Jupiter is the fifth planet in the Sol System, which in Spore can be found as an easter egg. It is a brown gas giant with a moon, Ganymede, but no rings.
Trivia
In reality, Jupiter has very thin rings of dust particles. Besides Ganymede, it also has three spherical moons: Io, Europa, and Callisto. However, as Spore only allows one moon per planet, only the largest among them is depicted.
In-game, Jupiter does not have the Great Red Spot. This may be interpreted as a sign that the Great Red Spot storm has ended, or that it may not even have started yet around the time Spore takes place. A more technical reason may be Maxis leaving it out during development due to it requiring a major change to the gas giant template.