Jupiter, the 5th planet from the Sun, is the larget planet in the Solar System! But, it is way smaller than the Sun. Jupiter and the Sun do not really look like they share similar features, but if Jupiter was the size of the Sun, it would become a star! How?
It is all because of the composition or what Jupiter and the Sun are made out of. Stars are usually made out of hydrogen and helium. The star squishes hydrogen atoms together to for helium, light, and heat! That process is called nucleosynthesis. Jupiter is also made out of hydrogen and helium, but since it is way smaller than the Sun, it does not have enough gravity to squish together hydrogen atoms. That is why if Jupiter was bigger, it would have more gravity, and would turn into a star, like the Sun!