Atomic weight, also known as atomic mass or atomic mass unit (AMU), is indeed an average value calculated based on the relative abundances of isotopes on Earth. However, in space or other celestial bodies, the atomic weights may differ due to variations in isotope abundances.
Isotopes are different forms of an element that have the same number of protons but different numbers of neutrons. These isotopes have slightly different atomic masses. On Earth, the atomic weight of an element is determined by the weighted average of the atomic masses of its isotopes, taking into account their relative abundances.
In space, the elemental composition may vary compared to Earth. Different regions of space, such as stars, planets, or interstellar clouds, can have different isotope abundances due to various factors like nucleosynthesis processes, stellar evolution, and chemical reactions. These variations can lead to differences in the atomic weights of elements found in space compared to their average values on Earth.
Scientists study the elemental composition of space by analyzing the light emitted or absorbed by celestial objects. This spectroscopic analysis helps determine the relative abundances of different isotopes and the atomic weights of elements in those specific environments.
It's important to note that while the atomic weights calculated based on Earth's isotopic abundances serve as useful reference values, they may not be directly applicable to space or other astronomical contexts where the isotopic compositions may differ.