Hurricanes on other planets?
Saturn has joined Earth as the second planet known to harbor hurricane-like storms in its atmosphere. A huge, clockwise-rotating hurricane-like cyclone with a deep "eye" surrounded by towering "eyewall" clouds was discovered swirling directly over Saturn's south pole by the Cassini spacecraft, NASA announced Thursday. This "Saturnicane" is huge--about 2/3 the diameter of the Earth--and is composed of clouds of liquid ammonia. The 5000-mile diameter storm has an "eyewall" about 185 miles (300 km) across, which surrounds a 930 mile (1500 km) wide "eye". The "eyewall" clouds soar 20-45 miles above the "eye"--about 2-5 times higher than the eyewall clouds of Earthly hurricanes. Winds blow at 350 mph around the storm. I hope we never see a whopper of a storm like that on Earth!
Figure 1. October 11, 2006 "Saturnicane" observed by the Cassini spacecraft over the south pole of Saturn.
The Saturnicane's "eyewall" clouds appear to be formed by convection--the same process that helps form hurricane eyewall clouds on Earth. Heat from below warms the air, generating rising air currents. As this air rises, it expands and cools, condensing the gaseous ammonia into liquid ammonia clouds. NASA scientists speculate that the phenomena only occurs in summer, which is in full swing over Saturn's southern hemisphere at present. It is unclear whether the storm's "eye" and "eyewall" behave in a similar fashion to those features in Earthly hurricanes. The fact that the storm is anchored directly over the south pole and is not composed of water clouds must mean that there are significant differences from the hurricanes we are familiar with. In an interview with Yahoo, astrophysicist Michael Flasar said, "I'm hoping that as we puzzle over it, it will become even more exciting as we start to connect the dots in our brains. But right now, the wheels are a little creaky," Flasar said. "We're all arguing with each other about what it might or might not be."
Figure 1. The relative sizes of Earth (8000 miles in diameter), the October 11, 2006 "Saturnicane" (5000 miles in diameter), and Super Typhoon Tip of 1979 (1400 miles in diameter), the largest tropical cyclone ever observed on Earth.
What about other planets?
Mars also plays host to huge cyclones. These extratropical cyclones have clouds made of water ice, but do not resemble hurricanes. A Martian cyclone 1000 miles in diameter was observed in 1998 by the Hubble Space Telescope. The Great Red Spot on Jupiter is also a storm of huge dimensions with incredible wind speeds, but this storm is not hurricane-like--there is no "eyewall" surrounding a cloud-free "eye".
Figure 2. Martian cyclone 1000 miles in diameter spotted near Mars' north pole by the Hubble Space Telescope on April 27, 1999. Image credit: NASA and hubble.org.