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Cassini Captures Jupiter As Earth Team Tracks Storm Progression
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Cassini Photo Release: This true color image of Jupiter is composed of three images taken in the blue, green and red regions of the spectrum. All images were taken from a distance of 77.6 million km on October 8, 2000, around 16:57 UTC/SCET (spacecraft event time). The resolution is 466 km. Different chemical compositions of the cloud particles lead to different colors; the cloud patterns reflect different physical conditions -- updrafts and downdrafts -- in which the clouds form. The bluish areas are believed to be regions devoid of clouds and covered by high haze. The Great Red Spot (below and to the right of center) is a giant atmospheric storm about 2 Earths across and over 300 years old, with peripheral winds of 300 miles per hour. This image shows that it is trailed to the west by a turbulent region, caused by an atmospheric flow around the northern perimeter of the Spot. The small very white features in this region are lightning storms, which were seen by the Galileo spacecraft when it photographed the night side of Jupiter. Cassini will track these lightning storms and measure their lifetimes and motions when it passes Jupiter in late December and looks back at the dark side of the planet.

Credit: NASA/JPL/UoA
Image Preparation: Dyer Lytle
Image Design: Carolyn Porco
Cassini Imaging Diary: Jupiter
Cassini Jupiter Flyby Port

Pasadena - Oct. 24, 2000
For the first time, scientists have been able to watch the process of two of Jupiter's giant "white oval" storms, each about half the size of Earth, colliding and merging to form an even bigger storm.

"Usually when we've seen two of them approaching each other, they bounce back away from each other," said Dr. Glenn Orton, senior research scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and member of a team of Spanish, French and American astronomers that used NASA's Hubble Space Telescope and ground-based telescopes to study the ovals this year.

Dr. Agustin Sanchez-Lavega, an astronomer at Universidad del Pais Vasco, Bilbao, Spain, reported the team's observations today at the meeting of the American Astronomical Society's Division of Planetary Sciences in Pasadena.

The researchers speculate that a similar merger took place centuries ago and may have built Jupiter's famous Great Red Spot, a storm that is twice as wide as the Earth and has persisted in Jupiter's southern hemisphere for more than 300 years.

Seeing the collision of two storms will help scientists understand more about the dynamics of Jupiter's atmosphere, Sanchez-Lavega said. One question has been how deeply the roots of a storm at Jupiter's cloud tops extend into lower layers. In this year's merger, the upper layer seemed to move differently than underlying clouds.

These four images of clouds in a portion of Jupiter's southern hemisphere show steps in the consolidation of three "white oval" storms into one over a three-year span of time. They were obtained on four dates, from Sept. 18, 1997, to Sept. 2, 2000, by NASA's Hubble Space Telescope.

Three white oval storms, in a band of Jupiter's atmosphere farther south than the Great Red Spot, became active about 60 years ago. In the following decades until 1998, they sometimes approached each other but never collided.

In early 1998, two of the ovals were approaching each other as Jupiter went out of sight from Earth, behind the Sun. When the planet came back into view, the two had become one.

"We weren't able to see how they came together that time," Orton said.

Last year, the oval resulting from the 1998 combination approached the remaining one of the original three ovals. Each was a swirling high-pressure vortex, upwelling at the center and spinning winds counterclockwise to about 470 kilometers per hour (290 miles per hour). One was about 9,000 kilometers (about 5,600 miles) across, the other slightly smaller.

A third, darker oval, swirling clockwise instead of counterclockwise, formed temporarily between the two white ovals. That type of interceding system may be what usually keeps white ovals from colliding, the team proposed. But in this case, the middle storm appears to have been pushed even farther south and torn apart as all three passed near the Great Red Spot last December.

The disappearance of the opposite-swirling storm from between them cleared the way for the two white ovals to meet.

Their collision dance began in March and lasted about three weeks. At the cloud tops, the storms circled around each other counterclockwise, then consolidated into a single oval about one- third wider than either of the ovals had been beforehand.

In deeper clouds, the interaction did not include the storms circling each other, but it did produce complex cloud structures from stretching and contracting of the ovals and went through an intermediate phase as a single oval with a double nucleus.

The ovals' approach and merger was viewed in various wavelengths, showing events at different depths, with a planetary telescope at Pic-du-Midi in France, NASA's Infrared Telescope Facility in Hawaii, and the orbiting Hubble Space Telescope, a facility of NASA and the European Space Agency.

Related Links
Galileo Jupiter Portal
Views of Jupiter
Cassini Imaging Diary: Jupiter
Cassini Jupiter Flyby Port
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Astronomer Detects A Cloudy Titan
Flagstaff - Oct. 18, 2000
A Northern Arizona University (NAU) astronomer, and her colleagues, recently discovered daily clouds in the atmosphere of Saturn's largest moon, Titan. This discovery adds to the growing body of evidence that Titan uniquely resembles Earth with clouds, rain and seas.

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