The Sun is a massive, incandescent ball of plasma. Its composition is primarily a blend of the two lightest elements in the universe. This stellar furnace converts matter into energy through processes dependent on its elemental makeup. The intense heat and pressure strip electrons from atoms, creating the plasma state.
The Primary Elements: Hydrogen and Helium
The Sun’s mass is dominated by the two lightest elements: hydrogen (H) and helium (He). By mass, hydrogen constitutes approximately 73% of the Sun, while helium accounts for about 25%. All other elements combined make up only a small percentage.
The immense gravity compresses this material to incredible densities, especially in the core where fusion occurs. Hydrogen serves as the primary fuel source for the star’s energy production. The Sun has steadily converted hydrogen into helium, shifting the elemental ratio compared to the surface.
Hydrogen abundance is a remnant of the early universe. Helium was created both during the universe’s initial moments and continuously within the Sun’s core. These two elements define the Sun’s physical structure and energy output.
The Abundance of Heavier Elements
The remaining 1% to 2% of the Sun’s mass consists of all other elements, which astronomers collectively term “metals.” These heavier elements originated from previous generations of stars that exploded and seeded the interstellar medium. Oxygen (O) is the most abundant of these “metals,” making up approximately 1% of the Sun’s total mass.
Following oxygen, the next most common elements are carbon (C) and neon (Ne). Iron (Fe) is also present in significant quantities, along with smaller amounts of nitrogen (N), silicon (Si), and magnesium (Mg). These trace elements play a role in the Sun’s opacity and energy transport.
How Scientists Measure Solar Composition
Scientists cannot take a physical sample from the Sun, so they rely on spectroscopy to determine its elemental makeup. This method involves analyzing the light emitted from the Sun’s outer layers, specifically the photosphere. The light is split into a continuous spectrum, which is then examined for specific dark lines.
These dark lines, known as Fraunhofer lines, are the chemical “fingerprints” of elements. They are created when cooler atoms in the Sun’s upper atmosphere absorb light at specific wavelengths. Since every element absorbs light at a unique set of wavelengths, the pattern of these dark lines identifies the elements present in the solar atmosphere.
For deeper layers, scientists use helioseismology, which studies the acoustic waves traveling through the Sun’s interior. By measuring how these sound waves travel and are reflected, researchers can infer internal properties like density, temperature, and composition. This method confirms models of the Sun’s internal structure and elemental distribution.
The Role of Composition in Solar Energy Generation
The Sun’s elemental composition dictates its function as a star through nuclear fusion in its core. The immense amount of hydrogen provides the necessary fuel. At the core’s extreme temperature of around 15 million degrees Celsius and crushing pressure, hydrogen nuclei are forced together.
This process, known as the proton-proton chain reaction, involves four hydrogen nuclei fusing to form a single helium nucleus. The resulting helium nucleus has slightly less mass than the original hydrogen nuclei. This mass difference is converted into energy, released as light and heat according to Einstein’s famous equation, \(E=mc^2\).
The Sun constantly fuses about 620 million metric tons of hydrogen into helium every second. The vast hydrogen reservoir ensures the Sun’s stability and longevity. This fusion process enables the Sun to continuously shine and provide energy to the solar system.