Final answer:
Jupiter has an immense amount of internal heat due to primordial heat from its formation and subsequent contraction over time. Its heat generation was first indicated by radio wave emissions in the 1950s, signifying a strong magnetic field. This makes Jupiter's atmosphere unique, behaving partly like that of a planet and partly like a star.
Step-by-step explanation:
We know that Jupiter has so much heat because it has the largest internal energy source in our solar system. This energy amounts to approximately 4 × 10¹⁷ watts, equivalent to energy produced by 4 million billion 100-watt lightbulbs. The source of this heat is primarily primordial heat, left from the planet's formation 4.5 billion years ago. In addition to retaining this initial heat, Jupiter may also generate heat through the process of contraction, which is significant given its massive size.
We received our first hint that Jupiter was generating its own heat in the late 1950s when astronomers discovered that it emitted radio waves indicative of a strong magnetic field, which is atypical of thermal radiation. This heat generation means that Jupiter's atmosphere is a cross between that of a normal planetary atmosphere, which gets most of its energy from the Sun, and a star's atmosphere, which is heated by internal energy sources.