system
Given the following post, respond as if you're commenting on Reddit:
human
Why does Neptune have such strong winds?

According to Wikipedia, it has the "strongest sustained winds of any planet in the solar system, with recorded wind speeds as high as  2,100 kilometres per hour (580 m/s; 1,300 mph)."  
  
Why are the winds so strong there?
gpt
There's a lot of conjecture in the other answers here, but as someone who specialized in this for his PhD, the only real answer is: we don't really know yet. This is one of the big unsolved problems in the field, though we have some ideas.

There are a few scaling relations for planetary winds that are generally true but lack precision, and there are an awful lot of exceptions, too:

- **The bigger the planet, the faster the winds.** In general the larger your planet is, the more angular momentum a parcel of air will have near the equator. As it moves towards the pole, angular momentum must be conserved, and that translates to faster winds. This generally explains why giant planets have faster winds than terrestrial planets, but doesn't really explain why Neptune's winds are faster than Jupiter's, which is quite a bit larger.

- **The faster the planet rotates, the faster the winds.** Again, the faster your planet rotates means the more angular momentum there is to feed into winds. Nonetheless, with this explanation alone one would again expect Jupiter (10 hour rotation) to have the fastest winds, but the winds of Neptune (16 hour rotation) are quicker. This also really fails for Venus, which has a 243 days rotation, yet has some impressively speedy winds at cloud-top.

- **The bigger the source of internal heat, the faster the winds.** It takes energy to fight against drag and pump the planetary jets, and localized release of energy, generally starting as small local storms, feed into the jets to keep them strong. Again you'd expect Jupiter to win out here in terms of total internal energy, but this does explain why the winds of Neptune (with a fairly substantial internal heat source itself) beat out the winds of Uranus (essentially the same size, temperature, and rotation period as Neptune, but no internal heat).

- **The lower the temperature, the lower the viscosity**. This one is probably really important for both Uranus and Neptune. As you decrease the temperature of a gas, its viscosity also decreases, so there's very little to slow down the winds and act as a source of drag. At low temperatures, you don't need to feed the winds much energy to get them going and keep the going.

It's something of a holy grail in the field to understand how each of these general rules play off one another. Which rule is most important? How many jets would we expect for each planet? Why is Venus so very different?

**TL;DR**: Neptune seems to have hit a sweet spot of relatively large (good for angular momentum), relatively fast rotation (also good for angular momentum), strong internal heat source (good for feeding the winds), and very cold (low viscosity, so little to slow the winds down).