Final answer:
Giant planets feature extremely high temperatures and pressures within their interiors, originating from their formation and ongoing contraction. Jupiter is the hottest with significant internal heat, while Uranus lacks a detectable internal heat source.
Step-by-step explanation:
Extreme Conditions in the Interiors of Giant Planets
The interiors of giant planets such as Jupiter, Saturn, Uranus, and Neptune experience extreme conditions due to their large sizes and formation process. These planets were first heated by internal heat sources during their formation when the collapse of surrounding gas onto their cores produced significant amounts of heat. Jupiter, the largest of them, was the hottest. Some of the primordial heat remains within these planets. Now, they can also generate heat by slowly contracting, which is particularly effective given their massive size. The pressure and temperature within these giants are far too low for nuclear fusion, which is the process powering stars, but they're still hot enough to have deep atmospheres, liquid hydrogen mantles (in Jupiter and Saturn), and significant magnetic fields, especially in the case of Jupiter.
While these planets have cooled since their formation to their current states, the temperatures and pressures deep inside remain much higher than the surfaces, creating an environment inhospitable for human life but fascinating for study. Uranus is an exception among the giant planets as it does not have a measurable internal heat source compared to the others.