QUESTION:
The bright spot on Neptune that was seen in 1989 either has more methane or
less.  Do you know which?  Does this methane have any effect on the planet?

ANSWER from Heidi Hammel on June 10, 1996:
We think that the bright spots on Neptune are places where there lots of
clouds made of condensed methane, ice crystals made of methane ice instead
of water ice like many of the clouds on Earth.  So why does the methane
condense in just those spots? We think it could be because there is more
methane gas in those locations, which is bubbling up from deeper down in
the atmosphere.  We call this process of stuff bubbling from deeper down
"convection," and it happens
here on Earth with big thunderclouds made of water.

This methane may have a big effect on the planet's atmosphere. One of the
most important drivers of weather on a planet is sunlight, and when you
have clouds, you change the amount of sunlight that can get deeper into
the atmosphere.  This changes the temperature, and temperature makes a
difference for the kind of chemistry that goes on.

You may have heard similar kinds of talk about how certain gases may be
playing similar roles in changing our own Earth's atmosphere: methane,
carbon dioxide, and water are some of the most important ones.  Many
scientists are studying how these gases affect the Earth's "energy balance"
(energy coming in from the sunlight, and energy being scattered by clouds or
radiated away as heat).   Understanding these things allows us to model
processes like "global warming," which may have a big effect on our future!