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Mars is the fourth
planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...

planet
from the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
and the second-smallest planet in the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

Solar System
, being larger than only
Mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

Mercury
. In English, Mars carries the name of the Roman god of war and is often referred to as the "Red Planet". The latter refers to the effect of the
iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, ...
prevalent on Mars's surface, which gives it a reddish appearance (as shown), that is distinctive among the astronomical bodies visible to the naked eye. Mars is a
terrestrial planet A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate Rock (geology), rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Su ...
with a thin
atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a planet or other material body, that is held in ...

atmosphere
, with surface features reminiscent of the
impact crater An impact crater is an approximately circular depression (geology), depression in the surface of a planet, natural satellite, moon, or other solid body in the Solar System or elsewhere, formed by the hypervelocity collision, impact of a smaller ...

impact crater
s of the
Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia (continent), Australia), it is the largest natural satellite in the Solar System relative to the size of its plane ...

Moon
, and the valleys, deserts and
polar ice caps A polar ice cap or polar cap is a high-latitude In geography, latitude is a geographic coordinate that specifies the north– south position of a point on the Earth's surface. Latitude is an angle (defined below) which ranges from 0° at ...
of
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
. The days and seasons are comparable to those of Earth, because the
rotation period The rotation period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) is as its ''sidereal period, sidereal rotation period'' i.e. the time that the object takes to complete a single revolution around its axis of rotation rela ...
as well as the tilt of the rotational axis relative to the ecliptic plane are similar. Mars is the site of
Olympus Mons Olympus Mons (; Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in re ...

Olympus Mons
, the largest
volcano A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet a ...

volcano
and highest known mountain on any planet in the Solar System, and of
Valles Marineris Valles Marineris (; Latin for ''Mariner program, Mariner Valleys'', named after the ''Mariner 9'' Mars orbiter of 1971–72 which discovered it) is a system of canyons that runs along the Mars, Martian surface east of the Tharsis region. At more ...
, one of the largest canyons in the Solar System. The smooth Borealis basin in the Northern Hemisphere covers 40% of the planet and may be a giant impact feature. Mars has
two moons Two Moons (1847–1917), or ''Ishaynishus'' (Cheyenne The Cheyenne ( ) are one of the indigenous people of the Great Plains whose language is of the Algonquian language family. The Cheyenne comprise two Native American tribes, the Só'taeo'o ...
, Phobos and Deimos, which are small and irregularly shaped. These may be captured
asteroid An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Historically, these terms have been applied to any astronomical object orbiting the Sun that did not resolve into a disc in a telescope and was not observ ...

asteroid
s, similar to
5261 Eureka 5261 Eureka is the first Mars trojan The Mars trojans are a group of Trojan (celestial body), Trojan objects that share the orbit of the planet Mars around the Sun. They can be found around the two Lagrangian points 60° ahead of and behind Mars ...
, a
Mars trojan The Mars trojans are a group of Trojan (celestial body), Trojan objects that share the orbit of the planet Mars around the Sun. They can be found around the two Lagrangian points 60° ahead of and behind Mars. The origin of the Mars trojans is no ...
. Mars has been explored by several uncrewed spacecraft. ''
Mariner 4 Mariner 4 (together with Mariner 3 known as Mariner-Mars 1964) was the fourth in a series of spacecraft intended for planetary exploration in a flyby mode. It was designed to conduct closeup scientific observations of Mars and to transmit thes ...
'' was the first spacecraft to visit Mars; launched by
NASA The National Aeronautics and Space Administration (NASA; ) is an independent agency A regulatory agency or regulatory authority, is a Public benefit corporation Public-benefit corporation is a term that has different meanings in differen ...

NASA
on 28 November 1964, it made its closest approach to the planet on 15 July 1965. ''Mariner 4'' detected the weak Martian radiation belt, measured at about 0.1% that of Earth, and captured the first images of another planet from deep space. The latest spacecraft to successfully land on Mars are CNSA's ''Tianwen-1'' lander and ''Zhurong'' rover, landed on 14 May 2021. ''Zhurong'' rover was successfully deployed on 22 May 2021, which makes China the second country to successfully deploy a rover on Mars, after the United States. There are investigations assessing the past habitability of Mars, as well as the possibility of extant life. Astrobiology missions are planned, such as the European Space Agency's ''
Rosalind Franklin Rosalind Elsie Franklin (25 July 192016 April 1958) was an English chemist and X-ray crystallographer whose work was central to the understanding of the molecular structures of DNA (deoxyribonucleic acid), RNA (ribonucleic acid), viruses, co ...
'' rover. Liquid cannot exist due to low atmospheric pressure, which is less than 1% of the atmospheric pressure on Earth, except at the lowest elevations for short periods. The two polar ice caps appear to be made largely of water. The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the planetary surface to a depth of . In November 2016, NASA reported finding a large amount of underground ice in the
Utopia Planitia Utopia Planitia (Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 mill ...

Utopia Planitia
region. The volume of water detected has been estimated to be equivalent to the volume of water in
Lake Superior Lake Superior is the largest and northernmost of the Great Lakes of North America, and among freshwater lakes, it is the world's List of lakes by area, largest by surface area and the List of lakes by volume, third-largest by volume.The Caspian ...

Lake Superior
. Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its reaches −2.94, which is surpassed only by
Venus Venus is the second planet from the Sun. It is named after the Venus (mythology), Roman goddess of love and beauty. As List of brightest natural objects in the sky, the brightest natural object in Earth's night sky after the Moon, Venus can ...

Venus
, the Moon and . Optical ground-based telescopes are typically limited to resolving features about across when Earth and Mars are closest because of Earth's atmosphere.


Physical characteristics

Mars is approximately half the diameter of Earth, with a surface area only slightly less than the total area of Earth's dry land. Mars is less dense than Earth, having about 15% of Earth's volume and 11% of Earth's
mass Mass is the quantity Quantity is a property that can exist as a multitude or magnitude, which illustrate discontinuity and continuity. Quantities can be compared in terms of "more", "less", or "equal", or by assigning a numerical value ...
, resulting in about 38% of Earth's surface gravity. The red-orange appearance of the Martian surface is caused by
iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is ...
, or rust. It can look like butterscotch; other common surface colors include golden, brown, tan, and greenish, depending on the
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

mineral
s present.NASA – ''Mars in a Minute: Is Mars Really Red?''Transcript


Internal structure

Like Earth, Mars has differentiated into a dense metallic
core Core or cores may refer to: Science and technology * Core (anatomy) In common parlance, the core of the body is broadly considered to be the torso. Functional movements are highly dependent on this part of the body, and lack of core muscular dev ...
overlaid by less dense materials. Current models of its interior imply a core consisting primarily of iron and nickel with about 16–17%
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
. This
iron(II) sulfide Iron(II) sulfide or ferrous sulfide (Br.E. sulphide) is one of a family chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more th ...
core is thought to be twice as rich in lighter elements as Earth's. The core is surrounded by a silicate
mantle Mantle may refer to: *Mantle (geology) A mantle is a layer inside a planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a n ...
that formed many of the
tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building A mountain is an elevated portion of the Earth's crust, gen ...
and volcanic features on the planet, but it appears to be dormant. Besides silicon and oxygen, the most abundant elements in the Martian crust are
iron Iron () is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

iron
,
magnesium Magnesium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

magnesium
,
aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
,
calcium Calcium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

calcium
, and
potassium Potassium is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, b ...

potassium
. The average thickness of the planet's crust is about , with a maximum thickness of . Meanwhile, Earth's crust averages in thickness. Mars is seismically active, with
InSight The Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (''InSight'') mission is a robotic Robotics is an interdisciplinarity, interdisciplinary field that integrates computer science and engineering. Robotics in ...

InSight
recording over 450
marsquake Illustration of the shadow zone of a P-wave for Earth. S-waves don't penetrate the outer core">S-wave.html" ;"title="P-wave for Earth. S-wave">P-wave for Earth. S-waves don't penetrate the outer core A marsquake is a Quake (natural phenomenon), qua ...
s and related events in 2019. In 2021 it was reported that based on eleven low-frequency
Marsquake Illustration of the shadow zone of a P-wave for Earth. S-waves don't penetrate the outer core">S-wave.html" ;"title="P-wave for Earth. S-wave">P-wave for Earth. S-waves don't penetrate the outer core A marsquake is a Quake (natural phenomenon), qua ...
s detected by the the core of Mars is indeed liquid and has a radius of about and a temperature around 1900–2000 K. The Martian core radius is more than half the radius of Mars and about half the size of the Earth's core. This is somewhat larger than models predicted, suggesting that the core contains some amount of lighter
element Element may refer to: Science * Chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all ...
s like
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
and
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
in addition to the iron–nickel alloy and about 15% of sulfur. The core of Mars is overlain by the rocky
mantle Mantle may refer to: *Mantle (geology) A mantle is a layer inside a planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a n ...
, which, however, does not seem to have a layer analogous to the Earth's lower mantle. The martial mantle appears to be solid down to the depth of about 500 km, where the low-velocity zone (partially melted
asthenosphere The asthenosphere ( grc, ἀσθενός 'asthenos''meaning "without strength", and thus "weak", and 'sphaira''meaning "sphere") is the highly viscous The viscosity of a fluid In physics, a fluid is a substance that continually Defor ...
) begins. Below the asthenosphere the velocity of seismic waves starts to grow again and at the depth of about 1050 km there lies the boundary of the transition zone. At the surface of Mars there lies a crust with the average thickness of about 24–72 km.


Surface geology

Mars is a
terrestrial planet A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate Rock (geology), rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Su ...
whose surface consists of minerals containing
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

silicon
and
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
,
metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

metal
s, and other elements that typically make up
rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition and the way in w ...
. The Martian surface is primarily composed of
tholeiitic The tholeiitic magma series is one of two main magma series in subalkaline igneous rocks, the other being the Calc-alkaline magma series, calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the e ...
basalt Basalt (, ) is a fine-grained extrusive A volcanic rock from Italy with a relatively large six-sided phenocryst (diameter about 1 mm) surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope Extr ...

basalt
, although parts are more
silica Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any su ...

silica
-rich than typical basalt and may be similar to
andesitic Andesite ( or ) is an extrusive A volcanic rock from Italy with a relatively large six-sided phenocryst (diameter about 1 mm) surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope Extrusive rock ref ...
rocks on Earth, or silica glass. Regions of low
albedo Albedo (prounounced ; la, albedo, meaning 'whiteness') is the measure of the diffuse reflection Diffuse reflection is the reflectionReflection or reflexion may refer to: Philosophy * Self-reflection Science * Reflection (physics), a comm ...

albedo
suggest concentrations of
plagioclase feldspar . (unknown scale) Plagioclase is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagiocla ...
, with northern low albedo regions displaying higher than normal concentrations of sheet silicates and high-silicon glass. Parts of the southern highlands include detectable amounts of high-calcium
pyroxenes The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth ...
. Localized concentrations of
hematite Hematite (), also spelled as haematite, is a common iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member o ...

hematite
and
olivine The mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. R ...

olivine
have been found. Much of the surface is deeply covered by finely grained
iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is ...
dust. Although Mars has no evidence of a structured global
magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. For instance, a vector field in the plane can be visualised as a collection of arrows with ...

magnetic field
, observations show that parts of the planet's crust have been magnetized, suggesting that alternating polarity reversals of its dipole field have occurred in the past. This
paleomagnetism Paleomagnetism, American and British English spelling differences#ae and oe, or palaeomagnetism, is the study of the record of the Earth's magnetic field in rocks, sediment, or archeological materials. Magnetic minerals in rocks can lock-in a re ...
of magnetically susceptible minerals is similar to the alternating bands found on Earth's ocean floors. One theory, published in 1999 and re-examined in October 2005 (with the help of the ''
Mars Global Surveyor ''Mars Global Surveyor'' (MGS) was an American robotic space probe A space probe or a spaceprobe is a robotic spacecraft that doesn't Earth orbit, orbit the Earth (planet), Earth, but instead explores farther into outer space. A space probe ...

Mars Global Surveyor
''), is that these bands suggest plate tectonic activity on Mars four billion years ago, before the planetary
dynamo A dynamo is an that creates using a . Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later devices were based, including the , the , and the . Today, the simple ...

dynamo
ceased to function and the planet's magnetic field faded. It is thought that, during the Solar System's formation, Mars was created as the result of a
stochastic process In probability theory and related fields, a stochastic () or random process is a mathematical object usually defined as a Indexed family, family of random variables. Stochastic processes are widely used as mathematical models of systems and phen ...

stochastic process
of run-away accretion of material from the
protoplanetary disk A protoplanetary disk is a rotating circumstellar disc A circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accumulation of matter composed of gas, Cosmic dust, dust, planetesimals, asteroids, or collision fragments i ...

protoplanetary disk
that orbited the Sun. Mars has many distinctive chemical features caused by its position in the Solar System. Elements with comparatively low boiling points, such as
chlorine Chlorine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemica ...

chlorine
,
phosphorus Phosphorus is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical el ...

phosphorus
, and
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
, are much more common on Mars than Earth; these elements were probably pushed outward by the young Sun's energetic
solar wind The solar wind is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, i ...

solar wind
. After the formation of the planets, all were subjected to the so-called "
Late Heavy Bombardment The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized event thought to have occurred approximately 4.1 to 3.8 billion year A year is the orbital period The orbital period is the time a given astronomical object takes ...
". About 60% of the surface of Mars shows a record of impacts from that era, whereas much of the remaining surface is probably underlain by immense impact basins caused by those events. There is evidence of an enormous impact basin in the Northern Hemisphere of Mars, spanning , or roughly four times the size of the Moon's South Pole – Aitken basin, the largest impact basin yet discovered. This theory suggests that Mars was struck by a
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It was the first and the largest Kuiper belt object to be discovered. After Pluto wa ...

Pluto
-sized body about four billion years ago. The event, thought to be the cause of the Martian hemispheric dichotomy, created the smooth Borealis basin that covers 40% of the planet. The geological history of Mars can be split into many periods, but the following are the three primary periods: *
Noachian The Noachian is a geologic system and early time period on the planet Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury (planet), Mercury. In English, Mars carri ...
period (named after
Noachis Terra Noachis Terra (lit. "Land of Noah In the traditions of Abrahamic religions, Noah ''Nukh''; am, ኖህ, ''Noḥ''; ar, نُوح '; grc, Νῶε ''Nôe'' () features as the tenth and last of the Antediluvian , pre-Flood Patriarchs (Bible), pa ...

Noachis Terra
): Formation of the oldest extant surfaces of Mars, 4.5 to 3.5 billion years ago. Noachian age surfaces are scarred by many large impact craters. The
Tharsis Tharsis () is a vast volcanic plateau centered near the equator in the western hemisphere of Mars. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Ascrae ...

Tharsis
bulge, a volcanic upland, is thought to have formed during this period, with extensive flooding by liquid water late in the period. *
Hesperian The Hesperian is a geologic system and time period on the planet Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury (planet), Mercury. In English, Mars carries th ...
period (named after
Hesperia Planum Hesperia Planum is a broad lava plain in the southern highlands of the planet Mars. The plain is notable for its moderate number of impact craters and abundant wrinkle ridges. It is also the location of the ancient volcano Tyrrhena Mons (Tyrrhena ...

Hesperia Planum
): 3.5 to between 3.3 and 2.9 billion years ago. The Hesperian period is marked by the formation of extensive lava plains. * Amazonian period (named after
Amazonis Planitia Amazonis Planitia is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium Planitia, Elysium volcanic provinces, to the west of Olympus Mons, in the Amazonis quadrangle, Amazonis and Memnonia quadrangles, centered at ...

Amazonis Planitia
): between 3.3 and 2.9 billion years ago to the present. Amazonian regions have few craters but are otherwise quite varied.
Olympus Mons Olympus Mons (; Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in re ...

Olympus Mons
formed during this period, with lava flows elsewhere on Mars. Geological activity is still taking place on Mars. The
Athabasca Valles The Athabasca Valles are a late Amazonian-period outflow channel system in the central Elysium Planitia Elysium Planitia, located in the Elysium and Aeolis Aeolis (Ancient Greek Ancient Greek includes the forms of the Greek langu ...
is home to sheet-like lava flows created about 200  Mya. Water flows in the
graben In geology Geology (from the γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is a branch of concerned with both the liquid and , the of which it is composed, and the processes by which they change over ti ...

graben
s called the
Cerberus Fossae The Cerberus Fossae are a series of semi-parallel fissures on Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury (planet), Mercury. In English, Mars carries the nam ...

Cerberus Fossae
occurred less than 20 Mya, indicating equally recent volcanic intrusions. On 19 February 2008, images from the ''
Mars Reconnaissance Orbiter ''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft File:Space Shuttle Columbia launching.jpg, 275px, The US Space Shuttle flew 135 times from 1981 to 2011, supporting Spacelab, ''Mir'', the Hubble Space Telescope, and the ISS. (''Columbi ...

Mars Reconnaissance Orbiter
'' showed evidence of an avalanche from a cliff.


Soil

The '' Phoenix'' lander returned data showing Martian soil to be slightly alkaline and containing elements such as
magnesium Magnesium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

magnesium
,
sodium Sodium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical eleme ...

sodium
,
potassium Potassium is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, b ...

potassium
and
chlorine Chlorine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemica ...

chlorine
. These nutrients are found in soils on Earth, and they are necessary for growth of plants. Experiments performed by the lander showed that the Martian soil has a
basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming language In computer science Computer science deals with the theoretical foundations of information, algorithms and the ar ...
of 7.7, and contains 0.6% of the
salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure fo ...
perchlorate A perchlorate is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having v ...
, concentrations that are . Streaks are common across Mars and new ones appear frequently on steep slopes of craters, troughs, and valleys. The streaks are dark at first and get lighter with age. The streaks can start in a tiny area, then spread out for hundreds of metres. They have been seen to follow the edges of boulders and other obstacles in their path. The commonly accepted theories include that they are dark underlying layers of soil revealed after avalanches of bright dust or s. Several other explanations have been put forward, including those that involve water or even the growth of organisms.


Hydrology

Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is less than 1% that of Earth's, except at the lowest elevations for short periods. The two polar ice caps appear to be made largely of water. The volume of water ice in the south polar ice cap, if melted, would be enough to cover the entire surface of the planet with a depth of . A
permafrost Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surfa ...

permafrost
mantle stretches from the pole to latitudes of about 60°. Large quantities of ice are thought to be trapped within the thick
cryosphere The cryosphere (from the Greek ''kryos'', "cold", "frost" or "ice" and ''sphaira'', "globe, ball") is an all-encompassing term for those portions of Earth Earth is the third planet from the Sun and the only astronomical object known to ...
of Mars. Radar data from ''
Mars Express ''Mars Express'' is a space exploration Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is carried out mainly by astronomers with telescopes, its physical exploration ...

Mars Express
'' and the ''
Mars Reconnaissance Orbiter ''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft File:Space Shuttle Columbia launching.jpg, 275px, The US Space Shuttle flew 135 times from 1981 to 2011, supporting Spacelab, ''Mir'', the Hubble Space Telescope, and the ISS. (''Columbi ...

Mars Reconnaissance Orbiter
'' (MRO) show large quantities of ice at both poles (July 2005) and at middle latitudes (November 2008). The Phoenix lander directly sampled water ice in shallow Martian soil on 31 July 2008.
Landforms A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws o ...

Landforms
visible on Mars strongly suggest that liquid water has existed on the planet's surface. Huge linear swathes of scoured ground, known as
outflow channels Image:Kasei Valles topo.jpg, 300px, Kasei Valles, seen in MOLA elevation data. Flow was from bottom left to right. North is up. Image is approx. across. The channel system extends another south of this image to Echus Chasma. Outflow channels are ...
, cut across the surface in about 25 places. These are thought to be a record of erosion caused by the catastrophic release of water from subsurface aquifers, though some of these structures have been hypothesized to result from the action of glaciers or lava. One of the larger examples,
Ma'adim Vallis Ma'adim Vallis is one of the largest outflow channels on Mars, about 700 km long and significantly larger than Earth, Earth's Grand Canyon. It is over 20 km wide and 2 km deep in some places. It runs from a region of southern lowlands ...
, is long, much greater than the Grand Canyon, with a width of and a depth of in places. It is thought to have been carved by flowing water early in Mars's history. The youngest of these channels are thought to have formed as recently as only a few million years ago. Elsewhere, particularly on the oldest areas of the Martian surface, finer-scale, dendritic networks of valleys are spread across significant proportions of the landscape. Features of these valleys and their distribution strongly imply that they were carved by
runoff Runoff, run-off or RUNOFF may refer to: * RUNOFF Runoff, run-off or RUNOFF may refer to: * RUNOFF, the first computer text-formatting program * Runoff or run-off, another name for bleed (printing), bleed, printing that lies beyond the edges to wh ...
resulting from precipitation in early Mars history. Subsurface water flow and groundwater sapping may play important subsidiary roles in some networks, but precipitation was probably the root cause of the incision in almost all cases. Along crater and canyon walls, there are thousands of features that appear similar to terrestrial
gullies A gully is a landform created by running water, erosion, eroding sharply into soil, typically on a hillside. Gullies resemble large ditches or small valleys, but are metres to tens of metres in depth and width. When the gully formation is in pr ...
. The gullies tend to be in the highlands of the Southern Hemisphere and to face the Equator; all are poleward of 30° latitude. A number of authors have suggested that their formation process involves liquid water, probably from melting ice, although others have argued for formation mechanisms involving carbon dioxide frost or the movement of dry dust. No partially degraded gullies have formed by weathering and no superimposed impact craters have been observed, indicating that these are young features, possibly still active. Other geological features, such as
deltas A river delta is a landform A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Lan ...

deltas
and
alluvial fans Alluvium (from the Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Re ...
preserved in craters, are further evidence for warmer, wetter conditions at an interval or intervals in earlier Mars history. Such conditions necessarily require the widespread presence of crater lakes across a large proportion of the surface, for which there is independent mineralogical, sedimentological and geomorphological evidence. Further evidence that liquid water once existed on the surface of Mars comes from the detection of specific minerals such as
hematite Hematite (), also spelled as haematite, is a common iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member o ...

hematite
and
goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" Polymorphism (materials science), polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite ha ...

goethite
, both of which sometimes form in the presence of water. In 2004, ''Opportunity'' detected the mineral
jarosite Jarosite is a basic hydrate, hydrous sulfate of potassium and ferric iron (Fe-III) with a chemical formula of KFe3(SO4)2(OH)6. This sulfate mineral is formed in ore deposits by the oxidation of iron sulfides. Jarosite is often produced as a byprod ...

jarosite
. This forms only in the presence of acidic water, which demonstrates that water once existed on Mars. More recent evidence for liquid water comes from the finding of the mineral
gypsum Gypsum is a soft sulfate mineral The sulfate minerals are a class of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with ...

gypsum
on the surface by NASA's Mars rover Opportunity in December 2011. It is estimated that the amount of water in the upper mantle of Mars, represented by
hydroxyl ion A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group ( ...
s contained within the minerals of Mars's geology, is equal to or greater than that of Earth at 50–300 parts per million of water, which is enough to cover the entire planet to a depth of . In 2005, radar data revealed the presence of large quantities of water ice at the poles and at mid-latitudes. The Mars rover ''
Spirit Spirit may refer to: *Spirit (animating force) In folk belief, spirit is the vitalism , vital principle or animating force within all life , living things. As recently as 1628 and 1633 respectively, both William Harvey and René Descartes st ...

Spirit
'' sampled chemical compounds containing water molecules in March 2007. On 18 March 2013,
NASA The National Aeronautics and Space Administration (NASA; ) is an independent agency A regulatory agency or regulatory authority, is a Public benefit corporation Public-benefit corporation is a term that has different meanings in differen ...

NASA
reported evidence from instruments on the ''Curiosity'' rover of
mineral hydration Mineral hydration is an inorganic chemical reaction where water is added to the crystal structure of a mineral, usually creating a new mineral, usually called a '' hydrate''. In geological terms, the process of mineral hydration is known as ''ret ...
, likely hydrated
calcium sulfate Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO4 and related hydrate In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that cove ...

calcium sulfate
, in several rock samples including the broken fragments of "Tintina" rock and as well as in
veins Veins are blood vessels in humans, and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary vein, pulmonary and umbilical veins, both of which ca ...
and nodules in other rocks like and . Analysis using the rover's DAN instrument provided evidence of subsurface water, amounting to as much as 4% water content, down to a depth of , during the rover's traverse from the ''Bradbury Landing'' site to the ''Yellowknife Bay'' area in the ''Glenelg, Mars, Glenelg'' terrain. In September 2015, NASA announced that they had found conclusive evidence of hydrated brine flows on recurring slope lineae, based on spectrometer readings of the darkened areas of slopes. These observations provided confirmation of earlier hypotheses based on timing of formation and their rate of growth, that these dark streaks resulted from water flowing in the very shallow subsurface. The streaks contain hydrated salts, perchlorates, which have water molecules in their crystal structure. The streaks flow downhill in Martian summer, when the temperature is above −23° Celsius, and freeze at lower temperatures. Researchers suspect that much of the low northern plains of the planet were Mars ocean hypothesis, covered with an ocean hundreds of meters deep, though this remains controversial. In March 2015, scientists stated that such an ocean might have been the size of Earth's Arctic Ocean. This finding was derived from the ratio of water to deuterium in the modern Martian atmosphere compared to that ratio on Earth. The amount of Martian deuterium is eight times the amount that exists on Earth, suggesting that ancient Mars had significantly higher levels of water. Results from the ''Curiosity'' rover had previously found a high ratio of deuterium in Gale Crater, though not significantly high enough to suggest the former presence of an ocean. Other scientists caution that these results have not been confirmed, and point out that Martian climate models have not yet shown that the planet was warm enough in the past to support bodies of liquid water. Near the northern polar cap is the wide Korolev (Martian crater), Korolev Crater, where the
Mars Express ''Mars Express'' is a space exploration Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is carried out mainly by astronomers with telescopes, its physical exploration ...

Mars Express
orbiter found it to be filled with approximately of water ice. The crater floor lies about below the rim, and is covered by a deep central mound of permanent water ice, up to in diameter. In February 2020, research determined that seasonally-appearing streaks known as recurring slope lineae are caused by brief inflows of briny water. In 2021, the ExoMars Trace Gas Orbiter has spotted water in the canyon system, Valles Marineris.


Polar caps

Mars has two permanent polar ice caps. During a pole's winter, it lies in continuous darkness, chilling the surface and causing the Deposition (phase transition), deposition of 25–30% of the atmosphere into slabs of Carbon dioxide, CO2 ice (dry ice). When the poles are again exposed to sunlight, the frozen CO2 Sublimation (physics), sublimes. These seasonal actions transport large amounts of dust and water vapor, giving rise to Earth-like frost and large cirrus clouds. Clouds of water-ice were photographed by the ''Opportunity rover, Opportunity'' rover in 2004. The caps at both poles consist primarily (70%) of water ice. Frozen carbon dioxide accumulates as a comparatively thin layer about one metre thick on the north cap in the northern winter only, whereas the south cap has a permanent dry ice cover about eight metres thick. This permanent dry ice cover at the south pole is peppered by Swiss cheese features, flat floored, shallow, roughly circular pits, which repeat imaging shows are expanding by meters per year; this suggests that the permanent CO2 cover over the south pole water ice is degrading over time. The northern polar cap has a diameter of about during the northern Mars summer, and contains about of ice, which, if spread evenly on the cap, would be thick. (This compares to a volume of for the Greenland ice sheet.) The southern polar cap has a diameter of and a thickness of . The total volume of ice in the south polar cap plus the adjacent layered deposits has been estimated at 1.6 million cubic km. Both polar caps show spiral troughs, which recent analysis of SHARAD ice penetrating radar has shown are a result of katabatic winds that spiral due to the Coriolis Effect. The seasonal frosting of areas near the southern ice cap results in the formation of transparent 1-metre-thick slabs of dry ice above the ground. With the arrival of spring, sunlight warms the subsurface and pressure from subliming CO2 builds up under a slab, elevating and ultimately rupturing it. This leads to Martian geyser, geyser-like eruptions of CO2 gas mixed with dark basaltic sand or dust. This process is rapid, observed happening in the space of a few days, weeks or months, a rate of change rather unusual in geology – especially for Mars. The gas rushing underneath a slab to the site of a geyser carves a spiderweb-like pattern of radial channels under the ice, the process being the inverted equivalent of an erosion network formed by water draining through a single plughole.


Geography and naming of surface features

Although better remembered for mapping the Moon, Johann Heinrich Mädler and Wilhelm Beer were the first areographers. They began by establishing that most of Mars's surface features were permanent and by more precisely determining the planet's rotation period. In 1840, Mädler combined ten years of observations and drew the first map of Mars. Rather than giving names to the various markings, Beer and Mädler simply designated them with letters; Meridian Bay (Sinus Meridiani) was thus feature "''a''". Today, features on Mars are named from a variety of sources. Classical albedo features on Mars, Albedo features are named for classical mythology. Craters larger than 60 km are named for deceased scientists and writers and others who have contributed to the study of Mars. Craters smaller than 60 km are named for towns and villages of the world with populations of less than 100,000. Large valleys are named for the word "Mars" or "star" in various languages; small valleys are named for rivers. Large
albedo Albedo (prounounced ; la, albedo, meaning 'whiteness') is the measure of the diffuse reflection Diffuse reflection is the reflectionReflection or reflexion may refer to: Philosophy * Self-reflection Science * Reflection (physics), a comm ...

albedo
features retain many of the older names but are often updated to reflect new knowledge of the nature of the features. For example, ''Olympus Mons, Nix Olympica'' (the snows of Olympus) has become ''
Olympus Mons Olympus Mons (; Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in re ...

Olympus Mons
'' (Mount Olympus). The surface of Mars as seen from Earth is divided into two kinds of areas, with differing albedo. The paler plains covered with dust and sand rich in reddish iron oxides were once thought of as Martian "continents" and given names like Arabia Terra (''land of Arabia'') or
Amazonis Planitia Amazonis Planitia is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium Planitia, Elysium volcanic provinces, to the west of Olympus Mons, in the Amazonis quadrangle, Amazonis and Memnonia quadrangles, centered at ...

Amazonis Planitia
(''Amazonian plain''). The dark features were thought to be seas, hence their names Mare Erythraeum, Mare Sirenum and Aurorae Sinus. The largest dark feature seen from Earth is Syrtis Major Planum. The permanent northern polar ice cap is named Planum Boreum, whereas the southern cap is called Planum Australe. Mars's equator is defined by its rotation, but the location of its Prime Meridian was specified, as was Earth's (at Greenwich), by choice of an arbitrary point; Mädler and Beer selected a line for their first maps of Mars in 1830. After the spacecraft Mariner 9 provided extensive imagery of Mars in 1972, a small crater (later called Airy-0), located in the Sinus Meridiani ("Middle Bay" or "Meridian Bay"), was chosen by Merton Davies of the Rand Corporation for the definition of 0.0° longitude to coincide with the original selection. Because Mars has no oceans and hence no "sea level", a zero-elevation surface had to be selected as a reference level; this is called the ''areoid'' of Mars, analogous to the terrestrial geoid. Zero altitude was defined by the height at which there is of atmospheric pressure. This pressure corresponds to the triple point of water, and it is about 0.6% of the sea level surface pressure on Earth (0.006 atm).


Quadrangles

For mapping purposes, the United States Geological Survey divides the surface of Mars into thirty cartographic Quadrangle (geography), quadrangles, each named for a classical albedo feature it contains.


Impact topography

The Martian dichotomy, dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. Research in 2008 has presented evidence regarding a theory proposed in 1980 postulating that, four billion years ago, the Northern Hemisphere of Mars was struck by an object one-tenth to two-thirds the size of Earth's
Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia (continent), Australia), it is the largest natural satellite in the Solar System relative to the size of its plane ...

Moon
. If validated, this would make the Northern Hemisphere of Mars the site of an
impact crater An impact crater is an approximately circular depression (geology), depression in the surface of a planet, natural satellite, moon, or other solid body in the Solar System or elsewhere, formed by the hypervelocity collision, impact of a smaller ...

impact crater
in size, or roughly the area of Europe, Asia, and Australia combined, surpassing the South Pole–Aitken basin as the largest impact crater in the Solar System. Mars is scarred by a number of impact craters: a total of 43,000 craters with a diameter of or greater have been found. The largest confirmed of these is the Hellas Planitia, Hellas impact basin, a light albedo feature clearly visible from Earth. Due to the smaller mass and size of Mars, the probability of an object colliding with the planet is about half that of Earth. Mars is located closer to the asteroid belt, so it has an increased chance of being struck by materials from that source. Mars is more likely to be struck by short-period comets, ''i.e.'', those that lie within the orbit of Jupiter. Martian craters can have a morphology that suggests the ground became wet after the meteor impacted.


Volcanoes

The shield volcano
Olympus Mons Olympus Mons (; Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in re ...

Olympus Mons
(''Mount Olympus'') is an extinct volcano in the vast upland region
Tharsis Tharsis () is a vast volcanic plateau centered near the equator in the western hemisphere of Mars. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Ascrae ...

Tharsis
, which contains several other large volcanoes. Olympus Mons is roughly three times the height of Mount Everest, which in comparison stands at just over . It is either the tallest or second-tallest mountain in the Solar System, depending on how it is measured, with various sources giving figures ranging from about high.


Tectonic sites

The large canyon,
Valles Marineris Valles Marineris (; Latin for ''Mariner program, Mariner Valleys'', named after the ''Mariner 9'' Mars orbiter of 1971–72 which discovered it) is a system of canyons that runs along the Mars, Martian surface east of the Tharsis region. At more ...
(Latin for "Mariner program, Mariner Valleys", also known as Agathadaemon in the old canal maps), has a length of and a depth of up to . The length of Valles Marineris is equivalent to the length of Europe and extends across one-fifth the circumference of Mars. By comparison, the Grand Canyon on Earth is only long and nearly deep. Valles Marineris was formed due to the swelling of the Tharsis area, which caused the crust in the area of Valles Marineris to collapse. In 2012, it was proposed that Valles Marineris is not just a
graben In geology Geology (from the γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is a branch of concerned with both the liquid and , the of which it is composed, and the processes by which they change over ti ...

graben
, but a plate boundary where of Transform fault, transverse motion has occurred, making Mars a planet with possibly a two-tectonic plate arrangement.


Holes

Images from the Thermal Emission Imaging System (THEMIS) aboard NASA's 2001 Mars Odyssey, Mars Odyssey orbiter have revealed seven possible cave entrances on the flanks of the volcano Arsia Mons. The caves, named after loved ones of their discoverers, are collectively known as the "seven sisters". Cave entrances measure from wide and they are estimated to be at least deep. Because light does not reach the floor of most of the caves, it is possible that they extend much deeper than these lower estimates and widen below the surface. "Dena" is the only exception; its floor is visible and was measured to be deep. The interiors of these caverns may be protected from micrometeoroids, UV radiation, solar flares and high energy particles that bombard the planet's surface.


Atmosphere

Mars lost its magnetosphere 4 billion years ago, possibly because of numerous asteroid strikes, so the
solar wind The solar wind is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, i ...

solar wind
interacts directly with the Martian ionosphere, lowering the atmospheric density by stripping away atoms from the outer layer. Both ''
Mars Global Surveyor ''Mars Global Surveyor'' (MGS) was an American robotic space probe A space probe or a spaceprobe is a robotic spacecraft that doesn't Earth orbit, orbit the Earth (planet), Earth, but instead explores farther into outer space. A space probe ...

Mars Global Surveyor
'' and ''
Mars Express ''Mars Express'' is a space exploration Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is carried out mainly by astronomers with telescopes, its physical exploration ...

Mars Express
'' have detected ionised atmospheric particles trailing off into space behind Mars, and this atmospheric loss is being studied by the MAVEN orbiter. Compared to Earth, the celestial body atmosphere, atmosphere of Mars is quite rarefied. Atmospheric pressure on the surface today ranges from a low of on
Olympus Mons Olympus Mons (; Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in re ...

Olympus Mons
to over in Hellas Planitia, with a mean pressure at the surface level of . The highest atmospheric density on Mars is equal to that found above Earth's surface. The resulting mean surface pressure is only 0.6% of that of Earth . The scale height of the atmosphere is about , which is higher than Earth's , because the surface gravity of Mars is only about 38% of Earth's. The atmosphere of Mars consists of about 96% carbon dioxide, 1.93% argon and 1.89% nitrogen along with traces of
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
and water. The atmosphere is quite dusty, containing particulates about 1.5 µm in diameter which give the Martian sky a tawny (color), tawny color when seen from the surface. It may take on a pink (color), pink hue due to iron oxide particles suspended in it.


Methane

Methane has been detected in the Atmosphere of Mars#Methane, Martian atmosphere; it occurs in extended plumes, and the profiles imply that the methane is released from discrete regions. The concentration of methane fluctuates from about 0.24 Parts per billion, ppb during the northern winter to about 0.65 Parts per billion, ppb during the summer. Estimates of its lifetime range from 0.6 to 4 years, so its presence indicates that an active source of the gas must be present. Methane could be produced by non-biological process such as serpentinite, serpentinization involving water, carbon dioxide, and the mineral
olivine The mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. R ...

olivine
, which is known to be common on Mars. Methanogenic microorganism, microbial life forms in the subsurface are among possible sources. But even if rover missions determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach.


Aurora

In 1994, the European Space Agency's Mars Express found an ultraviolet glow coming from "magnetic umbrellas" in the Southern Hemisphere. Mars does not have a global magnetic field which guides charged particles entering the atmosphere. Mars has multiple umbrella-shaped magnetic fields mainly in the Southern Hemisphere, which are remnants of a global field that decayed billions of years ago. In late December 2014, NASA's MAVEN spacecraft detected evidence of widespread auroras in Mars's Northern Hemisphere and descended to approximately 20–30° North latitude of Mars's equator. The particles causing the aurora penetrated into the Martian atmosphere, creating auroras below 100 km above the surface, Earth's auroras range from 100 km to 500 km above the surface. Magnetic fields in the solar wind drape over Mars, into the atmosphere, and the charged particles follow the solar wind magnetic field lines into the atmosphere, causing auroras to occur outside the magnetic umbrellas. On 18 March 2015, NASA reported the detection of an aurora that is not fully understood and an unexplained dust cloud in the atmosphere of Mars. In September 2017, NASA reported radiation levels on the surface of the planet Mars were temporarily Orders of magnitude (radiation), doubled, and were associated with an aurora 25 times brighter than any observed earlier, due to a massive, and unexpected, Coronal mass ejection, solar storm in the middle of the month.


Climate

Of all the planets in the Solar System, the seasons of Mars are the most Earth-like, due to the similar tilts of the two planets' rotational axes. The lengths of the Martian seasons are about twice those of Earth's because Mars's greater distance from the Sun leads to the Martian year being about two Earth years long. Martian surface temperatures vary from lows of about at the winter polar caps to highs of up to in equatorial summer. The wide range in temperatures is due to the thin atmosphere which cannot store much solar heat, the low atmospheric pressure, and the low Volumetric heat capacity, thermal inertia of Martian soil. The planet is 1.52 times as far from the Sun as Earth, resulting in just 43% of the amount of sunlight. If Mars had an Earth-like orbit, its seasons would be similar to Earth's because its axial tilt is similar to Earth's. The comparatively large Orbital eccentricity, eccentricity of the Martian orbit has a significant effect. Mars is near Apsis, perihelion when it is summer in the Southern Hemisphere and winter in the north, and near Apsis, aphelion when it is winter in the Southern Hemisphere and summer in the north. As a result, the seasons in the Southern Hemisphere are more extreme and the seasons in the northern are milder than would otherwise be the case. The summer temperatures in the south can be warmer than the equivalent summer temperatures in the north by up to . Mars has the largest dust storms in the Solar System, reaching speeds of over . These can vary from a storm over a small area, to gigantic storms that cover the entire planet. They tend to occur when Mars is closest to the Sun, and have been shown to increase the global temperature.


Orbit and rotation

Mars's average distance from the Sun is roughly , and its orbital period is 687 (Earth) days. The solar day (or Sol (day on Mars), sol) on Mars is only slightly longer than an Earth day: 24 hours, 39 minutes, and 35.244 seconds. A Martian year is equal to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours. The axial tilt of Mars is 25.19° relative to its orbital plane, which is similar to the axial tilt of Earth. As a result, Mars has seasons like Earth, though on Mars they are nearly twice as long because its orbital period is that much longer. In the present day epoch, the orientation of the north pole of Mars is close to the star Deneb. Mars has a relatively pronounced orbital eccentricity of about 0.09; of the seven other planets in the Solar System, only
Mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

Mercury
has a larger orbital eccentricity. It is known that in the past, Mars has had a much more circular orbit. At one point, 1.35 million Earth years ago, Mars had an eccentricity of roughly 0.002, much less than that of Earth today. Mars's Milankovitch cycles, cycle of eccentricity is 96,000 Earth years compared to Earth's cycle of 100,000 years. For the last 35,000 years, the orbit of Mars has been getting slightly more eccentric because of the gravitational effects of the other planets. The closest distance between Earth and Mars will continue to mildly decrease for the next 25,000 years.


Habitability and search for life

During the late nineteenth century, it was widely accepted in the astronomical community that Mars had life-supporting qualities, including oxygen and water. However, in 1894 William Wallace Campbell, W. W. Campbell at Lick Observatory observed the planet and found that "if water vapor or oxygen occur in the atmosphere of Mars it is in quantities too small to be detected by spectroscopes then available". This contradicted many of the measurements of the time and was not widely accepted. Campbell and Vesto Slipher, V. M. Slipher repeated the study in 1909 using better instruments, but with the same results. It wasn't until the findings were confirmed by Walter Sydney Adams, W. S. Adams in 1925 that the myth of the Earth-like habitability of Mars was finally broken. However, even in the 1960s, articles were published on Martian biology, putting aside explanations other than life for the seasonal changes on Mars. Detailed scenarios for the metabolism and chemical cycles for a functional ecosystem have been published. The current understanding of planetary habitabilitythe ability of a world to develop environmental conditions favorable to the emergence of lifefavors planets that have liquid water on their surface. Most often this requires the orbit of a planet to lie within the Planetary Habitability Index, habitable zone, which for the Sun extends from just beyond Venus to about the semi-major axis of Mars. During perihelion, Mars dips inside this region, but Mars's thin (low-pressure) atmosphere prevents liquid water from existing over large regions for extended periods. The past flow of liquid water demonstrates the planet's potential for habitability. Recent evidence has suggested that any water on the Martian surface may have been too salty and acidic to support regular terrestrial life. The lack of a magnetosphere and the extremely thin atmosphere of Mars are a challenge: the planet has little heat transfer across its surface, poor insulation against bombardment of the
solar wind The solar wind is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, i ...

solar wind
and insufficient atmospheric pressure to retain water in a liquid form (water instead Sublimation (phase transition), sublimes to a gaseous state). Mars is nearly, or perhaps totally, geologically dead; the end of volcanic activity has apparently stopped the recycling of chemicals and minerals between the surface and interior of the planet. ''In situ'' investigations have been performed on Mars by the Viking program#Viking landers, ''Viking'' landers, Spirit (rover), ''Spirit'' and ''Opportunity'' rovers, Phoenix (spacecraft), ''Phoenix'' lander, and ''Curiosity'' rover. Evidence suggests that the planet was once significantly more habitable than it is today, but whether living organisms ever existed there remains unknown. The Viking probes of the mid-1970s carried experiments designed to detect microorganisms in Martian soil at their respective landing sites and had positive results, including a temporary increase of production on exposure to water and nutrients. This sign of life was later disputed by scientists, resulting in a continuing debate, with NASA scientist Gilbert Levin asserting that Viking may have found life. A re-analysis of the Viking data, in light of modern knowledge of extremophile forms of life, has suggested that the Viking tests were not sophisticated enough to detect these forms of life. The tests could even have killed a (hypothetical) life form. Tests conducted by the Phoenix Mars lander have shown that the soil has an alkaline and it contains magnesium, sodium, potassium and chloride. The soil nutrients may be able to support life, but life would still have to be shielded from the intense ultraviolet light. A recent analysis of martian meteorite EETA79001 found 0.6 ppm , 1.4 ppm , and 16 ppm , most likely of Martian origin. The suggests the presence of other highly oxidizing oxychlorines, such as or , produced both by UV oxidation of Cl and X-ray radiolysis of . Thus, only highly refractory and/or well-protected (sub-surface) organics or life forms are likely to survive. Scientists have proposed that carbonate globules found in meteorite Allan Hills 84001, ALH84001, which is thought to have originated from Mars, could be fossilized microbes extant on Mars when the meteorite was blasted from the Martian surface by a meteor strike some 15 million years ago. This proposal has been met with skepticism, and an exclusively inorganic origin for the shapes has been proposed. Small quantities of methane and formaldehyde detected by Mars orbiters are both claimed to be possible evidence for life, as these chemical compounds would quickly break down in the Martian atmosphere. Alternatively, these compounds may instead be replenished by volcanic or other geological means, such as serpentinite. Impactite, Impact glass, formed by the impact of meteors, which on Earth can preserve signs of life, has also been found on the surface of the impact craters on Mars. Likewise, the glass in impact craters on Mars could have preserved signs of life if life existed at the site. A 2014 analysis of the Phoenix WCL showed that the in the Phoenix soil has not interacted with liquid water of any form, perhaps for as long as 600 million years. If it had, the highly soluble in contact with liquid water would have formed only , which suggests a severely arid environment with minimal or no liquid water interaction. In May 2017, evidence of the Earliest known life forms, earliest known life Evolutionary history of life#Colonization of land, on land on Earth may have been found in 3.48-billion-year-old geyserite and other related mineral deposits (often found around hot springs and geysers) uncovered in the Pilbara Craton of Western Australia. These findings may be helpful in deciding where best to search for early signs of Life on Mars, life on the planet Mars.


Moons

Mars has two relatively small (compared to Earth's) natural moons, Phobos (about in diameter) and Deimos (about in diameter), which orbit close to the planet. Asteroid capture is a long-favored theory, but their origin remains uncertain. Both satellites were discovered in 1877 by Asaph Hall; they are named after the characters Phobos (mythology), Phobos (panic/fear) and Deimos (mythology), Deimos (terror/dread), who, in Greek mythology, accompanied their father Ares, god of war, into battle. Mars (mythology), Mars was the Roman equivalent to Ares. In modern Greek language, Greek, the planet retains its ancient name ''Ares'' (Aris: ''Άρης''). From the surface of Mars, the motions of Phobos and Deimos appear different from that of the
Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia (continent), Australia), it is the largest natural satellite in the Solar System relative to the size of its plane ...

Moon
. Phobos rises in the west, sets in the east, and rises again in just 11 hours. Deimos, being only just outside synchronous orbitwhere the orbital period would match the planet's period of rotationrises as expected in the east but slowly. Despite the 30-hour orbit of Deimos, 2.7 days elapse between its rise and set for an equatorial observer, as it slowly falls behind the rotation of Mars. Because the orbit of Phobos is below synchronous altitude, the tidal forces from the planet Mars are gradually lowering its orbit. In about 50 million years, it could either crash into Mars's surface or break up into a ring structure around the planet. The origin of the two moons is not well understood. Their low albedo and carbonaceous chondrite composition have been regarded as similar to asteroids, supporting the capture theory. The unstable orbit of Phobos would seem to point towards a relatively recent capture. But both have circular orbits, near the equator, which is unusual for captured objects and the required capture dynamics are complex. Accretion early in the history of Mars is plausible, but would not account for a composition resembling asteroids rather than Mars itself, if that is confirmed. A third possibility is the involvement of a third body or a type of impact disruption. More-recent lines of evidence for Phobos having a highly porous interior, and suggesting a composition containing mainly phyllosilicates and other minerals known from Mars, point toward an origin of Phobos from material ejected by an impact on Mars that reaccreted in Martian orbit, similar to the Giant impact hypothesis, prevailing theory for the origin of Earth's moon. Although the visible and near-infrared (VNIR) spectra of the moons of Mars resemble those of outer-belt asteroids, the thermal infrared spectra of Phobos are reported to be inconsistent with chondrites of any class. Mars may have moons smaller than in diameter, and a dust ring is predicted to exist between Phobos and Deimos.


Exploration

Dozens of crewless spacecraft, including orbiters, Mars lander, landers, and Mars rover, rovers, have been sent to Mars by the Soviet space program, Soviet Union, the NASA, United States, ESA, Europe, ISRO, India, the Mohammed bin Rashid Space Centre, United Arab Emirates, and CNSA, China to study the planet's surface, climate, and geology. Once spacecraft visited the planet during NASA's Mariner program, Mariner missions in the 1960s and 1970s, many previous concepts of Mars were radically broken. The results of the Viking life-detection experiments aided an intermission in which the hypothesis of a hostile, dead planet was generally accepted. Mariner 9 and Viking allowed better maps of Mars to be made using the data from these missions, and the
Mars Global Surveyor ''Mars Global Surveyor'' (MGS) was an American robotic space probe A space probe or a spaceprobe is a robotic spacecraft that doesn't Earth orbit, orbit the Earth (planet), Earth, but instead explores farther into outer space. A space probe ...

Mars Global Surveyor
mission, which launched in 1996 and operated until late 2006, allowed for complete, extremely detailed maps of the Martian topography, magnetic field and surface minerals to be obtained. These maps are available online; for example, at Google Mars. Both the
Mars Reconnaissance Orbiter ''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft File:Space Shuttle Columbia launching.jpg, 275px, The US Space Shuttle flew 135 times from 1981 to 2011, supporting Spacelab, ''Mir'', the Hubble Space Telescope, and the ISS. (''Columbi ...

Mars Reconnaissance Orbiter
and
Mars Express ''Mars Express'' is a space exploration Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is carried out mainly by astronomers with telescopes, its physical exploration ...

Mars Express
continued exploring with new instruments and supporting lander missions. NASA provides two online tools: Mars Trek, which provides visualizations of the planet using data from 50 years of exploration, and Experience Curiosity, which simulates traveling on Mars in 3-D with Curiosity. , Mars is host to fourteen functioning spacecraft: eight in orbit''2001 Mars Odyssey'', ''
Mars Express ''Mars Express'' is a space exploration Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is carried out mainly by astronomers with telescopes, its physical exploration ...

Mars Express
'', ''
Mars Reconnaissance Orbiter ''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft File:Space Shuttle Columbia launching.jpg, 275px, The US Space Shuttle flew 135 times from 1981 to 2011, supporting Spacelab, ''Mir'', the Hubble Space Telescope, and the ISS. (''Columbi ...

Mars Reconnaissance Orbiter
'', ''MAVEN'', ''Mars Orbiter Mission'', ''ExoMars Trace Gas Orbiter'', the Emirates Mars Mission, ''Hope'' orbiter, and the ''Tianwen-1'' orbiterand six on the surfacethe Mars Science Laboratory ''Curiosity (rover), Curiosity'' rover, the ''
InSight The Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (''InSight'') mission is a robotic Robotics is an interdisciplinarity, interdisciplinary field that integrates computer science and engineering. Robotics in ...

InSight
'' lander, the Perseverance (rover), ''Perseverance'' rover, the Ingenuity (helicopter), ''Ingenuity'' helicopter, the ''Tianwen-1'' lander, and the ''Zhurong'' rover. The public can request images of Mars via the ''Mars Reconnaissance Orbiter'' HiWish program. The Mars Science Laboratory, named ''Curiosity'', launched on 26 November 2011, and reached Mars on 6 August 2012 UTC. It is larger and more advanced than the Mars Exploration Rovers, with a movement rate up to per hour. Experiments include a laser chemical sampler that can deduce the make-up of rocks at a distance of . On 10 February 2013, the Mars Science Laboratory, ''Curiosity'' rover obtained the first deep rock samples ever taken from another planetary body, using its on-board drill. The same year, it discovered that Mars's soil contains between 1.5% and 3% water by mass (albeit attached to other compounds and thus not freely accessible). Observations by the ''
Mars Reconnaissance Orbiter ''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft File:Space Shuttle Columbia launching.jpg, 275px, The US Space Shuttle flew 135 times from 1981 to 2011, supporting Spacelab, ''Mir'', the Hubble Space Telescope, and the ISS. (''Columbi ...

Mars Reconnaissance Orbiter
'' had previously revealed the possibility of flowing water during the warmest months on Mars. On 24 September 2014, Mars Orbiter Mission (MOM), launched by the Indian Space Research Organisation (ISRO), reached Mars's orbit. ISRO launched MOM on 5 November 2013, with the aim of analyzing the Martian atmosphere and topography. The Mars Orbiter Mission used a Hohmann transfer orbit to escape Earth's gravitational influence and catapult into a nine-month-long voyage to Mars. The mission is the first successful Asian interplanetary mission. The European Space Agency, in collaboration with Roscosmos, launched the ExoMars Trace Gas Orbiter and Schiaparelli EDM lander, ''Schiaparelli'' lander on 14 March 2016. While the Trace Gas Orbiter successfully entered Mars orbit on 19 October 2016, ''Schiaparelli'' crashed during its landing attempt. In May 2018, NASA's ''InSight'' lander was launched, along with the twin Mars Cube One, MarCO CubeSats that flew by Mars and acted as telemetry relays during the landing. The mission arrived at Mars in November 2018. InSight detected potential seismic activity (a "
marsquake Illustration of the shadow zone of a P-wave for Earth. S-waves don't penetrate the outer core">S-wave.html" ;"title="P-wave for Earth. S-wave">P-wave for Earth. S-waves don't penetrate the outer core A marsquake is a Quake (natural phenomenon), qua ...
") in April 2019. In 2019, MAVEN spacecraft mapped high-altitude global wind patterns at Mars for the first time. It was discovered that the winds which are miles above the surface retained information about the land forms below. The United Arab Emirates' ''Emirates Mars Mission, Mars Hope'' orbiter was launched on 19 July 2020, and successfully entered orbit around Mars on 9 February 2021. The probe will conduct a global study of the Martian atmosphere. With this accomplishment, UAE became the second country, after India, to reach Mars on its first attempt.
NASA The National Aeronautics and Space Administration (NASA; ) is an independent agency A regulatory agency or regulatory authority, is a Public benefit corporation Public-benefit corporation is a term that has different meanings in differen ...

NASA
launched the Mars 2020 mission on 30 July 2020. The ''Perseverance (rover), Perseverance'' rover and the ''Ingenuity (helicopter), Ingenuity'' helicopter successfully landed on the surface of Mars on 18 February 2021. The mission will cache samples for future retrieval and return of them to Earth. China's ''Tianwen-1'' lander-rover vehicle successfully landed on Mars on 14 May 2021 (15 May Beijing Time).


Astronomy on Mars

With the presence of various orbiters, landers, and rovers, it is possible to practice astronomy from Mars. Although Mars's moon Phobos appears about one-third the angular diameter of the full moon on Earth, Deimos appears more or less star-like, looking only slightly brighter than Venus does from Earth. Various phenomena seen from Earth have also been observed from Mars, such as meteors and auroras. The angular diameter, apparent sizes of the moons Phobos and Deimos are sufficiently smaller than that of the Sun; thus, their partial "eclipses" of the Sun are best considered transit (astronomy), transits (see transit of Deimos from Mars, transit of Deimos and transit of Phobos from Mars, Phobos from Mars). transit of Mercury from Mars, Transits of Mercury and transit of Venus, Venus have been observed from Mars. A transit of Earth from Mars, transit of Earth will be seen from Mars on 10 November 2084.


Future

The current concept for the Mars sample-return mission would launch in 2026 and feature hardware built by NASA and ESA. The European Space Agency will launch the ExoMars rover and ExoMars 2020 surface platform, surface platform sometime between August and October 2022. A planned twin-spacecraft NASA Mars orbiter called EscaPADE (Escape and Plasma Acceleration and Dynamics Explorers) are meant to study the structure, composition, variability and dynamics of Mars' magnetosphere and atmospheric escape processes. They had a planned launch in August 2022 as secondary payloads on the Psyche (spacecraft), Psyche, but were removed due to complications with the trajectory. A new launch opportunity will appear sometime in 2024, with the EscaPADE being rideshares. The IRSO has plans for a second mission to Mars, called Mars Orbiter Mission 2 (Also known as Mangalyaan-2), which will be an orbiter mission. Several plans for a human mission to Mars have been proposed throughout the 20th and 21st centuries, but no human mission has yet launched. SpaceX founder Elon Musk SpaceX Mars transportation infrastructure, presented a plan in September 2016 to, optimistically, launch a crewed mission to Mars in 2024 at an estimated development cost of US$10 billion, but this mission is not expected to take place before 2027. In October 2016, President Barack Obama renewed United States policy to pursue the goal of sending humans to Mars in the 2030s, and to continue using the International Space Station as a technology incubator in that pursuit. The NASA Authorization Act of 2017 directed NASA to get humans near or on the surface of Mars by the early 2030s. In addition, China plans to send a crewed Mars mission in 2033.


Viewing

The mean of Mars is +0.71 with a standard deviation of 1.05. Because the orbit of Mars is eccentric, the magnitude at opposition (planets), opposition from the Sun can range from about −3.0 to −1.4. The minimum brightness is magnitude +1.86 when the planet is near Apsis, aphelion and in conjunction (astronomy), conjunction with the Sun. At its brightest, Mars (along with Jupiter) is second only to Venus in luminosity. Mars usually appears distinctly yellow, orange, or red.
NASA The National Aeronautics and Space Administration (NASA; ) is an independent agency A regulatory agency or regulatory authority, is a Public benefit corporation Public-benefit corporation is a term that has different meanings in differen ...

NASA
's ''Spirit'' rover has taken pictures of a greenish-brown, mud-colored landscape with blue-grey rocks and patches of light red sand. When farthest away from Earth, it is more than seven times farther away than when it is closest. When least favorably positioned, it can be lost in the Sun's glare for months at a time. At its most favorable times — at 15-year or 17-year intervals, and always between late July and late September — a lot of surface detail can be seen with a telescope. Especially noticeable, even at low magnification, are the polar ice caps. As Mars approaches opposition, it begins a period of Apparent retrograde motion, retrograde motion, which means it will appear to move backwards in a looping motion with respect to the background stars. The duration of this retrograde motion lasts for about 72 days, and Mars reaches its peak luminosity in the middle of this motion.


Closest approaches


Relative

The point at which Mars's geocentric longitude is 180° different from the Sun's is known as opposition (planets), opposition, which is near the time of closest approach to Earth. The time of opposition can occur as much as 8.5 days away from the closest approach. The distance at close approach varies between about due to the planets' ellipse, elliptical orbits, which causes comparable variation in angular size. The second-to-last Mars opposition occurred on 27 July 2018, at a distance of about . The last Mars opposition occurred on 13 October 2020, at a distance of about . The average time between the successive oppositions of Mars, its synodic period, is 780 days; but the number of days between the dates of successive oppositions can range from 764 to 812.


Absolute, around the present time

Mars made its closest approach to Earth and maximum apparent brightness in nearly 60,000 years, , magnitude (astronomy), magnitude −2.88, on 27 August 2003, at 09:51:13 UTC. This occurred when Mars was one day from opposition and about three days from its perihelion, making it particularly easy to see from Earth. The last time it came so close is estimated to have been on 12 September Middle Paleolithic, 57,617 BC, the next time being in 2287. This record approach was only slightly closer than other recent close approaches. For instance, the minimum distance on 22 August 1924, was , and the minimum distance on 24 August 2208, will be . Every 15 to 17 years, Mars comes into opposition near its perihelion. These perihelic oppositions make a closer approach to earth than other oppositions which occur every 2.1 years. Mars comes into perihelic opposition in 2003, 2018 and 2035, with 2020 and 2033 being close to perihelic opposition.


Historical observations

The history of observations of Mars is marked by the oppositions of Mars when the planet is closest to Earth and hence is most easily visible, which occur every couple of years. Even more notable are the perihelic oppositions of Mars, which occur every 15 or 17 years and are distinguished because Mars is close to perihelion, making it even closer to Earth.


Ancient and medieval observations

The ancient Sumerians believed that Mars was Nergal, the god of war and plague. During Sumerian times, Nergal was a minor deity of little significance, but, during later times, his main cult center was the city of Nineveh. In Mesopotamian texts, Mars is referred to as the "star of judgement of the fate of the dead." The existence of Mars as a wandering object in the night sky was also recorded by the ancient Egyptian astronomy, Egyptian astronomers and, by 1534 BCE, they were familiar with the Apparent retrograde motion, retrograde motion of the planet. By the period of the Neo-Babylonian Empire, the Babylonian astronomy, Babylonian astronomers were making regular records of the positions of the planets and systematic observations of their behavior. For Mars, they knew that the planet made 37 Orbital period, synodic periods, or 42 circuits of the zodiac, every 79 years. They invented arithmetic methods for making minor corrections to the predicted positions of the planets. In Ancient Greece, the planet was known as grc, Pyroeis, Πυρόεις, label=none. In the fourth century BCE, Aristotle noted that Mars disappeared behind the Moon during an occultation, indicating that the planet was farther away. Ptolemy, a Greek living in Alexandria, attempted to address the problem of the orbital motion of Mars. Ptolemy's model and his collective work on astronomy was presented in the multi-volume collection ''Almagest'', which became the authoritative treatise on History of astronomy#Medieval Western Europe, Western astronomy for the next fourteen centuries. Literature from ancient China confirms that Mars was known by Chinese astronomy, Chinese astronomers by no later than the fourth century BCE. In the East Asian cultures, Mars is traditionally referred to as the "fire star" (Chinese: ), based on the Five elements (Chinese philosophy), Five elements. During the seventeenth century, Tycho Brahe measured the diurnal parallax of Mars that Johannes Kepler used to make a preliminary calculation of the relative distance to the planet. When the telescope became available, the diurnal parallax of Mars was again measured in an effort to determine the Sun-Earth distance. This was first performed by Giovanni Domenico Cassini in 1672. The early parallax measurements were hampered by the quality of the instruments. The only occultation of Mars by Venus observed was that of 13 October 1590, seen by Michael Maestlin at Heidelberg. In 1610, Mars was viewed by Italian astronomer Galileo Galilei, who was first to see it via telescope. The first person to draw a map of Mars that displayed any terrain features was the Dutch astronomer Christiaan Huygens.


Martian "canals"

By the 19th century, the resolution of telescopes reached a level sufficient for surface features to be identified. On 5 September 1877, a perihelic opposition of Mars occurred. During that day, the Italian astronomer Giovanni Schiaparelli used a telescope in Milan to help produce the first detailed map of Mars. These maps notably contained features he called ''canali'', which were later shown to be an optical illusion. These ''canali'' were supposedly long, straight lines on the surface of Mars, to which he gave names of famous rivers on Earth. His term, which means "channels" or "grooves", was popularly mistranslated in English as "canals". Influenced by the observations, the orientalist Percival Lowell founded an Lowell Observatory, observatory which had telescopes. The observatory was used for the exploration of Mars during the last good opportunity in 1894 and the following less favorable oppositions. He published several books on Mars and life on the planet, which had a great influence on the public. The ''canali'' were independently found by other astronomers, like Henri Joseph Perrotin and Louis Thollon in Nice, using one of the largest telescopes of that time. The seasonal changes (consisting of the diminishing of the polar caps and the dark areas formed during Martian summer) in combination with the canals led to speculation about life on Mars, and it was a long-held belief that Mars contained vast seas and vegetation. As bigger telescopes were used, fewer long, straight ''canali'' were observed. During an observation in 1909 by Camille Flammarion with an telescope, irregular patterns were observed, but no ''canali'' were seen.


In culture

file:Mars symbol (fixed width).svg, frameless, 80px Mars is named after the Ancient Rome, Roman Mars (mythology), god of war. In different cultures, Mars represents masculinity and youth. Gender symbol, Its symbol, a circle with an arrow pointing out to the upper right, is also used as a symbol for the male gender. The symbol dates from at latest the 11th century, at which time it was an arrow across or through a circle. The Greek Oxyrhynchus Papyri appear to show a different symbol, of uncertain depiction.


Intelligent "Martians"

The idea that Mars was populated by intelligent Martians became widespread in the late 19th century. Giovanni Schiaparelli, Schiaparelli's "canali" observations combined with Percival Lowell's books on the subject put forward the standard notion of a planet that was a drying, cooling, dying world with ancient civilizations constructing irrigation works.Many other observations and proclamations by notable personalities added to what has been termed "Mars Fever". In 1899, while investigating atmospheric radio noise using his receivers in his Colorado Springs lab, inventor Nikola Tesla observed repetitive signals that he later surmised might have been radio communications coming from another planet, possibly Mars. In a 1901 interview, Tesla said:
It was some time afterward when the thought flashed upon my mind that the disturbances I had observed might be due to an intelligent control. Although I could not decipher their meaning, it was impossible for me to think of them as having been entirely accidental. The feeling is constantly growing on me that I had been the first to hear the greeting of one planet to another.
Tesla's theories gained support from Lord Kelvin who, while visiting the United States in 1902, was reported to have said that he thought Tesla had picked up Martian signals being sent to the United States. Kelvin denied this report shortly before leaving: "What I really said was that the inhabitants of Mars, if there are any, were doubtless able to see New York, particularly the glare of the electricity." In a ''New York Times'' article in 1901, Edward Charles Pickering, director of the Harvard College Observatory, said that they had received a telegram from Lowell Observatory in Arizona that seemed to confirm that Mars was trying to communicate with Earth.
Early in December 1900, we received from Lowell Observatory in Arizona a telegram that a shaft of light had been seen to project from Mars (the Lowell observatory makes a specialty of Mars) lasting seventy minutes. I wired these facts to Europe and sent out neostyle copies through this country. The observer there is a careful, reliable man and there is no reason to doubt that the light existed. It was given as from a well-known geographical point on Mars. That was all. Now the story has gone the world over. In Europe, it is stated that I have been in communication with Mars, and all sorts of exaggerations have spring up. Whatever the light was, we have no means of knowing. Whether it had intelligence or not, no one can say. It is absolutely inexplicable.
Pickering later proposed creating a set of mirrors in Texas, intended to signal Martians. In recent decades, the high-resolution mapping of the surface of Mars, culminating in
Mars Global Surveyor ''Mars Global Surveyor'' (MGS) was an American robotic space probe A space probe or a spaceprobe is a robotic spacecraft that doesn't Earth orbit, orbit the Earth (planet), Earth, but instead explores farther into outer space. A space probe ...

Mars Global Surveyor
, revealed no artifacts of habitation by "intelligent" life, but pseudoscientific speculation about intelligent life on Mars still continues from commentators such as Richard C. Hoagland. Reminiscent of the ''canali'' controversy, these speculations are based on small scale features perceived in the spacecraft images, such as "pyramids" and the "Cydonia (Mars), Face on Mars". Planetary astronomer Carl Sagan wrote:
Mars has become a kind of mythic arena onto which we have projected our Earthly hopes and fears.


In literature and media

The depiction of Mars in fiction has been stimulated by its dramatic red color and by nineteenth-century scientific speculations that its surface conditions might support not just life but intelligent life. This gave way to many science fiction stories involving these concepts, such as H. G. Wells' ''The War of the Worlds'', in which Martians seek to escape their dying planet by invading Earth, Ray Bradbury's ''The Martian Chronicles'', in which human explorers accidentally destroy a Martian civilization, as well as Edgar Rice Burroughs' Barsoom, ''Barsoom'' series, C. S. Lewis' novel ''Out of the Silent Planet'' (1938), and a number of Robert A. Heinlein stories before the mid-sixties. Some writers referenced Mars in their novels, such as Jonathan Swift, who referenced Mars's moons in the 19th chapter of his novel ''Gulliver's Travels, a''bout 150 years before their actual discovery by Asaph Hall, detailing reasonably accurate descriptions of their orbits. Since then, depictions of Martians have also extended to animation. A comic figure of an intelligent Martian, Marvin the Martian, appeared in ''Haredevil Hare'' (1948) as a character in the Looney Tunes animated cartoons of Warner Brothers, and has continued as part of popular culture to the present. After the Mariner program, Mariner and Viking program, Viking spacecraft had returned pictures of Mars as it really is, a lifeless and canal-less world, these ideas about Mars were abandoned, and a vogue for accurate, realist depictions of human colonies on Mars developed, the best known of which may be Kim Stanley Robinson's Mars trilogy, ''Mars'' trilogy. Pseudo-scientific speculations about the Cydonia (Mars), Face on Mars and other enigmatic landmarks spotted by space probes have meant that ancient civilizations continue to be a popular theme in science fiction, especially in film. The many failures in Mars exploration probes resulted in a satirical counter-culture blaming the failures on an Earth-Mars "Bermuda Triangle", a "Exploration of Mars#Mars Curse, Mars Curse", or a "Great Galactic Ghoul" that feeds on Martian spacecraft.


See also

* List of missions to Mars * Mars monolith * Mineralogy of Mars * Outline of Mars * Timekeeping on Mars * List of gravitationally rounded objects of the Solar System#Planets, Wikipedia table comparing stats of planets in the Solar System


Notes


References


External links

*
Mars Exploration Program
at NASA.gov
Mars Trek – An integrated map browser of maps and datasets for Mars

Google Mars
an
Google Mars 3D
interactive maps of the planet
Geody Mars
mapping site that supports NASA World Wind, Celestia, and other applications
Interactive 3D Gravity simulation of the Martian system and all the operational spacecraft in orbit around it as of the 12'th of June 2020


Images


Mars images
by NASA's Planetary Photojournal
Mars images
by NASA's Mars Exploration Program
Mars images
by Malin Space Science Systems
HiRISE image catalog
by the University of Arizona


Videos


Rotating color globe of Mars
by the National Oceanic and Atmospheric Administration
Rotating geological globe of Mars
by the United States Geological Survey * by The Science Channel (2012, 4:31)
Flight Into Mariner Valley
by Arizona State University
High resolution video
simulation of rotating Mars by Seán Doran, showing Arabia Terra,
Valles Marineris Valles Marineris (; Latin for ''Mariner program, Mariner Valleys'', named after the ''Mariner 9'' Mars orbiter of 1971–72 which discovered it) is a system of canyons that runs along the Mars, Martian surface east of the Tharsis region. At more ...
and
Tharsis Tharsis () is a vast volcanic plateau centered near the equator in the western hemisphere of Mars. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Ascrae ...

Tharsis
(se
album
for more)
Mars rover captures high-resolution panorama of its home
(
NASA The National Aeronautics and Space Administration (NASA; ) is an independent agency A regulatory agency or regulatory authority, is a Public benefit corporation Public-benefit corporation is a term that has different meanings in differen ...

NASA
)


Cartographic resources


Mars nomenclature
an
quadrangle maps with feature names
by the United States Geological Survey
Geological map of Mars
by the United States Geological Survey
Viking orbiter photomap
by Eötvös Loránd University
Mars Global Surveyor topographical map
by Eötvös Loránd University {{Featured article Mars, Articles containing video clips Astronomical objects known since antiquity Planets of the Solar System Terrestrial planets