Planetary Noble Gases

Allende from Lewis et al. 1975 Bruderheim from Berkeley standard Bruderheim (circulated by J. H. Reynolds) Orgueil and Ivuna from Mazor, Heymann, and Anders (1970). 

so that it is hard to make a reliable and accurate independent estimate of cosmic D/H. Instead, the greater interest is typically in the converse calculation estimation of cosmic D/H from the difference between solar 3He/4He and primordial cosmic 3He/4He (e.g., Geiss Reeves, 1972). Although this calculation was originally based on meteorite He as a proxy for primordial solar system He, it has become evident that meteoritic He is not necessarily representative of cosmic He (Section 3.4), so that estimation of primordial D/H must be based on other data, such as the composition of He in the atmosphere of Jupiter [see Table 3.3(a)]. 

Like solar, the term planetary, as used to describe noble gases, carries a set of connotations well beyond the dictionary definition. Planetary is also used to refer to a pattern of noble gas elemental abundances, and the terms solar and planetary evolved to describe contrasting patterns. The defining feature of planetary noble gases is a much stronger (than in the case of solar gases) elemental fractionation pattern in 

4 Compiled by Pepin (1991) and references therein. Data are based on SNC meteorites (see Section 6.9). 

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Besides the problem of accounting for the chemical abundances of planetary noble gases, there are characteristic differences in isotopic composition between planetary noble gases in meteorites and the solar gases that presumably represent the nebula from which meteorites formed. For Ar and Kr the differences are modest or perhaps nonexistent or can ultimately be explained in terms of a reasonable degree of mass-dependent isotopic fractionation. For Ne (Figure 3.3) and Xe (Figure 7.6), the... 

As already noted, the origin of planetary noble gases remains mysterious. Equilibrium solubility of gases in solids yields concentrations far too low adsorption may... 

While considerations of the origin of planetary noble gases have been predominantly focused on those presently found in the atmosphere, noble gases still within the Earth provide further constraints about volatile trapping during planet formation. A wide range of noble-gas information for the Earth s mantle has been obtained from mantle-derived materials, and indicates that there are separate reservoirs within the Earth that have distinctive characteristics that were established early in Earth history. These must be included in comprehensive models of Earth volatile history. Also, data are now available for the atmospheres of both Venus and Mars, as well as from the interior of Mars, so that the evolution of Earth volatiles can be considered within the context of terrestrial-planet formation across the solar system. 

Rayleigh distillation and planetary noble gases. It has been suggested that the abundance pattern of trapped Q-phase noble gases— the most abundant and widely distributed primordial component in meteorites (Wider 1994 Busemann et al. 2000 ... 

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