Jupiter is the king of the planets. From rim to rim, it’s 11 times wider than Earth, with a diameter of about 88,000 miles. If Jupiter were hollow, you could fit roughly 1,300 Earths inside it. Its mass is even more lopsided - Jupiter is more massive than all the other planets in our solar system combined.
It’s so big and heavy that it doesn’t quite orbit the Sun the way smaller planets do. Technically, Jupiter and the Sun both orbit a common center of mass, called the barycenter, that sits just outside the Sun’s surface. The Sun wobbles slightly to balance Jupiter’s gravitational pull. (Astronomers actually use this kind of wobble to find planets around other stars.)
For all that size, Jupiter is mostly gas - about 90% hydrogen and 10% helium, similar to the Sun’s chemistry. If Jupiter had been about 80 times more massive when it formed, it might have ignited fusion and become a small star instead of a planet. As it is, it’s our solar system’s biggest “failed star.”
