Jupiter is mostly made of what the sun and Saturn are made of. They consist of hydrogen and helium. Although Jupiter is made of hydrogen and helium, like Saturn it lacks enough of these to undergo fusion and become a star.
Jupiter is made of 90 percent of hydrogen, and the other 10 percent it mostly helium. If all of the planets in the solar system had formed as part of the gas giant, it still would not have sufficient mass for fusion.
And did you know that if you combine all the planets in our solar system, they’re still 2.5times smaller than Jupiter? That’s a pretty big place.
You can read more at space.com.
Quick fact #1: Helium cannot combine with other elements.
Quick fact #2: Hydrogen in the sun fuses into helium.