Rain and snow was a regular occurrence on Mars in the past; especially in the Noachian and early Hesperian epochs. [2] [3] [4] [5] [6] [7] Water was theorized to seep into the ground until it reached a formation that would not allow it to penetrate further (such a layer is called an aquitard and is believed to be impermeable). Water then accumulated forming a saturated layer. Deep aquifers may still exist. [8]
Researchers have found that Mars had a planet-wide groundwater system and several prominent features on the planet have been produced by the action of groundwater. [9] [10] When water rose to the surface or near the surface, various minerals were deposited and sediments became cemented together. Some of the minerals were sulfates that were probably produced when water dissolved sulfur from underground rocks, and then became oxidized when it came into contact with the air. [11] [12] [13] While traveling through the aquifer, the water passed through igneous rock basalt, which would have contained sulfur.
In an aquifer, water occupies open space (pore space) that lies between rock particles. This layer would spread out, eventually coming to be under most of the Martian surface. The top of this layer is called the water table. Calculations show that the water table on Mars was for a time 600 meters below the surface. [14] [15]
The InSight lander uncovered in September 2019 unexplained magnetic pulses, and magnetic oscillations consistent with an existing planet-wide reservoir of liquid water deep underground. [8]
Researchers have concluded that Gale Crater has experienced many episodes of groundwater surge with changes in the groundwater chemistry. These chemical changes would support life. [16] [17] [18] [19] [20] [21]
Some locations on the Red Planet show groups of layered rocks. [22] [23] Rock layers are present under the resistant caps of pedestal craters, on the floors of many large impact craters, and in the area called Arabia. [24] [25] In some places the layers are arranged into regular patterns. [26] [27] It has been suggested that the layers were put into place by volcanoes, the wind, or by being at the bottom of a lake or sea. Calculations and simulations show that groundwater carrying dissolved minerals would surface in the same locations that have abundant rock layers. According to these ideas, deep canyons and large craters would receive water coming from the ground. Many craters in the Arabia area of Mars contain groups of layers. Some of these layers may have resulted from climate change.
The tilt of the rotational axis of Mars has repeatedly changed in the past. Some changes are large. Because of these variations of climate, at times the atmosphere of Mars would have been much thicker and contained more moisture. The amount of atmospheric dust also has increased and decreased. It is believed that these frequent changes helped to deposit material in craters and other low places. The rising of mineral-rich ground water cemented these materials. The model also predicts that after a crater is full of layered rocks, additional layers will be laid down in the area around the crater. So, the model predicts that layers may also have formed in intercrater regions; layers in these regions have been observed.
Layers can be hardened by the action of groundwater. Martian ground water probably moved hundreds of kilometers, and in the process it dissolved many minerals from the rock it passed through. When ground water surfaces in low areas containing sediments, water evaporates in the thin atmosphere and leaves behind minerals as deposits and/or cementing agents. Consequently, layers of dust could not later easily erode away since they were cemented together. On Earth, mineral-rich waters often evaporate forming large deposits of various types of salts and other minerals. Sometimes water flows through Earth's aquifers, and then evaporates at the surface just as is hypothesized for Mars. One location this occurs on Earth is the Great Artesian Basin of Australia. [28] On Earth the hardness of many sedimentary rocks, like sandstone, is largely due to the cement that was put in place as water passed through.
In February 2019, European scientists published geological evidence of an ancient planet-wide groundwater system that was, arguably, connected to a putative vast ocean. [29] [30]
Many areas on Mars show inverted relief. In those places, former stream channels are displayed as raised beds, instead of stream valleys. Raised beds form when old stream channels become filled with material that is resistant to erosion. After later erosion removes surrounding soft materials, more resistant materials that were deposited in the stream bed are left behind. Lava is one substance that can flow down valleys and produce such inverted terrain. However, fairly loose materials can get quite hard and erosion resistant when cemented by minerals. These minerals can come from groundwater. It is thought that a low point, like a valley focuses groundflow, so more water and cements move into it, and this results in a greater degree of cementation. [9]
Terrain inversion can also happen without cementation by groundwater, however. If a surface is being eroded by wind, the necessary contrast in erodibility can arise simply from variations in grain size of loose sediments. Since wind can carry away sand but not cobbles, for example, a channel bed rich in cobbles could form an inverted ridge if it was originally surrounded by much finer sediments, even if the sediments were not cemented. This effect has been invoked for channels in Saheki crater. [31]
Places on Mars that contain layers in the bottoms of craters often also have inverted terrain.
Spacecraft sent to Mars provided a wealth of evidence for groundwater being a major cause of many rock layers on the planet. The Opportunity Rover studied some areas with sophisticated instruments. Opportunity’s observations showed that groundwater repeatedly had risen to the surface. Evidence for water coming to the surface a number of times include hematite concretions (called "blue berries"), cementation of sediments, alteration of sediments, and clasts or skeletons of formed crystals. [32] [33] [34] To produce skeleton crystals, dissolved minerals were deposited as mineral crystals, and then the crystals were dissolved when more water came to the surface at a later time. The shape of the crystals could still be made out. [35] Opportunity found hematite and sulfates in many places as it traveled on the surface of Mars, so it is assumed that the same types of deposits are widespread, just as predicted by the model. [36] [37] [38] [39]
Orbiting probes showed that the type of rock around Opportunity was present in a very large area that included Arabia, which is about as large as Europe. A spectroscope, called CRISM, on the Mars Reconnaissance Orbiter found sulfates in many of the same places that the upwelling water model had predicted, including some areas of Arabia. [40] The model predicted deposits in Valles Marineris canyons; these deposits have been observed and found to contain sulfates. [41] Other locations predicted to have upwelling water, for example chaos regions and canyons associated with large outflows, have also been found to contain sulfates. [42] [43] Layers occur in the types of locations predicted by this model of groundwater evaporating at the surface. They were discovered by the Mars Global Surveyor and HiRISE onboard Mars Reconnaissance Orbiter. Layers have been observed around the site that Opportunity landed and in nearby Arabia. The ground under the cap of pedestal craters sometimes displays numerous layers. The cap of a pedestal crater protects material under it from eroding away. It is accepted that the material that now is only found under the pedestal crater’s cap formerly covered the whole region. Hence, layers now just visible under pedestal craters once covered the whole area. Some craters contain mounds of layered material that reach above the crater’s rim. Gale Crater and Crommelin (Martian crater) are two craters that hold large mounds. Such tall mounds were formed, according to this model, by layers that first filled the crater, and then continued to build up around the surrounding region. Later erosion removed material around the crater, but left a mound in the crater that was higher than its rim. Note that although the model predicts upwelling and evaporation that should have produced layers in other areas (Northern lowlands), these areas do not show layers because the layers were formed long ago in the Early Hesperian Epoch and were therefore subsequently buried by later deposits.
Strong evidence for groundwater making lakes in deep craters was described by a group of European scientists in February 2019. [29] [30] [44] [45] Craters examined did not show inlets or outlets; therefore, water for the lake would have come from the ground. These craters had floors lying roughly 4000 m below Martian 'sea level'. Features and minerals on the floors of these craters could only have formed in the presence of water. Some of the features were deltas and terraces. [46] [44] Some of the craters studied were Oyama, Pettit, Sagan, Tombaugh, Mclaughlin, du Martheray, Nicholson, Curie, and Wahoo. It seems that if a crater was deep enough, water came out of the ground and a lake was formed. [44]
The Meridiani Planum (alternately Meridiani plain, Meridiani plains, Terra Meridiani, or Terra Meridiani plains) is either a large plain straddling the equator of Mars and covered with a vast number of spherules containing a lot of iron oxide or a region centered on this plain that includes some adjoining land. The plain sits on top of an enormous body of sediments that contains a lot of bound water. The iron oxide in the spherules is crystalline (grey) hematite (Fe2O3).
Martian spherules (also known as hematite spherules, blueberries, & Martian blueberries) are small spherules (roughly spherical pebbles) that are rich in an iron oxide (grey hematite, α-Fe2O3) and are found at Meridiani Planum (a large plain on Mars) in exceedingly large numbers.
NASA's 2003 Mars Exploration Rover Mission has amassed an enormous amount of scientific information related to the Martian geology and atmosphere, as well as providing some astronomical observations from Mars. This article covers information gathered by the Opportunity rover during the initial phase of its mission. Information on science gathered by Spirit can be found mostly in the Spirit rover article.
The geology of Mars is the scientific study of the surface, crust, and interior of the planet Mars. It emphasizes the composition, structure, history, and physical processes that shape the planet. It is analogous to the field of terrestrial geology. In planetary science, the term geology is used in its broadest sense to mean the study of the solid parts of planets and moons. The term incorporates aspects of geophysics, geochemistry, mineralogy, geodesy, and cartography. A neologism, areology, from the Greek word Arēs (Mars), sometimes appears as a synonym for Mars's geology in the popular media and works of science fiction. The term areology is also used by the Areological Society.
The Medusae Fossae Formation is a large geological formation of probable volcanic origin on the planet Mars. It is named for the Medusa of Greek mythology. "Fossae" is Latin for "trenches". The formation is a collection of soft, easily eroded deposits that extends discontinuously for more than 5,000 km along the equator of Mars. Its roughly-shaped regions extend from just south of Olympus Mons to Apollinaris Patera, with a smaller additional region closer to Gale Crater.
The Arabia quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Arabia quadrangle is also referred to as MC-12.
The Oxia Palus quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Oxia Palus quadrangle is also referred to as MC-11.
The Aeolis quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Aeolis quadrangle is also referred to as MC-23 . The Aeolis quadrangle covers 180° to 225° W and 0° to 30° south on Mars, and contains parts of the regions Elysium Planitia and Terra Cimmeria. A small part of the Medusae Fossae Formation lies in this quadrangle.
The Coprates quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Coprates quadrangle is also referred to as MC-18. The Coprates quadrangle contains parts of many of the old classical regions of Mars: Sinai Planum, Solis Planum, Thaumasia Planum, Lunae Planum, Noachis Terra, and Xanthe Terra.
The Margaritifer Sinus quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Margaritifer Sinus quadrangle is also referred to as MC-19. The Margaritifer Sinus quadrangle covers the area from 0° to 45° west longitude and 0° to 30° south latitude on Mars. Margaritifer Sinus quadrangle contains Margaritifer Terra and parts of Xanthe Terra, Noachis Terra, Arabia Terra, and Meridiani Planum.
Almost all water on Mars today exists as ice, though it also exists in small quantities as vapor in the atmosphere. What was thought to be low-volume liquid brines in shallow Martian soil, also called recurrent slope lineae, may be grains of flowing sand and dust slipping downhill to make dark streaks. While most water ice is buried, it is exposed at the surface across several locations on Mars. In the mid-latitudes, it is exposed by impact craters, steep scarps and gullies. Additionally, water ice is also visible at the surface at the north polar ice cap. Abundant water ice is also present beneath the permanent carbon dioxide ice cap at the Martian south pole. More than 5 million km3 of ice have been detected at or near the surface of Mars, enough to cover the whole planet to a depth of 35 meters (115 ft). Even more ice might be locked away in the deep subsurface. Some liquid water may occur transiently on the Martian surface today, but limited to traces of dissolved moisture from the atmosphere and thin films, which are challenging environments for known life. No evidence of present-day liquid water has been discovered on the planet's surface because under typical Martian conditions, warming water ice on the Martian surface would sublime at rates of up to 4 meters per year. Before about 3.8 billion years ago, Mars may have had a denser atmosphere and higher surface temperatures, potentially allowing greater amounts of liquid water on the surface, possibly including a large ocean that may have covered one-third of the planet. Water has also apparently flowed across the surface for short periods at various intervals more recently in Mars' history. Aeolis Palus in Gale Crater, explored by the Curiosity rover, is the geological remains of an ancient freshwater lake that could have been a hospitable environment for microbial life. The present-day inventory of water on Mars can be estimated from spacecraft images, remote sensing techniques, and surface investigations from landers and rovers. Geologic evidence of past water includes enormous outflow channels carved by floods, ancient river valley networks, deltas, and lakebeds; and the detection of rocks and minerals on the surface that could only have formed in liquid water. Numerous geomorphic features suggest the presence of ground ice (permafrost) and the movement of ice in glaciers, both in the recent past and present. Gullies and slope lineae along cliffs and crater walls suggest that flowing water continues to shape the surface of Mars, although to a far lesser degree than in the ancient past.
Columbus is a crater in the Terra Sirenum of Mars. It is 119 km in diameter and was named after Christopher Columbus, Italian explorer (1451–1506). The discovery of sulfates and clay minerals in sediments within Columbus crater are strong evidence that a lake once existed in the crater. Research with an orbiting near-infrared spectrometer, which reveals the types of minerals present based on the wavelengths of light they absorb, found evidence of layers of both clay and sulfates in Columbus crater. This is exactly what would appear if a large lake had slowly evaporated. Moreover, because some layers contained gypsum, a sulfate which forms in relatively fresh water, life could have formed in the crater.
Henry is a large crater in the Arabia quadrangle of Mars. It is 171 kilometres (106 mi) in diameter and was named after the brothers Paul Henry and Prosper Henry, both of whom were French telescope makers and astronomers.
In planetary geology, a pedestal crater is a crater with its ejecta sitting above the surrounding terrain and thereby forming a raised platform. They form when an impact crater ejects material which forms an erosion-resistant layer, thus causing the immediate area to erode more slowly than the rest of the region. Some pedestals have been accurately measured to be hundreds of meters above the surrounding area. This means that hundreds of meters of material were eroded away. The result is that both the crater and its ejecta blanket stand above the surroundings. Pedestal craters were first observed during the Mariner missions.
Bouguer Crater is an impact crater in the Sinus Sabaeus quadrangle of Mars, located at 18.7° S and 332.8° W It is 107 km in diameter and was named after Pierre Bouguer, French physicist-hydrographer (1698–1758).
To date, interplanetary spacecraft have provided abundant evidence of water on Mars, dating back to the Mariner 9 mission, which arrived at Mars in 1971. This article provides a mission by mission breakdown of the discoveries they have made. For a more comprehensive description of evidence for water on Mars today, and the history of water on that planet, see Water on Mars.
The Mars Reconnaissance Orbiter's HiRISE instrument has taken many images that strongly suggest that Mars has had a rich history of water-related processes. Many features of Mars appear to be created by large amounts of water. That Mars once possessed large amounts of water was confirmed by isotope studies in a study published in March 2015, by a team of scientists showing that the ice caps were highly enriched with deuterium, heavy hydrogen, by seven times as much as the Earth. This means that Mars has lost a volume of water 6.5 times what is stored in today's polar caps. The water for a time would have formed an ocean in the low-lying Mare Boreum. The amount of water could have covered the planet about 140 meters, but was probably in an ocean that in places would be almost 1 mile deep.
The composition of Mars covers the branch of the geology of Mars that describes the make-up of the planet Mars.
In summer 1965, the first close-up images from Mars showed a cratered desert with no signs of water. However, over the decades, as more parts of the planet were imaged with better cameras on more sophisticated satellites, Mars showed evidence of past river valleys, lakes and present ice in glaciers and in the ground. It was discovered that the climate of Mars displays huge changes over geologic time because its axis is not stabilized by a large moon, as Earth's is. Also, some researchers maintain that surface liquid water could have existed for periods of time due to geothermal effects, chemical composition or asteroid impacts. This article describes some of the places that could have held large lakes.
Equatorial layered deposits (ELD’s) have been called interior layered deposits (ILDs) in Valles Marineris. They are often found with the most abundant outcrops of hydrated sulfates on Mars, and thus are likely to preserve a record of liquid water in Martian history since hydrated sulfates are formed in the presence of water. Layering is visible on meter scale, and when the deposits are partly eroded, intricate patterns become visible. The layers in the mound in Gale Crater have been extensively studied from orbit by instruments on the Mars Reconnaissance Orbiter. The Curiosity Rover landed in the crater, and it has brought some ground truth to the observations from satellites. Many of the layers in ELD’s such as in Gale Crater are composed of fine-grained, easily erodible material as are many other layered deposits. On the basis of albedo, erosion patterns, physical characteristics, and composition, researchers have classified different groups of layers in Gale Crater that seem to be similar to layers in other (ELD’s). The groups include: a small yardang unit, a coarse yardang unit, and a terraced unit. Generally, equatorial layered deposits are found ~ ±30° of the equator. Equatorial Layered Deposits appear in various geological settings such as cratered terrains, chaotic terrains, the Valles Marineris chasmata, and large impact craters.
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