Noble gases planetary components

One striking exception was the very early discovery of I decay to Xe (Jeffery and Reynolds 1961). This discovery reflects the particular properties of rare gases which are nearly absent in telluric planetary bodies. Because they are not diluted by high abrmdances of isotopically normal noble gases, anomalies in rare noble gas components were the first to be detected. This is also the reason for the Xe record of the fission of Pu (Rowe and Kuroda 1965). From the available data on short-lived nuclides at that time, it was concluded that the last nucleosynthetic input into the protosolar cloud predated the formation of the planets by 100-200 Ma. 

Table 10.2 Trapped planetary noble gas components in meteorites ...

Recognition that nontrivial to major fractions of the noble gases in meteorites are exotic components imported into the solar system in presolar grains widens the plausible latitude available to models for the origin of planetary gases, and especially for how closely the noble gas inventories of the major terrestrial planets, including Earth, might be related to those in meteorites. The latter question is related to the broader issue of how uniformly, or otherwise, presolar solids are distributed on a planetary scale, an issue not yet very well explored. 

It has been long recognized that the relative abundance of Xe in atmospheric noble gas is considerably lower than that in a characteristic noble gas component in meteorites, widely referred to as a planetary noble gas component. This is shown in Figure 7.11. 

Huss, G. R., Lewis, R. S., Hemkin, S. (1996) The normal planetary noble gas component in primitive chondrites Compositions, carrier, and metamorphic history. Geochim. Cos-mochim. Acta, 60, 3311-40. 

In the classical picture, i.e., before appreciation that presolar components were an important part of the total inventory of trapped gases in meteorites, neither the isotopic effects nor the generation of the elemental abundance pattern were ever explained satisfactorily in terms of quantitative models that gained consensus acceptance. Some aspects of this problem have become moot, however, since it is now recognized that planetary gas is composite planetary gas includes the contributions of the exotic noble-gas components (Table 2) imported into the solar system by presolar grains. These contributions, especially of the HE component, can be substantial (Huss and Lewis, 1995 also see Figure 7). 

Huss G. R. and Alexander E. C., Jr. (1987) On the pre-solar origin of the normal planetary noble gas component in meteorites. Proc. 17th Lunar Planet. Sci. Conf J. Geophys. Res. 92, E710-E716. 

Marti K. and Mathew K. (1998) Noble-gas components in planetary atmospheres and interiors in relation to solar wind and meteorites. Proc. Indian Acad. Sci. Earth Planet Sci. 107, 425-431. 

The solar system formed from a molecular cloud fragment—traditionally called the solar nebula—that was rather well mixed. Therefore, isotopic abundances in almost all available solar system materials are very similar to each other, and elemental abundances in primitive meteorites are also similar to the values in the Sun. The major exceptions to this rule are the noble gases. Because they are chemically inert and volatile, they are very strongly depleted in solid matter. As a consequence, numerous noble gas components can be recognized throughout the solar system which are not necessarily related to the composition of the bulk nebula. Still, one major question in cosmochemistry is to what extent planetary bodies contain reservoirs that reflect the noble gas composition in the nebula or the presolar cloud. 

Martel DJ, Deak J, Dovenyi P, Horvath F, O Nions RK, Oxbmgh ER, Stegna L, State M (1989) Leakage of helium from the Patmonian Basin. Nature 432 908-912 Marti K, Mathew KJ (1998) Noble-gas components in planetary atmospheres and interiors in relation to solar wind and meteorites. Proc Indian Acad Sci (Earth Planet Sci) 107 425-431 Marty B, Alle P (1994) Neon and argon isotopic constraints on Earth-atmosphere evolution. In Noble gas geochemistry and cosmochemistry. Matsuda J-1 (ed) Terra Scientific Publishing Co., Tokyo, p 191-204. 

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