March 31, 1999

Storms on Jupiter

Click on the image for a larger view.

1. Jupiter as viewed by NASA's Hubble Space Telescope (HST) in February 1995. The image shows the planet's characteristic bands of alternating bright and dark clouds, numerous bright and dark ovals, and many smaller eddies and vortices.

Image Credits: Reta Beebe and Amy Simon, New Mexico State University, and NASA (figures 1 and 2). Jet Propulsion Laboratory and Project Galileo (figure 3).

The dark and bright ovals seen in the above image represent gigantic and long-lasting storm systems in Jupiter's atmosphere. For instance, the prominent dark oval near the southeastern limb in the first image is Jupiter's largest storm, known as the Great Red Spot, which has been observed since the invention of the telescope more than 300 years ago. Its longitudinal dimension is nearly two times the size of the Earth.

The three white ovals west and slightly to the south of the Great Red Spot were first observed in 1938. Surprisingly, last February the two outer ovals merged into a single oval (see images 2 and 3 above).

Apparently, the storms represented by these two ovals had been kept apart by the slightly smaller oval between them, which rotates in a direction opposite to the two that merged. Scientists believe that this third storm had weakened. As it lost power, it lost its ability to act as a buffer between the other two, allowing them to merge.

The new, merged white oval is the strongest storm in the solar system after the Great Red Spot. In some ways such Jovian storms may be compared to hurricanes and typhoons on Earth, but there are differences.

Terrestrial hurricanes and typhoons are low-pressure systems above warm ocean surfaces. Air flows horizontally across the ocean surface toward the low of the storm's center, picks up moisture and heat, and rises in a large, tightening spiral (counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere). Such storms are called "cyclones." As the air rises, it cools and its moisture condenses into clouds and rain. In the upper levels of the storm, the clouds spread outward for many hundreds of miles, while dry, cloud-free air plunges downward into the narrow, low-pressure column at the center of the storm, called the "eye." It is the heat energy released during condensation that maintains the air circulation and high winds of the storm.

Storms on Jupiter, such as the Great Red Spot and the newly formed white oval, are "anticyclones" (at least in Jupiter's upper atmosphere observed by spacecraft). They are high-pressure systems in which warm gases from below are forced upward. At the tops of these storms, the atmospheric gases spread laterally outward and return to lower elevations in a ring around the perimeter of the ovals. There are no "eyes." Furthermore, the Jovian storms are probably not powered by condensation (though this is a controversial point among experts), but by shears between the high-speed jet streams of neighboring bands in Jupiter's upper atmosphere, which blow in opposite directions.

More Cool Stuff

For more information on the merging of the two white ovals, go to a press release of NASA's Jet Propulsion Laboratory (JPL) from October 14, 1998:

http://www.jpl.nasa.gov/galileo/news31.html

To access additional images from HST and the Galileo mission, go to Web sites at the Space Telescope Science Institute (STScI) and JPL:

http://oposite.stsci.edu/pubinfo/SolarSystemT.html

http://www.jpl.nasa.gov/galileo

As part of its Learning Technologies Project (LTP), NASA supports a number of educational Web sites that have excellent material on the space sciences:

http://observe.ivv.nasa.gov/nasa/education/edu/edudocs/topic_space.html