An atmosphere () is a layer of

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

or layers of gases that envelop a

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 ...

, and is held in place by the

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

of the planetary body. A planet retains an atmosphere when the gravity is great and the

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

of the atmosphere is low. A

stellar atmosphere The stellar atmosphere is the outer region of the volume of a star, lying above the stellar core, radiation zone and convection zone. Overview The stellar atmosphere is divided into several regions of distinct character: * The photosphere, which ...

is the outer region of a star, which includes the layers above the

opaque Opacity or opaque may refer to: * Impediments to (especially, visible) light: ** Opacities, absorption coefficients ** Opacity (optics), property or degree of blocking the transmission of light * Metaphors derived from literal optics: ** In lingu ...

photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...

; stars of low temperature might have outer atmospheres containing compound

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

s. The

atmosphere of Earth The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...

is composed of

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

(78%),

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 ...

(21%),

argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...

(0.9%),

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

(0.04%) and trace gases. Most organisms use oxygen for

respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellula ...

; lightning and bacteria perform

nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...

to produce

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

that is used to make

nucleotides Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules w ...

and

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

;

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

, and

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

use carbon dioxide for

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

. The layered composition of the atmosphere minimises the harmful effects of

sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

radiation, 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 ...

, and

cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

s to protect organisms from genetic damage. The current composition of the atmosphere of the Earth is the product of billions of years of biochemical modification of the

paleoatmosphere A paleoatmosphere (or ''palaeoatmosphere'') is an atmosphere, particularly that of Earth, at some unspecified time in the geological past. The composition of Earth's paleoatmosphere can be inferred today from the study of the abundance of Proxy (c ...

by living organisms
Evolution of the Atmosphere

Composition

The initial gaseous composition of an atmosphere is determined by the chemistry and temperature of the local

solar nebula The formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a ...

from which a

is formed, and the subsequent escape of some gases from the interior of the atmosphere proper. The original atmosphere of the planets originated from a rotating disc of gases, which collapsed onto itself and then divided into a series of spaced rings of gas and matter that, which later condensed to form the planets of 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 ...

. The atmospheres of the planets

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 ...

and

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

are principally composed of

and

. The composition of Earth's atmosphere is determined by the by-products of the life that it sustains. Dry air (mixture of gases) from

Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...

contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and traces of hydrogen, helium, and other "noble" gases (by volume), but generally a variable amount of water vapor is also present, on average about 1% at sea level. The low temperatures and higher gravity of the Solar System's

giant planet The giant planets constitute a diverse type of planet much larger than Earth. They are usually primarily composed of low-boiling-point materials (volatiles), rather than rock or other solid matter, but massive solid planets can also exist. Ther ...

s—

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 ...

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...

and

Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...

—allow them more readily to retain gases with low

molecular mass The molecular mass (''m'') is the mass of a given molecule: it is measured in daltons (Da or u). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The related quanti ...

es. These planets have hydrogen–helium atmospheres, with trace amounts of more complex compounds. Two satellites of the outer planets possess significant atmospheres. Titan, a moon of Saturn, and

Triton Triton commonly refers to: * Triton (mythology), a Greek god * Triton (moon), a satellite of Neptune Triton may also refer to: Biology * Triton cockatoo, a parrot * Triton (gastropod), a group of sea snails * ''Triton'', a synonym of ''Triturus' ...

, a moon of Neptune, have atmospheres mainly of

. When in the part of its orbit closest to the Sun,

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 ...

has an atmosphere of nitrogen and methane similar to Triton's, but these gases are frozen when it is farther from the Sun. Other bodies within the Solar System have extremely thin atmospheres not in equilibrium. These include 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 ...

(

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 ...

gas),

Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

(sodium gas),

Europa Europa may refer to: Places * Europe * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Cliff ...

(oxygen), Io (

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 ...

), and

Enceladus Enceladus is the sixth-largest moon of Saturn (19th largest in the Solar System). It is about in diameter, about a tenth of that of Saturn's largest moon, Titan. Enceladus is mostly covered by fresh, clean ice, making it one of the most refl ...

(

water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous pha ...

). The first exoplanet whose atmospheric composition was determined is

HD 209458 HD 209458 is an 8th- magnitude star in the constellation Pegasus. It is a G0V star, and is thus very similar to the Sun. Because it is located at a distance of about 159 light years, it is not visible to the unaided eye. With good bino ...

b, a gas giant with a close orbit around a star in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Pegasus Pegasus ( grc-gre, Πήγασος, Pḗgasos; la, Pegasus, Pegasos) is one of the best known creatures in Greek mythology. He is a winged divine stallion usually depicted as pure white in color. He was sired by Poseidon, in his role as hor ...

. Its atmosphere is heated to temperatures over 1,000 K, and is steadily escaping into space. Hydrogen, oxygen, carbon and sulfur have been detected in the planet's inflated atmosphere.

Structure of atmosphere

Earth

The

is composed of layers with different properties, such as specific gaseous composition, temperature, and pressure. The

troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...

is the lowest layer of the atmosphere. This extends from the planetary surface to the bottom of the

stratosphere The stratosphere () is the second layer of the atmosphere of the Earth, located above the troposphere and below the mesosphere. The stratosphere is an atmospheric layer composed of stratified temperature layers, with the warm layers of air ...

. The troposphere contains 75–80 per cent of the mass of the atmosphere, and is the atmospheric layer wherein the weather occurs; the height of the troposphere varies between 17km at the equator and 7.0km at the poles. The

extends from the top of the troposphere to the bottom of the

mesosphere The mesosphere (; ) is the third layer of the atmosphere, directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as altitude increases. This characteristic is used to define its limits: it ...

, and contains the

ozone layer The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. It contains a high concentration of ozone (O3) in relation to other parts of the atmosphere, although still small in rela ...

, at an altitude between 15km and 35km. It is the atmospheric layer that absorbs most of the

ultraviolet radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

that Earth receives from the Sun. The

ranges from 50km to 85km, and is the layer wherein most

meteors A meteoroid () is a small rocky or metallic body in outer space. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as mic ...

are incinerated before reaching the surface. The

thermosphere The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the ...

extends from an altitude of 85km to the base of the

exosphere The exosphere ( grc, ἔξω "outside, external, beyond", grc, σφαῖρα "sphere") is a thin, atmosphere-like volume surrounding a planet or natural satellite where molecules are gravitationally bound to that body, but where the densit ...

at 690km and contains the

ionosphere The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...

, where solar radiation ionizes the atmosphere. The density of the ionosphere is greater at short distances from the planetary surface in the daytime and decreases as the ionosphere rises at night-time, thereby allowing a greater range of radio frequencies to travel greater distances. The

begins at 690 to 1,000km from the surface, and extends to roughly 10,000km, where it interacts with the

magnetosphere In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...

of Earth.

Pressure

Atmospheric pressure is the

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...

(per unit-area) perpendicular to a unit-area of planetary surface, as determined by the

weight In science and engineering, the weight of an object is the force acting on the object due to gravity. Some standard textbooks define weight as a Euclidean vector, vector quantity, the gravitational force acting on the object. Others define weigh ...

of the vertical column of atmospheric gases. In said atmospheric model, the

atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, 7 ...

, the weight of the mass of the gas, decreases at high altitude because of the diminishing mass of the gas above the point of

barometric A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis ...

measurement. The units of air pressure are based upon the standard atmosphere (atm), which is 101.325

kPa KPA may refer to: * Keele Postgraduate Association, Keele University, UK, formerly Keele Research Association (KRA) * Kensington (Olympia) station, London, England, National Rail station code * Kenya Ports Authority * ''Kiln phosphoric acid'', a ...

(760

Torr The torr (symbol: Torr) is a unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (). Thus one torr is exactly (≈ ). Historically, one torr was intended to be the same as one "millimeter of mercury ...

, or 14.696

pounds per square inch The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2; abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied to ...

(psi). The height at which the atmospheric pressure declines by a factor of '' e'' (an

irrational number In mathematics, the irrational numbers (from in- prefix assimilated to ir- (negative prefix, privative) + rational) are all the real numbers that are not rational numbers. That is, irrational numbers cannot be expressed as the ratio of two integ ...

equal to 2.71828) is called the

scale height In atmospheric, earth, and planetary sciences, a scale height, usually denoted by the capital letter ''H'', is a distance (vertical or radial) over which a physical quantity decreases by a factor of e (the base of natural logarithms, approximate ...

(''H''). For an atmosphere of uniform temperature, the scale height is proportional to the atmospheric temperature, and is inversely proportional to the product of the mean

of dry air, and the local acceleration of gravity at the point of barometric measurement.

Escape

Surface gravity The surface gravity, ''g'', of an astronomical object is the gravitational acceleration experienced at its surface at the equator, including the effects of rotation. The surface gravity may be thought of as the acceleration due to gravity experien ...

differs significantly among the planets. For example, the large gravitational force of the giant planet

retains light gases such as

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 ...

and

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

that escape from objects with lower gravity. Secondly, the distance from the Sun determines the energy available to heat atmospheric gas to the point where some fraction of its molecules'

thermal motion A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

exceed the planet's

escape velocity In celestial mechanics, escape velocity or escape speed is the minimum speed needed for a free, non- propelled object to escape from the gravitational influence of a primary body, thus reaching an infinite distance from it. It is typically ...

, allowing those to escape a planet's gravitational grasp. Thus, distant and cold Titan,

, and

are able to retain their atmospheres despite their relatively low gravities. Since a collection of gas molecules may be moving at a wide range of velocities, there will always be some fast enough to produce a slow leakage of gas into space. Lighter molecules move faster than heavier ones with the same thermal

kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its accele ...

, and so gases of low

molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

are lost more rapidly than those of high molecular weight. It is thought that

and

may have lost much of their water when, after being photodissociated into hydrogen and oxygen by solar

radiation, the hydrogen escaped.

Earth's magnetic field Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic f ...

helps to prevent this, as, normally, the solar wind would greatly enhance the escape of hydrogen. However, over the past 3 billion years Earth may have lost gases through the magnetic polar regions due to auroral activity, including a net 2% of its atmospheric oxygen. The net effect, taking the most important escape processes into account, is that an intrinsic magnetic field does not protect a planet from atmospheric escape and that for some magnetizations the presence of a magnetic field works to increase the escape rate. Other mechanisms that can cause atmosphere depletion are

-induced sputtering,

impact Impact may refer to: * Impact (mechanics), a high force or shock (mechanics) over a short time period * Impact, Texas, a town in Taylor County, Texas, US Science and technology * Impact crater, a meteor crater caused by an impact event * Impact ...

erosion,

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...

, and sequestration—sometimes referred to as "freezing out"—into the

regolith Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestria ...

and

polar 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 ...

Terrain

Atmospheres have dramatic effects on the surfaces of rocky bodies. Objects that have no atmosphere, or that have only an exosphere, have terrain that is covered in craters. Without an atmosphere, the planet has no protection from

meteoroid A meteoroid () is a small rocky or metallic body in outer space. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as micr ...

s, and all of them collide with the surface as

meteorites A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object en ...

and create craters. Most meteoroids burn up as

before hitting a planet's surface. When

meteoroids A meteoroid () is a small rocky or metallic body in outer space. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as micr ...

do impact, the effects are often erased by the action of wind.

Wind erosion Aeolian processes, also spelled eolian, pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth (or other planets). Winds may erode, transport, and deposit materials ...

is a significant factor in shaping the terrain of rocky planets with atmospheres, and over time can erase the effects of both craters and

volcanoes 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 ...

. In addition, since

liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...

s can not exist without pressure, an atmosphere allows liquid to be present at the surface, resulting in

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

s and

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

and Titan are known to have liquids at their surface and terrain on the planet suggests that

had liquid on its surface in the past.

Atmospheres in the Solar System

Solar system escape velocity vs surface temperature

Atmosphere of 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 r ...

Atmosphere of Mercury Mercury, being the closest to the Sun, with a weak magnetic field and the smallest mass of the recognized terrestrial planets, has a very tenuous and highly variable atmosphere (surface-bound exosphere) containing hydrogen, helium, oxygen, sodi ...

Atmosphere of Venus The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of supercritical carbon dioxide and is much denser and hotter than that of Earth. The temperature at the surface is 740 K (467 °C, 872 ° ...

Atmosphere of Earth The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...

Atmosphere of the Moon The atmosphere of the Moon is a very scant presence of gases surrounding the Moon. For most practical purposes, the Moon is considered to be surrounded by vacuum. The elevated presence of atomic and molecular particles in its vicinity compared to ...

Atmosphere of Mars The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.8%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and no ...

Atmosphere of Ceres Ceres (; minor-planet designation: 1 Ceres) is a dwarf planet in the asteroid belt between the orbits of Mars and Jupiter. It was the first asteroid discovered, on 1 January 1801, by Giuseppe Piazzi at Palermo Astronomical Observatory in Sic ...

Atmosphere of Jupiter The atmosphere of Jupiter is the largest planetary atmosphere in the Solar System. It is mostly made of molecular hydrogen and helium in roughly Sun#Composition, solar proportions; other chemical compounds are present only in small amounts and in ...

** Atmosphere of Io ** Atmosphere of Callisto ** Atmosphere of Europa ** Atmosphere of Ganymede *

Atmosphere of Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Eart ...

Atmosphere of Titan The atmosphere of Titan is the dense layer of gases surrounding Titan, the largest moon of Saturn. It is the only thick atmosphere of a natural satellite in the Solar System. Titan's lower atmosphere is primarily composed of nitrogen (94.2%), ...

Atmosphere of Enceladus Enceladus is the sixth-largest moon of Saturn (19th largest in the Solar System). It is about in diameter, about a tenth of that of Saturn's largest moon, Titan. Enceladus is mostly covered by fresh, clean ice, making it one of the most ref ...

Atmosphere of Uranus The atmosphere of Uranus is composed primarily of hydrogen and helium. At depth it is significantly enriched in volatiles (dubbed "ices") such as water, ammonia and methane. The opposite is true for the upper atmosphere, which contains very few ...

** Atmosphere of Titania *

Atmosphere of Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...

Atmosphere of Triton The atmosphere of Triton is the layer of gases surrounding Triton. The surface pressure is only 14 microbars (1.4 Pa or 0.0105 mmHg), of the surface pressure on Earth, and it is composed of nitrogen, similar to those of Titan and Earth. It exte ...

Atmosphere of Pluto The atmosphere of Pluto is the tenuous layer of gases surrounding Pluto. It consists mainly of nitrogen (N2), with minor amounts of methane (CH4) and carbon monoxide (CO), all of which are vaporized from their ices on Pluto's surface. It contain ...

Outside the Solar System

Main article:

Extraterrestrial atmosphere The study of extraterrestrial atmospheres is an active field of research, both as an aspect of astronomy and to gain insight into Earth's atmosphere. In addition to Earth, many of the other astronomical objects in the Solar System have atmosphe ...

* Atmosphere of

HD 209458 b HD 209458 b, which is also nicknamed Osiris after the Egyptian god, is an exoplanet that orbits the solar analog HD 209458 in the constellation Pegasus, some from the Solar System. The radius of the planet's orbit is , or one-eighth the radius o ...

Circulation

The circulation of the atmosphere occurs due to thermal differences when

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

becomes a more efficient transporter of heat than

thermal radiation Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) is ...

. On planets where the primary heat source is solar radiation, excess heat in the tropics is transported to higher latitudes. When a planet generates a significant amount of heat internally, such as is the case for

, convection in the atmosphere can transport thermal energy from the higher temperature interior up to the surface.

Importance

From the perspective of a planetary

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...

, the atmosphere acts to shape a planetary surface.

Wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...

picks up

dust Dust is made of fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian process), volcanic eruptions, and pollution. Dust in homes ...

and other particles which, when they collide with the terrain, erode the

relief Relief is a sculptural method in which the sculpted pieces are bonded to a solid background of the same material. The term ''relief'' is from the Latin verb ''relevo'', to raise. To create a sculpture in relief is to give the impression that the ...

and leave

deposits A deposit account is a bank account maintained by a financial institution in which a customer can deposit and withdraw money. Deposit accounts can be savings accounts, Transaction account#Current accounts, current accounts or any of several othe ...

( eolian processes).

Frost Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a gas) ...

and precipitations, which depend on the atmospheric composition, also influence the relief. Climate changes can influence a planet's geological history. Conversely, studying the surface of the Earth leads to an understanding of the atmosphere and climate of other planets. For a

meteorologist A meteorologist is a scientist who studies and works in the field of meteorology aiming to understand or predict Earth's atmospheric phenomena including the weather. Those who study meteorological phenomena are meteorologists in research, while t ...

, the composition of the Earth's atmosphere is a factor affecting the

climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...

and its variations. For a

biologist A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual Cell (biology), cell, a multicellular organism, or a Community (ecology), community of Biological inter ...

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

, the Earth's atmospheric composition is closely dependent on the appearance of the life and its

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

References

External links

Properties of atmospheric strata – The flight environment of the atmosphereAtmosphere – Everything you need to know
{{Authority control Gases Planetary science

Composition

Structure of atmosphere

Earth

Pressure

Escape

Terrain

Atmospheres in the Solar System

Outside the Solar System

Circulation

Importance

See also

References

Further reading

External links