Solar system abundances of the elements

There are several basic features to note about the chemical abundances of the solar system. First, the Sun, and thus the solar system, consists dominantly of hydrogen and helium, with these two elements making up 98% of the mass of the solar system. Outside of the Sun, hydrogen and helium are found primarily in the gas-giant planets. 

Second, lithium, beryllium, and boron have very low abundances. These elements are, for the most part, not made in stars and were not made efficiently in the Big Bang. They are produced via cosmic ray interactions. Nuclei of heavier atoms, when hit by fast moving protons or other nuclei, can break into pieces, including protons, neutrons, alpha particles, and heavier fragments. Some of these fragments are lithium, beryllium, and boron nuclei. 

carbon, nitrogen, and oxygen, the elements that catalyze hydrogen burning in the Sun, are relatively abundant in the solar system. Oxygen is somewhat more abundant than carbon the C/O ratio is 0.54. Because CO is a very stable molecule, most of the carbon and oxygen in the early solar system was tied up in CO. The excess oxygen that remained controlled the chemical environment of the early solar system. 

Among the elements that make up rocks and minerals, silicon, magnesium, and iron are of almost equal abundance followed by sulfur, aluminum, calcium, sodium, nickel, and chromium. Two of the most common minerals in meteorites and in the terrestrial planets are olivine ((Mg,Fe)2Si04) and pyroxene ((Mg,Fe,Ca)Si03). The composition obtained by averaging these two minerals is very similar to the bulk solar system composition, so it is really no surprise that they are so abundant. 

---

Percentage of meteorites seen to fall. Chondrites. Over 90% of meteorites that are observed to fall out of the sky are classified as chondrites, samples that are distinguished from terrestrial rocks in many ways (3). One of the most fundamental is age. Like most meteorites, chondrites have formation ages close to 4.55 Gyr. Elemental composition is also a property that distinguishes chondrites from all other terrestrial and extraterrestrial samples. Chondrites basically have undifferentiated elemental compositions for most nonvolatile elements and match solar abundances except for moderately volatile elements. The most compositionaHy primitive chondrites are members of the type 1 carbonaceous (Cl) class. The analyses of the small number of existing samples of this rare class most closely match estimates of solar compositions (5) and in fact are primary source solar or cosmic abundances data for the elements that cannot be accurately determined by analysis of lines in the solar spectmm (Table 2). Table 2. Solar System Abundances of the Elements ... 

Anders, E. and Ebihara, M., 1982. Solar-system abundances of the elements. Geochim. Cosmochim. Acta, 46 2363-2380. 

In the final section of this chapter, we discussed the formation of galaxies and the formation and chemical evolution of the Milky Way. This sequence of events set the stage for the formation of the solar system. In Chapter 4, we will look at the resulting abundances of the elements and isotopes, both in the solar system and in the galaxy. The solar system abundances of the elements are a fundamental constraint for understanding the Sun, the planets, and the smaller bodies in the solar system. 

In this chapter, we discuss the abundances of the elements and isotopes in the solar system. First, we look at the techniques used to determine solar system abundances, including spectroscopy of the stellar photosphere, measurements of solar wind, and analyses of chondritic meteorites. The solar system abundances of the elements and isotopes are then presented. These abundances are then compared to the abundances in the solar neighborhood of the galaxy and elsewhere. Finally, we introduce how solar system abundances provide a basis for much of what we do in cosmochemistry. 

Table 4.1 shows the solar system abundances of the elements as determined by the methods discussed above. For some elements, the photospheric abundances provide the best estimate, whereas for others, the meteorite data must be used. In some cases, the data are equally reliable and an average of the values determined from the solar photosphere and Cl chondrites is used. The abundances of the noble gases come from indirect measurements or theoretical considerations. The method for determining each abundance is indicated in the far right column of Table 4.1. 

The solar system abundances of the elements are the result of the Big Bang, which produced hydrogen and helium, 7.5 billion years of stellar nucleosynthesis, which produced most of the rest of the elements, and the physical processes that mixed the materials together to form the Sun s parent molecular cloud. The unique features of the solar system composition may also reflect the stochastic events that occurred in the region where the Sun formed just prior to solar system formation. 

Lodders, K. (2003) Solar system abundances and condensation temperatures of the elements. Astrophysical Journal, 591, 1220-1247. A comprehensive discussion of the solar system abundances of the elements from the perspective of a cosmochemist. 

Palme, H. and Jones, A. (2004) Solar System abundances of the elements, in Treatise on Geochemistry Volume 2 The Mantle and Core (eds R.W. Carlson, H.D. Holland and K.K. Turekian Editors-in-Chief), Elsevier Science, pp. 41-61. 

Comparison with Anders and Grevesse abundance table Solar System Abundances of the Elements... 

Although the elemental composition of the solar system is roughly similar to that of many other stars, in particular with respect to the relative abundances of the nongaseous elements, there are, in detail, compositional differences among stars and there are, in addition, truly exotic stars that make the term cosmic abundances of elements questionable. We will therefore use the term solar system abundances of the elements in this chapter. 

The solar system abundances of the elements Li, Be, and B are four to seven orders of magnitude lower than those of the elements that immediately follow them C, N, and O. Explain. 

Lodders K (2010) Solar system abundances of the elements. In Goswami A, Reddy BE (eds) Principles and perspectives in cosmochemistry. Astrophysics and space science proceedings. Springer, New York, pp 379 17... 

---