Geology of Mars
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Mars is the fourth planet from the sun, known as the 'red planet' due to its iron oxide-rich surface. It has a thin atmosphere primarily composed of carbon dioxide and is home to the largest volcano and canyon in the solar system. Various successful missions have explored Mars, revealing its geological history, including evidence of past water presence and conditions that may have supported life.
Geology of Mars
- 1. 1 INTRODUCTION Mars is the fourth planet in our solar system next to our own planet Earth at a mean distance of 227.94 million km or 1.5 AU. It is the second smallest planet after Mercury and the outermost of the inner, terrestrial planets. Mars was named after the Roman god of war because of its red color resembling the blood. It is often described as the "Red Planet" because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a terrestrial planet with a thin atmosphere, having surface features similar to both of the impact craters of the Moon and the volcanoes, valleys, deserts, and polar ice caps of Earth. It is home to the highest mountain of our solar system: Olympus Mons and the largest known canyon: Valles Marineris. The rotational period and seasonal cycles of Mars are similar to those of Earth, as is the tilt that produces the seasons. Mars has two moons, Phobos and Deimos, which are small and irregularly shaped which may be captured asteroids. The mean radius of the planet is almost half of the Earth- some 3390 km. Its volume is also quite less- about 15% of the Earth’s volume, which comes to be around 1631×107 km3. Mars has a mass of 6417×1019 kg. It has a weak gravity- about 37% that of the Earth. It also has a very thin atmosphere, which is almost entirely comprised of Carbon dioxide (about 96%) with small amounts of Nitrogen and Argon. The average temperature on the planet’s surface is about -63⁰C. Mars can easily be seen from Earth with the naked eye with its reddish coloring with its apparent magnitude reaches −3. Until the first successful Mars flyby in 1965 by Mariner 4, many speculated about the presence of liquid water on the planet's surface. This was based on observed periodic variations in light and dark patches, particularly in the polar latitudes, which appeared to be seas and continents. Long, dark striations were interpreted by some as irrigation channels for liquid water. These straight line features were later explained as optical illusions, though geological evidence gathered by unmanned missions suggests that Mars once had large- scale water coverage on its surface at some earlier stage of its life. The Mars rover Spirit sampled chemical compounds containing water molecules in March 2007. The Phoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008. Mars as seen from Hubble Space Telescope
- 2. 2 Mars is currently host to five functioning spacecraft: three in orbit – the Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter – and two on the surface – Mars Exploration Rover Opportunity and the Mars Science Laboratory Curiosity. Defunct spacecraft on the surface include Mars Exploration rover-A Spirit and several other inert landers and rovers such as the Phoenix lander, which completed its mission in 2008. Observations by the Mars Reconnaissance Orbiter have revealed possible flowing water during the warmest months on Mars. In 2013, NASA's Curiosity rover discovered that Mars' soil contains between 1.5% and 3% water by mass. This report attempts in summarizing the geological information about Mars. Comparison between Mars and the Earth Earth Mars Average Distance from Sun 150 million km 228 million km Average Speed in Orbiting Sun 29.8 km per second 23.3 km per second Average Diameter 12756 km 6791 km Tilt of Axis 23.5 degrees 25 degrees Length of Year 365.25 Days 687 Earth Days Length of Day 23 hours 56 minutes 24 hours 37 minutes Gravity 2.66 times that of Mars 0.375 that of Earth Average Surface Temperature 13.8 degree C -63 degree C Composition of Atmosphere nitrogen, oxygen, argon, others mostly carbon dioxide, some water vapor Number of Moons 1 2
- 3. 3 Exploration of Mars The exploration of Mars has taken place over hundreds of years, beginning in earnest with the invention and development of the telescope during the 1600s. Increasingly detailed views of the planet from Earth inspired speculation about its environment and possible life – even intelligent civilizations – that might be found there. Probes sent from Earth beginning in the late 20th century have yielded a dramatic increase in knowledge about the Martian system, focused primarily on understanding its geology and habitability potential. Engineering interplanetary journeys is very complicated, so the exploration of Mars has experienced a high failure rate, especially in earlier attempts. Roughly two-thirds of all spacecraft destined for Mars failed before completing their missions, and there are some that failed before their observations could begin. However, missions have also met with unexpected levels of success, such as the twin Mars Exploration Rovers operating for years beyond their original mission specifications. Since 6 August 2012, there have been two scientific rovers on the surface of Mars beaming signals back to Earth (Opportunity of the Mars Exploration Rover mission, and Curiosity of the Mars Science Laboratory mission), and three orbiters currently surveying the planet: Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter. Two orbiters launched in November 2013, Mars Orbiter Mission of ISRO and MAVEN of NASA are currently on their way to Mars.
- 4. 4 On 24 January 2014, NASA reported that current studies on the planet Mars by the Curiosity and Opportunity rovers will now be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotropic and/or chemo-litho-autotrophic microorganisms, as well as ancient water, including fluvio- lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable. The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on the planet Mars is now a primary NASA objective. Till date 43 missions have been sent to Mars, of which only 15 have been successful. The following missions proved to be successful in one or the other sense and provided useful data about the geology and composition of Mars. 1. Mariner Program: In 1964 and 1968, NASA sent four probes to Mars- Mariner 3-4, 6-7 and Mariner 8-9 respectively. Mars was visited by Mariner 4 in 1965 and was photographed by it, becoming the first planet to be photographed. In 1969, Mariner 9 became the first man-made object to orbit another planet. It photographed the surface of Mars. These pictures were the first to offer more detailed evidence that liquid water might at one time have flowed on the planetary surface. They also finally discerned the true nature of many Martian albedo features. For example, Nix Olympica was one of only a few features that could be seen during the planetary dust-storm, revealing it to be the highest mountain (volcano, to be exact) on any planet in the entire Solar System, and leading to its reclassification as Olympus Mons. 2. Viking Program: The Viking program launched Viking 1 and 2 spacecraft to Mars in 1975; The program consisted of two orbiters and two landers – these were the first two spacecraft to successfully land and operate on Mars. The Viking orbiters revealed that large floods of water carved deep valleys, eroded grooves into bedrock, and traveled thousands of kilometers. Areas of branched streams, in the southern hemisphere, suggest that rain once fell. 3. Mars Pathfinder: It was a NASA spacecraft that landed a base station with a roving probe on Mars on July 4, 1997. It consisted of a lander and a small 10.6 kilograms wheeled robotic rover named Sojourner, which was the first rover to operate on the surface of Mars. Sojourner studied some of the big chunks of rocks spread near its landing site with respect to their chemistry and mineralogy. 4. Mars Global Surveyor (MGS): It was the first fully successful mission overall, to the red planet in two decades when it was launched on November 7, 1996, and entered orbit on September 12, 1997. The spacecraft began its primary mapping mission in March 1999. It observed the planet from a low-altitude, nearly polar orbit. The mission studied the entire Martian surface, atmosphere, and interior, and returned more data about the red planet than all previous Mars missions combined. Among key scientific findings, Global Surveyor took pictures of gullies and debris flow features that suggest there may be current sources of liquid water, similar to an aquifer, at or near the surface of the planet. Similar channels on Earth are formed by flowing water, but on Mars the temperature is normally too cold and the atmosphere too thin to sustain liquid water. Nevertheless, many scientists hypothesize that liquid
- 5. 5 groundwater can sometimes surface on Mars, erode gullies and channels, and pool at the bottom before freezing and evaporating. Magnetometer readings showed that the planet's magnetic field is not globally generated in the planet's core, but is localized in particular areas of the crust. Data from the spacecraft's laser altimeter gave scientists their first 3-D views of Mars' north polar ice cap. 5. Mars Odyssey: In 2001 NASA's Mars Odyssey orbiter arrived at Mars. Its mission is to use spectrometers and imagers to hunt for evidence of past or present water and volcanic activity on Mars. In 2002, it was announced that the probe's gamma ray spectrometer and neutron spectrometer had detected large amounts of hydrogen, indicating that there are vast deposits of water ice in the upper three meters of Mars' soil within 60° latitude of the south pole. 6. Mars Exploration Rovers (MER)- Spirit and Opportunity: NASA's Mars Exploration Rover Mission is an ongoing robotic space mission involving two rovers, Spirit and Opportunity, exploring the planet Mars. The mission's scientific objective was to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars. In particular, samples sought include those that have minerals deposited by water-related processes such as precipitation, evaporation, sedimentary cementation, or hydrothermal activity; to determine the distribution and composition of minerals, rocks, and soils surrounding the landing sites; to determine what geologic processes have shaped the local terrain and influenced the chemistry. Such processes could include water or wind erosion, sedimentation, hydrothermal mechanisms, volcanism, and cratering. Search for iron-containing minerals, and to identify and quantify relative amounts of specific mineral types that contain water or were formed in water, such as iron-bearing carbonates. Characterize the mineralogy and textures of rocks and soils to determine the processes that created them. 7. Mars Reconnaissance Orbiter (MRO): Mars Reconnaissance Orbiter is a multipurpose spacecraft designed to conduct reconnaissance and exploration of Mars from orbit which was launched on August 12, 2005, and attained Martian orbit on March 10, 2006. It is currently imaging the Martian surface at very high resolution. 8. Mars Science Laboratory (MSL)- Curiosity Rover: The NASA Mars Science Laboratory mission with its rover named Curiosity, was launched on November 26, 2011. The rover carries instruments designed to look for past or present conditions relevant to the past or present habitability of Mars. The Curiosity rover landed on Mars on Aeolis Palus in Gale Crater. The geological goals of this mission are to investigate the chemical, isotopic, and mineralogical composition of the Martian surface and near-surface geological materials and interpret the processes that have formed and modified rocks and soils. 9. Mars Orbiter Mission (MOM) or Mangalyaan: It is a Mars orbiter launched in November 2013 by ISRO and it’s India’s first interplanetary mission. Though the primary objective of the Mars Orbiter Mission is to develop the technologies required for design, planning, management and operations of an interplanetary mission, the spacecraft will be exploring Mars' surface features, morphology, mineralogy and Martian atmosphere using indigenous scientific instruments.
- 6. 6 Gravity and Magnetism The gravity of Mars is nearly 37% of the Earth’s gravity. The gravitational acceleration on the surface of Mars is 3.71 m/s2 as compared to 9.8 m/s2 of Earth. As we know, gravitational pull of a planet is proportional to its mass. Mass of Mars is almost 11% that of the Earth, implying the lower gravitational pull than that of the Earth’s. Gravity of Mars has been measured by many previous and ongoing missions to Mars and this value is now recognized as standard. Currently Mars shows almost no magnetism. As there’s no magnetic dipole similar to that of the Earth, it is suspected that Mars has a cooled, solid core, unlike Earth’s liquid core, which is thought to be responsible for the generation of the magnetic field. The first indication of the weak magnetic field of Mars was obtained during the Mariner 4 spacecraft flyby in 1965. But recent studies of magnetism in surface rocks of Martian surface by the Mars Global Surveyor spacecraft suggest that the Red Planet was magnetized more widely and strongly in its geologic past. Scientists think Mars had the ability to generate a strong magnetic field in its core during its first half-billion to 1 billion years. The Martian field flipped polarity (swapping magnetic north and south) just as Earth's magnetic field has done repeatedly. But perhaps because the Martian core cooled, its magnetic dynamo shut down within a billion years of the planet's birth.
- 7. 7 Geography of Mars Many times called as Areography (Ares-Greek for Mars), the geography of Mars includes mapping and naming the surface of Mars. Martian geography is mainly focused on what is called physical geography on Earth; that is the distribution of physical features across Mars and their cartographic representations. The first observations of Mars were from ground-based telescopes. In September 1877, Italian astronomer Giovanni Schiaparelli published the first detailed map of Mars. These maps notably contained features he called canali ("channels"), that were later shown to be an optical illusion. Following these observations, it was a long held belief that Mars contained vast seas and vegetation. It was not until spacecraft visited the planet during NASA's Mariner missions in the 1960s, that these myths were dispelled. Some maps of Mars were made using the data from these missions, but it wasn't until the Mars Global Surveyor mission, launched in 1996 and ending in late 2006, that complete, extremely detailed maps were obtained. These maps are now available online. Currently we have more detailed maps of Mars than our own planet’s ocean floor. Albedo Features The classical albedo features of Mars are the light and dark features that can be seen on the planet Mars through an Earth-based telescope. Before the age of space probes, several astronomers created maps of Mars on which they gave names to the features they could see. Today, the improved understanding of Mars enabled by space probes has rendered many of the classical names obsolete for the purposes of cartography; however, some of the old names are still used to describe geographical features on the planet. These albedo contrasts rarely correspond to topographic features and in many cases obscure them. The lighter patches at the poles were correctly believed to be a frozen substance, either water or carbon dioxide, but the nature of the dark patches seen against the general reddish tint of Mars was uncertain for centuries. When Giovanni Schiaparelli began observing Mars in 1877, he believed that the darker features were seas and lakes and named them in Latin accordingly (mare for sea and lacus for lake). They are now known to be areas where the wind has swept away High resolution colorized map of Mars based on Viking orbiter images. Surface frost and water ice fog brighten the impact basin Hellas to the right of lower center; Syrtis Major just above it is darkened by winds that sweep dust off its basaltic surface. Summer view of North and south polar ice caps are shown at upper and lower right.
- 8. 8 the surface dust, leaving a darker, rockier surface; their borders change in response to windstorms on the Martian surface that pick up the dust, widening or narrowing the features. In 1958, the International Astronomical Union created a list of officially recognized Martian albedo features. Many of the names used for topographic features on Mars are still based on the classical nomenclature of the feature's location; for instance, the albedo feature Ascraeus Lacus provides the basis of the name of the volcano Ascraeus Mons. Various albedo features can be seen in the map of Mars given on the previous page. Zero Elevation and Zero Meridian Since Mars has no oceans and hence no sea level, it is convenient to define an arbitrary zero-elevation level or datum for mapping the surface. The datum for Mars is arbitrarily defined in terms of a constant atmospheric pressure. From the Mariner 9 mission up until 2001, this was chosen as the point where there exists the triple point for water which is 6.105 mbar. In 2001, Mars Orbiter Laser Altimeter data led to a new convention of zero elevation defined as the equipotential surface (gravitational plus rotational) whose average value at the equator is equal to the mean radius of the planet. Mars' equator is defined by its rotation, but the location of its Prime Meridian was specified, as was Earth's, by choice of an arbitrary point which was accepted by later observers. The German astronomers Wilhelm Beer and Johann Heinrich Mädler selected a small circular feature as a reference point when they produced the first systematic chart of Mars features in 1830-32. In 1877, their choice was adopted as the prime meridian by the Italian astronomer Giovanni Schiaparelli when he began work on his notable maps of Mars. After the spacecraft Mariner 9 provided extensive imagery of Mars in 1972, a small crater (later called Airy-0), located in the Sinus Meridiani region (Middle Bay or Meridian Bay) along the line of Beer and Mädler, was chosen and accepted worldwide. Map of Quadrangles The following imagemap of the planet Mars is divided into the 30 quadrangles defined by the United States Geological Survey. The quadrangles are numbered with the prefix MC for Mars Chart. North is at the top; 0 meridian is at the far left. The map images were taken by the Mars Global Surveyor.
- 9. 9 Interior of Mars The interior of Mars is poorly known. Planetary scientists have yet to conduct a successful seismic experiment via spacecraft that would provide direct information on internal structure and so must rely on indirect inferences. Though it is widely accepted that Mars is well differentiated similar to other terrestrial planets. Thus it has an interior differentiated into an outer crust, middle mantle and inner core. However, missions to explore Mars have only been successful in understanding its crust. The interior of the Red planet still remains unknown, but many theories about its origin, structure and composition have been postulated by planetary and geoscientists. The moment of inertia of Mars indicates that it has a central core with a radius of about 900–2000 km. Isotopic data from meteorites determined to have come from Mars demonstrate unequivocally that the planet differentiated—separated into a metal-rich core and rocky mantle—at the end of the planetary accretion period 4.5 billion years ago. The planet has no detectable magnetic field that would indicate convection in the core today. Large regions of magnetized rock have been detected in the oldest terrains, however, which suggests that very early Mars did have a magnetic field but that it disappeared as the planet cooled and the core solidified. Martian meteorites also suggest that the core may be more sulfur-rich than Earth’s core and the mantle more iron-rich. The Martian core is probably made of a mixture of iron, sulfur and maybe oxygen. Like Earth, the mantle of Mars is probably made of silicates; however, it's much smaller, at 1,300 to 1,800 kilometers thick. The mantle is thought to be more iron rich than the Earth’s mantle. There must have been convection currents active in the mantle at one time. These currents would account for the formation of the crustal upwarps or bulges, such as the Tharsis region, the Martian volcanoes and the fractures that formed Valles Marineris. On Mars, the crust is also thin, but isn't broken into plates like the Earth's crust. Although we do not know of currently active volcanoes or Mars-quakes, evidence of quakes occurring as recently as a few million years ago suggest they are possible. The average thickness of Martian crust is thought to be around 100 km, which is pretty much thicker than that of the Earth. The future space probes and landers planned to Mars will be carrying high-tech seismometers and other geophysical instruments which will help improve our understanding of the Martian interior.
- 10. 10 Composition of Mars Mars is a terrestrial planet, which means that its bulk composition, like Earth's, consists of silicates, metals and other elements that typically make up a rock. Also like Earth, Mars is a differentiated planet, meaning that it has a central core made up of metallic iron and nickel surrounded by a less dense, silicate mantle and crust. The planet's distinctive red color is due to the oxidation of iron on its surface. Much of what we know about the elemental composition of Mars comes from orbiting spacecraft and landers. Most of these spacecraft carry spectrometers and other instruments to measure the surface composition of Mars by either remote sensing from orbit or in situ analyses on the surface. We also have many actual samples of Mars in the form of meteorites that have made their way to Earth. Elemental Composition Based on various data sources, scientists think that the most abundant chemical elements in the Martian crust, besides silicon and oxygen, are iron, magnesium, aluminum, calcium, and potassium. These elements are major components of the minerals comprising igneous rocks. The elements titanium, chromium, manganese, sulfur, phosphorus, sodium, and chlorine are less abundant but are still important components of many accessory minerals in rocks and of secondary minerals in the dust and soils (or regolith). Hydrogen is present as water (H2O) ice and in hydrated minerals. Carbon occurs as carbon dioxide (CO2) in the atmosphere and as dry ice at the poles. An unknown amount of carbon is also stored in carbonates. Molecular nitrogen (N2) makes up 2.7 percent of the atmosphere. As far as we know, organic compounds are absent except for a trace of methane detected in the atmosphere. The exact percentage of elemental composition of either Martian surface (crust) or the interior is unavailable and studies are ongoing on the chemistry by the rovers. The elemental composition of Mars is different from Earth’s in several significant ways. First, Martian meteorite analysis suggests that the planet's mantle is about twice as rich in iron as the Earth's mantle. Second, its core is more rich in sulfur. Third, the Martian mantle is richer in potassium and phosphorus than Earth's, and fourth, the Martian crust contains a higher percentage of volatile elements such as sulfur and chlorine than the Earth's crust does. Many of these conclusions are supported by in situ analyses of rocks and soils on the Martian surface. Primary Rocks and Minerals Mars is fundamentally an igneous planet. Rocks on the surface and in the crust consist predominantly of pyrogenetic minerals. Most of our current knowledge about the mineral composition of Mars comes from spectroscopic data from orbiting spacecraft, in situ analyses of rocks and soils from six landing sites, and study of the Martian meteorites. Spectrometers currently in orbit include THEMIS (Mars Odyssey), OMEGA (Mars Express), and CRISM (Mars Reconnaissance Orbiter). The two Mars exploration rovers each carry an Alpha Particle X-ray Spectrometer (APXS), a thermal emission spectrometer (Mini-TES), and Mössbauer spectrometer to identify minerals on the surface.
- 11. 11 On October 17, 2012, the Curiosity rover on the planet Mars performed the first X-ray diffraction analysis of Martian soil. The results from the rover's CheMin analyzer revealed the presence of several minerals, including feldspars, pyroxenes and olivine, and suggested that the Martian soil in the sample was similar to the weathered basaltic soils of Hawaiian volcanoes. The dark areas of Mars are characterized by the mafic rock-forming minerals olivine, pyroxene, and plagioclase feldspar. Olivine occurs all over the planet, but some of the largest concentrations are in Nili Fossae, an area containing Noachian-aged rocks (equivalent of Earth’s Haedean-Archaen Eons-about 3 to 4 billion years old). Another large olivine-rich outcrop is in Ganges Chasma, an eastern side chasm of Valles Marineris. Olivine is unstable at surface pressure-temperature conditions, hence it weathers rapidly into chloritic and clay minerals in the presence of liquid water. Therefore, areas with large outcroppings of olivine-bearing rock indicate that liquid water has not been abundant since the rocks formed. Pyroxene minerals are also widespread across the surface. Both low-calcium i.e. ortho and high-calcium i.e. clino-pyroxenes are present, with the high-calcium varieties associated with younger volcanic shields and the low- calcium forms (enstatite-ferrosilite) more common in the old highland terrain. Because enstatite melts at a higher temperature than its high-calcium cousin diopside, some researchers have argued that its presence in the highlands indicates that older magmas on Mars had higher temperatures than younger ones. Between 1997 and 2006, the Thermal Emission Spectrometer (TES) on the Mars Global Surveyor (MGS) spacecraft mapped the global mineral composition of the planet. TES identified two global-scale volcanic units on Mars. Type 1 characterizes the Noachian-aged highlands and consists of unaltered plagioclase and clino-pyroxene- rich basalts. Type 2 is common in the younger plains north of the dichotomy boundary and is more silica rich than the other type. The lavas of Type 2 have been interpreted as andesites or basaltic andesites, indicating the lavas in the northern plains originated from more chemically evolved, volatile-rich magmas. However, other researchers have suggested that Type 2 represents First X-ray diffraction view of Martian rock. Analysis revealed feldspar, pyroxenes & olivine. Mars Odyssey THEMIS false-color image of olivine basalts in the Valles Marineris. Layers rich in olivine appear purple Sojourner rover analyzing the rock Yogi, photographed by camera on the Pathfinder lander
- 12. 12 weathered basalts with thin coatings of silica glass or other secondary minerals that formed through interaction with water- or ice-bearing materials. True intermediate and felsic rocks are present on Mars, but exposures are uncommon. Both TES and the Thermal Emission Imaging System (THEMIS) on the Mars Odyssey spacecraft have identified high silica rocks in Syrtis Major and near the southwestern rim of the Antoniadi crater. The rocks have spectra resembling quartz- rich dacites and granitic rocks, suggesting that at least some parts of the Martian crust may have a diversity of igneous rocks similar to Earth's. Some geophysical evidence suggests that the bulk of the Martian crust may actually consist of basaltic andesites or andesites. The andesitic crust is hidden by overlying basaltic lavas that dominate the surface composition, but is volumetrically minor. Rocks studied by Spirit Rover in Gusev crater can be classified in different ways. The amounts and types of minerals make the rocks primitive basalts—also called picritic basalts. The rocks are similar to ancient terrestrial rocks called basaltic komatiites. Rocks of the plains also resemble the basaltic shergottites, meteorites which came from Mars. In the journal Science from September 2013, researchers described a different type of rock called Jake M, as it was the first rock analyzed by the Alpha Particle X-ray Spectrometer instrument on the Curiosity rover, and it was different from other known Martian igneous rocks as it is alkaline (>15% nepheline) and relatively fractionated. This rock is similar to oligoclase-bearing basalts which are typically found at ocean islands and continental rifts. Its discovery may mean that alkaline magmas may be more common on Mars than on Earth and that Curiosity could encounter even more fractionated alkaline rocks (for example, phonolites and trachytes). Using Curiosity rover’s Sample Analysis at Mars (SAM) mass spectrometer, scientists measured isotopes of helium, neon, and argon that cosmic rays produce as they go through rock. The fewer of these isotopes they find, the more recently the rock has been exposed near the surface. The 4-billion-year-old lakebed rock drilled by Curiosity was uncovered between 30 million and 110 million years ago by winds which sandblasted away 2 meters of overlying rock. Secondary Minerals Minerals produced through hydrothermal alteration and weathering of primary basaltic minerals are also present on Mars. Secondary minerals include hematite, phyllosilicates like clay minerals, goethite, jarosite (a hydrous sulphate of K and Fe3+), iron sulfate minerals, opaline silica and gypsum. Many of these secondary minerals require liquid water to form. Opaline silica and iron sulphate minerals form in acidic (low pH) water. Sulphates have been found in a variety of locations, including near Juventae Chasma, Ius Chasma, Melas Chasma, Candor Chasma and Ganges Chasma. These sites all contain fluvial landforms indicating that abundant water was once present. Spirit rover has discovered sulfates and goethite in the Columbia Hills. On March 18, 2013, NASA reported evidence from instruments on the Curiosity rover of hydrated minerals, likely hydrated calcium sulfate i.e. Gypsum, in several rock samples as well as in veins and nodules in other rocks. Analysis using the rover's instruments provided evidence of subsurface water, amounting to as much as 4% water content, down to a depth of 60 cm.
- 13. 13 Some of the mineral classes detected may have formed in environments suitable (i.e. enough water and the proper pH) for life. The mineral smectite (a type of clay mineral) forms in near-neutral waters. Phyllosilicates and carbonates are good for preserving organic matter, so they may contain evidence of past life. Sulfate deposits preserve fossils and fossils of microorganisms form in iron oxides like hematite. The presence of opaline silica points toward a hydrothermal environment that could support life. Silica is also excellent for preserving evidence of microbes. The most conspicuous of all secondary minerals found on Mars are the hematite spherules (informally known as blueberries). These are abundant spherical hematite inclusions discovered by the Mars rover Opportunity at Meridiani Planum. They are found in situ embedded in a sulfate salt evaporite matrix, and also loose on the surface. The shapes by themselves don't reveal the particles' origin with certainty. Not only are there spherules on the surface but they are also found deeper in the Martian soil. Sedimentary Rocks Layered sedimentary deposits are widespread on Mars. These deposits probably consist of both- lithified sediments and semi- or unconsolidated sediments. Thick sedimentary deposits occur in the interior of several canyons in Valles Marineris, within large craters in Arabia and Meridiani Planum and probably comprise much of the deposits in the northern lowlands. The Mars Exploration Rover Opportunity landed in an area containing cross-bedded (mainly eolian) sandstones (see picture on next page). Fluvial-deltaic deposits are present in Eberswalde Crater and elsewhere, and photo- geologic evidence suggests that many craters and low lying inter-crater areas in the southern highlands contain Noachian-aged lake sediments. While the possibility of carbonates on Mars has been of great interest to exobiologists and geochemists alike, there was little evidence for significant quantities of carbonate deposits on the surface. In the summer of 2008, the Phoenix Mars lander found between 3–5 % by weight calcite (CaCO3) and an alkaline soil. In 2010, analyses by the Mars Exploration Rover Spirit identified outcrops rich in magnesium-iron carbonate (16–34 wt%) in the Columbia Hills of Gusev crater. The magnesium-iron carbonate (magnesite-siderite) most likely precipitated from carbonate-bearing solutions under hydrothermal Cross-bedded sandstones inside Victoria Crater Conglomerate as seen by Curiosity rover Hematite spherules Cross bedded sandstone in Victoria crater
- 14. 14 conditions at near-neutral pH in association with volcanic activity during the Noachian Period. Carbonates (calcium or iron carbonates) were discovered in a crater on the rim of Huygens Crater, located in the Iapygia quadrangle. The impact on the rim exposed material that had been dug up from the impact that created Huygens crater. These minerals represent evidence that Mars once was had a thicker carbon dioxide atmosphere with abundant moisture. These kind of carbonates only get deposited in marine environments. They were found with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter. Earlier, the instrument had detected clay minerals. The carbonates were found near the clay minerals. Both of these minerals form in wet environments. It is supposed that billions of years ago Mars was much warmer and wetter. At that time, carbonates would have formed from water and the carbon dioxide-rich atmosphere. Later the deposits of carbonate would have been buried. The double impact has now exposed the minerals. Earth has vast carbonate deposits in the form of limestone. Dust and Soil Much of the Martian surface is deeply covered by dust as fine as talcum powder i.e. clay sized. The global predominance of dust obscures the underlying bedrock, making spectroscopic identification of primary minerals impossible from orbit over many areas of the planet. The red/orange appearance of the dust is caused by ferric oxide and the ferric hydroxide mineral- goethite. The Mars Exploration Rovers identified magnetite as the mineral responsible for making the dust magnetic. It probably also contains some titanium. The global dust cover and the presence of other wind-blown sediments has made soil compositions remarkably uniform across the Martian surface. Analysis of soil samples from the Viking landers in 1976, Pathfinder, and the Mars Exploration rovers show nearly identical mineral compositions from widely separated locations around the planet. The soils also consist of finely broken up basaltic rock fragments. Meteorites found on Mars The rovers operating on the Martian surface came across many meteorites. Opportunity rover encountered the most meteorites. The rover found meteorites just sitting on plains near its landing site. The first one analyzed with Opportunity's instruments was called Heat-shield Rock, as it was found near where Opportunity's heat shield landed. Examination with the Miniature Thermal Emission Spectrometer (Mini-TES) and Mossbauer spectrometer lead to its classification as an IAB meteorite. It was determined that it was composed of 93% iron and 7% nickel. Some other meteorites examined were stony, stony-iron and iron meteorites. It is Composition of Martian soil as analyzed by the rovers
- 15. 15 estimated that Mars will have a lot more meteorites preserved than the Earth because of the very less active geological processes. Martian Meteorites Martian meteorites refer to the meteorites found on the Earth which were ejected from Mars as asteroid or comets made impact on its surface and eventually landed on Earth. Of over 61,000 meteorites that have been found on Earth, 132 were identified as Martian as of March 2014. Martian meteorites should not be confused with meteorites found on Mars. These meteorites are thought to be from Mars because they have elemental and isotopic compositions that are similar to rocks and atmosphere gases analyzed by spacecraft on Mars. Martian meteorites are divided into three rare groups of achondritic (stony) meteorites: shergottites, nakhlites and chassignites. Consequently, Martian meteorites as a whole are sometimes referred to as the SNC group. They have isotope ratios that are said to be consistent with each other and inconsistent with the Earth. (a) Sherghottites: Roughly three-quarters of all Martian meteorites can be classified as shergottites. They are igneous rocks of mafic to ultramafic lithology. They fall into three main groups- the basaltic, olivine-phyric and lherzolitic shergottites, based on their crystal size and mineral content. The shergottites appear to have crystallised as recently as 180 million years ago, which is a surprisingly young age considering how ancient the majority of the surface of Mars appears to be, and the small size of Mars itself. Because of this, some have advocated the idea that the shergottites are much older than this. This "Shergottite Age Paradox" remains unsolved and is still an area of active research and debate. (b) Nakhlites: They are igneous rocks that are rich in augite and were formed from basaltic magma about 1.3 billion years ago. They contain augite and olivine crystals. Their crystallization ages, compared to a crater count chronology of different regions on Mars, suggest the nakhlites formed on the large volcanic construct of either Tharsis, Elysium, or Syrtis Major Planum. It has been shown that the nakhlites were suffused with liquid water around 620 million years ago and that they were ejected from Mars around 10.75 million years ago by an asteroid impact. They fell to Earth within the last 10,000 years. (c) Chassignites: These are the rarest of all Martian meteorites, only two known specimens have been yet found. Their composition is almost entirely olivine i.e. of the monomineralic rock dunite with small traces of feldspars and some oxides. A Sherghottite meteorite
- 16. 16 Global Physiography Most of our current knowledge about the geology of Mars comes from studying landforms and relief features seen in images taken by orbiting spacecrafts. Mars has a number of distinct, large-scale surface features that indicate the types of geological processes that have operated on the planet over time. This section introduces several of the larger physiographic regions of Mars. Together, these regions illustrate how geologic processes involving volcanism, tectonism, water, ice and impacts have shaped the planet on a global scale. Hemispheric Dichotomy The northern and southern hemispheres of Mars are strikingly different from each other in topography and physiography. This dichotomy is a fundamental global geologic feature of the planet. Simply stated, the northern part of the planet is an enormous topographic depression. About one-third of the planet’s surface (mostly in the northern hemisphere) lies 3–6 km lower in elevation than the southern two-thirds. This is a first- order relief feature similar to the elevation difference between Earth’s continents and ocean basins. The hemisphere south of the dichotomy boundary (often called the southern highlands or uplands) is very heavily cratered and ancient, characterized by rugged surfaces that date back to the period of heavy bombardment. In contrast, the lowlands north of the dichotomy boundary have few large craters, are very smooth and flat, and have other features indicating that extensive resurfacing has occurred since the southern highlands formed. The other distinction between the two hemispheres is in their crustal thickness. Topographic and geophysical gravity data indicate that the crust in the southern highlands has a maximum thickness of about 58 km (36 mi), while crust in the northern lowlands peaks at around 32 km (20 mi) in thickness. The location of the dichotomy boundary varies in latitude across. The origin and age of the hemispheric dichotomy are still debated. Hypotheses of origin generally fall into two categories: one, the dichotomy was produced by a mega-impact event or several large impacts early in the planet’s history (exogenic theories) or two, the dichotomy was produced by crustal thinning in the northern hemisphere by mantle convection or other chemical and thermal processes in the planet’s interior (endogenic theories). One endogenic model proposes an early episode of plate tectonics producing a thinner crust in the Mars Orbital Laser Altimeter (MOLA) colorized shaded-relief maps showing elevations in the western and eastern hemispheres of Mars. (Left): The western hemisphere is dominated by the Tharsis region (red and brown). Tall volcanoes appear white. Valles Marineris (blue) is the long gash-like feature to the right. (Right): Eastern hemisphere shows the cratered highlands (yellow to red) with the Hellas basin (deep blue/purple) at lower left. The Elysium province is at the upper right edge. Areas north of the dichotomy boundary appear as shades of blue on both maps. The hemispheric dichotomy is clearly visible here.
- 17. 17 north, similar to what is occurring at spreading plate boundaries on Earth. Whatever its origin, the Martian dichotomy appears to be extremely old. 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 impact craters from the period of heavy bombardment that are now covered by a veneer of younger deposits. Crater counting studies of QCDs suggest that the underlying surface in the northern hemisphere is at least as old as the oldest exposed crust in the southern highlands. The ancient age of the dichotomy places a significant constraint on theories of its origin. The topographic map of Mars given on the previous page shows the hemispheric dichotomy clearly. Crustal Bulges and Volcanic Provinces Straddling the dichotomy boundary in Mars’ western hemisphere is a massive volcano-tectonic province known as the Tharsis region or the Tharsis bulge. This immense, elevated structure is thousands of kilometers in diameter and covers up to 25% of the planet’s surface. Averaging 7–10 km above datum (Martian "sea" level), Tharsis contains the highest elevations on the planet and the largest known volcanoes in the Solar System. Three enormous volcanoes, Ascraeus Mons, Pavonis Mons, and Arsia Mons (collectively known as the Tharsis Montes), sit aligned NE-SW along the crest of the buldge. The vast Alba Mons (formerly Alba Patera) occupies the northern part of the region. The huge shield volcano Olympus Mons lies off the main buldge, at the western edge of the province. The extreme massiveness of Tharsis has placed tremendous stresses on the planet’s lithosphere. As a result, immense extensional fractures (grabens and rift valleys) radiate outward from Tharsis, extending halfway around the planet. A smaller volcanic center lies several thousand kilometers west of Tharsis in Elysium. The Elysium volcanic complex is about 2,000 kilometers in diameter and consists of three main volcanoes, Elysium Mons, Hecates Tholus, and Albor Tholus. The Elysium group of volcanoes is thought to be somewhat different from the Tharsis Montes, in that development of the former involved both lavas and pyroclastics. Large Impact Basins Several enormous, circular impact basins are present on Mars. The largest one that is readily visible is the Hellas basin located in the southern hemisphere, it is the second largest confirmed The Tharsis bulge, showing the Tharsis Montes (right) along their NE-SW axis and the giant Olympus Mons (upper left corner) The Hellas basin
- 18. 18 impact structure on the planet, centered at about 64°E longitude and 40°S latitude. The central part of the basin (Hellas Planitia) is 1,800 km in diameter and surrounded by a broad, heavily eroded annular rim structure characterized by closely spaced rugged irregular mountains, which probably represent uplifted, jostled blocks of old pre-basin crust. Ancient, low-relief volcanic constructs are located on the northeastern and southwestern portions of the rim. 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 Isidis basin (roughly 1,000 km in diameter) lies on the dichotomy boundary at about 87°E longitude. The northeastern portion of the basin rim has been eroded and is now buried by northern plains deposits, giving the basin a semicircular outline. One additional large basin, Utopia, is completely buried by northern plains deposits. Its outline is clearly discernable only from altimetry data. All of the large basins on Mars are extremely old, dating back to the late heavy bombardment. Equatorial Canyon Systems Near the equator in the western hemisphere lies an immense system of deep, interconnected canyons and troughs collectively known as the Valles Marineris. The canyon system extends eastward from Tharsis for a length of over 4,000 km, nearly a quarter of the planet’s circumference. If placed on Earth, Valles Marineris would span the width of North America. In places, the canyons are up to 300 km wide and 10 km deep. Often compared to Earth’s Grand Canyon, the Valles Marineris has a very different origin than its tinier, so-called counterpart on Earth. The Grand Canyon is largely a product of water erosion, while the Martian equatorial canyons were of tectonic origin, i.e. they were formed mostly by faulting. They could be similar to the East African Rift valleys. The canyons represent the surface expression of powerful extensional strain in the Martian crust, probably due to loading from the Tharsis bulge. Chaos Terrain Chaos terrain on Mars is distinctive; nothing on Earth compares to it. Chaos terrain generally consists of irregular groups of large blocks, some tens of km across and a hundred or more meters high. The tilted and flat topped blocks form depressions hundreds of meters deep. A chaotic region can be recognized by mesas, buttes and hills, chopped through with valleys which in places look almost patterned. Chaos terrain is presumably formed by sudden melting of subterranean ice in the form of huge discharge of water. Some parts of this chaotic area have not collapsed completely—they are still formed into large mesas, so they may still contain water ice. The Hydraotes Chaos terrain (420 km across) in the Oxia Palus quadrangle
- 19. 19 Polar Ice Caps The polar ice caps are well-known telescopic features of Mars, first identified by Christian 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 (CO2) ice that condenses out of the atmosphere as temperatures fall to 148 K, the frost point of CO2, during the polar wintertime. In the north, the CO2 ice completely dissipates (sublimes) in summer, leaving behind a residual cap of water (H2O) ice. At the south pole, a small residual cap of CO2 ice remains in summer. Both residual ice caps overlie thick layered deposits of interbedded ice and dust. In the north, the layered deposits form a 3 km-high, 1,000 km-diameter plateau called Planum Boreum. A similar kilometers-thick plateau, Planum Australe, lies in the south. Both plana (the Latin plural of planum) are sometimes treated to be synonymous with the "polar ice caps", but the permanent ice (seen as the high albedo, white surfaces in images) forms only a relatively thin cover on top of the layered deposits. The layered deposits probably represent alternating cycles of dust and ice deposition caused by climate changes related to variations in the planet's orbital parameters over time. The polar layered deposits are some of the youngest geologic units on Mars. Planum Boreum or the Northern Polar Ice Cap on Mars
- 20. 20 Common Landforms on Mars The following landforms are very commonly seen on the Martian surface. Some of them are tectonic in origin, some sedimentary while some are volcanic in origin. Major landforms observed are volcanoes, many types of impact craters, valleys and canyons, gulies, fans, lava flows, mesas and buttes, chaos terrain, dunes, etc. Volcanoes Mars is only about one-half the size of Earth and yet has several volcanoes that surpass the scale of the largest terrestrial volcanoes. The most massive volcanoes are located on huge uplifts or domes in the Tharsis and Elysium regions of Mars. Located on the northwest flank of Tharsis bulge are three large shield volcanoes: Ascraeus Mons, Pavonis Mons and Arsia Mons. Beyond the dome's northwest edge is Olympus Mons, the largest of the Tharsis volcanoes. Olympus Mons is classified as a shield volcano. It is 24 km high, 550 km in diameter and is rimmed by a 6 km high scarp. It is one of the largest volcanoes in the Solar System. By comparison the largest volcano on Earth is Mauna Loa which is 9 km high and 120 km across. Elysium Planitia has smaller volcanoes than the Tharsis region, but a more diverse volcanic history. The three volcanoes include Hecates Tholus, Elysium Mons and Albor Tholus. The large shield volcanoes on Mars resemble Hawaiian shield volcanoes. They both have effusive eruptions which are relatively quiet and basaltic in nature. Both have summit pits or calderas and long lava flows or channels. The biggest difference between Martian and Terrestrial volcanoes is size. The volcanoes in the Tharsis region are 10 to 100 times larger than those on Earth. They were built from large magma chambers deep within the Martian crust. The Martian flows are also much longer. This is probably due to larger eruption rates and to lower gravity. One of the reasons volcanoes of such magnitude were able to form on Mars is because the hot volcanic regions in the mantle remained fixed relative to the surface for hundreds of millions of years. On Earth, the tectonic flow of the crust across the hot volcanic regions prevent large volcanoes from forming. These volcanoes have a relatively short life time. As the plate moves new volcanoes form and the old ones become silent. Not all Martian volcanoes are classified as shields with effusive eruption styles. North of the Tharsis region lies Alba Patera. This volcano is comparable to Olympus Mons in its horizontal extent but not in height. Its base diameter is 1,500 km but is less than 7 km high. Ceraunius Tholus is one of the smaller volcanoes. It is about the size of the Big Island of Hawaii. It exhibits explosive eruption characteristics and probably consists of ash deposits. Tyrrhena Patera and Hadriaca Patera both have deeply eroded features which indicate explosive ash eruptions. Olympus Mons volcano, showing its peripheral scarp and the summit shows many over-lapping calderas
- 21. 21 Lava Flows and Volcanic Plains Volcanic plains are widespread on Mars. Two types of plains are commonly recognized: those where lava flow features are common, and those where flow features are generally absent but a volcanic origin is inferred by other characteristics. Plains with abundant lava flow features occur in and around the large volcanic provinces of Tharsis and Elysium. Flow features include both sheet flow and tube- and channel-fed flow morphologies. Sheet flows show complex, overlapping flow lobes and may extend for many hundreds of kilometers from their source areas. Lava flows can form a lava tube when the exposed upper layers of lava cool and solidify to form a roof while the lava underneath continues flowing. Often, when all the remaining lava leaves the tube, the roof collapses to make a channel or line of pit craters. An unusual type of flow feature occurs in the Cerberus plains south of Elysium and in Amazonis. These flows have a broken platey texture, consisting of dark, kilometer-scale slabs embedded in a light- toned matrix. They have been attributed to rafted slabs of solidified lava floating on a still-molten subsurface. Others have claimed the broken slabs represent pack ice that froze over a sea that pooled in the area after massive releases of groundwater from the Cerberus Fossae area. The second type of volcanic plains (ridged plains) are characterized by abundant wrinkle ridges. Volcanic flow features are rare or absent. The ridged plains are believed to be regions of extensive flood basalts, by analogy with the lunar maria. Ridged plains make up about 30% of the Martian surface and are most prominent in Lunae, Hesperia, and Malea Plana, as well as throughout much of the northern lowlands. Ridged plains are all Hesperian in age and represent a style of volcanism globally predominant during that time period. The Hesperian Period is named after the ridged plains in Hesperia Planum. Lava flows seen on the western flank of Olympus Mons Two overlapping lava flows towards west of Olympus Mons showing wrinkled ridges; the flow on the right is younger
- 22. 22 Gullies Gullies are small, incised networks of narrow channels and their associated downslope sediment deposits, found on Mars. They are named for their resemblance to terrestrial gullies. First discovered on images from Mars Global Surveyor, they occur on steep slopes, especially on the walls of craters. Usually, each gully has a dendritic alcove at its head, a fan-shaped apron at its base, and a single thread of incised channel linking the two, giving the whole gully an hourglass shape. They are believed to be relatively young because they have few, if any craters. A subclass of gullies is also found cut into the faces of sand dunes, that are themselves considered to be quite young. Most gullies occur 30 degrees poleward in each hemisphere, with greater numbers in the southern hemisphere. Some studies have found that gullies occur on slopes that face all directions; others have found that the greater number of gullies are found on poleward facing slopes, especially from 30-44 S. Although thousands have been found, they appear to be restricted to only certain areas of the planet. In the northern hemisphere, they have been found in Arcadia Planitia, Tempe Terra, Acidalia Planitia, and Utopia Planitia. In the south, high concentrations are found on the northern edge of Argyre basin, in northern Noachis Terra, and along the walls of the Hellas outflow channels. On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers believe that the processes carving the gullies involve liquid water. However, this remains a topic of active research. Because the gullies are so young, this would suggest that liquid water has been present on Mars in its very recent geological past, with consequences for the potential habitability of the modern surface. In 2014, NASA reported that gullies on the surface of Mars were mostly formed by the seasonal freezing of carbon dioxide, and not by that of liquid water as considered earlier. Fans and Cones The role of liquid water on Mars has been a topic of much debate and interest since Mariner 9 returned images of the surface showing channels resembling terrestrial fluvial channels. Alluvial fans identified on Mars are one of the more definitive evidences for liquid water flowing on the Martian surface and preserve Gullies on the rim of the Newton Crater
- 23. 23 information about the hydrologic conditions at the time of their formation. These fans are found in three clusters located in Margaritifer Terra, Terra Sabaea, and Tyrrhena Terra. The fans are located in craters dated to the Noachian period and the fans themselves are dated to the Noachian-Hesperian boundary. A theoretical relationship between the slope of alluvial fans and the water to sediment discharge ratio tested against laboratory and field data under terrestrial conditions is utilized to determine overland runoff volumes and minimum flow durations required for the formation of large alluvial fans on Mars. These volumes were calculated for both gravel and sand fans forming by either expanding sheet-floods or channelized flow. Where possible, bankfull water discharge at the apex of fans was determined from the width of feeder channels. The large volumes of water required to form the fans and the large discharge at the apex of the fan suggest that groundwater would not be an adequate source for water to form these alluvial fans. Valley Networks and Outflow Channels Valley networks are branching networks of valleys on Mars that superficially resemble terrestrial river drainage basins. They are found mainly incised into the terrain of the Martian southern highlands, and are typically - though not always - of Noachian age (approximately four billion years old). The individual valleys are typically less than 5 kilometers wide, though they may extend for up to hundreds or even thousands of kilometers across the Martian surface. The form, distribution, and implied evolution of the valley networks are of great importance for what they may tell us about the history of liquid water on the Martian surface, and hence Mars' climate history. Some authors have argued that the properties of the networks demand that a A fan (right) and cones (left) on the rim of the Gusev crater A valley network on Mars showing dendritic pattern
- 24. 24 hydrological cycle must have been active on ancient Mars, though this remains contentious. Objections chiefly arise from repeated results from models of Martian paleoclimate suggesting high enough temperatures and pressures to sustain liquid water on the surface have not ever been possible on Mars. The advent of very high resolution images of the surface from the HiRISE, THEMIS and CTX satellite cameras as well as the Mars Orbital Laser Altimeter (MOLA) digital terrain models have drastically improved our understanding of the networks in the last decade. Outflow channels are extremely long, wide swathes of scoured ground on Mars, commonly containing the streamlined remnants of pre-existing topography and other linear erosive features indicating sculpting by fluids moving downslope. Channels extend many hundreds of kilometers in length and are typically greater than one kilometer in width; the largest valley (Kasei Vallis) is around 3,500 km (2,200 mi) long, greater than 400 km (250 mi) wide and exceeds 2.5 km (1.6 mi) in depth cut into the surrounding plains. These features tend to appear fully sized at fractures in the Martian surface, either from chaos terrains or from canyon systems or other tectonically controlled, deep graben, though there are exceptions. Besides their exceptional size, the channels are also characterized by low sinusitis and high width: depth ratios compared both to other Martian valley features and to terrestrial river channels. Crater counts indicate that most of the channels were cut since the early Hesperian age, though the age of the features is variable between different regions of Mars. Some outflow channels in the Amazonis and Elysium Planitiae regions have yielded ages of only tens of million years, extremely young by the standards of Martian topographic features. On the basis of their geomorphology, locations and sources, the channels are today generally thought to have been carved by outburst floods (huge, rare, episodic floods of liquid water), although some authors still make the case for formation by the action of glaciers, lava, or debris flows. Calculations indicate that the volumes of water required to cut such channels at least equal and most likely exceed by several orders of magnitude the present discharges of the largest terrestrial rivers, and are probably comparable to the largest floods known to have ever occurred on Earth. Such exceptional flow rates and the View of the massive Ares Vallis showing the huge outflow channels which are emerging from the chaotic terrains The erosional, streamlined features in Ares Vallis
- 25. 25 implied associated volumes of water released could not be sourced by precipitation but rather demand the release of water from some long-term store, probably a subsurface aquifer sealed by ice and subsequently breached by meteorite impact or igneous activity. The outflow channels contrast with the Martian valley networks, which much more closely resemble the dendritic planform more typical of terrestrial river drainage basins. Outflow channels tend to be named after the names for Mars in various ancient world languages, or more rarely for major terrestrial rivers. These outflow channels often show erosional features such as streamlined island like landmasses. Mesas and Buttes Though not very common, mesa and butte like erosional landforms are seen on Mars by the orbiting spacecrafts. Such landmasses can be found in the huge outflow channels and chaotic terrains. They are thought to have formed in similar fashion as their terrestrial siblings. The huge outbursts of floods which carved the outflow channels shaped them as they stood out beacause of their resistivity towards erosion. In chaos terrains, they are thought to be remnant ground-ice-sheets, yet to be melted. Dunes Many locations on Mars have sand dunes. A sand sea, made up of aeolian dune fields referred to as the Circumpolar Dune Field surrounds most of the north polar cap. The dunes are covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. Many Martian dunes strongly resemble terrestrial dunes but images acquired by the High-Resolution Imaging Science Experiment on the Mars Reconnaissance Orbiter have shown that Martian dunes in the north polar region are subject to modification via grainflow triggered by seasonal CO2 sublimation, a process not seen on Earth. Many dunes are black because they are derived from the dark volcanic rock basalt. Extraterrestrial sand seas such as those found on Mars are referred to as "undae" from the Latin for waves. Mesas and buttes on Mars Longitudinal dunes in Noachis region (left) and Barchan dunes in Hellespontus region (right) as seen by HiRISE onboard MRO
- 26. 26 Impact Craters An impact crater is an approximately circular depression in the surface formed by the hypervelocity impact of a smaller body with the surface. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters typically have raised rims and floors that are lower in elevation than the surrounding terrain. Impact craters range from small, simple, bowl-shaped depressions to large, complex, multi-ringed impact basins. Impact craters are the dominant geographic features on Mars. The cratering on very old surfaces on Mars, witness a period of intense early bombardment in the inner Solar System around 3.9 billion years ago. Mars is host to a wide variety of impact craters from few meters to few thousand kilometers in diameter. The largest known impact crater on Mars is the Hellas planitia which is about 2000 km in diameter and about 7 km deep. Some of the oldest known impact craters on Mars are nearly 4 billion years old. The lack of active geology on Mars leads to the preservation of these craters, unlike those on the Earth. Although some craters in northern planes on Mars are found to be buried underneath a veneer of fine wind blown sediments while some are featuring gullies. Gale crater with its central peak- Aeolis Mons, ellipse in the upper left part of the crater shows landing site of the Curiosity rover Various types of impact craters on Mars, rampart crater (left) showing its ejecta blanket around it & gullies on the rim, crater with remnant water ice in central depression (centre) and a crater with concentric ridges (right)
- 27. 27 Geological History Much of a planet's history can be deciphered by looking at its surface and asking what came first and what came next. For example, a lava flow that spreads out and fills a large impact crater is clearly younger than the crater, and a small crater on top of the same lava flow is younger than both the lava and the larger crater. This principle, called the law of superposition, and other principles of stratigraphy, first formulated by Nicholas Steno in the 17th century. The same principles are use for Mars. Another stratigraphic principle used on planets where impact craters are well preserved is that of crater number density. The number of craters greater than a given size per unit surface area provide a relative age for that surface. Heavily cratered surfaces are old, and sparsely cratered surfaces are young. Old surfaces have a lot of big craters, and young surfaces have mostly small craters or none at all. These stratigraphic concepts form the basis for the Martian geologic timescale. Absolute and Relative Ages By using stratigraphic principles, rock units' ages can usually only be determined relative to each other. For example, knowing that Mesozoic rock strata making up the Cretaceous System lie on top of (and are therefore younger than) rocks of the Jurassic System reveals nothing about how long ago the Cretaceous or Jurassic Periods were. Other methods, such as radiometric dating, are needed to determine absolute ages in geologic time. Generally, this is only known for rocks on the Earth. Assigning absolute ages to rock units on Mars is much more problematic. Numerous attempts have been made over the years to determine an absolute Martian chronology (timeline) by comparing estimated impact cratering rates for Mars to those on the Moon. If the rate of impact crater formation on Mars by crater size per unit area over geologic time (the production rate or flux) is known with precision, then crater densities also provide a way to determine absolute ages. Unfortunately, practical difficulties in crater counting and uncertainties in estimating the flux still create huge uncertainties in the ages derived from these methods. Martian meteorites have provided datable samples that are consistent with ages calculated thus far, but the locations on Mars from where the meteorites came (provenance) are unknown, limiting their value as chronostratigraphic tools. Absolute ages determined by crater density should therefore be taken with some skepticism. Crater density timescale Studies of impact crater densities on the Martian surface have delineated three broad periods in the planet's geologic history. The periods were named after places on Mars that have large-scale surface features, such as large craters or widespread lava flows, that date back to these time periods. The absolute ages given here are only approximate. From oldest to youngest, the time periods are: Pre-Noachian: It represents the interval from the accretion and differentiation of the planet about 4.5 billion years ago (Gya) to the formation of the Hellas impact basin, between 4.1 and 3.8 Gya. Most of the
- 28. 28 geologic record of this interval has been erased by subsequent erosion and high impact rates. The crustal dichotomy is thought to have formed during this time, along with the Argyre and Isidis basins. Noachian Period (named after Noachis Terra): Formation of the oldest extant surfaces of Mars between 4.1 and about 3.7 billion years ago (Gya). Noachian-aged surfaces are scarred by many large impact craters. The Tharsis bulge is thought to have formed during the Noachian, along with extensive erosion by liquid water producing river valley networks. Large lakes or oceans may have been present. Hesperian Period (named after Hesperia Planum): 3.7 to approximately 3.0 Gya. Marked by the formation of extensive lava plains. The formation of Olympus Mons probably began during this period. Catastrophic releases of water carved extensive outflow channels around Chryse Planitia and elsewhere. Ephemeral lakes or seas formed in the northern lowlands. Amazonian Period (named after Amazonis Planitia): 3.0 Gya to present. Amazonian regions have few meteorite impact craters but are otherwise quite varied. Lava flows, glacial/periglacial activity, and minor releases of liquid water continued during this period. The date of the Hesperian/Amazonian boundary is particularly uncertain and could range anywhere from 3.0 to 1.5 Gya. Basically, the Hesperian is thought of as a transitional period between the end of heavy bombardment and the cold, dry Mars seen today. Mineral alteration timescale In 2006, researchers using data from the OMEGA Visible and Infrared Mineralogical Mapping Spectrometer on board the Mars Express orbiter proposed an alternative Martian timescale based on the predominant type of mineral alteration that occurred on Mars due to different styles of chemical weathering in the planet’s past. They proposed dividing the history of the Mars into three eras: the Phyllocian, Theiikian and Siderikan. Phyllocian (named after phyllosilicate or clay minerals that characterize the era) lasted from the formation of the planet until around the Early Noachian (about 4.0 Gya). OMEGA identified outcropping of phyllosilicates at numerous locations on Mars, all in rocks that were exclusively Pre-Noachian or Noachian in age (most notably in rock exposures in Nili Fossae and Mawrth Vallis). Phyllosillicates require a water-rich, alkaline environment to form. The Phyllocian era correlates with the age of valley network formation on Mars, suggesting an early climate that was conducive to the presence of abundant surface water. It is thought that deposits from this era are the best candidates in which to search for evidence of past life on the planet. Theiikian (named after sulphurous in Greek, for the sulphate minerals that were formed) lasted until about 3.5 Gya. It was an era of extensive volcanism, which released large amounts of sulphur dioxide (SO2) into the atmosphere. The SO2 combined with water to create a sulphuric acid-rich environment that allowed the formation of hydrated sulphates (notably kieserite and gypsum). Martian crater density time-scale, in millions of years
- 29. 29 Siderikan (named for iron in Greek, for the iron oxides that formed) lasted from 3.5 Gya until the present. With the decline of volcanism and available water, the most notable surface weathering process has been the slow oxidation of the iron-rich rocks by atmospheric peroxides producing the red iron oxides that give the planet its familiar colour. Modern Geological Processes Mars, though thought to be geologically inactive, shows some signs of geological processes. Landslides, glacial activities, avalanches and aeolian processes are active today on Mars. Slight changes in local terrain observed in images captured by many spacecrafts are inferred to be results of landslides. Canyons, valleys and crater rims are the most prone areas to landslides, sometimes referred as debris flows. The HiRISE onboard the NASA’s Mars Reconnaissance Orbiter (MRO) captured the adjoining image showing a debris field formed after a landslide took place on the northern slopes in the central region of Valles Marineris. Scientists have observed avalanches also on Mars. Martian polar caps contain a semi-permanent residual cap beneath a surface seasonal cap that waxes and wanes. The residual caps are largely water, but each year as the winter cold deepens the water caps become surfaced with frozen CO2, which was thought to sublime gently in spring. This photograph proved otherwise. The close-ups show two separate CO2/dust avalanches cascading down the side of a single 700-meter scarp. Four different avalanches were observed in the same MRO HiRISE shot; the upper fall is 160 m wide. Analysis suggests the falls originated on the sides of the scarp rather than the top and were triggered by spring sublimation of dry ice. Mars is still a planet of dramatic changes. Martian mineral alteration time-scale, in millions of years A landslide in Valles Marineris Avalanches seen in an MRO HiRISE shot
- 30. 30 Geological Map of Mars
- 31. 31 References http://www.Marspedia.org http://www.solarviews.com/eng/Marsvolc.htm http://nineplanets.org/Mars.html http://spaceref.com/Mars http://csep10.phys.utk.edu/astr161/lect/Mars/Mars.html http://astroengine.com www.google.co.in MRO HiRISE website: http://www.uahirise.org NASA websites: www.nasa.gov science.nasa.gov Mars.nasa.gov http://solarsystem.nasa.gov/planets http://www.jpl.nasa.gov Euripian Space Agency website: http://www.esa.int/ESA Planetary Science and Exploration Program Newsletter (January 2014, Volume 4, Issue 1) Mars Express: The Scientific Investigations (ESA SP-1291, June 2009)