Atmosphere 202899 226010562 2008-07-16T12:48:35Z 82.99.223.131 {{Redirect|Atmospheres|the hip hop music duo|Atmosphere (music group)}} {{otheruses}} [[Image:PIA04866 modest.jpg|thumb|right|View of [[Jupiter]]'s active atmosphere, including the [[Great Red Spot]].]] An '''atmosphere''' (from [[Greek language|Greek]] ''ατμός'' - ''atmos'', "[[vapor]]" + ''σφαίρα'' - ''sphaira'', "[[sphere]]") is a layer of [[gas]]es that may surround a material body of sufficient [[mass]].<ref>[http://www.ontariosciencecentre.ca/school/clc/visits/glossary.asp Ontario Science Centre website]</ref> The gases are attracted by the [[gravity]] of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low. Some [[planet]]s consist mainly of various gases, and therefore have very deep atmospheres (see [[gas giant]]s). The term [[stellar atmosphere]] is used for the outer region of a star, and typically includes the portion starting from the opaque [[photosphere]] outwards. Relatively low temperature stars may form compound molecules in their outer atmosphere. [[Earth's atmosphere]] protects living organisms from [[ultraviolet ray]]s. ==Pressure== {{main|atmospheric pressure}} [[Atmospheric pressure]] is the force per unit area that is applied perpendicularly to a surface by the surrounding gas. It is determined by a planet's gravitational force in combination with the total mass of a column of air above a location. Units of air pressure are based on the internationally-recognized [[Atmosphere (unit)|standard atmosphere]] (atm), which is defined as 101,325 [[Pascal (unit)|Pa]] (or 1,013,250 [[dyne]]s per [[square metre|cm²]]). The pressure of an atmosphere decreases with altitude due to the diminishing mass of gas above each location. The height at which the pressure from an atmosphere declines by a factor of ''[[e (mathematical constant)|e]]'' (an [[irrational number]] with a value of 2.71828...) is called the [[scale height]] and is denoted by ''H''. For an atmosphere with a uniform temperature, the scale height is proportional to the temperature and inversely proportional to the mean [[molecular mass]] of dry air times the planet's gravitational acceleration. For such a model atmosphere, the pressure declines exponentially with increasing altitude. However, atmospheres are not uniform in temperature, so the exact determination of the atmospheric pressure at any particular altitude is more complex. ==Escape== {{main|Atmospheric escape}} [[Surface gravity]], the force that holds down an atmosphere, differs significantly among the planets. For example, the large gravitational force of the giant planet [[Jupiter]] is able to retain light gases such as [[hydrogen]] and [[helium]] that escape from lower gravity objects. Second, the distance from the sun determines the energy available to heat atmospheric gas to the point where its molecules' [[thermal motion]] exceed the planet's [[escape velocity]], the speed at which gas molecules overcome a planet's gravitational grasp. Thus, the distant and cold [[Titan (moon)|Titan]], [[Triton (moon)|Triton]], and [[Pluto]] are able to retain their atmospheres despite relatively low gravities. [[Interstellar planet]]s, theoretically, may also retain thick atmospheres. Since a gas at any particular temperature will have molecules moving at a wide range of velocities, there will almost always be some slow leakage of gas into space. Lighter molecules move faster than heavier ones with the same thermal [[kinetic energy]], and so gases of low [[molecular mass|molecular weight]] are lost more rapidly than those of high molecular weight. It is thought that Venus and Mars may have both lost much of their water when, after being photodissociated into hydrogen and oxygen by solar [[ultraviolet]], the hydrogen escaped. [[Earth]]'s [[magnetic field]] helps to prevent this, as, normally, the solar wind would greatly enhance the escape of hydrogen. However, over the past 3 billion years the Earth may have lost gases through the magnetic polar regions due to auroral activity, including a net 2% of its atmospheric oxygen.<ref>{{cite journal | author=Seki, K.; Elphic, R. C.; Hirahara, M.; Terasawa, T.; Mukai, T. | title=On Atmospheric Loss of Oxygen Ions from Earth Through Magnetospheric Processes | journal=Science | year=2001 | volume=291 | issue=5510 | pages=1939–1941 | url=http://www.sciencemag.org/cgi/content/full/291/5510/1939 | accessdate=2007-03-07 | doi=10.1126/science.1058913 | pmid=11239148}}</ref> Other mechanisms that can cause [[atmospheric escape|atmosphere depletion]] are [[solar wind]]-induced sputtering, [[impact event|impact]] erosion, [[weathering]], and sequestration &mdash; sometimes referred to as "freezing out" &mdash; into the [[regolith]] and [[polar ice cap|polar caps]]. ==Composition== [[Image:Top of Atmosphere.jpg|thumb|290px|right|Atmospheric gases scatter blue light more than other wavelengths, giving the Earth a blue halo when seen from space.]] Initial atmospheric makeup is generally related to the chemistry and temperature of the local [[solar nebula]] during planetary formation and the subsequent escape of interior gases. These original atmospheres underwent much evolution over time, with the varying properties of each planet resulting in very different outcomes. The atmospheres of the planets [[Venus]] and [[Mars]] are primarily composed of [[carbon dioxide]], with small quantities of [[nitrogen]], [[argon]], [[oxygen]] and traces of other gases. The atmospheric composition on Earth is largely governed by the by-products of the very life that it sustains. [[Earth atmosphere|Earth's atmosphere]] consists principally of a roughly 78:20 ratio of nitrogen and oxygen, plus substantial water vapor (a gas), with a minor proportion of carbon dioxide. There are traces of hydrogen, and of argon, helium and other "noble" gases (and of volatile pollutants). Exact measurements are difficult, except for particular locales at a particular time. The low temperatures and higher gravity of the [[gas giant]]s &mdash; [[Jupiter]], [[Saturn]], [[Uranus]], and [[Neptune]] &mdash; allows them to more readily retain gases with low [[molecular mass]]es. These planets have hydrogen-helium atmospheres, with trace amounts of more complex compounds. Two satellites of the outer planets possess non-negligible atmospheres: [[Titan (moon)|Titan]], a moon of Saturn, and [[Triton (moon)|Triton]], a moon of Neptune, which are mainly [[nitrogen]]. [[Pluto]], in the nearer part of its orbit, has an atmosphere of nitrogen and methane similar to Triton's, but these gases are frozen when farther from the Sun. Other bodies within the Solar System have extremely thin atmospheres not in equilibrium. These include [[Moon|the Moon]] ([[sodium]] gas), [[Mercury (planet)|Mercury]] (sodium gas), [[Europa (moon)|Europa]] (oxygen), [[Io (moon)|Io]] ([[sulfur]]), and [[Enceladus (moon)|Enceladus]] (water vapor). The atmospheric composition of an [[extra-solar planet]] was first determined using the [[Hubble Space Telescope]]. Planet [[HD 209458]]b is a gas giant with a close orbit around a star in the [[constellation]] [[Pegasus]]. The atmosphere is heated to temperatures over 1,000&nbsp;K, and is steadily escaping into space. Hydrogen, oxygen, carbon and sulfur have been detected in the planet's inflated atmosphere.<ref>{{cite news | author=Weaver, D.; Villard, R. | title=Hubble Probes Layer-cake Structure of Alien World's Atmosphere | publisher=Hubble News Center | date=2007-01-31 | url=http://hubblesite.org/newscenter/newsdesk/archive/releases/1991/12/text/ | accessdate=2007-03-11 }}</ref> ==Structure== ===Earth=== {{main|Earth's atmosphere}} The [[Earth's atmosphere]] consists, from the ground up, of the [[troposphere]] (which includes the [[planetary boundary layer]] or peplosphere as lowest layer), [[stratosphere]], [[mesosphere]], [[ionosphere]] (or [[thermosphere]]), [[exosphere]] and the [[magnetosphere]]. Each of the layers has a different [[lapse rate]], defining the rate of change in temperature with height. Three quarters of the atmosphere lies within the troposphere, and the depth of this layer varies between 17&nbsp;km at the equator and 7&nbsp;km at the poles. The [[ozone layer]], which absorbs [[ultraviolet]] energy from the Sun, is located primarily in the stratosphere, at altitudes of 15 to 35&nbsp;km. The [[Kármán line]], located within the thermosphere at an altitude of 100&nbsp;km, is commonly used to define the boundary between the Earth's atmosphere and outer space. However, the exosphere can extend from 500 up to 10,000&nbsp;km above the surface, where it interacts with the planet's magnetosphere. ===Others=== Other astronomical bodies such as these listed have known atmospheres. ====In our solar system==== <div class="references-small" style="-moz-column-count:3; column-count:3;"> *[[Atmosphere of Mercury]] *[[Atmosphere of Venus]] *[[Atmosphere of the Moon]] *[[Atmosphere of Mars]] *[[Atmosphere of Jupiter]] *[[Atmosphere of Io]] *[[Atmosphere of Europa]] *[[Atmosphere of Ganymede]] *[[Saturn|Atmosphere of Saturn]] *[[Atmosphere of Titan]] *[[Enceladus (moon)#Atmosphere|Atmosphere of Enceladus]] *[[Atmosphere of Uranus]] *[[Atmosphere of Neptune]] *[[Atmosphere of Triton]] *[[Atmosphere of Pluto]] </div> ====Outside our solar system==== *Atmosphere of [[HD 209458 b]] ==Circulation== {{main|Atmospheric circulation}} The circulation of the atmosphere occurs due to thermal differences when [[convection]] becomes a more efficient transporter of heat than [[thermal radiation]]. 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 [[Jupiter]], convection in the atmosphere can transport thermal energy from the higher temperature interior up to the surface. ==Importance== From the perspective of the planetary [[geologist]], the atmosphere is an evolutionary agent essential to the [[Comparative anatomy|morphology]] of a [[planet]]. The [[wind]] transports [[dust]] and other particles which erodes the [[Terrain|relief]] and leaves [[Deposition (sediment)|deposits]] ([[eolian]] processes). [[Frost line|Frost]] and [[Precipitation (meteorology)|precipitation]]s, which depend on the composition, also influence the relief. Climate changes can influence a planet's geological history. Conversely, studying surface of earth leads to an understanding of the atmosphere and climate of a planet - both its present state and its past. For a [[meteorologist]], the composition of the atmosphere determines the [[climate]] and its variations. For a [[biologist]], the composition is closely dependent on the appearance of the life and its [[evolution]]. ==References== <references/> == See also == {{portal|Atmospheric sciences}} * [[Atmometer]] (evaporimeter) * [[Edge of space]] * [[Ionosphere]] * [[Stellar atmosphere]] * [[Table of Global Climate System Components]] {{Atmospheres}} [[Category:Planetary science]] [[Category:Planetary atmospheres]] [[Category:Atmosphere]] [[Category:Greek loanwords]] [[als:Atmosphäre]] [[bn:বায়ুমণ্ডল]] [[zh-min-nan:Tāi-khì-chân]] [[br:Atmosfer (planedennoù)]] [[ca:Atmosfera d'un cos celest]] [[cs:Atmosféra]] [[cy:Awyrgylch]] [[da:Atmosfære (himmellegeme)]] [[de:Atmosphäre]] [[es:Atmósfera]] [[eo:Atmosfero (astro)]] [[fa:جو (هواشناسی)]] [[fr:Atmosphère (astronomie)]] [[ko:대기]] [[hi:वायुमण्डल]] [[hr:Atmosfera]] [[io:Atmosfero]] [[id:Atmosfer benda langit]] [[ia:Atmosphera]] [[is:Andrúmsloft]] [[it:Atmosfera]] [[lmo:Atmusfera]] [[hu:Légkör]] [[ml:അന്തരീക്ഷം]] [[nl:Atmosfeer (astronomie)]] [[ja:大気圏]] [[no:Atmosfære]] [[nn:Atmosfære]] [[nrm:Atmosphéthe]] [[uz:Atmosfera]] [[pt:Atmosfera]] [[sco:Atmosphere]] [[sq:Atmosfera]] [[scn:Attimusfera]] [[sk:Atmosféra (kozmického telesa)]] [[fi:Planeettojen kaasukehät]] [[th:บรรยากาศ]] [[tr:Atmosfer]] [[yi:אטמאספער]] [[zh-yue:大氣層]] [[zh:大气层]]