Volatile element depletion inner Solar System

Most meteorites are depleted in moderately volatile and highly volatile elements (see Figures 2-4). The terrestrial planets Earth, Moon, Mars, and the asteroid Vesta show similar or even stronger depletions (e.g., Palme et aL, 1988 Palme, 2001). The depletion patterns in meteorites and in the inner planets are qualitatively similar to those in the ISM. It is thus possible that the material in the inner solar system inherited the depletions from the ISM by the preferential accretion of dust grains and the loss of gas during the collapse of the molecular cloud that led to the formation of the solar system. There is, however, little support for this hypothesis ... 

The bulk compositions of the bodies in the inner solar system show a marked depletion of volatile elements compared to the solar composition. Cassen (2001) has shown that the depletions of the moderately volatile elements (those with... 

Depletion of rare gases in Earth s atmosphere in comparison with cosmic abundances suggests that any primary atmosphere captured at the planet s early accretion could have been lost by an impact with one or more large bodies during the later stages of the accretion [66,74], and by T-tauri solar winds of high-energy particles which could readily blow volatile elements out of the inner Solar System [75]. 

Fig. 14. Uranium is refractory like the rare earths, so that K/U ratios are an analogue for K/La ratios (fig. 11). K and U data are available for a wide variety of solar system material, since both elements are readily determined by gamma-ray spectroscopy. Both are incompatible in igneous processes and so tend to preserve their bulk planetary ratios during differentiation. This diagram illustrates that substantial volatile element depletion was widespread in the inner solar nebula, so that similar variations to K/U in volatile element/rare earth ratios are lo be expected. (From Taylor 1987a.)...

The surface of Venus has K/U ratios of the same order as those of terrestrial surface rocks (Surkov 1981), so that it also is depleted in volatile elements relative to primitive nebula values. This relative depletion of the more volatile elements thus appears to have been a widespread feature of the inner solar nebula rather than being a feature unique to the earth. Accordingly, a widespread loss of volatile elements occurred in the irmer solar system prior to the accretion of the terrestrial planets (Taylor 1987a). No information is yet available for the rare earth elements on Venus, but on the basis of the discussion above, they are probably similar to the terrestrial abundance levels. 

---