Atmosphere

The atmosphere [ atmosfɛ ː rə ] (from Greek ἀτμός ( ATMOS ) " vapor, mist, and breath " and σφαῖρα ( sfaira ) " ball ") is the gaseous envelope around larger celestial bodies - in particular around stars and planets. They usually comprise a mixture of different gases which may be retained by the gravitational field of the celestial body. The atmosphere at the surface closest and goes to great heights smoothly into interplanetary space. It determines in the case of their existence much the appearance of a celestial body.

The atmospheres of hot stars reach deep into the room. For gas planets, they are much cooler and separated from the deeper layers of the celestial body not sharp. For large rocky planets and the Saturn moon Titan 's atmosphere a ( named after the earth) and earthly sphere is above the pedosphere ( betretbarer soil) and the underlying lithosphere.

• 2.1 atmosphere of stars
• 2.2 atmospheres of gas giants
• 2.3 atmospheres of Earth-like planets
• 2.4 atmospheres of moons
• 2.5 atmospheres of exoplanets
• Table 2.6 atmosphere

• 3.1 Pressure History
• 3.2 Subdivisions

Creation of an atmosphere

Physical requirements

In the formation of a planetary atmosphere, several factors play a role:

Planet mass and radius determine the gravitational field at the surface. This must be sufficiently strong so that usually resulting from outgassing gas particles remain bound to the celestial bodies and can not evaporate into space.

Gas density, temperature and gravity

According to the kinetic theory of gases, the particles move randomly and thereby faster the higher the temperature of the gas and the lighter they are. If the attraction is too low, the sky body loses in the long term rapid ( low specific gravity ) parts of its gaseous envelope. The Planetary Science speaks of positive particle balance when the outgassing of the rock makes up more lost than by overcoming the gravitational goes. If this balance is negative for heavier gases, there is no atmosphere to form.

Therefore, besides the size of the celestial body 's surface temperature plays ( which must not be too high ) play a significant role. The nature of the formed gases is important because a planet or large moon can hold an atmosphere of hydrogen or helium much heavier than a shell of oxygen, nitrogen or carbon dioxide. This is because light gas particles at the same temperature to move much faster than heavier. Atmospheres containing elements such as hydrogen to a greater extent, so are mainly found in very massive gas giants like Jupiter or Saturn, which have a very strong gravity.

Ultimately, only a small minority of the heavenly bodies will be able to create an atmosphere and to retain them in the long term. For example, the Earth's Moon has no permanent atmosphere, but only short-term, near-surface gases.

Atmospheres of various celestial bodies

Comparing the celestial bodies of our solar system and the stars together, then shows the influence of the relevant factors in the formation of an atmosphere and reveals quite different atmospheres.

Atmosphere of stars

The sun or the different stars have far-reaching atmospheres that begin with the photosphere, chromosphere and transition region and end with corona, solar wind and heliosphere in the broadest sense, deep in interplanetary space at the heliopause. The atmosphere of the Sun consists mainly of hydrogen (about 73%) and helium ( about 25%) that influence in the form of ionized plasma ( solar wind and solar storm ) the atmospheres of celestial bodies remaining in the system.

Atmospheres of gas giants

The composition of the atmosphere of the gas giants like Jupiter, Saturn, Uranus and Neptune similar to the star based mainly on the fabrics hydrogen and helium. Your core is, however cold and the radiation pressure is absent, as in the stars.

• Jupiter and Saturn consist in the interior of liquid hydrogen with a core made of a metallic hydrogen.
• Uranus and Neptune, however, have an icy mantle and core of water or ice, ammonia, methane and rock.

Atmospheres of Earth-like planets

• The Earth's atmosphere is a nitrogen / oxygen mixture. She is able to hold heavy items such as argon ( Ar) in the atmosphere, light elements / molecules such as hydrogen ( H2) or helium ( He) only to lose it in the course of their development.
• The atmosphere of Venus consists mainly of CO2, but otherwise the atmosphere most similar to Earth.
• Mars has, like the Venus CO2 atmosphere. The largest part of the atmosphere of Mars was probably downright removed over time by the solar wind and carried away into space.
• Mercury has no atmosphere in the traditional sense, but comparable to the Earth's atmosphere only a exosphere. The high proportions of hydrogen and helium most likely come from the solar wind.

Atmospheres of moons

• In addition to some planet and the large Saturn moon Titan has a dense atmosphere composed mostly of nitrogen.
• The Jupiter's moons Europa and Ganymede have a small oxygen atmosphere they can keep by their gravity, however, is not of biological origin.
• The Jupiter's moon Callisto has a thin carbon dioxide atmosphere.
• Jupiter 's moon Io has a thin atmosphere of sulfur dioxide.
• The Neptune moon Triton has a thin nitrogen -methane atmosphere
• Saturn's moon Rhea has a thin atmosphere of oxygen and carbon dioxide
• The other satellites of the solar system and the Earth's moon have like the planet Mercury only one exosphere.

Atmospheres of exoplanets

Even with planets of other star systems - the Extrasolar planet - could by various methods are demonstrated by the presence of atmospheres, but so far only in the radius of about 300 light years of our solar system around.

Atmosphere table

An overview of the celestial bodies of the solar system with respect to their atmospheric pressure at the surface and their chemical composition in percent by volume. Listed are the main components of the atmosphere and the water resources.

Structure and gradients using the example of the Earth's atmosphere

Pressure curve

The pressure curve of an atmosphere in the case of the atmosphere of the air pressure is determined in the lower ranges of the hydrostatic equation can be written for thin in comparison to the planet radius atmospheres as follows:

The factors are the pressure p, the height h, the gravitational acceleration g and the density ρ. In the case of constant temperature, the equation reduces to the barometric formula. However, in the outer region, this description is no longer valid because moving the components due to the low density of Kepler orbits or the magnetic field lines and interact with each other any more. For technical modeling, the International Standard Atmosphere (ISA ) is used, which is a pure idealized reflection on the entire planet. The ISA describes the temperature profile according to the polytropic equation of state. For this, the atmosphere in the troposphere and the upper and lower stratosphere is divided. In the lower stratosphere (11-20 km altitude) mainly takes place the international air traffic. However, supersonic flights in the upper stratosphere.

Subdivisions

Typically, an atmosphere is not a homogeneous gaseous envelope, but due to numerous internal and external influences in several, more or less clearly delimited from one another, divide layers are mainly due to the temperature dependence of chemical processes in the atmosphere and the radiation permeability depends on the height. Essentially, one can distinguish the following layers after the temperature profile:

• On the planet's surface usually starts the troposphere, to prevail in convection. It is limited by the tropopause.
• Above it lies the stratosphere, in which the radiation dominates the energy transport. It is limited by the stratopause.
• In the mesosphere, is mainly by carbon dioxide, energy radiated, so that a strong cooling occurs in this layer. It is limited by the mesopause.
• In the thermosphere and the ionosphere most of the molecules are dissociated by absorbed solar radiation and even ionized. The temperature is increased considerably.
• The outermost layer is the exosphere, from the predominantly atomic or ionized constituents can escape from the gravitational field of the planet. It is bounded in the presence of a magnetic field through the magnetopause.

This outline is only a rough division again, and not every layer is detectable in all atmospheres. So has the Venus for example, no stratosphere, smaller planets and moons have only one exosphere, such as the Mercury. For formation and expression of twilight colors of the vertical structure of the atmosphere is crucial.

It is also possible the atmosphere can not be classified by the temperature history, but according to other factors, such as:

• The radio- physical state of the atmosphere ( ionosphere, magnetosphere, plasmasphere )
• According to physico - chemical processes ( ozone layer)
• The zone of life ( biosphere )
• The mixing ( homosphere, homo pause, heterosphere )
• The aerodynamic state ( Prandtl layer, Ekman layer, both as Peplosphäre free atmosphere)