Sciency Words: Belts and Zones

Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at two closely related terms:

BELTS and ZONES

Jupiter: it’s a big ball of hydrogen. Well, mostly hydrogen. The topmost layer of clouds—the part we can see in visible light—is primarily composed of ammonia, hydrogen sulfide, and water. A dash of other as-yet-unidentified chemicals are also mixed in for color.

If you’ve ever looked at Jupiter, you’ve noticed that it has stripes. The stripes are so pronounced that you can see them even with a cheap backyard telescope, and astronomers have been observing these stripes for centuries.

By a long-standing convention, the two different kinds of stripes seen on Jupiter are called belts and zones.

• Zones: Zones are characterized by their lightly colored clouds. Winds in zones generally blow west to east, and the cloud tops rise above the clouds in the neighboring belts.
• Belts: Belts are darker-colored, with winds blowing east to west. You may notice that Jupiter’s famous storms, such as the Great Red Spot, tend to appear where belts and zones border each other. The clouds in belts are known to sink to lower altitudes than the clouds in zones.

Jupiter isn’t the only planet with belts and zones. The Solar System’s other three gas giants show similar, though less visually distinctive, stripiness, and it’s a safe bet gas giants orbiting other stars will too.

This all seems straightforward enough, but while researching zones and belts for today’s post, I learned something that struck me as very odd. Zones, the clouds of which rise upwards, are often described as cold while belts, with their lower altitude clouds, are described as warm. Does this mean that on Jupiter, warm air sinks and cold air rises? Have the laws of thermodynamics been reversed?

Next Wednesday, I will attempt to solve this peculiar riddle.