QUESTION:
Is the weather on Neptune controlled by the same kinds of things that 
control the weather on earth? 

ANSWER from Heidi Hammel on April 17, 1996:
This is a great question: what is controlling the weather on Neptune?
The short answer is: we don't know yet!  The data that we took for the
LHST program, when combined with other studies of Neptune, are going
to help us answer this.

We suspect that sunlight -- as feeble and faint as it is out at 
Neptune's distance -- is one of the controlling factor for the weather, 
based on our studies of how the planet's brightness changes with time. 
Also, Neptune is an intrinsically warm planet - there is heat coming 
from inside it.

This heat, rising from deep down in the lowest clouds decks, 
almost certainly drives much of the intricate weather patterns we see.

What about tides from Neptune's moons?  Neptune's largest moon 
is Triton, but even this largest Neptune moon is smaller than our own 
Moon. The distance between a planet and its moon plays an important role 
in tides.  Triton is just a little bit closer to Neptune than our Moon 
is to the Earth, so might it have a similar effect, making up for the
smaller size?   

Maybe, but remember:  Neptune is very much larger than
the Earth: it would take a pretty big moon to have a similar effect on
Neptune.  The bottom line is that Triton might have a very slight
influence on Neptune's weather, but we haven't been able to detect it 
yet.

Another thing to note about Neptune's weather is that Neptune is 
a gas giant planet - that means that its atmosphere is very deep and 
very thick.

The planet's fast rotation (only 16 hours, compared with the 
Earth's 24 hours) has a very strong influence on weather, and is 
probably more important than tidal influences.

It is hard to study the seasons on Neptune, because its "year" 
(the time it takes to travel in a complete circle around the sun) is 165 
Earth years, and Neptune was only discovered 150 years ago!  We haven't 
even seen a full Neptunian year yet!  We have really only been able to 
study the planet's weather with good resolution for the last 20 years, 
or a little over 6 Neptunian weeks!