Lodders reported in 2003 that solar photospheric and meteoritic CI-chondrite abundance determinations for all elements are summarized and the best currently available photospheric abundances are selected. The meteoritic and solar abundances of a few elements (e.g., noble gases, beryllium, boron, phosphorous, sulfur) are discussed in detail. The photospheric abundances give mass fractions of hydrogen (X = 0.7491), helium (Y = 0.2377), and heavy elements (Z = 0.0133), leading to Z/X = 0.0177, which is lower than the widely used Z/X = 0.0245 from previous compilations. Recent results from standard solar models considering helium and heavy-element settling imply that photospheric abundances and mass fractions are not equal to protosolar abundances (representative of solar system abundances).
Protosolar elemental and isotopic abundances are derived from photospheric abundances by considering settling effects. Derived protosolar mass fractions
are X0 = 0.7110, Y0 = 0.2741, and Z0 = 0.0149. The solar system and photospheric abundance tables are used to compute self-consistent sets of condensation temperatures for all elements.
The condensation temperatures of the elements from a solar composition gas are widely used as a diagnostic of chemical fractionation processes in astronomy, planetary science, and meteoritics. Wildt (1933) and Russell (1934) did probably the earliest thermochemical computations for gas chemistry in the Sun and for cool stars that also took condensation into account. Lord (1965) picked up on this theme, and since then, many studies have been dedicated to finding the volatility trends of the elements, which are expressed by the condensation temperature of
an element and its compounds.
Important studies include:
Larimer (1967, 1973),
Grossman (1972),
Grossman & Larimer (1974),
Boynton (1975),
Wai & Wasson (1977, 1979),
Sears (1978),
Fegley & Lewis (1980),
Saxena & Eriksson (1983),
Fegley & Palme (1985),
Kornacki & Fegley (1986), and
Palme & Fegley (1990).
More recent studies have become quite detailed in investigating the condensation of major rock-forming elements under various potential nebular conditions, such as different dust-to-gas ratios (see, e.g., Ebel & Grossman 2000 and references therein). Still, the available condensation temperatures, which have been calculated for almost all naturally occurring elements, are a melange from several studies dating back to the 1970s and 1980s (see summary tables in Wasson 1985 or Lodders & Fegley 1998).
In addition, these condensation temperatures are a mixture of ‘‘condensation temperatures’’ and ‘‘50% condensation temperatures,’’ which
makes comparisons of volatility somewhat difficult. It should be noted that for some elements condensation temperatures are not known well, if at all. These elements include several alkalis (Rb, Cs), halogens (F, Cl, Br, I), and trace elements (Bi, In, Hg, Pb, Sn, and Tl). More importantly, the different condensation studies used different sets of solar elemental abundances as well as thermodynamic properties, depending on what was available at the time.
However, condensation temperatures of the elements change as solar abundances and thermodynamic properties
are revised and updated.
Recently, Allende Prieto, Lambert, & Asplund (2001, 2002) presented substantial downward revisions of the solar abundances of oxygen and carbon compared to previous compilations. Carbon and oxygen are two abundant elements governing much of the chemistry of the other, less abundant elements. A lower absolute oxygen abundance will lower condensation temperatures of O-bearing compounds. In addition to the absolute O abundance, the C/O ratio influences condensation temperatures.
The C/O ratio from the determination by Allende Prieto et al. (2001, 2002) is 0.5, which is slightly higher than the C/O ratio of 0.49 found by Grevesse & Sauval (1998), and clearly higher than 0.42 from Anders & Grevesse (1989). An increase in the C/O ratio toward unity lowers the condensation temperatures of oxides and silicates, and the initial oxide and silicate condensates are replaced by C-bearing compounds, such as:
Larimer 1975;
Larimer & Bartholomay 1979;
Lodders & Fegley 1993;
Krot et al. 2000).
Changes in abundances of other elements such as sulfur or phosphorus also mean that their condensation temperatures will change. The authors present updated solar abundances and selfconsistent condensation temperatures for all elements.
In Section 2, elemental abundances are selected. Data from solar spectroscopy (Section 2.1) meteoritic analyses (Section 2.2) are used to derive a recommended set of photospheric abundances (Section 2.3), which are then used to derive protosolar (=solar system) abundances in Section 2.4. The abundances of the isotopes for the solar system composition are given in Section 2.5. The condensation temperatures calculated for the photospheric and solar system abundances
The authors concluded that the heavy-element fractionation processes in the Sun make it necessary to distinguish two elemental abundance sets: the photospheric, fractionated abundances and the solar system, unfractionated abundances. Meteoritic abundances from CI chondrites are only suitable to refine the relative abundances of the heavy elements but cannot be used to constrain the absolute element/hydrogen ratios or the total mass fractions X, Y, and Z. When elemental abundances are normalized to the cosmochemical scale of Si = 106 atoms, only the H and He abundances are different for both
abundance sets. The solar photosphere has a lower metallicity of about 84% of that of the proto-Sun. The difference in metallicity causes higher condensation temperatures (by ~10 K) for the gas of solar system composition.
The 50% condensation temperatures give the volatility groupings for the elements with solar system abundances at 104 bar, as follows. Ultrarefractory elements with 50% condensation temperatures above 1650 K are the metals Os, Re, and W, the lithophile elements Al, Hf, Sc, Th, Y, Zr, and the heavy rare earth elements Gd, Tb, Dy, Ho, Er, Tm, and Lu. Highly refractory elements with 50% condensation temperatures between 1650 and 1500 K are the metals Ir, Mo, and Ru, and the lithophile elements Ca, Nb, Ta, Ti, U, and the light REE La, Pr, Nd, and Sm. Refractory elements have 50% condensation temperatures between 1500 and 1360 K. They include the metals Pt and Rh, and the lithophile elements Ba, Be, Ce, Sr, V, and Yb. The condensation temperature range of 1360–1290 K of the common elementsMg, Si, and Fe is shared by the metals Co, Cr, Ni, and Pd, and lithophile Eu. The moderately volatile elements have 50% condensation temperatures between 1290 and 704 K, before FeS appears. This group contains the siderophile elements Ag, As, Au, Bi, Cu, Ga, Ge, P, Pb, Sb, and Te, the lithophile elements Cs, B, K, Li, Na, Mn, Rb, and Zn, and the halogens Cl and F. Troilite condensation marks the high end of the temperature range for volatile element condensation between 704 and 371 K, where 50% condensation of the chalcophile elements Cd, In, S, Se, and Tl occurs. The siderophile Sn and the halogens Br and I also belong to the volatile elements. The highly volatile elements C, N, O,
noble gases, and Hg condense (if at all) below 371 K.
The recent downward revisions for C, N, and O abundances introduce significant changes in the mass of total condensate expected from both the photospheric and solarcomposition abundance sets, when compared to the solar abundances from Anders & Grevesse (1989). Table 11 summarizes the condensate mass distribution between rocky and icy matter for the three elemental abundance sets. The largest amount of condensate is obtained for the solar composition by Anders & Grevesse (1989), where ~1.9% of the total mass ends up in condensate (the contribution in mass from noble gas condensates is excluded here).
The solar system composition yields only 1.5% total condensate mass, the photospheric composition slightly less (1.3%). In all cases, the rocky matter makes up ~0.44% to 0.49% of the total mass, and most of the condensed mass is from lowtemperature ices. The Anders & Grevesse (1989) composition yields a water/ice to rock ratio of ~2, which is reduced to about unity for the solar system and photospheric compositions. These changes are important for modeling the chemistry of the outer solar nebula and for models of the formation of the giant planets and their satellites and of comets.
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