Composition of the sun
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Solar Chemical Composition: Hydrogen, Helium, and Metals
The Sun is primarily composed of hydrogen and helium, with a small fraction of heavier elements known as "metals" in astronomical terms. The most recent and comprehensive analyses show that the present-day solar photosphere consists of about 74% hydrogen (X), 24% helium (Y), and 1.4% metals (Z) by mass, with the metal-to-hydrogen ratio (Z/X) around 0.0187. These values are derived using advanced 3D hydrodynamic models and state-of-the-art spectroscopic techniques, which provide a more accurate picture than older 1D models 1467.
Elemental Abundances: From Light to Heavy Elements
Light Elements: Hydrogen, Helium, Carbon, Nitrogen, Oxygen
Hydrogen is the most abundant element in the Sun, followed by helium. The next most abundant elements are oxygen, carbon, and nitrogen. Recent studies confirm relatively low solar abundances for carbon, nitrogen, and oxygen, with values such as log C = 8.46, log N = 7.83, and log O = 8.69 (on a scale where log H = 12) 47. These results are consistent across different measurement methods, including atomic and molecular lines, though some discrepancies remain for nitrogen .
Intermediate and Iron Group Elements
Elements like sodium, magnesium, aluminum, silicon, sulfur, potassium, and calcium (Na to Ca) have been carefully measured using high-quality solar spectra and 3D models. Their abundances are generally in good agreement with those found in primitive meteorites, which are considered a reference for the early solar system . The iron group elements (scandium to nickel) have also been re-evaluated, with updated values that closely match meteoritic data, though some exceptions exist .
Heavy Elements: Copper to Thorium
For heavier elements, from copper (Cu) to thorium (Th), the latest analyses use both neutral and ionized spectral lines, correcting for non-local thermodynamic equilibrium effects. These studies find that the Sun's heavy element abundances are mostly consistent with those in the most pristine meteorites, but a few elements show notable differences .
Isotopic and Noble Gas Composition
The Sun is highly enriched in the isotope oxygen-16 compared to planetary materials, as shown by solar wind measurements. This suggests that rocky bodies in the inner solar system are relatively enriched in oxygen-17 and oxygen-18, likely due to chemical processes before planet formation . For noble gases like neon, direct measurements from the solar wind have improved abundance estimates, which are important for understanding the Sun's overall composition 47.
Methods and Uncertainties in Solar Composition Analysis
Determining the Sun's composition relies on analyzing the solar photosphere's spectrum, using sophisticated models to account for physical processes like convection and non-equilibrium effects. While the photosphere is usually taken as representative of the Sun's overall composition, there are small differences between the surface and the interior due to processes like diffusion and convection. Uncertainties remain for some elements, with errors exceeding 25% in a few cases, but overall agreement with meteoritic data is strong 149.
Solar Composition as a Cosmic Reference
The Sun's chemical composition serves as a fundamental reference for astronomy, as the abundances of other cosmic objects are often compared to solar values. The close match between solar and meteoritic abundances supports the use of the Sun as a standard, though small systematic differences related to condensation temperature have been observed, possibly linked to planet formation processes 410.
Conclusion
The Sun is composed mainly of hydrogen and helium, with a small but important fraction of heavier elements. Modern analyses using advanced models and high-quality data have refined our understanding of the solar composition, confirming its role as a cosmic benchmark. While most elemental abundances agree well with those in primitive meteorites, ongoing research continues to resolve small discrepancies and improve the precision of solar chemical measurements 12345678+2 MORE.
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