Which is the largest planet in the Solar System?

Jupiter has about 318 times the mass of the Earth and more than twice the mass of every other planet in the Solar System put together. It is made mostly of hydrogen and helium, like the Sun, and it has no surface to land on - the atmosphere simply thickens with depth until the hydrogen is compressed into something that behaves like a liquid metal.

It is often described as a failed star. That undersells how far it failed by: to start fusing hydrogen it would need to be around eighty times more massive than it is. It does radiate more heat than it receives from the Sun, though, left over from its formation and from slowly contracting.

The Great Red Spot is a storm wider than the Earth that has been under observation for at least 190 years and possibly more than 350. It has been visibly shrinking for the last century and nobody is certain whether it is dying or simply changing shape. Jupiter's other job is gravitational: it is massive enough to have shaped where everything else in the Solar System ended up, and in 1994 astronomers watched it tear apart and swallow the comet Shoemaker-Levy 9.