Q. Is the red spot on Jupiter part of the planet or part of its atmosphere?

Concord

A. They don't call Jupiter's Great Red Spot ``great'' for nothing. It's bigger than the Earth, 8,700 miles from north to south, 17,400 miles across the middle!

The Great Red Spot is part of Jupiter's atmosphere. Like a giant hurricane, it has a center and clouds swirling around it. They take an average of six earth days to make one complete rotation around the spot, traveling at about 180 miles per hour.

Jupiter has lots of ``spots,'' rotating weather systems that are tougher to see from Earth because they're smaller and mostly white. Nobody knows why the Red Spot is red. Astronomers think it may be because it has enough power to draw trace chemicals up from the planet's lower levels (Jupiter, like all the giant outer planets, is believed to have little or no solid surface.) But even the Voyager 1 and 2 spacecraft that flew by for a close look back in 1979 and the observations by Galileo, which has been orbiting Jupiter since Dec. 1995, weren't able to figure that one out.