Composition planetary atmospheres

Through spectroscopic observations and sometimes tenuous deductions there has accumulated a significant picture of the makeup of the planetary atmospheres. Doubt pervades much of this picture, yet it represents our starting place in knowledge as we venture outside our own atmosphere for the first time. Table 25-V summarizes a part of this information—the maximum surface temperatures and the chemical compositions. Naturally, these compositions are incomplete ... 

The composition of the planetary atmospheres is fairly constant. This is indeed surprising in view of the fact that molecules such as methane, ammonia, and carbon dioxide are easily decomposed by the ultraviolet radiation from the sun. Presumably other reactions regenerate those substances that are light sensitive. 

Composition of Planetary Atmosphere (Today) - Molar% in Volume... 

The temperature profile of a planetary atmosphere depends both on the composition and some simple thermodynamics. The temperature decreases with altitude at a rate called the lapse rate. As a parcel of air rises, the pressure falls as we have seen, which means that the volume will increase as a result of an adiabatic expansion. The change in enthalpy H coupled with the definition of the specific heat capacity... 

Elemental oxygen also is present in the sun in less than 1% mass composition, as a fusion product of carbon-12, and hehum-4. No planet or its moon in the solar system, other than the earth is known to contain molecular oxygen in its atmosphere, although CO2 is a major component of many planetary... 

Comparison of trapped gases in impact-melt glass in the EET 79001 Martian meteorite with the composition of the Martian atmosphere as measured by Viking landers. This remarkable agreement is the evidence that convinced most planetary scientists that SNC meteorites came from Mars. 

We emphasize the line shape problem perhaps a little more than usual in the spectroscopic literature. Collision-induced spectra have little structure. Yet, the diffuse line and band spectra extend over wide frequency bands and must often be subtracted, say from the complex spectra of planetary or stellar atmospheres, for a more detailed analysis of other, less well known components. The subtraction requires accurate knowledge of the profile and its variation with temperature, composition, etc., often over frequency bands of hundreds of cm-1. 

The necessary starting point for any study of the chemistry of a planetary atmosphere is the dissociation of molecules, which results from the absorption of solar ultraviolet radiation. This atmospheric chemistry must take into account not only the general characteristics of the atmosphere (constitution), but also its particular chemical constituents (composition). The absorption of solar radiation can be attributed to carbon dioxide (C02) for Mars and Venus, to molecular oxygen (02) for the Earth, and to methane (CH4) and ammonia (NH3) for Jupiter and the outer planets. 

Figure 3.9 shows the role of forest vegetation in C02 dynamics. In addition to these results, note that experiments with global models make it possible to trace the dependence of the composition of atmospheric gas on the structure of planetary forest cover. From the available estimates, the total area of forests for t0 = 1970 can be estimated at = crL(t0) 40.3 41.84 106 km2 (Watson et al., 2000), 1% constituting national parks and forest reserves. With the formulated scenario, let us assume tL = 2050, = (rx(t )) = 19.5 106 km2. As can be seen from Figure 3.6, the... 

Reflectance spectroscopy has proven to be the most powerful and versatile remote-sensing technique for determining surface mineralogy, chemical compositions and lithologies of planetary objects, as well as constituents of their atmospheres. Table 10.1 summarizes information that has been deduced for the terrestrial planets based on spectral properties of light in the visible and near-infrared regions reflected from their surfaces. 

For most of the chemical elements, the relative abundances of their stable isotopes in the Sun and solar nebula are well known, so that any departures from those values that may be found in meteorites and planetary materials can then be interpreted in terms of planet-forming processes. This is best illustrated for the noble gases neon, argon, krypton, and xenon. The solar isotopic abundances are known through laboratory mass-spectrometric analysis of solar wind extracted from lunar soils (Eberhardt et al., 1970) and gas-rich meteorites. Noble gases in other meteorites and in the atmospheres of Earth and Mars show many substantial differences from the solar composition, due to a variety of nonsolar processes, e.g., excesses of " Ar and... 

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