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's active atmosphere, including the Great Red Spot.An
atmosphere is a layer of
gases that may surround a material body of sufficient
mass. Ontario Science Centre website 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 planets consist mainly of various gases, and thus have very deep atmospheres (see gas giants).
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 rays.
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) (atm), which is defined as 1,013,250 dynes per
square metre.
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) (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
Surface gravity, the force that holds down an atmosphere, differssignificantly 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), Triton (moon), and
Pluto are able to retain their atmospheres despite relatively low gravities.
Interstellar planets, 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 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.
Other mechanisms that can cause
atmospheric escape are
solar wind-induced sputtering,
impact event erosion,
weathering, and sequestration — sometimes referred to as "freezing out" — into the
regolith and polar ice cap.
Composition
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'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 giants —
Jupiter, Saturn, Uranus, and Neptune — allows them to more readily retain gases with low molecular masses. 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), a moon of Saturn, and
Triton (moon), 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 (sodium gas), Mercury (planet) (sodium gas),
Europa (moon) (oxygen),
Io (moon) (
sulfur), and Enceladus (moon) (water vapor).
The atmospheric composition of an extra-solar planet was first determined using the
Hubble Space Telescope. Planet HD 209458b is a gas giant with a close orbit around a star in the constellation Pegasus. The 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
Earth
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 km at the equator and 7 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 km. The
Kármán line, located within the thermosphere at an altitude of 100 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 km above the surface, where it interacts with the planet's magnetosphere.
Others
Other astronomical bodies have known atmospheres.
In our solar system
Outside our solar system
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 of a
planet. The
wind transports
dust and other particles which erodes the
Terrain and leaves Deposition (sediment) (
eolian processes).
Frost line and
Precipitation (meteorology)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
See also
's active atmosphere, including the Great Red Spot.An
atmosphere is a layer of
gases that may surround a material body of sufficient mass. Ontario Science Centre website 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
planets consist mainly of various gases, and thus have very deep atmospheres (see
gas giants).
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 rays.
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) (atm), which is defined as 1,013,250
dynes per square metre.
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) (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
Surface gravity, the force that holds down an atmosphere, differssignificantly 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),
Triton (moon), and Pluto are able to retain their atmospheres despite relatively low gravities.
Interstellar planets, 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 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.
Other mechanisms that can cause atmospheric escape are solar wind-induced sputtering,
impact event erosion,
weathering, and sequestration — sometimes referred to as "freezing out" — into the
regolith and
polar ice cap.
Composition
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'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 giants — Jupiter,
Saturn, Uranus, and Neptune — allows them to more readily retain gases with low
molecular masses. 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), a moon of Saturn, and Triton (moon), 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 (
sodium gas), Mercury (planet) (sodium gas), Europa (moon) (oxygen),
Io (moon) (sulfur), and Enceladus (moon) (water vapor).
The atmospheric composition of an extra-solar planet was first determined using the Hubble Space Telescope. Planet
HD 209458b is a gas giant with a close orbit around a star in the
constellation Pegasus. The 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
Earth
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 km at the equator and 7 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 km. The Kármán line, located within the thermosphere at an altitude of 100 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 km above the surface, where it interacts with the planet's magnetosphere.
Others
Other astronomical bodies have known atmospheres.
In our solar system
Outside our solar system
- Atmosphere of HD 209458 b
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 of a planet. The wind transports
dust and other particles which erodes the Terrain and leaves Deposition (sediment) (eolian processes).
Frost line and Precipitation (meteorology)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
See also
- Stellar atmosphere
- Edge of space
- Ionosphere
atmosphere.co.uk
Scenic images of cities, towns, and rural landscapes throughout England, including aerial views and prehistoric places.
atmosphere.co.uk
ATMOSPHERE PICTURE LIBRARY. The Atmosphere Picture Library is based in England's west country. The photographs in the collection are taken by Bob Croxford.
AtmoSphere - pages/atmosphere.html
AtmoSphere. Learning about the atmosphere
AtmoSphere - pages/exosphere.html
Exosphere The exosphere is the most distant atmospheric region from the Earth's surface. The upper boundary of the layer extends to heights of perhaps 960 to 1000 km and is ...
Atmosphere - Wikipedia, the free encyclopedia
An atmosphere (from Greek ατμός - atmos, "vapor" + σφαίρα - sphaira, "sphere") is a layer of gases that may surround a material body of sufficient mass. [1] The gases ...
Earth's atmosphere - Wikipedia, the free encyclopedia
The Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly (by molar content/volume) 78.08% nitrogen, 20.95 ...
Atmosphere, Climate & Environment Information Programme
Monthly air quality measurements from 2000 until 2004, from about a dozen UK monitoring stations. Support for programme and website withdrawn in 2005.
Definition: atmosphere from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.
Atmosphere Equestrian: Horse and ponies for sale, teaching, livery ...
Atmosphere Equestrian, Gloucestershire offers dressage competition livery, lessons, schooling, breaking, full livery and more, at the Aderro Dressage Centre, 5 mins from M5 J14.
Atmosphere Lighting & Sound
Welcome to Atmosphere Lighting & Sound. Our site covers all aspects of information relating to the Professional Lighting & Sound Industry. We partner with such names as Numark ...
