Mars is the fourth
planet
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
from the
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
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 "Solar S ...
, only being larger than
Mercury. In the English language, Mars is named for the
Roman god of war. Mars is a
terrestrial planet
A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, ...
with a thin
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
(less than 1% that of Earth's), and has a crust primarily composed of elements similar to Earth's crust, as well as a core made of iron and nickel. Mars has surface features such as
impact crater
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...
s, valleys, dunes and
polar ice caps
A polar ice cap or polar cap is a high-latitude region of a planet, dwarf planet, or natural satellite that is covered in ice.
There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor a ...
. It has two small and irregularly shaped moons,
Phobos and
Deimos.
Some of the most notable surface features on Mars include
Olympus Mons
Olympus Mons (; Latin for Mount Olympus) is a large shield volcano on Mars. The volcano has a height of over 21.9 km (13.6 mi or 72,000 ft) as measured by the Mars Orbiter Laser Altimeter (MOLA). Olympus Mons is about two and a h ...
, the largest
volcano
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates are ...
and
highest known mountain in the Solar System and
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
Borealis basin
The North Polar Basin, more commonly known as the Borealis Basin, is a large Depression (geology), basin in the northern hemisphere of Mars that covers 40% of the planet. Some scientists have postulated that the basin formed during the Impact ev ...
in the Northern Hemisphere covers approximately 40% of the planet and may be a large impact feature.
Days and seasons on Mars are comparable to those of Earth, as the planets have a similar
rotation period
The rotation period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) may refer to its sidereal rotation period, i.e. the time that the object takes to complete a single revolution around its axis of rotation relative to the ...
and tilt of the
rotational axis relative to the
ecliptic plane
The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic again ...
. Liquid
water on the surface of Mars cannot exist due to low atmospheric pressure, which is less than 1% of the atmospheric pressure on Earth.
[ ] Both of Mars's polar ice caps appear to be made largely of water.
In the distant past, Mars was likely wetter, and thus possibly more suited for life. It is not known whether life has ever existed on Mars.
Mars has been explored by several uncrewed spacecraft, beginning with ''Mariner 4
Mariner 4 (together with Mariner 3 known as Mariner-Mars 1964) was the Mariner program, 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 ...
'' in 1965. NASA's ''Viking 1
''Viking 1'' was the first of two spacecraft, along with ''Viking 2'', each consisting of an orbiter and a lander, sent to Mars as part of NASA's Viking program. The lander touched down on Mars on July 20, 1976, the first successful Mars land ...
'' lander transmitted in 1976 the first images from the Martian surface. Two countries have successfully deployed rovers on Mars, the United States first doing so with ''Sojourner
A sojourner is a person who resides temporarily in a place.
Sojourner may also refer to:
* Sojourner Truth (1797–1883), abolitionist and women's rights activist
* Albert Sojourner (1872–1951), member of the Mississippi House of Representative ...
'' in 1997 and China with ''Zhurong
Zhurong (), also known as Chongli (), is an important personage in Chinese mythology and Chinese folk religion. According to the '' Huainanzi'' and the philosophical texts of Mozi and his followers, Zhurong is a god of fire and of the south.
Th ...
'' in 2021. There are also planned future missions to Mars, such as a Mars sample-return mission
A Mars sample-return (MSR) mission is a proposed mission to collect rock and dust samples on Mars and return them to Earth. Such a mission would allow more extensive analysis than that allowed by onboard sensors.
The three most recent concept ...
set to happen in 2026, and the ''Rosalind Franklin'' rover mission, which was intended to launch in 2018 but was delayed to 2024 at the earliest, with a more likely launch date at 2028.
Mars can be viewed from Earth with the naked eye, as can its reddish coloring. This appearance, due to the iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...
prevalent on its surface, has led to Mars often being called the Red Planet. It is among the brightest objects in Earth's sky, with an apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...
that reaches −2.94, comparable to that of Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
and surpassed only by Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
, the Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
and the Sun. Historically, Mars has been observed since ancient times, and over the millennia has been featured in culture and the arts in ways that have reflected humanity's growing knowledge of it.
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 opposition
Mars has an orbit with a semimajor axis of 1.524 astronomical units (228 million km), and an eccentricity of 0.0934.Jean Meeus, ''Astronomical Formulæ for Calculators''. (Richmond, VA: Willmann-Bell, 1988) 99. Elements by F. E. Ross The planet o ...
s of Mars, which are distinguished because Mars is close to perihelion, making it even closer to Earth.
Ancient and medieval observations
The ancient Sumer
Sumer () is the earliest known civilization in the historical region of southern Mesopotamia (south-central Iraq), emerging during the Chalcolithic and early Bronze Ages between the sixth and fifth millennium BC. It is one of the cradles of c ...
ians named Mars Nergal
Nergal ( Sumerian: d''KIŠ.UNU'' or ; ; Aramaic: ܢܸܪܓܲܠ; la, Nirgal) was a Mesopotamian god worshiped through all periods of Mesopotamian history, from Early Dynastic to Neo-Babylonian times, with a few attestations under indicating hi ...
, 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
Nineveh (; akk, ; Biblical Hebrew: '; ar, نَيْنَوَىٰ '; syr, ܢܝܼܢܘܹܐ, Nīnwē) was an ancient Assyrian city of Upper Mesopotamia, located in the modern-day city of Mosul in northern Iraq. It is located on the eastern ban ...
. 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 astronomers
Egyptian describes something of, from, or related to Egypt.
Egyptian or Egyptians may refer to:
Nations and ethnic groups
* Egyptians, a national group in North Africa
** Egyptian culture, a complex and stable culture with thousands of years of ...
and, by 1534 BCE, they were familiar with the retrograde motion
Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure). It may also describe other motions such as precession or ...
of the planet.[ By the period of the ]Neo-Babylonian Empire
The Neo-Babylonian Empire or Second Babylonian Empire, historically known as the Chaldean Empire, was the last polity ruled by monarchs native to Mesopotamia. Beginning with the coronation of Nabopolassar as the List of kings of Babylon, King of B ...
, the Babylonian astronomers
Babylonian astronomy was the study or recording of celestial objects during the early history of Mesopotamia.
Babylonian astronomy seemed to have focused on a select group of stars and constellations known as Ziqpu stars. These constellations m ...
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 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
Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...
, the planet was known as grc, Πυρόεις, label=none. Commonly, the Greek name for the planet now referred to as Mars, was Ares. It was the Romans who named the planet Mars, for their god of war, often represented by the sword and shield of the planet's namesake.
In the fourth century BCE, Aristotle
Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
noted that Mars disappeared behind the Moon during an occultation
An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...
, indicating that the planet was farther away. Ptolemy
Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importanc ...
, a Greek living in Alexandria
Alexandria ( or ; ar, ٱلْإِسْكَنْدَرِيَّةُ ; grc-gre, Αλεξάνδρεια, Alexándria) is the second largest city in Egypt, and the largest city on the Mediterranean coast. Founded in by Alexander the Great, 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 later called the ''Almagest
The ''Almagest'' is a 2nd-century Greek-language mathematical and astronomical treatise on the apparent motions of the stars and planetary paths, written by Claudius Ptolemy ( ). One of the most influential scientific texts in history, it canoni ...
'' (from the Arabic for "greatest"), which became the authoritative treatise on Western astronomy for the next fourteen centuries. Literature from ancient China confirms that Mars was known by Chinese astronomers by no later than the fourth century BCE.[ In the ]East Asian
East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea a ...
cultures, Mars is traditionally referred to as the "fire star" (Chinese: ), based on the ''Wuxing'' system.
During the seventeenth century A.D., Tycho Brahe
Tycho Brahe ( ; born Tyge Ottesen Brahe; generally called Tycho (14 December 154624 October 1601) was a Danish astronomer, known for his comprehensive astronomical observations, generally considered to be the most accurate of his time. He was k ...
measured the diurnal parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...
of Mars that Johannes Kepler
Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws ...
used to make a preliminary calculation of the relative distance to the planet. From Brahe's observations of Mars, Kepler deduced that the planet orbited the Sun not in a circle, but in an ellipse
In mathematics, an ellipse is a plane curve surrounding two focus (geometry), focal points, such that for all points on the curve, the sum of the two distances to the focal points is a constant. It generalizes a circle, which is the special ty ...
. Moreover, Kepler showed that Mars sped up as it approached the Sun and slowed down as it moved farther away, in a manner that later physicists would explain as a consequence of the conservation of angular momentum
In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity—the total angular momentum of a closed system ...
. 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
Giovanni Domenico Cassini, also known as Jean-Dominique Cassini (8 June 1625 – 14 September 1712) was an Italian (naturalised French) mathematician, astronomer and engineer. Cassini was born in Perinaldo, near Imperia, at that time in the C ...
in 1672. The early parallax measurements were hampered by the quality of the instruments.[ The only ]occultation
An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...
of Mars by Venus observed was that of 13 October 1590, seen by Michael Maestlin
Michael Maestlin (also Mästlin, Möstlin, or Moestlin) (30 September 1550 – 26 October 1631) was a German astronomer and mathematician, known for being the mentor of Johannes Kepler. He was a student of Philipp Apian and was known as the tea ...
at Heidelberg
Heidelberg (; Palatine German language, Palatine German: ''Heidlberg'') is a city in the States of Germany, German state of Baden-Württemberg, situated on the river Neckar in south-west Germany. As of the 2016 census, its population was 159,914 ...
.[ In 1610, Mars was viewed by Italian astronomer ]Galileo Galilei
Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
, 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
Christiaan Huygens, Lord of Zeelhem, ( , , ; also spelled Huyghens; la, Hugenius; 14 April 1629 – 8 July 1695) was a Dutch mathematician, physicist, engineer, astronomer, and inventor, who is regarded as one of the greatest scientists of ...
.
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. The Italian astronomer Giovanni Schiaparelli
Giovanni Virginio Schiaparelli ( , also , ; 14 March 1835 – 4 July 1910) was an Italian astronomer and science historian.
Biography
He studied at the University of Turin, graduating in 1854, and later did research at Berlin Observatory, ...
used a telescope in Milan
Milan ( , , Lombard: ; it, Milano ) is a city in northern Italy, capital of Lombardy, and the second-most populous city proper in Italy after Rome. The city proper has a population of about 1.4 million, while its metropolitan city h ...
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
Within visual perception, an optical illusion (also called a visual illusion) is an illusion caused by the visual system and characterized by a visual perception, percept that arguably appears to differ from reality. Illusions come in a wide v ...
. 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
Percival Lowell (; March 13, 1855 – November 12, 1916) was an American businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars, and furthered theories of a ninth planet within the Solar System. ...
founded an observatory which had 30- and 45-centimetre (12- and 18-in) 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 observed by other astronomers, like Henri Joseph Perrotin
Henri Joseph Anastase Perrotin (December 19, 1845 – February 29, 1904) was a French astronomer and a discoverer of minor planets. Some sources give his middle name as Athanase.
In his early career, he and Guillaume Bigourdan were assis ...
and Louis Thollon
Louis Thollon (2 May 1829 – 8 April 1887) was a French astronomer.
He was born in Ambronay, France. Beginning in 1881, Thollon joined the staff of the new Nice Observatory where he undertook a long-term observation program of the Sun using a spe ...
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 observations in 1909 by Antoniadi with an telescope, irregular patterns were observed, but no ''canali'' were seen.][
]
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 an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...
, 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 with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally ...
, or rust. It can look like butterscotch
Butterscotch is a type of confectionery whose primary ingredients are brown sugar and butter, but other ingredients are part of some recipes, such as corn syrup, cream, vanilla, and salt. The earliest known recipes, in mid-19th century Yorkshir ...
;[ 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. ( ...
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), everything except the appendages
* Core (manufacturing), used in casting and molding
* Core (optical fiber), the signal-carrying portion of an optical fiber
* Core, the centra ...
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 (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
.[ This ]iron(II) sulfide
Iron(II) sulfide or ferrous sulfide (Br.E. sulphide) is one of a family chemical compounds and minerals with the approximate formula . Iron sulfides are often iron-deficient non-stoichiometric. All are black, water-insoluble solids.
Preparatio ...
core is thought to be twice as rich in lighter elements as Earth's.[ The core is surrounded by a silicate mantle 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, the growth and behavior of the strong, old cores of continents k ...
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 with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
, magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
, aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
, calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
, and potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
. The average thickness of the planet's crust is about , with a maximum thickness of .[ By comparison, Earth's crust averages in thickness.
Mars is seismically active. ]InSight
Insight is the understanding of a specific cause and effect within a particular context. The term insight can have several related meanings:
*a piece of information
*the act or result of understanding the inner nature of things or of seeing intu ...
has detected and recorded over 450 marsquake
A marsquake is a quake which, much like an earthquake, would be a shaking of the surface or interior of the planet Mars as a result of the sudden release of energy in the planet's interior, such as the result of plate tectonics, which most quakes ...
s and related events in 2019. In 2021 it was reported that based on eleven low-frequency Marsquakes detected by the ''InSight'' lander 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 elements like oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
and hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
in addition to the iron–nickel alloy and about 15% of sulfur.
The core of Mars is overlaid by the rocky mantle, which, however, does not seem to have a layer analogous to the Earth's lower mantle
The lower mantle, historically also known as the mesosphere, represents approximately 56% of Earth's total volume, and is the region from 660 to 2900 km below Earth's surface; between the transition zone and the outer core. The preliminar ...
. The Martian mantle appears to be solid down to the depth of about 500 km, where the low-velocity zone (partially melted asthenosphere
The asthenosphere () is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between ~ below the surface, and extends as deep as . However, the lower boundary of the asthenosphere is not ...
) 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 rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, ...
with a surface that consists of minerals containing silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
and oxygen, metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
s, and other elements that typically make up rock
Rock most often refers to:
* Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids
* Rock music, a genre of popular music
Rock or Rocks may also refer to:
Places United Kingdom
* Rock, Caerphilly, a location in Wales ...
. 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 series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma ...
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
, although parts are more silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
-rich than typical basalt and may be similar to andesitic
Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...
rocks on Earth, or silica glass. Regions of low albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
suggest concentrations of plagioclase feldspar
Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more prope ...
, 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 minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...
. Localized concentrations of hematite
Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
and olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
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 with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally ...
dust.
Although Mars has no evidence of a structured global 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 (or palaeomagnetismsee ), is the study of magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called ''paleomagnetists.''
Certain magnetic minerals in rock ...
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 developed by NASA's Jet Propulsion Laboratory and launched November 1996. MGS was a global mapping mission that examined the entire planet, from the ionosphere down through the a ...
''), is that these bands suggest plate tectonic activity on Mars four billion years ago, before the planetary dynamo
file:DynamoElectricMachinesEndViewPartlySection USP284110.png, "Dynamo Electric Machine" (end view, partly section, )
A dynamo is an electrical generator that creates direct current using a commutator (electric), commutator. Dynamos were the f ...
ceased to function and the planet's magnetic field faded.
Scientists have theorized that during the Solar System's formation Mars was created as the result of a random process
In probability theory and related fields, a stochastic () or random process is a mathematical object usually defined as a family of random variables. Stochastic processes are widely used as mathematical models of systems and phenomena that appe ...
of run-away accretion of material from the protoplanetary disk
A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, be ...
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 with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
, phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
, and sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
, 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 particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
.[
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 years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypoth ...
". 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 is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
-sized body about four billion years ago. The event, thought to be the cause of the Martian hemispheric dichotomy, created the smooth Borealis basin
The North Polar Basin, more commonly known as the Borealis Basin, is a large Depression (geology), basin in the northern hemisphere of Mars that covers 40% of the planet. Some scientists have postulated that the basin formed during the Impact ev ...
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 characterized by high rates of meteorite and asteroid impacts and the possible presence of abundant surface water. The absolute age of the Noachian period is uncertain ...
period: 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 Asc ...
bulge, a volcanic upland, is thought to have formed during this period, with extensive flooding by liquid water late in the period. Named after Noachis Terra
Noachis Terra (; lit. "Land of Noah") is an extensive southern landmass (''terra'') of the planet Mars. It lies west of the giant Hellas impact basin, roughly between the latitudes −20° and −80° and longitudes 30° west and 30° east, cent ...
.
* Hesperian
The Hesperian is a system (stratigraphy), geologic system and geologic timescale, time period on the planet Mars characterized by widespread Volcanology of Mars, volcanic activity and catastrophic flooding that carved immense outflow channels acr ...
period: 3.5 to between 3.3 and 2.9 billion years ago. The Hesperian period is marked by the formation of extensive lava plains. 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 ( Tyrrhe ...
.
* Amazonian period: between 3.3 and 2.9 billion years ago to the present. Amazonian regions have few meteorite impact
An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or m ...
craters but are otherwise quite varied. Olympus Mons
Olympus Mons (; Latin for Mount Olympus) is a large shield volcano on Mars. The volcano has a height of over 21.9 km (13.6 mi or 72,000 ft) as measured by the Mars Orbiter Laser Altimeter (MOLA). Olympus Mons is about two and a h ...
formed during this period, with lava flows elsewhere on Mars. Named after Amazonis Planitia
Amazonis Planitia (, Latin ''Amāzŏnis'') is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium volcanic provinces, to the west of Olympus Mons, in the Amazonis and Memnonia quadrangles, centered at . The plain' ...
.
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 region of Mars, located to the south of the Elysium Rise. They are part of a network of outflow channels in this region that are understood ...
is home to sheet-like lava flows created about 200 mya. Water flows in the graben
In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults.
Etymology
''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...
s called the Cerberus Fossae
The Cerberus Fossae are a series of semi-parallel fissures on Mars formed by faults which pulled the crust apart in the Cerberus region. They are 1235 km across and centered at 11.28 °N and 166.37 °E.
Their northernmost latitude is 16.16 ...
occurred less than 20 Mya, indicating equally recent volcanic intrusions.[ The '']Mars Reconnaissance Orbiter
''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft designed to study the geology and climate of Mars, provide reconnaissance of future landing sites, and relay data from surface missions back to Earth. It was launched on August 12, 2005, an ...
'' has captured images of avalanches.
Soil
The ''Phoenix
Phoenix most often refers to:
* Phoenix (mythology), a legendary bird from ancient Greek folklore
* Phoenix, Arizona, a city in the United States
Phoenix may also refer to:
Mythology
Greek mythological figures
* Phoenix (son of Amyntor), a ...
'' lander returned data showing Martian soil to be slightly alkaline and containing elements such as magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
, sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
, potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
and chlorine
Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
. These nutrients are found in soils on Earth. 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 languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College ...
pH of 7.7, and contains 0.6% of the salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
perchlorate
A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. Per ...
, concentrations that are Martian soil#Toxicity, toxic to humans.
Dark slope streak, 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 dust devils.[ Several other explanations have been put forward, including those that involve water or even the growth of organisms.][
]
Hydrology
Water in its liquid form 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 .[ Water on terrestrial planets of the Solar System, Large quantities of ice are thought to be trapped within the thick cryosphere of Mars. Radar data from ''Mars Express'' and the '']Mars Reconnaissance Orbiter
''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft designed to study the geology and climate of Mars, provide reconnaissance of future landing sites, and relay data from surface missions back to Earth. It was launched on August 12, 2005, an ...
'' (MRO) show large quantities of ice at both poles,[ and at middle latitudes. The Phoenix lander directly sampled water ice in shallow Martian soil on 31 July 2008.]
Geomorphology, 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, 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, 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 only a few million years ago.][ Elsewhere, particularly on the oldest areas of the Martian surface, finer-scale, dendritic Valley networks (Mars), 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 surface runoff, runoff 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. 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 River delta, deltas and alluvial fans 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 Volcanic crater lake, 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 compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
and goethite, both of which sometimes form in the presence of water.
Observations and findings of water evidence
In 2004, ''Opportunity'' detected the mineral jarosite. This forms only in the presence of acidic water, showing that water once existed on Mars.[ The ''Spirit'' rover found concentrated deposits of ]silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
in 2007 that indicated wet conditions in the past, and in December 2011, the mineral gypsum, which also forms in the presence of water, was found on the surface by NASA's Mars rover Opportunity. It is estimated that the amount of water in the upper mantle of Mars, represented by hydroxyl ions contained within Martian minerals, 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 .
On 18 March 2013, NASA reported evidence from instruments on the Curiosity (rover), ''Curiosity'' rover of mineral hydration, likely hydrated calcium sulfate, in several Rock (geology), rock samples including the broken fragments of Tintina (rock), "Tintina" rock and List of rocks on Mars#Curiosity, "Sutton Inlier" rock as well as in vein (geology), veins and nodule (geology), nodules in other rocks like List of rocks on Mars#Curiosity, "Knorr" rock and List of rocks on Mars#Curiosity, "Wernicke" rock.[ ] Analysis using the rover's Curiosity (rover)#Dynamic Albedo of Neutrons (DAN), 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 strong evidence of hydrated brine flows in recurring slope lineae, based on spectrometer readings of the darkened areas of slopes. These streaks flow downhill in Martian summer, when the temperature is above −23° Celsius, and freeze at lower temperatures. These observations supported earlier hypotheses, based on timing of formation and their rate of growth, that these dark streaks resulted from water flowing just below the surface. However, later work suggested that the lineae may be dry, granular flows instead, with at most a limited role for water in initiating the process. A definitive conclusion about the presence, extent, and role of liquid water on the Martian surface remains elusive.
Researchers suspect much of the low northern plains of the planet were Mars ocean hypothesis, covered with an ocean hundreds of meters deep, though this theory 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, which the Mars Express orbiter found to be filled with approximately of water ice.
In November 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior.[ ] During observations from 2018 through 2021, the ExoMars Trace Gas Orbiter spotted indications of water, probably subsurface ice, in the Valles Marineris canyon system.
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 , 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 force, 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 names
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.
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 roughly 50 km are named for deceased scientists and writers and others who have contributed to the study of Mars. Smaller craters 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 (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
features retain many of the older names but are often updated to reflect new knowledge of the nature of the features. For example, ''Nix Olympica'' (the snows of Olympus) has become ''Olympus Mons
Olympus Mons (; Latin for Mount Olympus) is a large shield volcano on Mars. The volcano has a height of over 21.9 km (13.6 mi or 72,000 ft) as measured by the Mars Orbiter Laser Altimeter (MOLA). Olympus Mons is about two and a h ...
'' (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 (, Latin ''Amāzŏnis'') is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium volcanic provinces, to the west of Olympus Mons, in the Amazonis and Memnonia quadrangles, centered at . The plain' ...
(''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. 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, Harold Masursky, and Gérard de Vaucouleurs 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).][
For mapping purposes, the United States Geological Survey divides the surface of Mars into List of quadrangles on Mars, thirty cartographic quadrangles, each named for a classical albedo feature it contains.
]
Volcanoes
The shield volcano Olympus Mons
Olympus Mons (; Latin for Mount Olympus) is a large shield volcano on Mars. The volcano has a height of over 21.9 km (13.6 mi or 72,000 ft) as measured by the Mars Orbiter Laser Altimeter (MOLA). Olympus Mons is about two and a h ...
(''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 Asc ...
, which contains several other large volcanoes. The edifice is over wide. Because the mountain is so large, with complex structure at its edges, allocating a height to it is difficult. Its local relief, from the foot of the cliffs which form its northwest margin to its peak, is over , a little over twice the height of Mauna Kea as measured from its base on the ocean floor. The total elevation change from the plains of Amazonis Planitia
Amazonis Planitia (, Latin ''Amāzŏnis'') is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium volcanic provinces, to the west of Olympus Mons, in the Amazonis and Memnonia quadrangles, centered at . The plain' ...
, over to the northwest, to the summit approaches , roughly three times the height of Mount Everest, which in comparison stands at just over . Consequently, Olympus Mons is either the List of tallest mountains in the Solar System, tallest or second-tallest mountain in the Solar System; the only known mountain which might be taller is the Rheasilvia peak on the asteroid 4 Vesta, Vesta, at .
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. It is possible 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. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
. If this is the case, the Northern Hemisphere of Mars would be the site of an impact crater
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...
in size, or roughly the area of Europe, Asia, and Australia combined, surpassing Utopia Planitia and the Moon's 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 exposed crater is Hellas Planitia, Hellas, which is wide and deep, and is a light albedo feature clearly visible from Earth. There are other notable impact features, such as Argyre Planitia, Argyre, which is around in diameter, and Isidis Planitia, Isidis, which is around in diameter. 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
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
.
Martian craters can have a morphology that suggests the ground became wet after the meteor impacted.
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 Agathodaemon 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, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults.
Etymology
''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...
, 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 particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
interacts directly with the Martian ionosphere, lowering the atmospheric density by atmospheric stripping, stripping away atoms from the outer layer. Both ''Mars Global Surveyor
''Mars Global Surveyor'' (MGS) was an American robotic space probe developed by NASA's Jet Propulsion Laboratory and launched November 1996. MGS was a global mapping mission that examined the entire planet, from the ionosphere down through the a ...
'' and ''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 for Mount Olympus) is a large shield volcano on Mars. The volcano has a height of over 21.9 km (13.6 mi or 72,000 ft) as measured by the Mars Orbiter Laser Altimeter (MOLA). Olympus Mons is about two and a h ...
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 with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
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 hue due to iron oxide particles suspended in it. The concentration of Methane on Mars, methane in the Martian atmosphere fluctuates from about 0.24 Parts per billion, ppb during the northern winter to about 0.65 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 olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
, which is known to be common on Mars, or by Martian life.
Compared to Earth, its higher concentration of atmospheric CO2 and lower surface pressure may be why sound is attenuated more on Mars, where natural sources are rare apart from the wind. Using acoustic recordings collected by the ''Perseverance'' rover, researchers concluded that the speed of sound there is approximately 240 m/s for frequencies below 240 Hz, and 250 m/s for those above.
Aurora on Mars, Auroras have been detected on Mars.[ ] Because Mars lacks a global magnetic field, the types and distribution of auroras there differ from those on Earth; rather than being mostly restricted to polar regions, a Martian aurora can encompass the planet. 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 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 Mars sol, 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 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.][
Mars approaches Earth in a synodic period of 779.94 days. Earth orbits the Sun the closest to Mars's orbit around the Sun, and Mars orbit is the second closest to Earth after the orbit of Venus. Therefore, their closest approaches, the inferior conjunctions, are the second closest for Earth after those with Venus, and the closest for Mars to any other planet. The gravitational potential difference, and thus the Delta-v budget, delta-v needed to Transfer orbit, transfer between Mars and Earth is the second lowest for Earth and the lowest for Mars to any other planet, while transfers can possibly be optimized with Venus Flyby (spaceflight), flybys.]
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 the presence of 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". That observation 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 were being published as late as 1962.[
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 circumstellar habitable zone, habitable zone, which for the Sun is estimated to extend from within the orbit of Earth to about that 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 environmental conditions on Mars are a challenge to sustaining organic life: the planet has little heat transfer across its surface, it has poor insulation against Solar wind#Atmospheres, bombardment by the ]solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
due to the absence of a magnetosphere and has 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 landers, ''Viking'' landers, ''Spirit (rover), Spirit'' and ''Opportunity'' rovers, ''Phoenix
Phoenix most often refers to:
* Phoenix (mythology), a legendary bird from ancient Greek folklore
* Phoenix, Arizona, a city in the United States
Phoenix may also refer to:
Mythology
Greek mythological figures
* Phoenix (son of Amyntor), a ...
'' 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, ''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. Tests conducted by the ''Phoenix Mars'' lander have shown that the soil has an alkaline pH 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 2014 analysis of Martian meteorite EETA79001 found chlorate, perchlorate
A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. Per ...
, and nitrate ions in sufficiently high concentration to suggest that they are widespread on Mars. UV and X-ray radiation would turn chlorate and perchlorate ions into other, highly redox, reactive Oxyanion, oxychlorines, indicating that any organic molecules would have to be buried under the surface 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.[ ]
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. The origin of both moons is unclear, although a popular theory states that they were asteroids captured into Martian orbit.[
Both satellites were discovered in 1877 by Asaph Hall and were named after the characters Phobos (mythology), Phobos (the deity of panic and fear) and Deimos (mythology), Deimos (the deity of terror and dread), twins from Greek mythology who 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 Earth's satellite, the Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
. 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. Because the orbit of Phobos is below synchronous altitude, tidal forces from 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 satellites is not well understood. Their low albedo and carbonaceous chondrite composition have been regarded as similar to asteroids, supporting a capture theory. The unstable orbit of Phobos would seem to point toward a relatively recent capture. But both have circular orbits, near the equator that 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 for their origin as satellites of Mars 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 satellite. 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. It is also possible that Phobos and Deimos are fragments of an older moon, formed by debris from a large impact on Mars, and then destroyed by a more recent impact upon the satellite.
Mars may have yet-undiscovered 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. NASA's ''Mariner 4'' was the first spacecraft to visit Mars; launched 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.
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. After the results of the ''Viking'' life-detection experiments, the hypothesis of a hostile, dead planet was generally accepted.[ The data from ''Mariner 9'' and ''Viking'' allowed better maps of Mars to be made, and the '']Mars Global Surveyor
''Mars Global Surveyor'' (MGS) was an American robotic space probe developed by NASA's Jet Propulsion Laboratory and launched November 1996. MGS was a global mapping mission that examined the entire planet, from the ionosphere down through the a ...
'' mission, which launched in 1996 and operated until late 2006, produced complete, extremely detailed maps of the Martian topography, magnetic field and surface minerals. These maps are available online at websites including Google Mars. Both the ''Mars Reconnaissance Orbiter
''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft designed to study the geology and climate of Mars, provide reconnaissance of future landing sites, and relay data from surface missions back to Earth. It was launched on August 12, 2005, an ...
'' and ''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 are in orbit'': 2001 Mars Odyssey'', ''Mars Express'', ''Mars Reconnaissance Orbiter
''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft designed to study the geology and climate of Mars, provide reconnaissance of future landing sites, and relay data from surface missions back to Earth. It was launched on August 12, 2005, an ...
'', ''MAVEN'', ''ExoMars Trace Gas Orbiter'', the Emirates Mars Mission, ''Hope'' orbiter, and the ''Tianwen-1'' orbiter. Another six are on the surface: the ''InSight
Insight is the understanding of a specific cause and effect within a particular context. The term insight can have several related meanings:
*a piece of information
*the act or result of understanding the inner nature of things or of seeing intu ...
'' lander, the Mars Science Laboratory ''Curiosity (rover), Curiosity'' rover, the ''Perseverance (rover), Perseverance'' rover, the ''Ingenuity (helicopter), Ingenuity'' helicopter, the ''Tianwen-1'' lander, and the ''Zhurong
Zhurong (), also known as Chongli (), is an important personage in Chinese mythology and Chinese folk religion. According to the '' Huainanzi'' and the philosophical texts of Mozi and his followers, Zhurong is a god of fire and of the south.
Th ...
'' rover.
Planned missions to Mars include the ''Rosalind Franklin'' rover mission, designed to search for evidence of past life, which was intended to be launched in 2018 but has been repeatedly delayed, with a launch date pushed to 2024 at the earliest, with a more likely one sometime in 2028. A current concept for a joint NASA-European Space Agency, ESA mission to Mars sample-return mission, return samples from Mars would launch in 2026.
Several plans for a human mission to Mars have been proposed throughout the 20th and 21st centuries, but none have come to fruition. The NASA Authorization Act of 2017 directed NASA to study the feasibility of a crewed Mars mission in the early 2030s; the resulting report eventually concluded that this would be unfeasible. In addition, in 2021, China was planning to send a crewed Mars mission in 2033. Private spaceflight, Privately held companies such as SpaceX have also SpaceX Mars program, proposed plans to send humans to Mars, with the eventual goal to Colonization of Mars, settle on the planet. The moon Phobos has been proposed as an anchor point for a space elevator.
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.][
]
Viewing
The mean apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...
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
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
) is second only to Venus in luminosity. Mars usually appears distinctly yellow, orange, or red. When farthest away from Earth, it is more than seven times farther away than when it is closest. Mars is usually close enough for particularly good viewing once or twice at 15-year or 17-year intervals. As Mars approaches opposition, it begins a period of retrograde motion
Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure). It may also describe other motions such as precession or ...
, which means it will appear to move backwards in a looping curve with respect to the background stars. This retrograde motion lasts for about 72 days, and Mars reaches its peak luminosity in the middle of this interval.[
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 most recent 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.][
Mars comes into opposition from Earth every 2.1 years. The planets come into opposition near Mars's perihelion in 2003, 2018 and 2035, with the 2020 and 2033 events being particularly close to perihelic opposition.] 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.][
Optical ground-based telescopes are typically limited to resolving features about across when Earth and Mars are closest because of Earth's atmosphere.]
In culture
Mars is named after the Ancient Rome, Roman Mars (mythology), god of war. This association between Mars and war dates back at least to Babylonian astronomy, in which the planet was named for the god Nergal
Nergal ( Sumerian: d''KIŠ.UNU'' or ; ; Aramaic: ܢܸܪܓܲܠ; la, Nirgal) was a Mesopotamian god worshiped through all periods of Mesopotamian history, from Early Dynastic to Neo-Babylonian times, with a few attestations under indicating hi ...
, deity of war and destruction. It persisted into modern times, as exemplified by Gustav Holst's orchestral suite ''The Planets'', whose famous first movement labels Mars "the bringer of war". Gender symbol, The planet's symbol, a circle with a spear 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, though a possible predecessor has been found in the Greek Oxyrhynchus Papyri.[
]
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
Percival Lowell (; March 13, 1855 – November 12, 1916) was an American businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars, and furthered theories of a ninth planet within the Solar System. ...
'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".[ High-resolution mapping of the surface of Mars revealed no artifacts of habitation, but pseudoscientific speculation about intelligent life on Mars still continues. Reminiscent of the ''canali'' observations, these speculations are based on small scale features perceived in the spacecraft images, such as "pyramids" and the "Cydonia (Mars), Face on Mars". In his book ''Cosmos (Sagan book), Cosmos,'' planetary astronomer Carl Sagan wrote: "Mars has become a kind of mythic arena onto which we have projected our Earthly hopes and fears."][
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. 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; for many science-fiction authors, the new discoveries initially seemed like a constraint, but eventually the post-''Viking'' knowledge of Mars became itself a source of inspiration for works like Kim Stanley Robinson's Mars trilogy, ''Mars'' trilogy.
See also
* Flag of Mars
* List of missions to Mars
* Magnetic field of Mars
* Mars monolith
* Mineralogy of Mars
* Outline of Mars
* List of gravitationally rounded objects of the Solar System
Notes
References
External links
Mars Trek – An integrated map browser of maps and datasets for Mars
Google Mars
an
Google Mars 3D
interactive maps of the planet
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Mars,
Articles containing video clips
Astronomical objects known since antiquity
Planets of the Solar System
Terrestrial planets