An Ancient Storm in the Jovian Atmosphere, 1999.
© National Aeronautics & Space Administration / Science & Society
When 17th-century astronomers first turned their telescopes to Jupiter, they noted a conspicuous reddish spot on the giant planet. This Great Red Spot is still present in Jupiter's atmosphere, more than 300 years later. It is now known that it is a vast storm, spinning like a cyclone. Unlike a low-presure hurricane in the Caribbean Sea, however, the Red Spot rotates in a counterclockwise direction in the southern hemisphere, showing that it is a high-presure system. Winds inside this Jovian storm reach speeds of about 270 mph. The Red Spot is the largest known storm in the Solar System. With a diameter of 15,400 miles, it is almost twice the size of the entire Earth and one-sixth the diameter of Jupiter itself.