On Apr. 29, 2013, NASA announced that its Cassini probe had discovered an enormous hurricane in the atmosphere of Saturn. The hurricane is located at the north pole of Saturn, and has wind speeds of 530 kilometers per hour. Its eye wall is about 2,000 kilometers wide, nearly ten times larger than the eye walls of hurricanes on Earth. The large size of the hurricane is made possible in part by the fact that Saturn is just over nine times larger than Earth in diameter. A similar polar hurricane on Saturn’s south pole was spotted by Cassini in 2006.
“We did a double take when we saw this vortex because it looks so much like a hurricane on Earth,” said Andrew Ingersoll, a Cassini imaging team member at the California Institute of Technology in Pasadena. “But there it is at Saturn, on a much larger scale, and it is somehow getting by on the small amounts of water vapor in Saturn’s hydrogen atmosphere.”
Scientists hope that studying the hurricane will give insight into hurricanes on Earth. There are important differences between storms on Earth and storms on Saturn; for example, the Saturnian hurricane is locked into position over the planet’s north pole, while hurricanes on Earth tend to drift toward the poles, but never manage to get there. “The polar hurricane has nowhere else to go, and that’s likely why it’s stuck at the pole,” said Kunio Sayanagi, a Cassini imaging team associate at Hampton University in Hampton, Va. This suggests the possibility that at times in Earth’s past when the climate was warmer and more capable of producing strong hurricanes that long-lived polar storms could have developed on Earth.
But the similarities outweigh the differences. Both the Saturnian hurricane and hurricanes on Earth have a central eye with either no cloud cover or very low clouds. Both also have high clouds that form an eye wall, along with other high clouds that spiral around the eye. Hurricanes on both planets spin counter-clockwise in the northern hemisphere, which occurs because both planets rotate toward the east. (A planet with retrograde rotation would have hurricanes that spin in the opposite direction because the Coriolis effect would be reversed.)
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology, Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate in Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team consists of scientists from the United States, the United Kingdom, France and Germany. The imaging operations center is based at the Space Science Institute in Boulder, Colo.
Saturn and its rings completely fill the field of view of Cassini’s narrow-angle camera in this natural-color image taken on March 27, 2004. This was the last full picture of Saturn and its rings with the narrow-angle camera taken by the Cassini spacecraft on its approach to the planet.
This is a false-color image of Saturn’s north polar storm taken by NASA’s Cassini spacecraft on Nov. 27, 2012 using a combination of spectral filters sensitive to wavelengths of near-infrared light. The images filtered at 890 nanometers are projected as blue. The images filtered at 728 nanometers are projected as green, and images filtered at 752 nanometers are projected as red. (Visible light has wavelengths between 400 and 700 nanometers, while near-infrared light has wavelengths between 700 nanometers and 1400 nanometers.) In this scheme, red indicates low clouds and green indicates high clouds.
This is a true-color image of Saturn’s north polar storm taken by NASA’s Cassini spacecraft just after the spring equinox on Saturn. The north pole was previously hidden from the gaze of Cassini’s imaging cameras because it was winter in the northern hemisphere when the spacecraft arrived at the Saturn system in 2004.
Enter the Vortex
This is a false-color image of Saturn’s north polar storm taken by NASA’s Cassini spacecraft using a combination of spectral filters sensitive to wavelengths of near-infrared light. The images filtered at 890 nanometers are projected as blue. The images filtered at 728 nanometers are projected as green, and images filtered at 752 nanometers are projected as red. (Visible light has wavelengths between 400 and 700 nanometers, while near-infrared light has wavelengths between 700 nanometers and 1400 nanometers.)
The eye of the polar hurricane appears dark red while the fast-moving hexagonal jet stream framing it is a yellowish green. Low-lying clouds circling inside the hexagonal feature appear as muted orange color. A second, smaller vortex pops out in teal at the lower right of the image. The rings of Saturn appear in vivid blue at the top right.
At Saturn, this scheme means colors correlate to different altitudes in the planet’s polar atmosphere: red indicates deep, while green shows clouds that are higher in altitude. High clouds are typically associated with locations of intense upwelling in a storm. These images help scientists learn the distribution and frequencies of such storms. The rings are bright blue in this color scheme because there is no methane gas between the ring particles and the camera.
This is an artist’s concept of the Cassini spacecraft during the Saturn Orbit Insertion maneuver, just after the main engine has begun firing.