This is an infrared image of Jupiter showing regions which are hot.
Click on image for full size
NASA
The Source of Heat from Within Neptune
In astronomy, it is a usual procedure to calculate the luminosity of a star, and this calculation indicates the energy and the temperature of the star.
When the luminosity of the outer planets was calculated, that of Neptune was found to be relatively high, indicating that Neptune is giving off more energy than it is receiving from the sun. The same phenomena is seen at Jupiter and Saturn.
There are several ways in which astronomical objects produce energy from inside. The first is thermonuclear fusion. This method of energy production is reserved for stars. Another method is by way of radioactive material within the ground. This method is at work in most terrestrial bodies.
For the giant planets the method which seems to be at work is the mere fact that energy is given off from when a planetary body is in the process of shrinking together, or collapsing on itself.
The fact that Neptune is still collapsing together indicates that the process of planet formation is still going on. This process is providing the heat from within which causes the unusual motions in the atmosphere.
You might also be interested in:

Some materials give off radiation. We say that those substances are "radioactive". Radioactive materials are often, though not always, hazardous to living things. There are many different types of radioactive
...more
Motions, or currents in the interior of a gas-giant planet such as Neptune may be very different from the motions typical of the Earth's interior. A second idea for the motions in the interior of a gas-giant
...more
In astronomy, it is a usual procedure to calculate the luminosity of a star, and this calculation indicates the energy and the temperature of the star. When the luminosity of the outer planets was calculated,
...more
Motions in the interior of a planet helps to carry heat from the core to the planet's surface. The drawing to the left illustrates a kind of global motion that is typical of motions in the atmosphere as
...more
This image shows the new Great Dark Spot of Neptune, which was discovered using the Hubble Space Telescope. The image shown here, shows a "hole" in the clouds of Neptune in pink, in the northern hemisphere,
...more
Atmospheres of the giant planets have definitely evolved from their formation out of the primitive solar nebula. How much they have evolved remains to be seen, however. Because of their enormous gravity,
...more
This image shows some cirrus clouds, extending for many kilometers across the disc of Neptune. These clouds are somewhat high up, for they can be seen to cast shadows on the lower clouddeck, which is 35
...more
This image of Neptune uses false colors to bring out the hazes of smog, which can be seen in red along the limb of Neptune, at the edge of the picture. These hazes of smog are found at very high altitudes,
...more