A spacecraft hurtling toward a 2004 encounter with Saturn has given planetary scientists a foretaste of discoveries to come, after turning its instruments on Jupiter when the craft swung by the giant planet for a gravitational kick toward its destination.
Combined with data taken at the same time from the Galileo spacecraft, which has been orbiting Jupiter for the past five years, Cassini's data are helping researchers unravel mysteries about weather on Jupiter as well as in its interplanetary neighborhood.
One of the long-standing puzzles has been the weather's stability on Jupiter, notes Andrew Ingersoll, with the California Institute of Technology. Jupiter's great red spot, for example, is an enormous storm that has lasted for at least 300 years.
"There's a lot of energy in this atmosphere. Where is it coming from?" he asked during a briefing last weekend on initial Cassini - Galileo results. Some scientist, he continues, hold that the energy is in "the big guys" - the red spot and the wide bands of high-level, powerful winds that gird the planet. The smaller storms feed off these like parasites. Other researchers hold that the energy comes from deep within the atmosphere, forming small thunderstorms which then get gobbled up by larger weather systems.
Detailed movies pieced together from individual images from Cassini's cameras suggest that the second explanation may be the right one. As Cassini's close encounter with Jupiter continues, the imaging team will use different filters to peer deeper into the cloud-shrouded atmosphere and look for clearer answers to the energy question.
A unique imaging system on-board Cassini also has revealed that Jupiter is swathed in a nebula of material that stretches as far as 13 million miles from the planet. The nebula consists of material spewed from volcanoes on the Jovian moon Io, whose crust is constantly being torn as the moon moves through Jupiter's powerful gravitational field. Much of that material is captured in a doughnut-shaped "torus" around Jupiter, but some escapes to form the nebula.
Cassini also recorded the Jovian equivalent of whale songs - plaintive wailings from radio signals triggered by shock waves that are set up when the solar wind slams into Jupiter's magnetosphere.
These results represent data from the first 10 days of Cassini's 60-day encounter with Jupiter. The craft reached its closest approach - about 6 million miles away - on Dec. 30. Anticipating more Jovian-size surprises, Dr. Ingersoll says, "Stay tuned, folks. There's lots more to come."
(c) Copyright 2001. The Christian Science Publishing Society