The relative amount of each element or isotope in a given object such as a planet, star, or galaxy. Cosmic abundance refers to the proportions in the Universe as a whole. The amount of an element may be expressed either as the number of atoms, or by mass. The standard cosmic abundance is based on that of the Solar System, which has been determined from the Sun’s spectrum and from analysis of meteoric debris. The cosmic abundance is dominated by hydrogen, with about 25% helium by mass and all remaining elements amounting to less than 2%.
Cosmic Abundance of The Most Common Elements
Element | Percentage abundance by mass | Percentage abundance by number of atoms |
Hydrogen | 73.5 | 92.1 |
Helium | 24.9 | 7.8 |
Oxygen | 0.73 | 0.061 |
Carbon | 0.29 | 0.030 |
Iron | 0.16 | 0.004 |
Neon | 0.12 | 0.008 |
Nitrogen | 0.10 | 0.008 |
Silicon | 0.07 | 0.003 |
Magnesium | 0.05 | 0.002 |
Sulphur | 0.04 | 0.001 |
Argon | 0.02 | 0.001 |
Nickel | 0.01 | 0.0002 |