Humans first witnessed Earth as a complete orb floating in the inky blackness of space in December when Apollo 8 carried astronauts around the Moon.
Atmospheric pressure Atmospheric pressure at a particular location is the force per unit area perpendicular to a surface determined by the weight of the vertical column of atmosphere above that location. On Earth, units of air pressure are based on the internationally recognized standard atmosphere atmwhich is defined as It is measured with a barometer.
Atmospheric pressure decreases with increasing altitude due to the diminishing mass of gas above. The height at which the pressure from an atmosphere declines by a factor of e an irrational number with a value of 2.
For an atmosphere with a uniform temperature, the scale height is proportional to the temperature and inversely proportional to the product of the mean molecular mass of dry air and the local acceleration of gravity at that location. For such a model atmosphere, the pressure declines exponentially with increasing altitude.
However, atmospheres are not uniform in temperature, so estimation of the atmospheric pressure at any particular altitude is more complex.
Atmospheric escape Surface gravity differs significantly among the planets. For example, the large gravitational force of the giant planet Jupiter retains light gases such as hydrogen and helium 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 exceed the planet's escape velocityallowing those to escape a planet's gravitational grasp.
Thus, distant and cold TitanTritonand Pluto 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 energyand so gases of low molecular weight are lost more rapidly than those of high molecular weight.
It is thought that Venus and Mars may have lost much of their water when, after being photo dissociated into hydrogen and oxygen by solar ultravioletthe hydrogen escaped. Earth 's magnetic field helps to prevent this, as, normally, the solar wind would greatly enhance the escape of hydrogen.
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 meteoroidsand all of them collide with the surface as meteorites and create craters.
Most meteoroids burn up as meteors before hitting a planet's surface. When meteoroids do impact, the effects are often erased by the action of wind. In addition, since liquid s can not exist without pressure, an atmosphere allows liquid to be present at the surface, resulting in lakesrivers and oceans.
Earth and Titan are known to have liquids at their surface and terrain on the planet suggests that Mars had liquid on its surface in the past. Composition[ edit ] Earth's atmospheric gases scatter blue light more than other wavelengths, giving Earth a blue halo when seen from space A planet's initial atmospheric composition is related to the chemistry and temperature of the local solar nebula during planetary formation and the subsequent escape of interior gases.
The original atmospheres started with a rotating disc of gases that collapsed to form a series of spaced rings that condensed to form the planets. The planet's atmospheres were then modified over time by various complex factors, resulting in quite different outcomes.
The atmospheres of the planets Venus and Mars are primarily composed of carbon dioxidewith small quantities of nitrogenargonoxygen and traces of other gases. The composition of Earth's atmosphere is largely governed by the by-products of the life that it sustains.
Dry air from Earth's atmosphere contains The low temperatures and higher gravity of the Solar System's giant planets — JupiterSaturnUranus and Neptune —allow them more readily to 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 significant atmospheres. Titana moon of Saturn, and Tritona moon of Neptune, have atmospheres mainly of nitrogen. When in the part of its orbit closest to the Sun, Pluto 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 sodium gasMercury sodium gasEuropa oxygenIo sulfurand Enceladus water vapor.
The first exoplanet whose atmospheric composition was determined is HD ba gas giant with a close orbit around a star in the constellation Pegasus.Introduction.
Three centuries ago, the English scientist Isaac Newton calculated, from his studies of planets and the force of gravity, that the average density of the Earth is twice that of surface rocks and therefore that the Earth's interior must be composed of much denser material.
Introduction. Composition and structure of the Earth's atmosphere Composition of the air The Earth's atmosphere is a reservoir of several gases. The gas molecules in this reservoir are continuously exchanged because of the interaction of different sources and sinks.
From the perspective we get on Earth, our planet appears to be big and sturdy with an endless ocean of air. From space, astronauts often get the impression that the Earth is small with a thin, fragile layer of atmosphere.
Earth Introduction. Earth Statistics Earth Movies Views of the Earth Earth's Moon. The Moon Atmospheric composition. Introduction.
Composition and structure of the Earth's atmosphere Composition of the air The Earth's atmosphere is a reservoir of several gases. The gas molecules in this reservoir are continuously exchanged because of the interaction of different sources and sinks.
Earth's atmosphere consists of a number of layers that differ in properties such as composition, temperature and pressure. The lowest layer is the troposphere, which extends from the surface to the bottom of the stratosphere.
The Composition and Structure of Earth. Core, mantle, and crust are divisions based on composition. The crust makes up less than 1 percent of Earth by mass, consisting of oceanic crust and continental crust is often more felsic rock.
The mantle is hot and represents about 68 percent of Earth’s mass. Finally, the core is mostly iron metal.