Mass fractions solar

The geological sciences are involved in studying the naturally occurring materials of the earth and solar system (i) to understand the fimdamental processes of crustal formation on earth and solar system evolution, and (2) to evaluate the crustal materials of potential economic value to man. Prior to the 1930 s, analyses were carried out exclusively using classical analytical techniques, with detection limits on the order of o.oi-o.i % (mass fraction). The number of elements contained in any sample could be as extensive as the periodic table, but very few of these could be determined. The development of instrumental techniques revolutionized the analysis of geochemical samples, beginning in the 1930 s. 

Fig. 1. Left panel. Post-explosive yields versus mass of the Ge isotopes for a 25 M of solar composition by [10]. Arrows represent a production factor of 200 over the initial mass fraction of each isotope. Right panel. Logaritmic abundances relative to O and to solar ratio observed in the DLA-B/FJ0812+32 System (dust corrected) [5]. The observed [Zn/O] value is represented by a full square.

The result of all these processes is that the Sun was bom 4.6 Gyr ago with mass fractions X 0.70, Y 0.28, Z 0.02. These abundances (with perhaps a slightly lower value of Z) are also characteristic of the local ISM and young stars. The material in the solar neighbourhood is about 15 per cent gas (including dust which is about 1 per cent by mass of the gas) and about 85 per cent stars or compact remnants thereof these are white dwarfs (mainly), neutron stars and black holes. 

Species are given with their proto-solar abundance by mass fraction, after Lodders (2003). The last column gives the yield calculated by Nomoto et al. for core-collapse supemovae within a Salpeter IMF between mass limits of 0.07 and 50 Mq. 

Iron. Fe has 4 isotopes of which the heaviest Fe has a very small abimdance of about 0.3%. The precision of thermal ionization mass spectrometers is around 10 s on this isotope and there is only a hint in some normal inclusions for an excess in 5 Fe (VoUcening and Papanastassiou 1989). Recent ICPMS measurements at the 2 s precision level display normal isotopic compositions for Fe in planetary materials but no Allende inclusion was reported in this study (Kehm et al. 2003). If excesses of similar magnitude to Ca, Ti, Cr were present they would not be clearly resolved in agreement with the observations. When Fe and Fe are used to correct for instrumental mass fractionation, Fe exhibits normal abundances, suggesting all three isotopes are present in solar relative abundances. 

Isotope variations found in extraterrestrial materials have been classified according to different processes such as chemical mass fractionation, nuclear reactions, nucleosynthesis, and/or to different sources such as interplanetary dust, solar materials, and comet material. Various geochemical fingerprints point to the reservoir from which the planetary sample was derived and the environment in which the sample has formed. They can be attributed to a variety of processes, ranging from heterogeneities in the early solar nebula to the evolution of a planetary body. For more details the reader is referred to reviews of Thiemens (1988), Clayton (1993, 2004), and McKeegan and Leshin (2001). 

We thus arrive at the following composition for the ancestral cloud that spawned the Solar System in 1 gram of matter, we find 0.72 g of hydrogen, 0.26 g of helium and 0.02 g of heavier elements. Despite the superb efforts of past generations of stars, the Sun, like its nebulous father, is singularly poor in metals, since these make up a mere 2% mass fraction of its matter. This, however, is a small fortune compared with the ancient stars in the galactic halo. 

When differences in the oxygen isotopic composition of CAIs were first measured in 1973, Robert Clayton and his coworkers attributed these mass-independent variations to mixing of normal solar system gas (plotting on or above the terrestrial mass-fractionation... 

Over the years, numerous studies of CAIs have been carried out by a variety of techniques. MacPherson et al. (1995) compiled all available data and found that the 26A1/27A1 ratios for CAIs have a bi-modal distribution (Fig. 8.27). Many have ratios near 5 x 10-5, which they interpreted as the initial ratio for the solar system (the canonical ratio). Many others have initial ratios near zero. Resetting or isotopic disturbance by secondary processes is responsible for the low ratios in most cases. But a few CAIs formed with little or no 26Al. These so-called FUN CAIs (Fig. 8.27) also exhibit large isotopic mass fractionations and isotopic anomalies reflecting different mixtures of nucleosynthetic components. In 1995, evidence for 26A1 in objects other than CAIs was rare. 

Figure 2.15 Ne three-isotope plot for a grain-size suite of plagioclase separates from lunar high land soil that were treated by the CSSE treatment (see text). The best fitted line through the data from all etched samples (line p) passes close to the data point GCR (galactic cosmic ray) of cosmogenic Ne. On the left side, the path of mass fractionation of SWC (solar wind composition)-Ne intersects line p at a 20Ne/22Ne ratio of -11.3, which is interpreted to represent SEP (solar energetic particle) Ne (cf. Section 2.8). Open symbols unetched sample. Solid symbols etched samples. SF Solar flare Ne. Reproduced from Signer et al. (1993).

Hydrogen gas has been found occluded in meteorites, and also is present in nebulae, fixed stars, and in the Sun. Anders and Grevesse calculated mass fractions of H, He, and heavier elements (Li-U) in the solar system, and derived values of 70.683, 27.431, and 1.886%, respectively. The major planets (Jupiter, Neptune, Saturn, and Uranus) contain large amounts of hydrogen in their atmospheres, along with He, CH4, and NH3. 

Figure 7 Mass fractionation of xenon in the atmosphere relative to the solar value (Pepin and Porcelli, 2002) (reproduced by permission of Mineralogical Soeiety of America from Rev. Mineral. Geochem. 2002,47, 191-246).

Figure 9 Comparison of silicate mass fractions. Two assumptions for interior strueture are shown (i) differentiated—rock core, ice mantle, and (ii) homogeneous—uniformly mixed ice and roek. Also shown are silicate mass fractions for the Jupiter and Saturn systems and expected values for two models of the early solar nebula carbon chemistry (see text) (after Johnson et aL, 1987) (reproduced by permission of Ameriean Geophysieal Union from /. Geophys. Res. Space Phys. 1987, 92, 14884-14894).

---