Standard Abundance Distribution


Reference: Grevesse & Sauval (1998). See also the paper itself. A plot of the solar composition see Solar Composition.

The standard abundance distribution (SAD) is intended to be as nearly as possible the primordial solar nebula composition (PSNC). (Usually we just call it the solar composition for short.) The values are derived in two main ways: (1) from the solar photosphere using spectroscopy and radiative transfer modeling; (2) from abundances from meteors in particular the CI carbonaceous chondrites which are believed to largely primordial in composition. First, we should note that the solar photosphere may not be entirely primordial since various altering effects can occur near the surface of stars. Also certain elements are not detected in the solar photosphere or other solar components---this doesn't mean they are not there. The meteoritic abundances do not contain the most volatile elements: H, He, C, N, O, Ne, and Ar. These elements were evaporated from the meteorites even those that underwent minimal heating. Comet material, some of which may be even purer primordial, is not yet available for study. It has to be remarked that the primordial nebula was probably not completely homogeneous, and so the available SADs are some sort of mean.

PSNC is not universal composition, of course. We know that composition varies wildly in fact in the universe. Nonetheless, PSNC is typical of relatively recently formed stars and nebula. Thus, it provides a good standard for composition comparisons. Also it is the composition we can study in most detail.

PSNC for historical reasons is given relative to hydrogen in a rather peculiar way:

A_el=log(N_el/N_H)+12 ,

where the logarithm is base 10, N_el is the number abundance of the element, N_H is the number abundance of H, and 12 is added on to make A_H=12 exactly.

In the table below we give the recent SAD of Grevesse & Sauval (1998). We give both photospheric and meteoritic values. In most cases there is excellent agreement between the two. Of course, there is no absolute reason why they should agree. As mentioned above, there are processes that can alter both the solar surface and meteorites from PSNC. In particular the photospheric Li abundance is probably really much lower than the meteoric Li abundance: there are mechanisms that destroy Li in the Sun???. Where they are available, the meteoric abundances are probably to be preferred for representing the PSNC.

Notes on the table.

  1. Element name, symbol, atomic number, and atomic weight are given. The atomic weight is just an average over the isotopes available in the solar system: each isotope of an element has a definite atomic weight. Thus the atomic weights do not represent universal values. But given the processes that led to the solar system isotopic abundances are rather general, these atomic weights can usually be used for extra-solar system calculations unless there is some reason for other ones.

  2. Some elements are not given abundances. These elements have no stable or long-lived isotopes. They can be created in the lab and exist in some astrophysical environments, but they have very small natural abundances in the solar system????. When they are found in nature, it is because they are the decay products of longer lived radioactive elements: e.g., thorium and uranium. Thorium and uranium also have no stable isotopes, but they do have very long-lived radioactive isotopes, and so have persisted in finite abundance since the formation of the solar system. The elements heavier than C are mainly produced in supernova explosions.

  3. Values in square brackets are not derived from the photosphere, but from sunspots, solar corona, and/or solar wind particles.

  4. Values in parentheses are less accurate results.


Element Symbol At. No. At. Wt. log(Ab)_ph log(Ab)_me
Hydrogen H 1 1.0079 12.00 Helium He 2 4.0026 [10.93 0.004] Lithium Li 3 6.9400 1.10 0.10 3.31 0.04 Beryllium Be 4 9.0100 1.40 0.09 1.42 0.04 Boron B 5 10.8100 ( 2.55 0.30 ) 2.79 0.05 Carbon C 6 12.0100 8.52 0.06 Nitrogen N 7 14.0100 7.92 0.06 Oxygen O 8 16.0000 8.83 0.06 Fluorine F 9 19.0000 [ 4.56 0.3 ] 4.48 0.06 Neon Ne 10 20.1800 [ 8.08 0.06 ] Sodium Na 11 22.9900 6.33 0.03 6.32 0.02 Magnesium Mg 12 24.3000 7.58 0.05 7.58 0.01 Aluminium Al 13 26.9800 6.47 0.07 6.49 0.01 Silicon Si 14 28.0900 7.55 0.05 7.56 0.01 Phosphorus P 15 30.9700 5.45 (0.04) 5.56 0.06 Sulfur S 16 32.0700 7.33 0.11 7.20 0.06 Chlorine Cl 17 35.4500 [ 5.5 0.3 ] 5.28 0.06 Argon Ar 18 39.9500 [ 6.40 0.06] Potassium K 19 39.1000 5.12 0.13 5.13 0.02 Calcium Ca 20 40.0800 6.36 0.02 6.35 0.01 Scandium Sc 21 44.9600 3.17 0.10 3.10 0.01 Titanium Ti 22 47.8800 5.02 0.06 4.94 0.02 Vanadium V 23 50.9400 4.00 0.02 4.02 0.02 Chromium Cr 24 52.0000 5.67 0.03 5.69 0.01 Manganese Mn 25 54.9400 5.39 0.03 5.53 0.01 Iron Fe 26 55.8500 7.50 0.05 7.50 0.01 Cobalt Co 27 58.9300 4.92 0.04 4.91 0.01 Nickel Ni 28 58.6900 6.25 0.04 6.25 0.01 Copper Cu 29 63.5500 4.21 0.04 4.29 0.04 Zinc Zn 30 65.3900 4.60 0.08 4.67 0.04 Gallium Ga 31 69.7200 2.88 (0.10) 3.13 0.02 Germanium Ge 32 72.6100 3.41 0.14 3.63 0.04 Arsenic As 33 74.9200 2.37 0.02 Selenium Se 34 78.9600 3.41 0.03 Bromine Br 35 79.9000 2.63 0.04 Krypton Kr 36 83.8000 3.31 0.08 Rubidium Rb 37 85.4700 2.60 (0.15) 2.41 0.02 Strontium Sr 38 87.6200 2.97 0.07 2.92 0.02 Yttrium Y 39 88.9100 2.24 0.03 2.23 0.02 Zirconium Zr 40 91.2200 2.60 0.02 2.61 0.02 Neobium Nb 41 92.9100 1.42 0.06 1.40 0.02 Molybdenum Mo 42 95.9400 1.92 0.05 1.97 0.02 Technetium Tc 43 -98.0000 Ruthenium Ru 44 101.0700 1.84 0.07 1.83 0.04 Rhodium Rh 45 102.9100 1.12 0.12 1.10 0.04 Palladium Pd 46 106.4200 1.69 0.04 1.70 0.04 Silver Ag 47 107.8700 ( 0.94 0.25) 1.24 0.04 Cadmium Cd 48 112.4100 1.77 0.11 1.76 0.04 Indium In 49 114.8200 ( 1.66 0.15) 0.82 0.04 Tin Sn 50 118.7100 2.0 (0.3 ) 2.14 0.04 Antimony Sb 51 121.7600 1.0 (0.3 ) 1.03 0.07 Tellurium Te 52 127.6000 2.24 0.04 Iodine I 53 126.9045 1.51 0.08 Xenon Xe 54 131.2900 2.17 0.08 Cesium Cs 55 132.9100 1.13 0.02 Barium Ba 56 137.3300 2.13 0.05 2.22 0.02 Lanthanum La 57 138.9100 1.17 0.07 1.22 0.02 Cerium Ce 58 140.1200 1.58 0.09 1.63 0.02 Praseodymium Pr 59 140.9100 0.71 0.08 0.80 0.02 Neodymium Nd 60 144.2400 1.50 0.06 1.49 0.02 Promethium Pm 61 -145.0000 Samarium Sm 62 150.3600 1.01 0.06 0.98 0.02 Europium Eu 63 151.9600 0.51 0.08 0.55 0.02 Gadolinium Gd 64 157.2500 1.12 0.04 1.09 0.02 Terbium Tb 65 158.9300 (-0.1 0.3 ) 0.35 0.02 Dysprosium Dy 66 162.5000 1.14 0.08 1.17 0.02 Holmium Ho 67 164.9300 ( 0.26 0.16) 0.51 0.02 Erbium Er 68 167.2600 0.93 0.06 0.97 0.02 Thulium Tm 69 168.9300 ( 0.00 0.15) 0.15 0.15 Ytterbium Yb 70 173.0400 1.08 (0.15) 0.96 0.02 Lutetium Lu 71 174.9700 0.06 0.10 0.13 0.02 Hafnium Hf 72 178.4900 0.88 (0.08) 0.75 0.02 Tantalum Ta 73 180.9500 -0.13 0.02 Tungsten W 74 183.8400 ( 1.11 0.15) 0.69 0.03 Rhenium Re 75 186.2100 0.28 0.03 Osmium Os 76 190.2300 1.45 0.10 1.39 0.02 Iridium Ir 77 192.2200 1.35 (0.10) 1.37 0.02 Platinum Pt 78 195.0800 1.8 0.3 1.69 0.04 Gold Au 79 196.9700 ( 1.01 0.15) 0.85 0.04 Mercury Hg 80 200.5900 1.13 0.08 Thallium Tl 81 204.3800 ( 0.9 0.2 ) 0.83 0.04 Lead Pb 82 207.2000 1.95 0.08 2.06 0.04 Bismuth Bi 83 208.9800 0.71 0.04 Polonium Po 84 -209.0000 Astatine At 85 -210.0000 Radon Rn 86 -222.0000 Francium Fr 87 -223.0000 Radium Ra 88 226.0200 Actinium Ac 89 227.0300 Thorium Th 90 232.0400 0.09 0.02 Protactinium Pa 91 231.0400 Uranium U 92 238.0300 (-0.47) -0.50 0.04