2012 have detected carbon-dioxide, or dry ice, snow clouds on Mars and evidence of carbon-dioxide snow falling to the surface. The snowfalls occurred from clouds around the Red Planet's south pole in winter. The results show snowfall is especially vigorous on top of the residual cap. Water ice snow also occurs on the Red Planet

->More Ice Buried at Mars!
The high-tilt periods at Mars generated ice ages. One of them likely yielding ice sheets covering the mid, 35 to 60-degrees of latitude in both hemispheres-latitude regions of Mars millions of years ago. This discovery is solving an old puzzle posed to scientists, as aprons -gently sloping areas of rocky deposits at the bases of taller geographic features- were unexplained until now. Those features are just, in fact, glaciers of that ice age, as rocky debris eventually topped the glaciers and prevented the ice from vaporizing. Such glaciers were found, for example, in the Hellas Basin. Those glaciers, thus, with a half a mile-thickness (800 meters) and extending for dozens of miles (dozens of kilometers) from the mountains of cliffs' edges, are adding to the potential of buried, or frozen water at Mars, representing the largest reservoir of water ice on Mars that is not in the polar caps. Those glaciers at Mars are akin somewhat to massive ice glaciers which have been detected under rocky coverings, on Earth, in Antarctica!

Data from the Mars Reconnaissance Orbiter mission since 2006 are hinting to three very different periods of Mars history. Its observations of the heavily cratered terrains of Mars, the oldest on the planet, show that different types of ancient watery environments formed water-related minerals. Some of these would have been more favorable for life than others. In more recent times, water appears to have cycled as a gas between polar ice deposits and lower-latitude deposits of ice and snow. Extensive layering in ice or rock probably took hundreds of thousands to millions of years to form and, like ice ages on Earth, is linked to cyclic changes in the tilt of the planet's rotation axis and the changing intensity of sunlight near the poles. The present climate is also dynamic, with volatile carbon dioxide and summertime liquid water modifying gullies and forming new streaks. The orbiter has shown a partially frozen world, but not frozen in time, as change continues today. The action of water on and near the surface of Mars occurred for hundreds of millions of years, being at least regional and possibly global in extent, though possibly intermittent. The spacecraft has also observed signatures of a variety of watery environments, some acidic, some alkaline, which increase the possibility that there are places on Mars that could reveal evidence of past life. The Phoenix Mars Lander or observations by orbiters have identified buried layers of water ice at high and middle latitudes and frozen water in polar ice caps as Spirit recently found what could be snow melt turned into soil layers carrying hematite, silica and gypsum or ferric sulfates, as none of such minerals are found in the surface soil which is covered with wind-blown sand and dust. Several of Martian craters presents characteristic concentric crater fill, a distinctive Martian process marked by rings of surface fluctuations within a crater rim and might harbour vestiges of ancient glaciers. All such observations are a accumulating set of clues that Mars had -and may still have- small amounts of liquid water at some periods during ongoing climate cycles due to Mars spin-axis tilt varies over timescales of hundreds of thousands of years. The Phoenix lander however has shown how Martian soil has experienced very little interaction with liquid water over the past 600 million years or more. New evidence of a wet underground environment on Mars has surfaced by early 2013 as 57-mile (92-kilometer)-wide McLaughlin Crater's depth once allowed underground water to flow into the crater's interior and create a lake. Large and small inflow channels originating within the crater wall end near a level of a possible former lake. Minerals such as carbonates are best preserved under non-acidic conditions. Rocks exhumed from the subsurface by meteor impact, on a other hand, were altered early in Martian history, most likely by hydrothermal fluids as such fluids trapped in the subsurface could have periodically breached in deep basins such as McLaughlin Crater. Such a discovery might reveal that at least some areas are more likely to reveal signs of ancient life than others at Mars. Ancient water channels are extant below the Martian surface in Elysium Planitia, or the youngest volcanic area at Mars, constituting the true extent of Marte Vallis, and attributed to catastrophic flooding in the last 500 million years as Mars during this period had been considered cold and dry. The floods originated from a now-buried portion of the Cerberus Fossae fracture system. The water could have accumulated in an underground reservoir and been released by tectonic or volcanic activity

Life

-> Life on Mars! A renewed study of a Martian meteorite is showing that is really bears fossilized remains of Martian life! check more!

The surface of Mars is a very oxidizing, radiation-heavy environment. A general slow trend from warm to cold climate on Mars occurred from 3 to 4 billion years ago, around the same time life appeared on Earth, which could be a other argument to life on the Red Planet. Mars nowadays is 1,000 times drier than even the driest parts of the Atacama desert in Chile, which makes it less likely that microbial life as we know it exists on the planet's surface, even with some access to water. Earth deserts on the other hand, also knows dormant organisms which are simply surviving. As far as life on Mars is concerned, 1976 Viking missions, which were specifically designed for such a search, did not find any evidence of life. Mars would be self-sterilizing due to ultraviolet radiations, soil extreme dryness, and soil oxidizing mechanisms. It is thought however that life might have appeared or still exist at places protected against those martian defects such as in ice-water rich polar regions (where life similar to which seen in Antarctica might be found) or in underground regions of hydrothermal activity. One of the more intriguing fact is obviously ancient traces of life which were found on a martian rock having travelled as a meteorit down to Earth). Water under the form trapped at the polar caps of Mars, or frozen into the soil, is not likely to be a main contributor to life. Water, on the other hand, in the form of flowing, or pooled, is thought to increase the chance of some form of past or present life. One question of finding water-carved reliefs at Mars is that such reliefs may be too carved by lava flows. A 100-yard (100-meter) high volcanic cone in the 30-mile (50-kilometer) wide Nili Patera caldera on Mars, in the Syrtis Major volcanic region, is sporting steam fumarole, or hot spring deposits on the southern flanks and nearby terrains with hydrated silica more than three billion years old and might have constituted the most recent habitable microenvironments on Mars, among a otherwise dry and cold Mars. At some times and in some places, Mars has had favorable environments for microbial life. Such the Nili Patera caldera formed when a underground magma chamber collapsed. Silica deposits around hydrothermal vents in Iceland or Kamchatka are among the best parallels on Earth. Clay environments favourable to life are 700 million years older, or greater than such hot springs deposits. Deeply fractured areas around impact craters might have provided a safe haven in which microbes can flourish for long periods of time as fractures on rocks deep below enabled water and nutrients to flow in and support life. Micro-organisms for example have been discovered living deep underneath a site on Earthwhere an asteroid crashed some 35 million years ago. Volcanoes erupted beneath an ice sheet on Mars billions of years ago, showing there was extensive ice on ancient Mars in the past as that could have provided favorable conditions for microbial life. Des volcans sont entrés en éruption sous des couches de glace il y a des milliards d'années montrant que la glace était très présente sur l'ancienne Mars et, de plus, ce fait aurait pu créer des conditions favorables à la vie microbienne. Volcanoes erupted under ice layers billions yeaers ago at Mars, which hints to that ice was extensive upon ancient Mars and that, further, that might have yielded conditions favorable to microbial life

Life at Mars likely was linked -and may still be- to water. As far as the past is concerned, Mars would have endured some alternating periods when water, at some times, formed clay-rich minerals, and at others time, when water was salt-rich only and acidic. The second case obviously was less life-prone than the first one. The clay producing periods are detected at Mars due to the presence of carbonates, those minerals which are the product of the interaction between the Martian atmosphere carbon dioxide and materials altered by water, and resulting from the volcanic rocks of Mars. Clay are widespread at Mars, with clay minerals forming under wet and relatively neutral pH conditions. Areas with carbonates were found, in 2008, by the Mars Reconnaissance Orbiter mission in the following Martian regions: Nili Fossae, along the Isidis Basin; along, too, eroded mesas; inside the Jezero Crater; some traces of carbonates have been found too at Terra Tyrrhena and Libya Montes. Carbonates at Mars however seem well to exist in small quantities only. Silica, resulting from underground water percolating to the surface, are too a hint to the possibility of life at Mars. A good sum of the question of life on the Red Planet could be that Mars had water, once, as the areas with really favourable conditions for life, are few in number however

A nocturnal frost cycle is having, with temperatures as low as minus 50 degrees C. and the soil at minus 70 degrees C. each night, the humidity in the air disappearing about totally. A part of that only may become frost in the early morning as the humidity is mostly absorbed into the Martian soil. The frost, at Mars, is made of a thin film, which, in fact, neither is dew nor frost but thin of about two water molecules only, and not able to flow, but more mobile than ice however. At the difference of such films which are seen in some Antarctic locations and able there to harbour life, the thinness of the films at Mars aren't that able. Transient overnight carbon dioxide frost, even at middle and low latitudes is extensive at Mars due to cold-enough nighttime surface temperatures, as areas in the Tharsis, Arabia and Elysium regions feature such nightly temperatures. All three are dust-covered to the extent that surface temperatures change much quicker than in areas with exposed-bedrock surfaces as they are also warmer regions by daytime

It's possible, further, that forms of microbian life at Mars had molded their comportment upon the cycles yielded by the variation of the planet's axis tilt. They could have gone dormant like spores and wait until the tilt providing for fairer life conditions. Life, then, would have woke up, fixed some potential genetic damage, or reproduce. Mars axis tilt likely varied, with, for example, the tilt so pronounced some 4 or 5 million years ago that the poles were exposed to the Sun during half of the year and likely to a more humid atmosphere. The debate, among scientists, is that the tilt of the axis might have changed so slowly however that the climate changes would have had a lot of time to perform. That slowness, on the other hand, might have allowed plenty of time too for the water vapor to be eventually forced out of the atmosphere into the icy soil, allowing thus for life

During its mission, NASA's Phoenix polar lander confirmed and examined patches of the widespread deposits of underground water ice detected by the Odyssey orbiter, and identified a mineral called calcium carbonate that suggested occasional presence of thawed water. The lander also found soil chemistry with significant implications for life and observed falling snow. The mission's biggest surprise was the discovery of perchlorate, an oxidizing chemical on Earth that is food for some microbes and potentially toxic for others. The martian soil above the ice can act like a sponge, with perchlorate scavenging water from the atmosphere and holding on to it. Thus a thin film layer of water is extant and capable of being a habitable environment. The perchlorate results are shaping subsequent astrobiology research, as scientists investigate the implications of its antifreeze properties and potential use as an energy source by microbes. Discovery of the ice in the uppermost soil by Odyssey pointed the way for Phoenix. More recently, the Mars Reconnaissance Orbiter detected numerous ice deposits in middle latitudes at greater depth using radar and exposed on the surface by fresh impact craters. Ice-rich environments are an even bigger part of the planet than thought. In such vast regions places are more habitable than others. NASA's Phoenix mission's data have shown that Mars had diverse wet environments at many locations for differing durations during the planet's history, and climate-change cycles persist into the present era. Hydrothermal formation of clay-carbonate rocks in the Noachian era Nili Fossae region on Mars, which are valleys which cut into the ancient crust of Mars, exposing clay minerals, are presenting similarities with the Earth, Archean East Pilbara region of Western Australia. Should any life have existed there 4 billion years ago, they would have been preserved

The only organic chemicals identified when the Viking landers heated samples of Martian soil were chloromethane and dichloromethane -- chlorine compounds interpreted at the time as likely contaminants from the craft cleaning fluids. The late Phoenix polar lander, on the other hand, discovered perchlorate, the most important finding since the Viking era. Perchlorate is a ion of chlorine and oxygen as it becomes a strong oxidant when heated. It could lie in the Martian soil with organics around for billions of years without breaking them down. But, when heating the soil by the Vikings to check for organics, the perchlorate was to be seen destroying them rapidly. And chloromethane and dichloromethane are exactly those which resulted when a little perchlorate was added to desert soil from Chile containing organics and analyzed in the manner of the Viking tests. Viking scientists at the time, had concluded to contaminants as the chlorinated organics found had a ratio of two isotopes of chlorine in them matching the three-to-one ratio for those isotopes on Earth. For 30 years scientists may have looked at a jigsaw puzzle with a piece missing! The next NASA rover in 2012, with two kinds of life-searching processes should improve the knowledge. The ratio for the chlorate isotopes at Mars, however, should be clearly determined them. If it is found to be much different than Earth's, that would bring scientists back to the 1970s interpretation. Should organic compounds be able to persist in the surface soil of Mars, contrary to the predominant thinking for three decades, large, complex organic molecules, such as DNA could be found and be indicators of biological activity. Cautious astronomers, on the other hand, have always considered that the organics at Mars, on the other hand, can come from non-biological or biological sources as many meteorites might have brought organics to Mars too. Mars meteorites that landed on Earth -which Martian material which could journey to Earth through miscellaneous circumstances- show, as studied in 2012, strong evidence that very large molecules containing carbon, which is a key ingredient for the building blocks of life, can originate on the Red Planet as indicators that complex carbon chemistry has taken place on Mars. Such 'reduced carbon' is carbon that is bonded to hydrogen or itself as storage of reduced carbon molecules on Mars occurred throughout the planet's history and might have been similar to processes that occurred on the ancient Earth. Such a find is now allowing to Martian missions to search for molecules containing large chains of carbon and hydrogen like a evidence for past life on the planet, distinguishing non-biologically formed carbon molecules from potential life. Carbon molecules likely were created by volcanic activity on Mars and show that Mars has been doing organic chemistry for most of its history. Meteorite NWA 7034 is significantly older than most other Martian meteorites and found containing 10 times more water than other Martian meteorites from unknown origins. It formed 2.1 billion years ago during the beginning of the most recent geologic period on Mars, known as the Amazonian as it is a excellent match for surface rocks and outcrops NASA has studied remotely via Mars rovers and Mars-orbiting satellites. The fragments are primarily feldspar and pyroxene, most likely from volcanic activity. This unusual meteorite's chemistry matches that of the Martian crust as measured by NASA's Twin Rovers and Mars Odyssey Orbiter. This unique meteorite tells us what volcanism was like on Mars 2 billion years ago. It also gives us a glimpse of ancient surface and environmental conditions on Mars that no other meteorite has ever offered. Researchers theorize the large amount of water contained in NWA 7034 may have originated from interaction of the rocks with water present in Mars' crust. Most Martian meteorites are divided into three rock types, named after three meteorites; Shergotty, Nakhla, and Chassigny. These "SNC" meteorites currently number about 110. Their point of origin on Mars is not known. Although NWA 7034 has similarities to the SNC meteorites, including the presence of macromolecular organic carbon, this new meteorite has many unique characteristics

For centuries, scientists wondered if Mars might be covered with vegetation or even inhabited by intelligent beings as the 19th century was ablazed with the idea that the telescopes allowed for seeing chanels at the surface of Mars, which eventually prove to be optical delusions only. Mars also captured the human imagination like no other body in the solar system did. The novels of Burroughs and others tout the planet's allure and films have warned humanity of its dangers, with Orson Welles the author of a famed radio hoax during the 1930s, or Ray Bradbury wrote The Martian Chronicles

Fuzziness kept about life at Mars with discoveries by NASA's Curiosity rover by June 2018! The rover working in the Gale Crater, which once hold a lake of water, while not necessarily found evidence of life itself, found organic molecules in three-billion-year-old sedimentary rocks near the surface, in the top two inches of rock that was deposited when Mars may have been habitable. Organic molecules contain carbon and hydrogen, and also may include oxygen, nitrogen and other elements. While commonly associated with life, organic molecules also can be created by non-biological processes and are not necessarily indicators of life. Curiosity has not determined the source of the organic molecules. The discovery was made in sedimentary mudstone, which originated from silt as sulfur included into molecules likely preserved those. Organic carbon was also found with concentrations alike to that observed in Martian meteorites. The longevity of the Curiosity mission, which stayed at Mars during nearly three Martian years, or almost six Earth's, allow to discover in the area too a seasonal variation of a methane emission. There too, water-rock chemistry might have generated the methane, but scientists cannot rule out the possibility of biological origins. Methane at Mars until now had only be detected like large, unpredictable plumes as methane at Gale Crater repeatedly peaks during warm Martian summer months and drops during winter, a first time that that was observed. Both those finds gives scientists confidence that next Martian rovers, the NASA's Mars 2020 rover and European ESA’s ExoMars will find even more organics, both on the surface and in the shallow subsurface

Atmosphere

The loss of atmosphere to space has been a major driver of climate change on Mars as solar storms might have been a major driver of that loss. The majority of the CO2 on the planet also was lost, which prevents any possibility of terraforming at Mars. The thin CO2 atmosphere at Mars might rely upon a long-term, stable deposit of CO2 layers at the South pole. Those might have been due to the planet's axis wobble over the past 510,000 years bringing alternate layers of water and ice ice. There is a link between the upper and lower and middle atmosphere of Mars of the planet which clearly hints to the planet's atmosphere to behave like a single, interconnected system included when responding to ice caps sublimation. At very high altitudes Mars’ atmosphere is made up of plasma of electrically charged particles and gas molecules. Layers and rifts with different plasma density, are found in the electrically charged part of the upper atmosphere -- the ionosphere -- of Mars like those found at Earth. Martian atmosphere yields a wide scattering of the yellow and red colors of sunlight but dust in there allows blue light to pass more efficiently, which gives that blue hue to the Martian sky near the Sun. That is more pronounced at sunset when light journeys through a longer path in the atmosphere. Each year, the Martian atmosphere increases and decreases by 30 percent due to seasonal factors when one hemisphere receives more and more sunlight as the polar cap there begins to vaporize its carbon dioxyde. Mars atmosphere is very thin, the equivalent of 100,000 feet at Earth only. In the Martian atmosphere the predominant gas by far is carbon dioxide, making up 95.9 percent of the atmosphere's volume. The next four most abundant gases are argon, nitrogen, oxygen and carbon monoxide. Persistent water and a thicker atmosphere likely existed during Mars' distant past. The loss of a fraction of the atmosphere, resulting from a physical process favoring retention of heavier isotopes of certain elements, has been a significant factor in the evolution of the planet. The rate of loss of gas from the Martian atmosphere to space is controlled by the Sun as a polar plume of ions is escaping also. The atmosphere loss is the major force behind climate change at Mars, from a warm and wet to a cold and dry. Ozone at Martian poles is absorbing ultraviolet light, playing the same role than at Earth. As ozone however at Earth is destroyed during winter, it builds up during that season at Mars. A increase of 5 percent in heavier isotopes of carbon in the atmospheric carbon dioxide compared to estimates of the isotopic ratios present when Mars formed. These enriched ratios of heavier isotopes to lighter ones likely explains how the top of the atmosphere may have been lost to interplanetary space. Losses at the top of the atmosphere would deplete lighter isotopes. Methane, a simple precursor chemical for life, looks like it exists in traces only. Sources for methane on Mars could include comets, degradation of interplanetary dust particles by ultraviolet light, and interaction between water and rock. A potential biological source would be microbes. Sinks for removing methane from the atmosphere are photochemistry in the atmosphere and loss of methane to the surface. The crust and interior of Mars is also releasing small quantities of volatile molecules as those may also be incorporated into rocks in the crust through the action of fluids. The solar wind and the Sun’s ultraviolet radiation turns the uncharged atoms and molecules in Mars' upper atmosphere into electrically charged particles (ions). Once electrically charged, electric fields generated by the solar wind carry them away. The electric field is produced by the motion of the charged, electrically conducting solar wind across the interplanetary, solar-produced magnetic field, the same dynamic generators use to produce electrical power. Some atoms and molecules that have enough speed from solar heating to simply run away, they remain electrically neutral, but become hot enough to escape Mars' gravity. Also, solar extreme ultraviolet radiation can be absorbed by molecules, breaking them into their constituent atoms and giving each atom enough energy that it might be able to escape from the planet. The energetic particles from the Sun, on a other hand, can be absorbed by the upper atmosphere, increasing its temperature and causing it to swell up. More than 20 ancient crater impact larger than 600 miles across could have blasted large amounts of the martian atmosphere into space. However, huge martian volcanoes that erupted after the impacts, like Olympus Mons, could have replenished the martian atmosphere by venting massive amounts of gas from the planet's interior. Water vapor in the atmosphere also was lost to space, as any remaining water froze out as the temperatures dropped when the atmosphere disappeared. On Mars, hydrogen escapes faster because it is lighter than deuterium which in some water molecules can take the place of a hydrogen atom. Since the lighter version escapes more often, over time, the martian atmosphere has less and less hydrogen compared to the amount of deuterium remaining. The martian atmosphere therefore becomes richer and richer in deuterium. How Mars' atmosphere has become much less dense than it used to be, thick and mostly carbon dioxide, could be related to deeply buried carbonate layers, if widespread. The carbon that goes into formation of carbonate minerals can come from atmospheric carbon dioxide. Carbonate and clay minerals, deep underground, would have been buried by volcanic resurfacing and impact ejecta by a few miles (km). A range of iron-rich and calcium-rich carbonates generally might have needed, scientists think, more than a little bit of water reacting with igneous rocks. Calcium carbonate you typically find on Earth result from the formation of ocean and lake floors. Large quantities of carbonates thus might have formed through atmospheric carbon dioxide interacting with ancient bodies of water on Mars. Such a process would have led to some dramatic change in atmospheric density by early Mars. Under a much thicker atmosphere, liquid water on the surface of ancient Mars could have existed for extended periods. Carbonates found in rocks elsewhere and rich in magnesium could form on a other hand from reaction of volcanic deposits with moisture. A cloud of dust, on a other hand, is surrounding Mars that likely is interplanetary dust (debris from comets) that is falling in toward Mars as that infall is yielding a layer of metal ions in Mars's ionosphere. Gaseous nitric oxide and ozone exist in the atmosphere, with dynamical processes between the lower and upper atmosphere as some, turned-neutral particles from the solar wind penetrate unexpectedly deep into the upper atmosphere, rather than diverted by the ionosphere. The breaking of water vapor in the lower atmosphere into into hydrogen and oxygen by sunlight yields hydrogen in the upper atmosphere

click to a weather map of Mars as on Aug. 5, 2012 as acquired by the Mars Reconnaissance Orbiter (MRO). The orbiter is acquiring such a view once a day, giving unprecedented views about the Red Planet's weather. Such a daily map show the varied weather patterns at Mars like dust storms, water ice clouds, etc. map courtesy NASA/JPL-Caltech/Malin Space Science Systems

The Martian magnetic field might well have been active between 4.5 billion and 3.7 billion years ago unlike a previous calendar stating between 4.3 and 4.2 billion years ago.Chemistry that takes place in the surface material on Mars can explain why particular xeno n (Xe) and krypton (Kr) isotopes are more abundant in the Martian atmosphere than expected. The isotopes are formed in the loose rocks and material that make up the regolith due to interaction with cosmic rays. Such isotopes can then enter the atmosphere when the regolith is disturbed by impacts and abrasion and gas escapes from the regolith. Mars has electrically charged metal (like iron, magnesium or sodium) atoms (ions) high in its atmosphere, metal which comes from a constant rain of tiny meteoroids onto the Red Planet vaporizing in the atmosphere. Metal get some of their electrons torn away by other charged atoms and molecules in the ionosphere, transforming the metal atoms into electrically charged ions, a feat likely to occur also at other planets in the solar system and at Earth, and linked to any magnetosphere, or magnetosphere's remnant the magnetic fields of which organizes metal ions in layers. Mars sports escaping atmospheric particles at its poles, and a layer of metal particles high in its atmosphere (of metal ions (iron and magnesium)) that come from incoming solar-system debris, such as comet dust and meteorites. The incoming material is heated up by the atmosphere as it enters, burns up and vaporizes, and even ionizes), and lights up with aurora after being smacked by solar storms. Diffuse aurorae are widespread over the planet and do not depend on the presence of a global or local magnetic field to focus solar particles that drive them. Proton aurora are a variety of aurora at Mars. Mars atmosphere also harbours a modest ozone layer due to sunlight breaking up carbon dioxide molecules. Temperatures in the Martian atmosphere regularly rise and fall not just once each day, but twice, with a maximum in the middle of the day then a little after midnight, or a semi-diurnal pattern as until 2013 they had been thought to appear just in dusty seasons, related to sunlight warming dust in the atmosphere. Water-ice clouds are at the origin of that, as they absorb infrared light emitted from the surface during daytime and heat the middle atmosphere each day. Maximum temperature swings are occurring away from the tropics. Earth has also such atmospheric tides on Earth produce little temperature difference in the lower atmosphere. The Red Planet today has relatively few clouds compared to Earth. That's because the Martian atmosphere contains less than a tenth of a percent of the amount of water vapor found in Earth's atmosphere. Without much water vapor, and with temperatures averaging 176 degrees Fahrenheit (80 degrees Celsius) colder than on Earth, only thin ice clouds form. They tend to look like a thinner version of Earth's wispy cirrus clouds. Martian clouds do not get to the point where you couldn't see the Sun through them albeit being able to largely shade it. Mars also has thicker clouds made of frozen carbon dioxide -- commonly called dry ice --that form both high in the atmosphere and at the poles during winter. These clouds are dense enough to dim the sun's light by about 40 percent. As they are found only in limited regions near the planet's poles and equator, they are unlikely to affect the Martian climate as a whole. Such a relatively sparse cloud coverage on Mars allow temperatures to rise and fall dramatically. Without the cooling effect of significant cloud shade or the insulating effect of thick cloud blankets, the surface of Mars heats drastically during the day -- reaching temperatures around 65 degrees Fahrenheit (18 degrees Celsius) at the equator -- before the temperature plummets at night -- to equatorial surface temperatures as cold as minus 202 degrees Fahrenheit (minus 130 degrees Celsius). Dust particles generally make the Martian sky appear reddish as they create a bluish glow around the Sun. In terms of snow, detailed studies from orbit have shown that snowflakes are made from CO2 ice and the size of a red blood cell only (and slightly smaller at the south pole than in the North) as they likely look like fog when falling. Snowfall at the south pole of Mars is 50 percent larger than in the North as snow clouds, generally, spread to halfway to the equator during winter. Snowflakes are also a good indicator of how dust is spread around in Martian atmosphere as dust grain serve like a condensation anchor to them. Mysterious high-rise clouds seen appearing suddenly in the martian atmosphere on a handful of occasions might be linked to space weather. Such a plume, for example, topped-out high above the surface of Mars at a altitude around 155 miles (250 km), developing in less than 10 hours, covering a area of up to 621 x 310 miles (1000 x 500km), and remaining visible for around 10 days. Such a high altitude corresponds to the ionosphere of Mars as no explanation is extent for sure currently. That might result from the plumes occurring over a region of known strong crustal magnetic fields where the ionosphere is generally very disturbed, or that solar events like CMEs make that dust and ice grains residing at high altitudes are pushed around by the ionospheric plasma and magnetic fields, and then lofted to even higher altitudes by electrical charging

Martian storms whatever their size are Sun-powered. Sun is heating the atmosphere, this in turn warming the soil as the superior layer is staying cool. That is stirring up martian dust. Worst of Martian storms are comparable to a force 12 typhoon on Earth. When Mars approaches its perihelion (its nearest to the Sun, at southern summers) there is a larger potential for dust storms. Mars receives then 20 per cent more of sun energy than usual. Largest storms occur one to two months after perihelion. A lesser peak is already seen when the planet nears perihelion. Two places are known to be the birthplaces for dust storms: Hellas, and Thaumasia (region around Solis Lacus), as Lybia -east of Syrtis Major- is too. Most Martian dust storms are localized, smaller than about 1,200 miles (about 2,000 kilometers) across and dissipating within a few days. Some become regional, affecting up to a third of the planet and persisting up to three weeks. A few encircle Mars, covering the southern hemisphere but not the whole planet. Twice since 1997, global dust storms have fully enshrouded Mars for weeks as they are occurring once every three Mars years during southern spring and summer. The last such storm occurred in 2007. They can last weeks, or even months at the longest. The thin atmosphere makes these storms vastly different from anything encountered on Earth. The behavior of large regional dust storms in Martian years that include global dust storms is currently unclear. The winds in the strongest Martian storms top out at about 60 miles per hour (96km/h), which relative effect is increased to the much lesser density of Mars' atmosphere. Dust towers, or concentrated clouds of dust that warm in sunlight and rise high into the air up to a altitude of 50 miles, are also part of Martian dust storm. Large global dust storms put enough dust in the air to completely cover the planet and block out the Sun, but doing so ultimately dooms the storm itself as the radiative heat of sunlight reaching the surface of the planet is what drives these dust storms. During a dust storm, there's less direct sunlight and lower daytime temperatures, meaning fewer dust devils swirling across the surface. A large storm which occurred by 2018 might advance knowledge about such phenomenons as miscellaneous NASA missions had the opportunity to learn from

three spring dust storms seen at Mars, North, due to the temperatures constrast between the still frozen polar cap, and recently thawed surfaces. picture courtesy NASA/JPL/Malin Space Science Systems

Multiple regional dust storms are arising during the northern spring and summer. In most Martian years all such regional storms dissipate and none swells into a global dust storm. Such expansion happened in 1977, 1982, 1994, 2001 and 2007 only. Seasonal patterns in Martian dust storms and especially temperature, determine a pattern of three types of large regional dust storms occurring in sequence at about the same times each year during the southern hemisphere spring and summer. That is due to Sun heating dusty air more than clear one, bringing to a difference in some cases of more than 63° F (35° C). That in turn affects the global wind distribution. Temperature data were gathered from a broad layer of Martian atmosphere centered about 16 miles (25 kilometers) above the Martian surface. The storm cycle is like follow. Multiple small storms form sequentially near Mars' north pole in the northern autumn, similar to Earth's cold-season arctic storms affecting North America. Some break off and head farther South along preferential tracks. Should they cross into the southern hemisphere, where it is mid-spring, they get warmer and can explode into the much larger 'Type A dust storms.' In contrast, the Type B storm starts close to the south pole shortly before the beginning of southern summer. They origin may be from winds generated at the edge of the retreating south-polar carbon dioxide ice cap. Multiple storms may contribute to a regional haze. The Type C storm starts after the B storm ends. It originates in the North during northern winter (southern summer) and moves to the southern hemisphere like the Type A. From one year to another, the C storm varies more in strength, in terms of peak temperature and duration, than the A and B storms do. The Red Planet has been observed shrouded by planet-encircling dust nine times since 1924, with the five most recent planetary storms detected in 1977, 1982, 1994, 2001 and 2007. The actual number of such events is no doubt higher as not all events likely were observed from Earth or space missions. Global dust storms on Mars can affect the Martian atmosphere for several months and they can cause changes in atmospheric dynamics and inflation of the atmosphere primarily owing to solar heating of the dust

Martian dust devils are these spiraling columns of air, made visible by the dust they pull off the ground, which are traversing the landscape where they are occurring. A dust devil typically forms on a clear day when the ground is heated by the Sun during the summer season at Mars as they mostly occur during the daily peak heating at Mars. Dust devils at Mars are considerably larger than at Earth. They may reach 500 m wide and several thousand meter high as their terrestrial counterparts are about 10-100 m wide only (with winds circling the warm air column at about 20-60 mph (32-96 kph). Martian dust devils are an important erosion factor. They are transporting large quantities of dust. Dark (or light) track patterns are commonly found in many Mars regions and are changing from season to season. Dust devils at Earth are featuring large electric fields in excess of 4,000 volts/meter or more, and magnetic fields. It is still unsure, but likely that Martian dust devils have these same characteristics. Whirlwind patterns also exist, a very quick event of a few seconds

More About Mars Geology

The internal structure of Mars is poorly known, although evidence of recent volcanic activity suggests that its deep interior remains hot and convectively cooling. A liquid metallic core is overlain by a homogeneous silicate convecting mantle underneath an evolving heterogeneous lithospheric lid that includes a crust enriched in radiogenic elements. Mars' geologic record includes lighter rocks and minerals - which rose from the planet’s interior to form the Martian crust -- and heavier rocks and minerals that sank to form the Martian mantle and core. As Mars swiftly turned a 'fossile planet,' it did not churn its interior as much as the Earth did, preserving more record of its geological history. Mars is bashed by over 200 asteroids and comets every year. A current view of Mars geological history is now that Mars has been ruled by three main era. The Noachian which lasted from the planet's beginnings to about 3.8 billion years ago, the Hesperian, from 3.8 to 3.2 billion years ago, and the Amazonian from 3.2 to nowadays! Noachis Terra is one of the oldest known regions on the Red Planet, dating back at least 3.9 billion years, the earliest martian era as the Noachian epoch is named after it. Upper layers at Mars could be mostly volcanic while the lower influenced by the period of heavy bombardment and greater interactions with water. As the Noachian mostly is believed to have been a warm and wet phase as its beginnings endured the Heavy Bombardment Period -that period during which the lately formed planets of the solar system were pummeled with asteroids and comets which had been left over from the formation of the solar system- both the other eras are believed to have been calm in terms of geology. Some highlands mountains at Mars were uplifted during the formation of impact basins, which also triggered hydrothermal activity that contributed to mineral diversity. Mars got a crust 100 million years only after the dust began to condensate in the early solar system -like the Earth or Moon did- at about 4.4 billion years ago. Rare elements like nickel, osmium and iridium hint to that the crust was pummeled by chondritic meteors rich in those. Scientists found that globally Mars’ crust is less dense, on average, than previously thought, which implies smaller variations in crustal thickness which could have important implications about Mars’ formation and evolution. The average density of the Mars' crust is about 161 pounds per cubic foot (2,582 kilograms per meter cubed), comparable to the average density of the lunar crust, short from the previous 181 pounds per cubic foot. Denser crust lies beneath Mars’ giant volcanoes. It is the southern highlands of the planet which hold the clues to Mars' birth and early development. A fairly wet period on Mars likely occurred also between two and three billion years ago, or roughly a billion years after a well-documented earlier era of wet conditions, long after it is generally thought that most of Mars' original atmosphere had been lost and most of the remaining water on the planet had frozen. That yielded valleys feeding lakes with snowmelt-fed streams, which are seen on Mars between about 35 and 42 degrees latitude, both North and South, hinting to a global phenomenon. The Hesperian Period on Mars was characterized by extensive volcanic activity and catastrophic flooding which eventually left the planet with a much more arid climate. On the other hand, 5 violent volcanic episodes occurred at Mars 3.5 billion years, 1.5 billion years ago, 400-800 million years, 200 and 100 million years ago. During such episodes, flows of lava spanned over the Red Planet as the internal heat generated by the volcanoes caused water to flash flood on a wide scale. The most recent view of why those episodes occur is that such events are hinting to that Mars' geology tried several times to establish a plate tectonics of its own, with the crust broken into several plates. Each of the episodes almost achieved but not managed, actually, to form a tectonics at Mars. The proponents of such a view is adding that more volcanic episodes should be to come as the interior of Mars is not cold yet. A way do date the geological eras of a planet, is, like at Mars, to count the craters seen. The more a surface is punctuated with craters, the oldest. On another hand, Mars geology has been affected, especially by the poles, by the changes in Mars' tilt on its axis. Such changes have occurred during the past 4 million years. The most recent 300,000 years of Martian history are a period of less dramatic swings in the planet's tilt than during the preceding 600,000 years. Sections of high-contrast layering at the planet's poles correspond to periods of relatively small swings in the planet's tilt. Wind, meteorite impacts and seasonal frosts nowadays are continuing to affect the Martian surface today. Lava flows shaped like coils of rope have been discovered near the equator of Mars, a further evidence that Mars was volcanically active recently, within the past 20 million year. Rover Curiosity, on a other hand, discovered, by mid-2016, a unexpected silica mineral called tridymite in sedimentary rocks at Gale Crater on Mars, a mineral associated with 'silicic volcanism,' a one with high silica content and extremely high temperatures. The discovery might induce scientists to rethink the volcanic history of Mars, suggesting that the planet once had a much more violent and explosive volcanic history during the early evolution of the planet than previously thought

click to a diagram of Mars geological history. map courtesy ESA

Astronomers have determined a 'sea level' at Mars or a 'zero altitude' which is the geoid at the Mars' equator compared to which the averaged sum of altitudes above it equals the one of the altitudes below. Gravity also participates into that definition, with elevation defined relative to where it is the same as the average at the Martian equator. Mars is characterized by a strong difference between the northern, and the southern hemisphere, with North a lowland hundreds of yards lower than South. Souther highlands are futher heavily cratered. That dichotomy might have been caused by a titanic impact 3.9 billions years ago as a giant object slammed obliquely into northern Mars, turning nearly half of the planet's surface into the solar system's largest impact crater. The difference might originate too into super lava flows North. Recentest studies have shown that the less cratered North -that should be a hint to a younger terrain- might well altogether be old, in fact, as a lot of craters are extant but they are thinly buried beneath the northern plains! Only a few craters are still visible at the surface. The boundary between the Northern plains and Southern lowlands, on a other hand, features lobe-shaped formations commonly emanated from mesas with pitted, lineated textures that suggest the flow of water ice

Sitting near Mars' equator, Tharsis covers roughly a quarter of the Martian surface and is thought to have a played an important role in the planet's history, straddling the boundary between Mars' southern highlands and northern lowlands. Tharsis is also connected to the formation of Valles Marineris. The Tharsis region volcanic 'bulge' which includes Olympus Mons with the three smaller Tharsis Montes evenly spaced in a row is thought to have been volcanically active until 100-250 million years ago. The region started with a lighter andesitic lava that can form in the presence of water, and were then overlaid with heavier basaltic lava that makes up the current visible surface. Arsia Mons is the oldest, then Pavonis Mons formed and finally Ascraeus Mons (where the density of lava however decreased at a later stage and the top of the volcano of lower density). It might that three volcanoes be created by a single mantle plume that slowly moved sideways to create each of the three (wich is the opposite of Earth where crust plates move above a stationary plume to form chains of volcanoes, like the case in the Hawaiian Islands). The thickness of the outermost shell of Mars, or the lithosphere including also the upper portion of the mantle is different between between Olympus Mons and the Tharsis Montes, with the three smaller volcanoes having a much higher density underground, which could be dense pockets of solidified lava or an ancient network of underground magma chambers. Olympus Mons likely built upon a lithosphere of high rigidity, while the other volcanoes partially sank into a less rigid one. There were thus large spatial variations in the heat flux from the mantle at the time of their formation. Since the three Tharsis Montes sit on top of the Tharsis bulge, whereas Olympus Mons stands on the edge, the greater crustal thickness at the centre may have acted as an insulating lid to increase the temperature, creating a less rigid lithosphere. Here rising magma interacted with the pre-existing bulge, whereas the magma forming Olympus Mons ascended through the older crust that is supporting the Tharsis bulge, perhaps creating the observed density differences between the volcanoes. The Martian volcano Olympus Mons is about three times the height of Mount Everest, with gentle slopes sprawling across more than 150 miles (240 km) in area. This, and the fact that the volcano has a dissymetric shape is hinting to that a tall layer of clay sediments likely was lying there where the volcano developed helping to soften and lubricate the expansion of the materials. Like a volcanoe, Olympus Mons, a famed site at Mars, has an average elevation of 14 miles (22 km). Olympus Mons is the highest volcano in the solar system! A caldera is found at the top, with a depth of about 1.9 mile (3 km). After lava production had ceased the terrain, the summit of the volcanoe collapsed over the emptied magma chamber, with extensional fractures enlarging the phenomenon. Later lava production has produced new caldera collapses at different locations, partly destroying the circular fracture pattern of the oldest one. Relatively recent quakes on the surface of Mars are hinted to by boulders that fell off cliffs and spread according to a epicentre. That might also reveal the existence of active volcanoes, at least in a underground form of activity which further would yield reservoirs of liquid water. 'Marsquakes,' on a other hand, shook soft sediments from Mars' Candor Chasma canyon, inside Valles Marineris, which eventually accumulated in Martian lakes down range the valley. The wave form of the Mars quakes resembles the moon quakes. Most of the marsquakes are tiny, but a couple are nearly magnitude 4. Marsquakes come in two types. The most common shakes the ground at high frequencies and they might come from quakes that rupture the shallow Martian crust. Less common is a type that is detectable at lower frequencies, as they might travel from deeper within the planet, in the mantle. Mars is prone to marsquakes, the result of the planet cooling and shrinking, as it could also feature a plate tectonics; a hard layer might exist at about 50 miles in depth

Olympus Mons, a tall Martian volcano, with a caldera atop! picture courtesy ESA, derived from the Mars Orbiter Laser Altimeter (MOLA) topographic data superimposed with the Mars Orbiter Camera (MOC) wide-angle image mosaic

Small-scale volcanic features are further found on Mars surface like vents from which lava flowed in ancient eruptions. Mud volcanoes in some places at Mars are drawing out a mix of gas, liquid and mud from underground. At the Earth, such mud volcanoes are a good hint to petroleum reservoirs. At Mars, such structures range up to about tens of miles (tens of kilometers) in diameter and several hundred yards (several hundred meters) in height as they have a age of 2 to 3 billion years

Mars' red color is due to the fact that Martian soil is mainly composed of iron-bearing materials. A major ingredient of much of the Martian surface is basalt, an iron-rich rock typically associated with volcanoes on Earth. Such materials interacted along time with trace amounts of oxygen and water vapor in Mars' atmosphere resulting in iron oxide (Fe²O³) which is usually known under the name of rust. Most of iron oxide at Mars is under the form of red and fine powder with grains between hundreds of nanometers and a few microns. Gray hematite is another form of the same process. Hematite is green due to the form of its crystals. It's the coarser equivalent of rust. Hematite particles are the size of sand grains. Ground into smaller particles it would turn red. Curiosity rover in 2013 revealed a complex chemical composition of the rusty dust that includes, beyond iron oxides, hydrogen, which could be in the form of hydroxyl groups or water molecules. Nitrogen was found in Martian sediments in 2015, in the form of nitric oxide. Nitrogen is essential for all known forms of life, since it is used in the building blocks of larger molecules like DNA and RNA. Dark bedrock and fine-grained sand deposits ground down from ancient lava flows and other volcanic features areas, like at Sinus Sabaeus and Sinus Meridiani have their sand grains coarser and less reflective than the fine dust that gives the brighter regions of Mars their rusty appearance, hence those areas are darker

click to a geological map of Mars (left), to regions of Mars identified with clays minerals (green) and hydrated minerals (clays, sulfates, etc. blue) (center), or to iron at Mars (yellow and green, more abundant than blue), with also 5 NASA's missions (landers or rovers) landing sites (V1 and V2 for the Viking missions, PF for Pathfinder, G for Spirit at Gusev and M for Opportunity at Meridiani) (right). map courtesy NASA/JPL (left), NASA/ESA/JPL-Caltech/JHU-APLNASA (center), NASA (right)

Let's note, at last, that wind, generally, is an important factor of the relief at Mars (like with dunes, etc.) The Martian atmosphere is about a hundred times thinner than Earth's, so winds on Mars exert much less force than winds on Earth. High-altitude Martian wind patterns correlated with the Martian topography below, creating gravity waves. Atmospheric gravity waves are caused by the displacement of air masses from a resting state. Gravity tries to bring the fluid back to equilibrium, and in doing so, creates waves in the disturbed fluid. Time is the factor that makes Martian winds so dominant in shaping the landscape. On Mars, most dunes sand is composed of dark basalt. Depressions such as impact craters can act as traps for sediments that have been blown in from elsewhere. Barchans are the most common dune type found on Mars, and are also prevalent in Earth’s deserts. Having dunes upwind of sand sheets is the opposite than on Earth. 'Star dunes' form when the sand-moving wind comes from varying directions at different times of day or year. Scientists think that extreme high-speed winds were blowing at Mars in the past. Ripples on the surface of dunes were seen migrating by about 7 feet (2 meters) on a 3 and ½-month timespan as changes in the shape of dune edges or in streaks on the downwind faces of dunes were also observed. Ripples of dunes, in some regions, are static over time, despite winds, as they are, like the Meridiani Planum area, covered with erosion-resistant pebbles, nicknamed 'blueberries', with are water-related spherules about 0.04 to 0.12 inches (1 to 3 millimeters) in diameter and maybe too large for the wind to budge. On Mars, we can observe four classes of bedforms with dunes (in order of increasing wavelengths): ripples (less than 67 ft), transverse aeolian ridges (known as TARs; 67-233 ft), dark-toned dunes (333-3,300 ft), and what are called 'draa,' which are relatively uncommon and greater than 3,300 ft. The fact that we see active sand dunes on Mars today requires that sand particles must be resupplied to replace the grains that are lost over time. Source of that resupply is still ill-known. Wind-blown loose sand fragments may too by transported by wind and impact on some bedrock, slowly removing parts of the surface, like a sand-blaster. When the winds blow in the same direction for a long enough period, ‘wind-lanes’ can occur, which are features which have not been blown away. On the Earth, such features are called 'yardangs'. Such regions may vary in aspect as some neighbouring surface, for example, consists of more resistant material and remaining flat and unsculpted by wind. Light-toned ripples termed 'TAR,' or 'transverse aeolian ridges,' might be dust deposits, or perhaps coarse grained ripples coated in bright dust. TARs are less than 10-yards tall, and are much smaller than the sand dunes that reach impressive heights of over 130. TARs are generally older than sand dunes. A gigantic dune field cover an area the size of Texas in a band around the planet at the edge of Mars' north polar cap. Such dunes are covered by a seasonal cap of dry ice in the winter. Dunes generally, are among the most active landscapes on Mars albeit fairly static and shaped long ago when winds on the planet's surface were much stronger than those seen today. The larger populations of sand dunes at Mars exists in the Southern hemisphere, just west of the Hellas impact basin with Hellespontus region featuring numerous collections of dark, dune formations either inside craters or among extra-crater plains areas. Barchan and 'seif' (or linear) dunes are to be found in that region. Seasonal building or sublimation of carbon-dioxide ice which covers the region by winter is one agent of change, and stronger-than-expected wind gusts as another which come to partially erase scars of avalanches triggered. Dunes' motion in sand dune fields occurs on a surprisingly large scale, about the same as in dune fields on Earth which is unexpected because Mars has a much thinner atmosphere than Earth and its high-speed winds are less frequent and weaker than Earth's. Entire dunes as thick as 200 feet (61 meters) are moving as coherent units across the Martian landscape. By 60 degrees of latitude South, dunes displays increasing signs of degradation, and very modest in height, often consisting solely of flat sand sheets. Such features further are no longer changing position. Sand dunes on Mars move much slower than on Earth due to not enough wind energy, as three Martian areas -- Syrtis Major Planum volcanic plateau, the Hellespontus Montes mountain range, and the circumpolar ergs of Olympia Undae and Abalos Undae --exhibit the strongest sand movement due to stark transitions in topography and surface temperature. It might take two years on Mars to see the same movement seen in a season on Earth

click to a view of how beyond one tall dune in the Gusev Crater's Bagnold Dune Field which lines the northwestern flank of Mount Sharp, a view is provided upon a smoother terrain as the crater's wall is seen in the background. image site 'Amateur Astronomy'

Data from NASA's Mars Reconnaissance Orbiter (MRO) at Mars have shown what has been shaping the Martian polar ice sheets. On Earth, large ice sheets are mainly shaped by ice flow. On Mars, for example, the northern ice cap is a stack of ice and dust layers up to two miles deep. One of the most distinctive features of the northern ice cap is Chasma Boreale, a canyon about as long as Earth's Grand Canyon but deeper and wider as the polar cap is striated into spiral troughs. Both the canyon and the troughs have been found created and shaped primarily by wind, formed over millions of years as the ice sheet grew. By interacting with wind patterns, the shape of underlying, older ice controlled where and how the features grew. Those shapes seen at the Martian polar cap had remained unexplained for 40 years. It is thought that the north polar layered deposits likely formed recently (i.e., millions of years ago) as rhythmic variations in Mars' orbit changed the distribution of water ice around the planet. As ice moved to and from the polar region in response to a changing climate, layers of ice and dust built up at the poles. Periglacial processes in the polar areas, are also a factor of erosion at Mars

click to a view of a typical landscape at Mars in the Meridiani Planum plains. image site 'Amateur Astronomy' based on a picture NASA/JPL-Caltech/Cornell University

A typical Martian landscape is shown with the first image, above in the Meridiani Planum plains. The red Martian soil is well seen here, mostly a light-colored, 0.04" (1 mm)-fine-grained, layer of material, coating a dark-colored, coarser, layer, as the composition is mostly iron and silicon. Shallow depressions seen left of center, or to the right are recent impact craters. Lighter toned rock outcrops as seen in the left part of the picture might be barely emerging remains of large, buried craters. In a distance, what looks like mountain ranges are in fact the rim of a large, 14-mile (22 km) crater as peaks seen second from the left are on the other side of the crater relatively to the observer's position and the plains masking continuity between the rim. Other regions of Mars may feature volcanoes, canyons, more craters, or dead valleys which are thought to hint to a watery past. Another typical view below is the one take of walls of Gale Crater, with its characteristic terraced and valleyed slopes. Gale Crater spans 96 miles (154 kilometers) in diameter and like most of the large craters at Mars has been eroded as such a view is reminiscent of some desertic areas at Earth

click to a view of a typical landscape at Mars, the walls of Gale Crater. image site 'Amateur Astronomy'

The largest and most ancient giant impact basin on Mars, called Borealis, is nearly 6,000 miles wide and encompasses most of the northern hemisphere of the Red Planet as a smaller giant basin called Hellas is 1,200 miles wide and five miles deep. The 1100-mile (1800-km) wide and 3.1-mile (5-km) deep Argyre basin was created by a gigantic impact in the planet’s early history, and the second largest at Mars after Hellas. Argyre's impact occurred about 4 billion years ago. Chaotic terrains in the area are thought to have been created when large-scale melting of ground ice caused the ground to collapse as where the terrain has not collapsed completely, large mesas may still contain substantial water ice. Argyre took its name from 'Argyre' ‘island of silver’ in Greek and Roman mythology. Argyre Planitia, a flat region at the center of the area was mostly shaped by wind, glacial and lacustrine (lake-based) processes, creating a smooth appearance. Over billions of years, the southern uplands of Mars have been pockmarked by numerous impact features

click to a view of another typical landscape at Mars, a view inside Gale Crater, with a central peak which is not a rebound one. image site 'Amateur Astronomy'

click to a panoramic image of the inside of the Gale Crater viewed from a high ground. image site 'Amateur Astronomy' based upon a picture NASA/JPL-Caltech/MSSS

Dramatic underground explosions, perhaps involving ice, may yield pits seen inside Martian craters at their center, a common occurrence. When an asteroid hits the rocky surface of a planet, both it and the surface are compressed to high densities. Immediately after the impact, the compressed regions rapidly depressurise, exploding violently. In low-energy impacts, a simple bowl-shaped crater results. In more dramatic events, larger craters are produced with more complex features, such as uplifted central peaks or sunken pits. One idea for central pit formation is that when rock or ice melted during the impact drains away through fractures beneath the crater, it leaves a pit. Another theory is that subsurface ice is rapidly heated, vapourising in an explosion. As a result, the rocky surface is excavated forming an explosive pit surrounded by rocky debris. Central pit craters are common also on the icy moons orbiting the giant planets in our Solar System. Ejecta blankets are debris deposits surrounding the crater, excavated from inside the crater during its formation. They have petal-like lobes around their edges: these result from liquid water bound up in the ejected material, allowing it to flow along the surface and giving it a fluid appearance. Sun which hits polar deposits at the poles each spring, triggers avalanches falling from heights of 1,700ft

Mars' Moons

Phobos was discovered by Asaph Hall on August 17, 1877 at the U.S. Naval Observatory in Washington, D.C., and six days after he found the smaller, outer moon, named Deimos as he was deliberately searching for Martian moons. Both moons are named after the sons of Ares, as Phobos ('panic' or 'fear') and Deimos ('terror' or 'dread') accompanied their father into battle. Rising in the Martian West, it runs three laps around the Red Planet in the course of one Martian day, which is about 24 hours and 40 minutes (it is the only natural satellite in the solar system that circles its planet in a time shorter than the parent planet's day). Phobos was first imaged by NASA's Mariner 7 in 1969 as the Viking 1 orbiter took the first detailed photograph it by 1977. Phobos is in the course of being torn apart by the gravitational pull of Mars, which should occur within 30 to 50 million years, crashing into the planet or being scattered as a ring. Meanwhile, the opposite is true for Deimos: its orbit is slowly taking it away from Mars. Albeit both moons are made of the same material as asteroids -- especially, class-D asteroids of which one thinks that they are very fractured bodies, non-solid and containing gigantic caves -- their stable, nearly circular orbits and the fact that they are not as dense as members of the Asteroid Belt, better hint to that they are the result of remaining dust and rock from around Mars during its formation, or Phobos from debris by a large impactor at the Red Planet, like the one which created our Moon, or perhaps a larger existing moon was destroyed

click to a picture of Phobos as seen in March 2010 by the ESA Mars Express (the 'N' is for 'North'). picture ESA/DLR/FU Berlin (G. Neukum), natural color by site 'Amateur Astronomy' from the black-and-white photograph

The dimensions of Phobos are irregular, at 16.6 x 14 x 11.4 miles (26.8 × 22.4 × 18.4 km) in size. It circles Mars at a distance of 3720 miles (6,000 km) in the equatorial plane with a almost circular orbit as its rotational periods are locked bringing to that the moon, like our Moon, has a near and a far side. Evidence for organic molecules has been reported at Phobos. Phobos is closer to its parent planet than any other moon in the Solar System. The other moon of Mars is the smaller Deimos, with dimensions of 9.3 x 7.6 x 6.5 miles (15.0 × 12.2 × 10.4 km), and the same orbital characteristics, at 12,400 miles (20 000 km). Phobos and Deimos have orbital periods of 7 hours, 39.2 minutes and 1 day, 6 hours, 17.9 minutes respectively. Because Phobos orbits Mars in a shorter time than Mars' 24 hour, 37.4-minute rotational period, to an observer on Mars' surface it would appear to rise in the West and set in the East. From Mars' surface, Phobos appears about one-third the diameter of the Moon from Earth, whereas Deimos appears as a bright star. Phobos is one of the least reflective objects in the solar system. Russians, in collaboration with ESA, had planned a sample-return mission, the 'Phobos-Grunt,' in Russian ('Phobos' Soil'), which had not been launched however. Powerful solar eruption can electrically charge the night side of Phobos up to hundreds volts, presenting a complex electrical environment as similar conditions are expected at Deimos too because both moons do not have any atmosphere and directly exposed to the solar wind. The solar wind can have such charging effects in the lunar or astroidal shadowed craters