The dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. Research in 2008 has presented evidence regarding a theory proposed in 1980 postulating that, four billion years ago, the northern hemisphere of Mars was struck by an object one-tenth to two-thirds the size of Earth's Moon. If validated, this would make the northern hemisphere of Mars the site of an impact crater in size, or roughly the area of Europe, Asia, and Australia combined, surpassing the South Pole–Aitken basin as the largest impact crater in the Solar System.
Impact topography
Mars
Mars | Impact topography
Yes, impact craters The dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts The southern highlands, pitted and cratered by ancient impacts. It is scarred by a number of impact craters: a total of 43,000 craters with a diameter of or greater have been found.
what is the location of mars in the solar system
user
Mars is the fourth planet from the Sun
assistant
is it known by any other names?
user
Yes, "Red Planet" in English
assistant
are there any volcanoes there?
user
Yes, Olympus Mons
assistant
who named it?
user
Named after observations made by Mariner 9
assistant
what was that?
user
From Nix Olympica; a volcano. Astronomers adopted the name "Olympus Mons" for the albedo feature known as Nix Olympica
assistant
was that a spaceship that made the observations?
user
It was a robotic space probe
assistant
have any other space probes landed on the planet discussed above?
user
Yes, "Mariner 4", "Viking 1", etc
assistant
did the first one land on the planet or was it just a fly by?
user
A flyby mode
assistant
how did it meet its end?
user
The gas supply in the attitude control system was exhausted, and between December 10 and 11, a total of 83 micrometeoroid hits perturbation of the spacecraft's attitude and degradation of the signal strength
assistant
what is found at the polar regions of the planet?
user
The caps at both poles consist primarily (70%) of water ice; frozen carbon dioxide layer is in northern cap and south cap has a permanent dry ice cover
assistant
are there any features resulting from impacts?
user
This impact would have resulted in significant crustal melting and a general increase in the rate of crustal formation for a period of 40 million years following the impact. Such a large impact would have disturbed the mantle, altering the normal convection currents and causing upwellings which further increase the amount of melting at the impact site. Overall, such an event would actually increase the rate of cooling of the Martian interior. The lack of magnetic anomalies observed in the northern hemisphere could be explained by such an impact, as the shock waves produced might have demagnetized the crust.
North Polar Basin (Mars) | Formation of the Borealis Basin
At times the tilt has even been greater than 80 degrees Large changes in the tilt explains many ice-rich features on Mars. Studies have shown that when the tilt of Mars reaches 45 degrees from its current 25 degrees, ice is no longer stable at the poles. Furthermore, at this high tilt, stores of solid carbon dioxide (dry ice) sublimate, thereby increasing the atmospheric pressure. This increased pressure allows more dust to be held in the atmosphere. Moisture in the atmosphere will fall as snow or as ice frozen onto dust grains. Calculations suggest this material will concentrate in the mid-latitudes.
Nilosyrtis Mensae | Climate change caused ice-rich features
Both polar caps show spiral troughs, which recent analysis of SHARAD ice penetrating radar has shown are a result of katabatic winds that spiral due to the Coriolis Effect. The seasonal frosting of areas near the southern ice cap results in the formation of transparent 1-metre-thick slabs of dry ice above the ground. With the arrival of spring, sunlight warms the subsurface and pressure from subliming CO builds up under a slab, elevating and ultimately rupturing it. This leads to geyser-like eruptions of CO gas mixed with dark basaltic sand or dust. This process is rapid, observed happening in the space of a few days, weeks or months, a rate of change rather unusual in geology – especially for Mars.
Mars | Polar caps
This condensation and evaporation will cause the proportion of the noncondensable gases in the atmosphere to change inversely. The eccentricity of Mars' orbit affects this cycle, as well as other factors. In the spring and autumn wind due to the carbon dioxide sublimation process is so strong that it can be a cause of the global dust storms mentioned above. The northern polar cap has a diameter of approximately 1,000 km during the northern Mars summer, and contains about 1.6 million cubic kilometres of ice, which if spread evenly on the cap would be 2 km thick. (This compares to a volume of 2.85 million cubic kilometres for the Greenland ice sheet.) The southern polar cap has a diameter of 350 km and a maximum thickness of 3 km.
Climate of Mars | Polar caps
This increased pressure allows more dust to be held in the atmosphere. Moisture in the atmosphere will fall as snow or as ice frozen onto dust grains. Calculations suggest this material will concentrate in the mid-latitudes. General circulation models of the Martian atmosphere predict accumulations of ice-rich dust in the same areas where ice-rich features are found. When the tilt begins to return to lower values, the ice sublimates (turns directly to a gas) and leaves behind a lag of dust. The lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind.
Ismenius Lacus quadrangle | Climate change caused ice-rich features
This increased pressure allows more dust to be held in the atmosphere. Moisture in the atmosphere will fall as snow or as ice frozen onto dust grains. Calculations suggest this material will concentrate in the mid-latitudes. General circulation models of the Martian atmosphere predict accumulations of ice-rich dust in the same areas where ice-rich features are found. When the tilt begins to return to lower values, the ice sublimates (turns directly to a gas) and leaves behind a lag of dust. The lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind.
Casius quadrangle | Climate change caused ice-rich features
The dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. Research in 2008 has presented evidence regarding a theory proposed in 1980 postulating that, four billion years ago, the northern hemisphere of Mars was struck by an object one-tenth to two-thirds the size of Earth's Moon. If validated, this would make the northern hemisphere of Mars the site of an impact crater in size, or roughly the area of Europe, Asia, and Australia combined, surpassing the South Pole–Aitken basin as the largest impact crater in the Solar System.
Mars | Impact topography
While estimates of the mass ejected by a large, Borealis-size impact vary, simulations suggest that a body approximately 0.02 Mars masses (~0.002 Earth Masses) in size is capable of producing a sizable debris disk in Martian orbit, on the order of 5x10 kg, with a significant fraction of the material remaining close to Mars. This figure lies within the estimated mass range necessary to form the two moons, as other data suggests that only 1% of the mass of an accretion disk successfully forms moons. There are several other large impact basins on Mars that could have ejected enough debris to form the moons.
North Polar Basin (Mars) | Potential formation of Phobos and Deimos via Borealis impact
This increased pressure allows more dust to be held in the atmosphere. Moisture in the atmosphere will fall as snow or as ice frozen onto dust grains. Calculations suggest this material will concentrate in the mid-latitudes. General circulation models of the Martian atmosphere predict accumulations of ice-rich dust in the same areas where ice-rich features are found. When the tilt begins to return to lower values, the ice sublimates (turns directly to a gas) and leaves behind a lag of dust. The lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind.
Hellas quadrangle | Climate change caused ice-rich features
Mars is scarred by a number of impact craters: a total of 43,000 craters with a diameter of or greater have been found. The largest confirmed of these is the Hellas impact basin, a light albedo feature clearly visible from Earth. Due to the smaller mass and size of Mars, the probability of an object colliding with the planet is about half that of Earth. Mars is located closer to the asteroid belt, so it has an increased chance of being struck by materials from that source. Mars is more likely to be struck by short-period comets, "i.e.", those that lie within the orbit of Jupiter.
Mars | Impact topography
General circulation models of the Martian atmosphere predict accumulations of ice-rich dust in the same areas where ice-rich features are found. When the tilt begins to return to lower values, the ice sublimates (turns directly to a gas) and leaves behind a lag of dust. The lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind. Note, that the smooth surface mantle layer probably represents only relative recent material.
Nilosyrtis Mensae | Climate change caused ice-rich features
Colaprete et al. conducted simulations with the Mars General Circulation Model which show that the local climate around the Martian south pole may currently be in an unstable period. The simulated instability is rooted in the geography of the region, leading the authors to speculate that the sublimation of the polar ice is a local phenomenon rather than a global one. The researchers showed that even with a constant solar luminosity the poles were capable of jumping between states of depositing or losing ice. The trigger for a change of states could be either increased dust loading in the atmosphere or an albedo change due to deposition of water ice on the polar cap.
Climate of Mars | Polar changes
This increased pressure allows more dust to be held in the atmosphere. Moisture in the atmosphere will fall as snow or as ice frozen onto dust grains. Calculations suggest this material will concentrate in the mid-latitudes. General circulation models of the Martian atmosphere predict accumulations of ice-rich dust in the same areas where ice-rich features are found. When the tilt begins to return to lower values, the ice sublimates (turns directly to a gas) and leaves behind a lag of dust. The lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind.
Protonilus Mensae | Climate change caused ice-rich features
Such sublimation of water or other volatiles from the dirty ice that is the bedrock causes its decomposition. The non-ice remnants form debris avalanches descending from the slopes of the crater walls. Such avalanches are often observed near and inside impact craters and termed "debris aprons". Sometimes crater walls are cut by sinuous valley-like incisions called "gullies", which resemble certain Martian surface features. In the ice sublimation hypothesis, the low-lying dark material is interpreted as a blanket of primarily non-ice debris, which originated from the degraded rims of craters and has covered a predominantly icy bedrock.
Callisto (moon) | Surface features
The loss of the Martian magnetic field strongly affected surface environments through atmospheric loss and increased radiation; this change significantly degraded surface habitability. When there was a magnetic field, the atmosphere would have been protected from erosion by the solar wind, which would ensure the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars. The loss of the atmosphere was accompanied by decreasing temperatures. Part of the liquid water inventory sublimed and was transported to the poles, while the rest became trapped in permafrost, a subsurface ice layer. Observations on Earth and numerical modeling have shown that a crater-forming impact can result in the creation of a long-lasting hydrothermal system when ice is present in the crust.
Life on Mars | Past
The polar ice caps are well-known telescopic features of Mars, first identified by Christiaan Huygens in 1672. Since the 1960s, we have known that the seasonal caps (those seen in the telescope to grow and wane seasonally) are composed of carbon dioxide (CO) ice that condenses out of the atmosphere as temperatures fall to 148 K, the frost point of CO, during the polar wintertime. In the north, the CO ice completely dissipates (sublimes) in summer, leaving behind a residual cap of water (HO) ice. At the south pole, a small residual cap of CO ice remains in summer. Both residual ice caps overlie thick layered deposits of interbedded ice and dust.
Geology of Mars | Ice caps
In other words, areas with more of the rougher frost are warmer. Research, published in April 2011, described a large deposit of frozen carbon dioxide near the south pole. Most of this deposit probably enters Mars' atmosphere when the planet's tilt increases. When this occurs, the atmosphere thickens, winds get stronger, and larger areas on the surface can support liquid water. A large field of eskers exist around the south pole, called the Dorsa Argentea Formation, it is believed to be the remains of a giant ice sheet. This large polar ice sheet is believed to have covered about 1.5 million square kilometers.
Martian polar ice caps | South polar cap
This theory is somewhat problematic due to the lack of ice depositation after the 2001 global dust storm. Another issue is that the accuracy of the Mars General Circulation Model decreases as the scale of the phenomenon becomes more local. It has been argued that "observed regional changes in south polar ice cover are almost certainly due to a regional climate transition, not a global phenomenon, and are demonstrably unrelated to external forcing." Writing in a "Nature" news story, Chief News and Features Editor Oliver Morton said "The warming of other solar bodies has been seized upon by climate sceptics.
Climate of Mars | Polar changes
Mars does not possess a large moon to keep its tilt stable. Today, ice is concentrated at the poles, with a greater tilt, more ice will exist at mid-latitudes. These climate changes may be able to be measured with study of these layers. These triangular depressions are similar to those in scalloped terrain. However scalloped terrain, displays a gentle equator-facing slope and is rounded.
Hellas quadrangle | Exposed ice sheets
Over time, south polar pits merge to become plains, mesas turn into buttes, and buttes vanish forever. The round shape is probably aided in its formation by the angle of the sun. In the summer, the sun moves around the sky, sometimes for 24 hours each day, just above the horizon. As a result, the walls of a round depression will receive more intense sunlight than the floor; the wall will melt far more than the floor. The walls melt and recede, while the floor remains the same. Later research with the powerful HiRISE showed that the pits are in a 1-10 meter thick layer of dry ice that is sitting on a much larger water ice cap.
Martian polar ice caps | Swiss cheese appearance
In addition to Earth, the planet Mars also has polar ice caps. They consist of primarily water-ice with a few percent dust. Frozen carbon dioxide makes up a small permanent portion of the Planum Australe or the South Polar Layered Deposits. In both hemispheres a seasonal carbon dioxide frost deposits in the winter and sublimes during the spring. Data collected in 2001 from NASA missions to Mars show that the southern residual ice cap undergoes sublimation inter-annually. The most widely accepted explanation is that fluctuations in the planet's orbit are causing the changes.
Polar ice cap | Mars
Many features on Mars, including ones in Protonilus Mensae, are believed to contain large amounts of ice. The most popular model for the origin of the ice is climate change from large changes in the tilt of the planet's rotational axis. At times the tilt has even been greater than 80 degrees Large changes in the tilt explains many ice-rich features on Mars. Studies have shown that when the tilt of Mars reaches 45 degrees from its current 25 degrees, ice is no longer stable at the poles. Furthermore, at this high tilt, stores of solid carbon dioxide (dry ice) sublimate, thereby increasing the atmospheric pressure.
Protonilus Mensae | Climate change caused ice-rich features
Many features on Mars, including many in Casius quadrangle, are believed to contain large amounts of ice. The most popular model for the origin of the ice is climate change from large changes in the tilt of the planet's rotational axis. At times the tilt has even been greater than 80 degrees Large changes in the tilt explains many ice-rich features on Mars. Studies have shown that when the tilt of Mars reaches 45 degrees from its current 25 degrees, ice is no longer stable at the poles. Furthermore, at this high tilt, stores of solid carbon dioxide (dry ice) sublimate, thereby increasing the atmospheric pressure.
Casius quadrangle | Climate change caused ice-rich features
Its coma washed over Mars with the dense inner coma, reaching or almost reaching the planet's surface. The cometary magnetic field temporarily merged with and overwhelmed Mars' weak magnetic field.
C/2013 A1 (Siding Spring) | Actual effects
Chasma Australe, a major valley, cuts across the layered deposits in the South Polar cap. On the 90 E side, the deposits rest on a major basin, called Prometheus. Some of the layers in the south pole also show polygonal fracturing in the form of rectangles. It is thought that the fractures were caused by the expansion and contraction of water ice below the surface.
Martian polar ice caps | Layers
Many features on Mars, including ones in Hellas quadrangle, are believed to contain large amounts of ice. The most popular model for the origin of the ice is climate change from large changes in the tilt of the planet's rotational axis. At times the tilt has even been greater than 80 degrees Large changes in the tilt explains many ice-rich features on Mars. Studies have shown that when the tilt of Mars reaches 45 degrees from its current 25 degrees, ice is no longer stable at the poles. Furthermore, at this high tilt, stores of solid carbon dioxide (dry ice) sublimate, thereby increasing the atmospheric pressure.
Hellas quadrangle | Climate change caused ice-rich features
Many features on Mars, especially ones found in the Ismenius Lacus quadrangle, are believed to contain large amounts of ice. The most popular model for the origin of the ice is climate change from large changes in the tilt of the planet's rotational axis. At times the tilt has even been greater than 80 degrees Large changes in the tilt explains many ice-rich features on Mars. Studies have shown that when the tilt of Mars reaches 45 degrees from its current 25 degrees, ice is no longer stable at the poles. Furthermore, at this high tilt, stores of solid carbon dioxide (dry ice) sublimate, thereby increasing the atmospheric pressure.
Ismenius Lacus quadrangle | Climate change caused ice-rich features
Mars has ice caps at its north pole and south pole, which mainly consist of water ice; however, there is frozen carbon dioxide (dry ice) present on their surfaces. Dry ice accumulates in the north polar region (Planum Boreum) in winter only, subliming completely in summer, while the south polar region additionally has a permanent dry ice cover up to eight meters (25 feet) thick. This difference is due to the higher elevation of the south pole. So much of the atmosphere can condense at the winter pole that the atmospheric pressure can vary by up to a third of its mean value.
Climate of Mars | Polar caps
Mars has two permanent polar ice caps. During a pole's winter, it lies in continuous darkness, chilling the surface and causing the deposition of 25–30% of the atmosphere into slabs of CO ice (dry ice). When the poles are again exposed to sunlight, the frozen CO sublimes. These seasonal actions transport large amounts of dust and water vapor, giving rise to Earth-like frost and large cirrus clouds. Clouds of water-ice were photographed by the "Opportunity" rover in 2004. The caps at both poles consist primarily (70%) of water ice. Frozen carbon dioxide accumulates as a comparatively thin layer about one metre thick on the north cap in the northern winter only, whereas the south cap has a permanent dry ice cover about eight metres thick.
Mars | Polar caps
One possible explanation for the basin's low, flat and relatively crater-free topography is that the basin was formed by a single large impact. Two simulations of a possible impact sketched a profile for the collision: low velocity— per second—oblique angle and a diameter of . Topographical data from "Mars Global Surveyor" are consistent with the models and also suggest that the elliptical crater has axes of length and , centered on , though this has been partially obscured by later volcanic eruptions that created the Tharsis bulge along its rim. There is evidence for a secondary rim as well. This would make the North Polar Basin by far the largest impact crater in the Solar System, approximately four times the diameter of the next largest craters: Utopia Planitia, which is imbedded inside the North Polar Basin, the South Pole–Aitken basin on the Moon, and Hellas Planitia on Mars's southern hemisphere.
North Polar Basin (Mars) | Formation of the Borealis Basin
Scientists have even measured tiny changes in the gravity field of Mars due to the movement of carbon dioxide. The ice cap in the north is of a lower altitude (base at -5000 m, top at -2000 m) than the one in the south (base at 1000 m, top at 3500 m). It is also warmer, so all the frozen carbon dioxide disappears each summer. The part of the cap that survives the summer is called the north residual cap and is made of water ice. This water ice is believed to be as much as three kilometers thick. The much thinner seasonal cap starts to form in the late summer to early fall when a variety of clouds form.
Martian polar ice caps | North polar cap
There are also signs of carbon dioxide eruptions from the southern polar ice cap of Mars. In the latter two cases, instead of being driven by geothermal energy, the eruptions seem to rely on solar heating via a solid-state greenhouse effect.
Geyser | Introduction
Much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust. This ice-rich mantle, a few yards thick, smoothes the land. Because there are few craters on this mantle, the mantle is relatively young. Changes in Mars's orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas. During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water returns to the ground at lower latitudes as deposits of frost or snow mixed with dust.
Diacria quadrangle | Latitude dependent mantle
This permanent dry ice cover at the south pole is peppered by flat floored, shallow, roughly circular pits, which repeat imaging shows are expanding by meters per year; this suggests that the permanent CO cover over the south pole water ice is degrading over time. The northern polar cap has a diameter of about during the northern Mars summer, and contains about of ice, which, if spread evenly on the cap, would be thick. (This compares to a volume of for the Greenland ice sheet.) The southern polar cap has a diameter of and a thickness of . The total volume of ice in the south polar cap plus the adjacent layered deposits has been estimated at 1.6 million cubic km.
Mars | Polar caps
At times the tilt has even been greater than 80 degrees Large changes in the tilt explains many ice-rich features on Mars. Studies have shown that when the tilt of Mars reaches 45 degrees from its current 25 degrees, ice is no longer stable at the poles. Furthermore, at this high tilt, stores of solid carbon dioxide (dry ice) sublimate, thereby increasing the atmospheric pressure. This increased pressure allows more dust to be held in the atmosphere. Moisture in the atmosphere will fall as snow or as ice frozen onto dust grains. Calculations suggest this material will concentrate in the mid-latitudes.
Glaciers on Mars | Climate changes
The seasonal frosting of some areas near the southern ice cap results in the formation of transparent 1 m thick slabs of dry ice above the ground. With the arrival of spring, sunlight warms the subsurface and pressure from subliming CO builds up under a slab, elevating and ultimately rupturing it. This leads to geyser-like eruptions of CO gas mixed with dark basaltic sand or dust. This process is rapid, observed happening in the space of a few days, weeks or months, a rate of change rather unusual in geology—especially for Mars. The gas rushing underneath a slab to the site of a geyser carves a spider-like pattern of radial channels under the ice.
Martian polar ice caps | Introduction
Simulations indicate that within years, the planet would be able to achieve half the atmospheric pressure of Earth. Without solar winds stripping away at the planet, frozen carbon dioxide at the ice caps on either pole would begin to sublimate (change from a solid into a gas) and warm the equator. Ice caps would begin to melt to form an ocean. The researcher further argues that volcanic outgassing, which to some degree balances the current atmospheric loss on Earth, would replenish the atmosphere over time, enough to melt the ice caps and fill of Mars' prehistoric oceans.
Terraforming of Mars | Magnetic shield at L orbit
These are found near joints and fractures that allowed deep fluid circulation which caused chemical and thermal alteration of the rocks. So, the area around martian craters may contain a variety of minerals that were produced as an indirect result of an impact. Heat from impacts results from several processes. Immediately after an impact, there is a rebound off the floor which causes hotter rocks to be uplifted to the surface. However, most of the heat comes from the kinetic energy that is produced during the impact. This enormous heat creates several useful products that may start forming early and then continue for some time.
Ore resources on Mars | Heat from impacts
In this region, are many expanded secondary craters that probably form from impacts that destabilize a subsurface layer of excess ice, which subsequently sublimates. With sublimation the ice changes directly from a solid to gaseous form. In the impact, the excess ice is broken up, resulting in an increase in surface area. Ice will sublimate much more if there is more surface area. After the ice disappears into the atmosphere, dry soil material will collapse and cause the crater diameter to become larger. Places on Mars that display expanded craters may indicate where future colonists can find water ice.
Diacria quadrangle | <a href="Expanded%20Craters">Expanded Craters</a>
At times the tilt has even been greater than 80 degrees Large changes in the tilt explains many ice-rich features on Mars. Studies have shown that when the tilt of Mars reaches 45 degrees from its current 25 degrees, ice is no longer stable at the poles. Furthermore, at this high tilt, stores of solid carbon dioxide (dry ice) sublimate, thereby increasing the atmospheric pressure. This increased pressure allows more dust to be held in the atmosphere. Moisture in the atmosphere will fall as snow or as ice frozen onto dust grains. Calculations suggest this material will concentrate in the mid-latitudes.
Deuteronilus Mensae | Source of ice
Research based on slight changes in the orbits of spacecraft around Mars over 16 years found that each winter, approximately 3 trillion to 4 trillion tons of carbon dioxide freezes out of the atmosphere onto the winter hemisphere polar cap. This represents 12 to 16 percent of the mass of the entire Martian atmosphere. These observations support predictions from the Mars Global Reference Atmospheric Model—2010.
Martian polar ice caps | Freezing of atmosphere
The polar ice caps of Mars show geologic evidence of glacial deposits. The south polar cap is especially comparable to glaciers on Earth. Topographical features and computer models indicate the existence of more glaciers in Mars' past. At mid-latitudes, between 35° and 65° north or south, Martian glaciers are affected by the thin Martian atmosphere. Because of the low atmospheric pressure, ablation near the surface is solely caused by sublimation, not melting. As on Earth, many glaciers are covered with a layer of rocks which insulates the ice. A radar instrument on board the Mars Reconnaissance Orbiter found ice under a thin layer of rocks in formations called lobate debris aprons (LDAs).
Glacier | On Mars
In spite of this, there are far fewer craters on Mars compared with the Moon, because the atmosphere of Mars provides protection against small meteors and surface modifying processes have erased some craters. Martian craters can have a morphology that suggests the ground became wet after the meteor impacted.
Mars | Impact topography
The dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. Research in 2008 has presented evidence regarding a theory proposed in 1980 postulating that, four billion years ago, the northern hemisphere of Mars was struck by an object one-tenth to two-thirds the size of the Moon. If validated, this would make the northern hemisphere of Mars the site of an impact crater 10,600 km long by 8,500 km wide, or roughly the area of Europe, Asia, and Australia combined, surpassing the South Pole–Aitken basin as the largest impact crater in the Solar System.
LARLE crater | Martian impact craters
When they were formed, ice in the soil may have melted, turned the ground into mud, then flowed across the surface. Normally, material from an impact goes up, then down. It does not flow across the surface, going around obstacles, as it does on some Martian craters. Regions, called "Chaotic Terrain," seemed to have quickly lost great volumes of water, causing large channels to be formed. The amount of water involved was estimated to ten thousand times the flow of the Mississippi River. Underground volcanism may have melted frozen ice; the water then flowed away and the ground collapsed to leave chaotic terrain.
Viking program | Main findings
Anisimov "et al". (2007) assessed the literature on impacts of climate change in Polar regions. Model projections showed that Arctic terrestrial ecosystems and the active layer (the top layer of soil or rock in permafrost that is subjected to seasonal freezing and thawing) would be a small sink for carbon (i.e., net uptake of carbon) over this century (p. 662). These projections were viewed as being uncertain. It was judged that increased emissions of carbon from thawing of permafrost could occur. This would lead to an amplification of warming.
Physical impacts of climate change | Polar regions
While the north polar cap of Mars has a flat, pitted surface resembling cottage cheese, the south polar cap has larger pits, troughs and flat mesas that give it a Swiss cheese appearance. The upper layer of the Martian south polar residual cap has been eroded into flat-topped mesas with circular depressions. Observations made by Mars Orbiter Camera in 2001 have shown that the scarps and pit walls of the south polar cap had retreated at an average rate of about 3 meters (10 feet) since 1999. In other words, they were retreating 3 meters per Mars year. In some places on the cap, the scarps retreat less than 3 meters a Mars year, and in others it can retreat as much as 8 meters (26 feet) per Martian year.
Martian polar ice caps | Swiss cheese appearance
In this region, are many expanded secondary craters that probably form from impacts that destabilize a subsurface layer of excess ice, which subsequently sublimates. With sublimation the ice changes directly from a solid to gaseous form. In the impact, the excess ice is broken up, resulting in an increase in surface area. Ice will sublimate much more if there is more surface area. After the ice disappears into the atmosphere, dry soil material will collapse and cause the crater diameter to become larger. Places on Mars that display expanded craters may indicate where future colonists can find water ice.
Arcadia Planitia | Expanded craters
Nick Hoffman proposes that this might be the trigger that caused the formation of the flow deposits on the east end of the Valles Marineris System. He proposes that the impact heated up subsurface carbon dioxide permafrost causing explosive decompression that flooded down the Valles Marineris into the Northern Plains of Mars. The central uplift of Oudemans exposes layered rock that may be sedimentary. Layered rock exposed in the central uplifts are common in terrestrial impact structures, and there is abundant layering exposed in the nearby Valles Marineris canyon system suggesting that layered deposits extend throughout the region.
Oudemans (crater) | Description
Studies have shown that the off center cap is caused by much more snow falling on one side than the other. On the western hemisphere side of the south pole a low pressure system forms because the winds are changed by the Hellas Basin. This system produces more snow. On the other side, there is less snow and more frost. Snow tends to reflect more sunlight in the summer, so not much melts or sublimates (Mars climate causes snow to go directly from a solid to a gas). Frost, on the other hand has a rougher surface and tends to trap more sunlight, resulting in more sublimation.
Martian polar ice caps | South polar cap
Following the Mars flyby of the Mariner 4 spacecraft in 1966, scientists concluded that Mars' polar caps consist entirely of dry ice. However, findings made in 2003 by researchers at the California Institute of Technology have shown that Mars' polar caps are almost completely made of water ice, and that dry ice only forms a thin surface layer that thickens and thins seasonally. A phenomenon named dry ice storms was proposed to occur over the polar regions of Mars. They are comparable to Earth's thunderstorms, with crystalline CO taking the place of water in the clouds. Dry ice is also proposed as a mechanism for Geysers on Mars.
Dry ice | Extraterrestrial occurrence
Glaciers shaped much of the observable surface in large area of Mars, including fretted terrain. Much of the area in high latitudes, especially the Ismenius Lacus quadrangle, is believed to still contain enormous amounts of water ice. The ice was probably deposited as snow during a different climate in the past. The tilt of Mars changes far more than the Earth's tilt. At times the tilt changes such that the polar ice caps sublimate and the atmosphere carries the moisture to the mid-latitudes where snow falls and accumulates. The Earth's tilt is stabilized by our rather large moon. The two moons of Mars are tiny.
Fretted terrain | Glaciers
This hypothesis is in agreement with numerical models of impacts in the 30-60° range, which are shown to produce elliptical boundary basins similar to the structure identified on Mars. Demagnetization resulting from the high heat associated with such an impact can also serve to explain the apparent lack of magnetic anomalies in the northern plains. It also explains the younger surface age of the northern plains, as determined by significantly lesser crater density. Overall, this hypothesis appears to fare better than others that have been proposed.
Tectonics of Mars | Exogenic origins
Data obtained by the Mars Express satellite, made it possible in 2004 to confirm that the southern polar cap has an average of thick slab of CO ice with varying contents of frozen water, depending on its latitude: the bright polar cap itself, is a mixture of 85% CO ice and 15% water ice. The second part comprises steep slopes known as 'scarps', made almost entirely of water ice, that fall away from the polar cap to the surrounding plains. This transition area between the scarps and the permafrost is the 'cryptic region', where clusters of geysers are located. This model explores the possibility of active water-driven erosive structures, where soil and water derived from the shallow sub-surface layer is expelled up by CO gas through fissures eroding joints to create spider-like radiating tributaries capped with mud-like material and/or ice.
Geysers on Mars | Water-driven erosion
Exogenic hypotheses involve one or more large impacts as being responsible for the lowering of the northern plains. Although a multiple-impact origin has been proposed, it would have required an improbable preferential bombardment of the northern hemisphere. It is also unlikely that multiple impacts would have been able to strip ejecta from the northern hemisphere, and uniformly strip the crust to a relatively consistent depth of 3 km. Mapping of the northern plains and the dichotomy boundary shows that the crustal dichotomy is elliptical in shape. This suggests that formation of the northern plains was caused by a single oblique mega-impact.
Tectonics of Mars | Exogenic origins
Changes in Mars's orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas. During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water comes back to ground at lower latitudes as deposits of frost or snow mixed generously with dust. The atmosphere of Mars contains a great deal of fine dust particles. Water vapor will condense on the particles, then fall down to the ground due to the additional weight of the water coating. When ice at the top of the mantling layer goes back into the atmosphere, it leaves behind dust, which insulating the remaining ice.
Gorgonum Chaos | Gullies
Simulations show that a large impact into ice would generate a great burst of heat that would be sufficient to melt some of the ice. The resulting water could dissolve salts and minerals and produce a coating resistant to erosion. This new understanding of how these different craters have formed has helped the scientists to understand how ice-rich material was deposited in the mid-latitudes of both hemispheres a number of times in the Amazonian period on Mars, for example., During that time the obliquity (tilt) of the spin axis of Mars underwent many large variations. These changes caused the climate to change.
Pedestal crater | Description
These pulverized rock particles would remain in the atmosphere until dry deposition, and due to their size, they would also act as cloud condensation nuclei and would be washed out by wet deposition/precipitation, but even then, about 15% of the sun's radiation might not reach the surface. After the first 20 days, the land temperature might drop quickly, by about 13° C. After about a year, the temperature could rebound by about 6° C, but by this time about one-third of the Northern Hemisphere might be covered in ice. However, this effect could be largely mitigated, even reversed, by a release of enormous quantities of water vapor and carbon dioxide caused by the initial global heat pulse after the impact.
Impact winter | Mass ejection of regolith
For comparison, the Tunguska event was estimated to have an explosive force of about 10-15 megatons. Hamacher's result is dependent on the impactor's density, size, and impact velocity. In order to produce an impact crater with the dimensions of Umm al Binni lake, a Ni-Fe asteroid (density = 7860 kg/m^3, v = 15 km/s) would have been around 100 m in diameter while a comet (density = 500 kg/m^3, v = 25 km/s) would have been between 200 and 300 m in diameter. The resulting impact effects would have caused massive devastation to an area thousands of square kilometres in size, but would not have been sufficient on its own to have caused the wide-scale damage seen at distances exceeding ~100 kilometers from the impact and thus could not be responsible for many of the more distant devastating effects on its own.
Umm al Binni lake | Climate change and impact effects
Mars is scarred by a number of impact craters: a total of 43,000 craters with a diameter of 5 km or greater have been found. The largest confirmed of these is the Hellas impact basin, a light albedo feature clearly visible from Earth. Due to the smaller mass of Mars, the probability of an object colliding with the planet is about half that of the Earth. Mars is located closer to the asteroid belt, so it has an increased chance of being struck by materials from that source. Mars is also more likely to be struck by short-period comets, i.e.
LARLE crater | Martian impact craters
The planet Mars has two permanent polar ice caps. During a pole's winter, it lies in continuous darkness, chilling the surface and causing the deposition of 25–30% of the atmosphere into slabs of CO ice (dry ice). When the poles are again exposed to sunlight, the frozen CO sublimes. These seasonal actions transport large amounts of dust and water vapor, giving rise to Earth-like frost and large cirrus clouds. The caps at both poles consist primarily of water ice. Frozen carbon dioxide accumulates as a comparatively thin layer about one metre thick on the north cap in the northern winter, while the south cap has a permanent dry ice cover about 8 m thick.
Martian polar ice caps | Introduction
Atmospheric water vapor varies in abundance seasonally, with the greatest abundances in each hemisphere's summer after the seasonal polar caps have sublimated into the atmosphere. During winter, both water and carbon dioxide frost and ices form on Mars' surface. These ices form the seasonal and residual polar caps. The seasonal caps - which form each autumn and sublimate each spring - are dominated by carbon dioxide ice. The residual caps - which persist year after year - consist mostly of water ice at the north pole and water ice with a thin veneer (a few 10's of meters thick) of carbon dioxide ice at the south pole.
Compact Reconnaissance Imaging Spectrometer for Mars | Modern climates
Much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust. This ice-rich mantle, a few yards thick, makes the surface look very smooth. Because there are few craters on this mantle, the mantle is relatively young. Changes in Mars's orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas. During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water returns to the ground at lower latitudes as deposits of frost or snow mixed generously with dust.
Arcadia quadrangle | Latitude dependent mantle
A single mega-impact would produce a very large, circular depression in the crust. The proposed depression has been named the Borealis Basin. However, most estimations of the shape of the lowlands area produce a shape that in places dramatically deviates from the circular shape. Additional processes could create those deviations from circularity. Also if the proposed Borealis basin is a depression created by an impact, it would be the largest impact crater known in the Solar System. An object that large could have hit Mars sometime during the process of the Solar System accretion. It is expected that an impact of such magnitude would have produced an ejecta blanket that should be found in areas around the lowland and generate enough heat to form volcanoes.
Martian dichotomy | Single Impact Hypothesis
Research based on slight changes in the orbits of spacecraft around Mars over 16 years found 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. This represents 12 to 16 percent of the mass of the entire Martian atmosphere. These observation support predictions from the Mars Global Reference Atmospheric Model—2010.
Mare Boreum quadrangle | Freezing of atmosphere
At the time of the impact in the Late Pliocene, the Earth was cooling; but the impact and disruption to the weather could have triggered the start of ice cap formation in the Northern Hemisphere. The impact would have put a large amount of water and salt into the atmosphere, disrupted ice shelves, depleted the ozone layer, caused surface acidification, and increased the Earth's albedo.
Eltanin impact | Ice age trigger
They were thought to be connected with endogenic activity, but the high-resolution "Galileo" images showed that the bright, smooth plains correlate with heavily fractured and knobby terrain and do not show any signs of resurfacing. The "Galileo" images also revealed small, dark, smooth areas with overall coverage less than 10,000 km, which appear to embay the surrounding terrain. They are possible cryovolcanic deposits. Both the light and the various smooth plains are somewhat younger and less cratered than the background cratered plains. Impact crater diameters seen range from 0.1 km—a limit defined by the imaging resolution—to over 100 km, not counting the multi-ring structures.
Callisto (moon) | Surface features
The VBF may have been of varied thickness and may have contained varied amounts of ice. In the thin atmosphere of Mars, this layer would have slowly disappeared by sublimation (changing from a solid directly to a gas). Since some areas would have sublimated more than others, the upper lava cap would not be supported evenly and would crack. Cracks/troughs may have begun from sublimation and shrinkage along the edges of the lava cap. Stress from the undermining of the cap edge would have made cracks in the cap. Places with cracks would undergo more sublimation, then the cracks would widen and form the blocky terrain characteristic of regions of chaos.
Cebrenia quadrangle | Galaxias region
In the thin atmosphere of Mars, this layer would have slowly disappeared by sublimation (changing from a solid directly to a gas). Since some areas would have sublimated more than others, the upper lava cap would not be supported evenly and would crack. Cracks/troughs may have begun from sublimation and shrinkage along the edges of the lava cap. Stress from the undermining of the cap edge would have made cracks in the cap. Places with cracks would undergo more sublimation, then the cracks would widen and form the blocky terrain characteristic of regions of chaos. The sublimation process may have been aided by heat (geothermal flux) from magma movements.
Martian chaos terrain | Sublimation of an ice-rich layer
During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water comes back to ground at lower latitudes as deposits of frost or snow mixed generously with dust. The atmosphere of Mars contains a great deal of fine dust particles. Water vapor will condense on the particles, then fall down to the ground due to the additional weight of the water coating. When ice at the top of the mantling layer goes back into the atmosphere, it leaves behind dust, which insulating the remaining ice.
Ptolemaeus (Martian crater) | Ice-rich mantle
The multiple impact hypothesis is supported by correlation of segments of the dichotomy with the rims of several large impact basins. But there are large parts of the Borealis Basin outside the rims of those impact basins. If the Martian lowlands were formed by the multiple basins then their inner ejecta and rims should stand above upland elevations. The rims and ejecta blankets of the lowland impact craters are still much below the upland areas. There are also areas in the lowlands that are outside any of the impact basins, these areas must be overlain by multiple ejecta blankets and should stand at elevations similar to the original planetary surface.
Martian dichotomy | Multiple Impact Hypothesis
Whatever its origin, the Martian dichotomy appears to be extremely old. A new theory based on the Southern Polar Giant Impact and validated by the discovery of twelve hemispherical alignments shows that exogenic theories appear to be stronger than endogenic theories and that Mars never had plate tectonics that could modify the dichotomy. Laser altimeter and radar sounding data from orbiting spacecraft have identified a large number of basin-sized structures previously hidden in visual images. Called quasi-circular depressions (QCDs), these features likely represent derelict impact craters from the period of heavy bombardment that are now covered by a veneer of younger deposits.
Geology of Mars | Hemispheric dichotomy
For decades many features on Mars, including ones in Nilosyrtis Mensae, were believed to contain large amounts of ice. This idea was confirmed by radar studies with the SHAllow RADar (SHARAD) on the Mars Reconnaissance Orbiter. It showed that lobate debris aprons (LDA) and lineated valley fill (LVF) contain pure water ice covered with a thin layer of rocks that insulated the ice. Ice was found in many locations in the northern hemisphere, including Nilosyrtis Mensae. The most popular model for the origin of the ice is climate change from large changes in the tilt of the planet's rotational axis.
Nilosyrtis Mensae | Climate change caused ice-rich features
It also seems that Mars has had many ice ages in which ice was deposited, then later buried. These ice ages are caused by the frequent large changes in the tilt of the planet. The tilt of the spin axis of Mars is highly variable due to the lack of a large moon. Observations of many craters have shown that many craters are mostly full of sediments—ice could be one of the sediments. Many craters appear to be very shallow, but observations of younger craters have demonstrated that impact craters start out as sort of bowl shaped; hence a crater that today looks shallow has probably been filled with sediments.
Martian chaos terrain | Melting of buried ice
Because there are few craters on this mantle, the mantle is relatively young. An excellent view of this mantle is shown below in the picture of the Ptolemaeus Crater Rim, as seen by HiRISE. The ice-rich mantle may be the result of climate changes. Changes in Mars's orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas. During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water comes back to ground at lower latitudes as deposits of frost or snow mixed generously with dust.
Gullies on Mars | Snowpacks
Scientists have even measured tiny changes in the gravity field of Mars due to the movement of carbon dioxide. In other words, the winter buildup of ice changes the gravity of the planet. Mars has seasons that are similar to Earth's because its rotational axis has a tilt close to our own Earth's (25.19° for Mars, 23.45° for Earth). The south polar cap is higher in altitude and colder than the one in the north. The residual southern ice cap is displaced; that is, it is not centered on the south pole. However, the south seasonal cap is centered near the geographic pole.
Martian polar ice caps | South polar cap
That clearly is not the case either. One approach explaining the absence of ejecta blankets infers that no ejecta was ever present. Absence of ejecta could be caused by a large impactor scattering the ejecta into outer space. Another approach proposed the formation of the dichotomy by cooling at depth and crustal loading by later volcanism. The multiple-impact hypothesis is also statistically unfavorable, it is unlikely that multiple impacts basins occur and overlap primarily in the northern hemisphere.
Martian dichotomy | Multiple Impact Hypothesis
The south polar seasonal cap has a bizarre variety of bright and dark streaks and spots that appear during spring, as carbon dioxide ice sublimates. Prior to MRO there were various ideas for processes that could form these strange features, a leading model being carbon dioxide geysers. CRISM has watched the dark spots grow during southern spring, and found that bright streaks forming alongside the dark spots are made of fresh, new carbon dioxide frost, pointing like arrows back to their sources - the same sources as the dark spots. The bright streaks probably form by expansion, cooling, and freezing of the carbon dioxide gas, forming a "smoking gun" to support the geyser hypothesis.
Compact Reconnaissance Imaging Spectrometer for Mars | Modern climates
Both polar caps show spiral troughs, which were initially thought to form as a result of differential solar heating, coupled with the sublimation of ice and condensation of water vapor. Recent analysis of ice penetrating radar data from SHARAD has demonstrated that the spiral troughs are formed from a unique situation in which high density katabatic winds descend from the polar high to transport ice and create large wavelength bedforms. The spiral shape comes from Coriolis effect forcing of the winds, much like winds on earth spiral to form a hurricane. The troughs did not form with either ice cap, instead they began to form between 2.4 million and 500,000 years ago, after three fourths of the ice cap was in place.
Climate of Mars | Polar caps
By 2006, some changes were found. Later, with further analysis it was determined that the changes could have occurred by dry granular flows rather than being driven by flowing water. With continued observations many more changes were found in Gasa Crater and others. With more repeated observations, more and more changes have been found; since the changes occur in the winter and spring, experts are tending to believe that gullies were formed from dry ice. Before-and-after images demonstrated the timing of this activity coincided with seasonal carbon-dioxide frost and temperatures that would not have allowed for liquid water. When dry ice frost changes to a gas, it may lubricate dry material to flow especially on steep slopes.
Copernicus (Martian crater) | Description
The northern polar cap has a diameter of about 1000 km during the northern Mars summer, and contains about 1.6 million cubic km of ice, which if spread evenly on the cap would be 2 km thick. (This compares to a volume of 2.85 million cubic km (km) for the Greenland ice sheet.) The southern polar cap has a diameter of 350 km and a thickness of 3 km. The total volume of ice in the south polar cap plus the adjacent layered deposits has also been estimated at 1.6 million cubic km. Both polar caps show spiral troughs, which recent analysis of SHARAD ice penetrating radar has shown are a result of roughly perpendicular katabatic winds that spiral due to the Coriolis Effect.
Martian polar ice caps | Introduction
CO is the main component of the Martian atmosphere. It has a mean volume ratio of 94.9%. In winter polar regions, the surface temperature can be lower than the frost point of CO CO gas in the atmosphere can condense on the surface to form 1–2 m thick solid dry ice. In summer, the polar dry ice cap can undergo sublimation and release the CO back to the atmosphere. As a result, significant annual variability in atmospheric pressure (≈25%) and atmospheric composition can be observed on Mars. The condensation process can be approximated by the Clausius–Clapeyron relation for CO. Despite the high concentration of CO in the Martian atmosphere, the greenhouse effect is relatively weak on Mars (about 5 °C) because of the low concentration of water vapor and low atmospheric pressure.
Atmosphere of Mars | Carbon dioxide
The landscape polewards of around 30 degrees latitude on Mars has a distinctively different appearance to that nearer the equator, and is said to have undergone terrain softening. Softened terrain lacks the sharp ridge crests seen near the equator, and is instead smoothly rounded. This rounding is thought to be caused by high concentrations of water ice in soils. The term was coined in 1986 by Steve Squyres and Michael Carr from examining imagery from the Viking missions to Mars. Below 30 degrees of latitude, impact craters have steep walls; well-defined, sharp rims; and flat or smoothly bowl-shaped floors. Ridges on intercrater plains come to similarly well-defined, pointed crests.
Terrain softening | Introduction
Mars Reconnaissance Orbiter images suggest an unusual erosion effect occurs based on Mars' unique climate. Spring warming in certain areas leads to CO ice subliming and flowing upwards, creating highly unusual erosion patterns called "spider gullies". Translucent CO ice forms over winter and as the spring sunlight warms the surface, it vaporizes the CO to gas which flows uphill under the translucent CO ice. Weak points in that ice lead to CO geysers.
Climate of Mars | Carbon dioxide carving
Research based on slight changes in the orbits of spacecraft around Mars over 16 years found 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. This represents 12 to 16 percent of the mass of the entire Martian atmosphere. These observation support predictions from the Mars Global Reference Atmospheric Model—2010.
Mare Australe quadrangle | Freezing of atmosphere
Once inside the crater, shade and dust preserve the snow. The snow changes to ice. The many concentric lines are created by the many cycles of snow accumulation. Generally snow accumulates whenever the axial tilt reaches 35 degrees.
Common surface features of Mars | <a href="Concentric%20crater%20fill">Concentric crater fill</a>
The main body of the comet's tail was projected to miss Mars by some 10 Mars diameters. As a result, only higher-than-average-velocity meteoroid dust, ejected earlier in the approach of the comet, allow for impacts on Mars, its moons, and orbiting spacecraft. Dust particles ejected from the nucleus of the comet, at more than double the expected velocity when the comet was 3 AU from the Sun, could reach Mars approximately 43 to 130 min after the closest approach of the comet. There is a possibility for millimeter- to centimeter-size particles released more than 13 AU from the Sun, however, this is considered unlikely, although massive ejections from farther out have been deduced.
C/2013 A1 (Siding Spring) | Predicted effects
The gas rushing underneath a slab to the site of a geyser carves a spiderweb-like pattern of radial channels under the ice, the process being the inverted equivalent of an erosion network formed by water draining through a single plughole.
Mars | Polar caps
The south polar permanent cap is much smaller than the one in the north. It is 400 km in diameter, as compared to the 1100 km diameter of the northern cap. Each southern winter, the ice cap covers the surface to a latitude of 50°. Part of the ice cap consists of dry ice, solid carbon dioxide. Each winter the ice cap grows by adding 1.5 to 2 meters of dry ice from precipitation from a polar-hood of clouds. In summer, the dry ice sublimates (goes directly from a solid to a gas) into the atmosphere. During each year on Mars as much as a third of Mars' thin carbon dioxide (CO) atmosphere "freezes out" during the winter in the northern and southern hemispheres.
Martian polar ice caps | South polar cap
The basin floor contains thick, structurally complex sedimentary deposits that have a long geologic history of deposition, erosion, and internal deformation. The lowest elevations on the planet are located within the Hellas basin, with some areas of the basin floor lying over 8 km below datum. The two other large impact structures on the planet are the Argyre and Isidis basins. Like Hellas, Argyre (800 km in diameter) is located in the southern highlands and is surrounded by a broad ring of mountains. The mountains in the southern portion of the rim, Charitum Montes, may have been eroded by valley glaciers and ice sheets at some point in Mars's history.
Geology of Mars | Large impact basins
However no evidence suggests when it impacted. To survive impact largely undeformed it must have impacted at less than ~1.5 km/s. which sets boundaries on its entry dynamics and Mars' atmosphere at the time it impacted. In any case, the meteorite did not show much sign of rust. In the absence of detailed knowledge of the Mars environment, it is not possible to conclude whether it fell recently or not.
Heat Shield Rock | Analysis
The walls sublimate and recede, while the floor remains the same. As the seasonal frost disappears, the pit walls appear to darken considerably relative to the surrounding terrain. The SCFs have been observed to grow in size, year by year, at an average rate of 1 to 3 meters, suggesting that they are formed in a thin layer (8m) of carbon dioxide ice lying on top of water ice.
South (Martian crater) | Description
Large areas of the Martian surface are loaded with ice that is protected by a meters thick layer of dust and other material. However, if cracks appear, a fresh surface will expose ice to the thin atmosphere. In a short time, the ice will disappear into the cold, thin atmosphere in a process called sublimation (phase transition) . Dry ice behaves in a similar fashion on the Earth. On Mars sublimation has been observed when the Phoenix lander uncovered chunks of ice that disappeared in a few days. In addition, HiRISE has seen fresh craters with ice at the bottom.
Deuteronilus Mensae | Upper plains unit
At 75° north latitude, it is one of the highest-latitude impact craters known. The temperature is below the freezing point of water for much of the year, and the limited vegetation is slow-growing, leading to very little weathering. For this reason Haughton retains many geological features that lower-latitude craters lose to erosion. Because Haughton's geology and climatology are as close to Mars-like as can be had on Earth, Haughton and its environs have been dubbed by scientists working there as "Mars on Earth." For example, the center of the crater contains impact breccia (ejected rock which has fallen back into the impact zone and partially re-welded) that is permeated with permafrost, thus creating a close analog to what may be expected at crater sites on a cold, wet Mars.
Haughton impact crater | Description
Eventually, the heat from the deep subsurface together with the insulating qualities of the covering layer produced a thick water layer. Since dense materials tend to sink into water, the overlying rock broke under the strain. The dense, rocky cap fractured into various sized, tilted blocks. The melt water went to the top and made a channel which eroded more and more as water rushed outward. Along with water from other chaotic regions, there would have been enough erosive force to carve the large river valleys we now observe. There is ample evidence for buried deposits of ice in the form of glaciers, preserved under a thin covering of rock and dirt.
Martian chaos terrain | Melting of buried ice
Although water appears to have once been present on the Martian surface, ground ice currently exists from mid-latitudes to the poles. The soil and atmosphere of Mars contain many of the main elements crucial to life, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon. Any climate change induced in the near term is likely to be driven by greenhouse warming produced by an increase in atmospheric carbon dioxide () and a consequent increase in atmospheric water vapor. These two gases are the only likely sources of greenhouse warming that are available in large quantities in the Mars environment. Large amounts of water ice exist below the Martian surface, as well as on the surface at the poles, where it is mixed with dry ice, frozen .
Terraforming of Mars | Advantages
Large areas of the Martian surface are loaded with ice that is protected by a meters thick layer of dust and other material. However, if cracks appear, a fresh surface will expose ice to the thin atmosphere. In a short time, the ice will disappear into the cold, thin atmosphere in a process called sublimation. Dry ice behaves in a similar fashion on the Earth. On Mars sublimation has been observed when the Phoenix lander uncovered chunks of ice that disappeared in a few days. In addition, HiRISE has seen fresh craters with ice at the bottom. After a time, HiRISE saw the ice deposit disappear.
Common surface features of Mars | <a href="Upper%20plains%20unit">Upper plains unit</a>
Impact craters provide evidence of past impacts on other planets in the Solar System, including possible interplanetary terrestrial impacts. Without carbon dating, other points of reference are used to estimate the timing of these impact events. Mars provides some significant evidence of possible interplanetary collisions. The North Polar Basin on Mars is speculated by some to be evidence for a planet-sized impact on the surface of Mars between 3.8 and 3.9 billion years ago, while Utopia Planitia is the largest confirmed impact and Hellas Planitia is the largest visible crater in the Solar System. The Moon provides similar evidence of massive impacts, with the South Pole–Aitken basin being the biggest.
Impact event | Evidence of massive past impact events
There have been regional changes around the south pole (Planum Australe) over the past few Martian years. In 1999 the Mars Global Surveyor photographed pits in the layer of frozen carbon dioxide at the Martian south pole. Because of their striking shape and orientation these pits have become known as swiss cheese features. In 2001 the craft photographed the same pits again and found that they had grown larger, retreating about 3 meters in one Martian year. These features are caused by the sublimation of the dry ice layer, thereby exposing the inert water ice layer. More recent observations indicate that the ice at Mars' south pole is continuing to sublimate.
Climate of Mars | Evidence for recent climatic change
This hypothesis was confirmed theoretically by Robert Leighton and Bruce Murray in 1966. Today it is known that the winter caps at both poles are primarily composed of CO ice, but that a permanent (or perennial) cap of water ice remains during the summer at the northern pole. At the southern pole, a small cap of CO ice remains during summer, but this cap too is underlain by water ice. The final piece of the Martian climate puzzle was provided by Mariner 4 in 1965. Grainy television pictures from the spacecraft showed a surface dominated by impact craters, which implied that the surface was very old and had not experienced the level of erosion and tectonic activity seen on Earth.
Water on Mars | Historical background