Think of it as a two-for-one sail of the century Think of it as a two-for-one sail of the century.
NASA's
Cassini and Galileo spacecraft are both eyeing giant Jupiter, carrying out the first joint, on-the-spot, reconnaissance of the gaseous world, its turbulent atmosphere and entourage of discrete moons.Scientists are delighted with early results gleaned by the spacecraft duo as they carry out double-teaming duties around our solar system's "king of planets."
This is the first time in the
history of deep-space exploration that spacecraft from two independent robotic missions are working in tandem, observing Jupiter at the same time from such close range. Initial findings from the ongoing dual surveillance of Jupiter were detailed at a press conference, held December 30 at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. JPL manages the Cassini and Galileo missions for NASA's Office of Space Science.
Side order of science
The Cassini spacecraft made its closest approach to
Jupiter on December 30 at 5:12 a.m. Eastern Standard Time (10:12 GMT), slipping by the planet at 6 million miles (10 million kilometers) distance. That's well outside the orbits of Jupiter's four large moons -- Io, Europa, Callisto and Ganymede -- but within the orbits of nine small ones. By zooming by massive Jupiter, Cassini adds another burst of speed for the final leg of its ultimate destination -- Saturn.
The scientific opportunity at Jupiter is considered a side benefit. But the Jovian flyby also sharpens the skills of Cassini ground controllers.
"For us, Jupiter is a dress rehearsal of the activities we'll be carrying out at Saturn," said Dennis Matson, Cassini project scientist at JPL. "It gives us an opportunity to practice the techniques and the sequences that we've developed. With this dress rehearsal behind us, when we get to Saturn we will be able to carry it off perfectly," he said.
Durable Galileo
While Cassini's look-see at Jupiter is fleeting, the long-duration and surprisingly durable Galileo spacecraft continues to pump out science data. Looping around Jupiter since December 1995, Galileo has operated over
twice as long -- and received three times the cumulative radiation exposure -- than originally called for by mission planners.On Thursday, December 28, Galileo passed through the highest radiation environment it will experience in its current orbit of Jupiter. The craft flew within some 310,000 miles (500,000 kilometers) of Jupiter's cloud tops.
Visualize the invisible
"This is a unique science opportunity," said Jay Bergstralh, acting director of solar system exploration at NASA Headquarters. Cassini observations of Jupiter will continue into March 2001, he said, with the spacecraft trekking onward for another three-and-a-half years to reach
Saturn.One early surprise from the Cassini flyby was detailed by Tom Krimigis, a scientist with Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, and principal investigator for Cassini's magnetospheric imaging instrument.
Krimigis said the device has been able to "visualize the invisible," observing that Jupiter's moon, Io,
ejects volcanic material out to great distances away from the planet."This represents a new dimension that we did not know heretofore. Namely, that there is a big nebula [cloud of particles] that is created by the volcanoes of Io that actually accompanies Jupiter as it moves in its trajectory around the Sun," Krimigis said.
"We're excited about having two spacecraft operational at Jupiter at the same time," said William Kurth, co-investigator for plasma-wave instruments on both Galileo and Cassini from the University of Iowa in Iowa City.
Kurth said Cassini acts as an upstream weather station. It monitors the solar wind as it rifles toward Jupiter and the Galileo craft that is flying closer to the planet.
"We're able to tie what's coming in from the solar wind to the response of the magnetosphere," Kurth said.
Good-bye movies
Carolyn Porco, camera team leader for Cassini at the University of Arizona in Tucson, said the spacecraft images of Jupiter are incredibly sharp and clear.
"The camera is performing beyond our wildest imaginingsand that's saying something because we've been imagining this for a decade now," Porco said.
Porco said that Galileo and Cassini are providing a very complementary set of observations. While Galileo snaps very high-resolution pictures of sites, Cassini can stand back and watch for changes in targeted areas over time, she said.
Cassini observations, several in concert with Galileo, include taking photos of the planet's thin rings, looking for lightning storms on the planet and taking a succession of images to create
time-lapse movies of Jupiter's wild atmosphere."We should have a nice photo 'good-bye Jupiter' movie too," as Cassini departs the scene, Porco told SPACE.com.
Long-lived weather
"There's a lot of energy in Jupiter's atmosphere," said Andrew Ingersoll, camera team member for both Cassini and Galileo at the California Institute of Technology in Pasadena. "The question is where is it coming from," he said.
Jupiter is marked by a 300-year-old storm, better known as the
Great Red Spot, as well as super high-speed winds, Ingersoll said. Thanks to Cassini and Galileo data, as well as earlier data from Voyager spacecraft, scientists are beginning to unravel why Jupiter's weather is so long-lived. Spacecraft imagery clearly shows the energetic mixing, destruction and creation of varying sized features within Jupiter's complex and turbulent atmosphere.
"So stay tuned folks. There's lots more to come," Ingersoll said.
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