A star's nuclear fusion reaction converts hydrogen into helium, and generates energy through this process. A "new" star has a fairly low percentage of helium, but over the course of billions of years, it fuses the hydrogen "fuel" into helium "ash".
All of them, that's how a star gets to be "old" ... it converts its hydrogen into helium.
Im no astrophysicist but an older star would consume more of its hydrogen over time in comparison to helium through its fusion process. Over time concetrations would change resulting in a higher helium to hydrogen ratio.
The sun in composed of 25 percent helium. The other 75 percent is hydrogen. The sun also has small amounts of other elements such as neon, oxygen, carbon, and magnesium.
Helium atoms.
Helium.
Most stars - and specifically main-sequence stars - get their energy from converting hydrogen-1 to helium-4, so you would expect that the percentage of hydrogen will decrease over time, while the percentage of helium would increase over time. Please note that the rate of fusion depends a LOT on the mass of the star; so you might have a very massive star that's only a few million years old and has already burned up most of its fuel (hydrogen), and another star, a red dwarf, that's 10 billion years old and has only used a small percentage of its fuel.
Jupiter is a gas giant and does not have a solid surface like Earth, so it does not have a percentage of land. It is primarily composed of hydrogen and helium gases, with no solid landmass.
What is composed of only one type of molecule
Jupiter is composed mainly of gases (hydrogen and helium).
Main sequence stars, like our Sun, are mainly composed of hydrogen. These stars fuse hydrogen into helium in their cores, releasing energy in the form of light and heat. This process allows them to shine bright in the sky.
Roughly 90% of a star's total lifetime is spent on the main sequence, where it fuses hydrogen into helium in its core. After this stage, the star will evolve off the main sequence and follow a different path, such as becoming a red giant or a supernova.
Main sequence stars are composed primarily of hydrogen and helium, with small amounts of heavier elements. These stars generate energy through nuclear fusion in their cores, converting hydrogen into helium. The temperature and pressure conditions in the core of a main sequence star are ideal for sustaining this nuclear fusion process, which is what allows them to shine steadily over long periods of time.