After a looping journey through the inner solar system to gather speed, and a 4.5 month passage through the asteroid belt, Cassini finally arrived at Jupiter and began its encounter with the giant planet on October 1. The first images were magnificent, indicating a beautifully functioning spacecraft: the pointing is remarkably accurate and steady, Jupiter is richly detailed as it should be, and we have acquired startlingly sharp images of the planet in a variety of filters, from the ultraviolet into the near infrared.
The first color image from Cassini is being released today and can be found in the CICLOPS Imaging Diary.
The sequences that the Imaging Science team has planned for Cassini's distant Jupiter flyby include repeated imaging of the planet throughout the 5-month long encounter to study the time-variability and light-scattering characteristics of its atmosphere; a close approach of 4.4 million km to the small outer Jovian satellite Himalia (believed to be a captured asteroid) to determine its size and composition; imaging of the rings to determine their extent, structure, time-variability, and the size of their constituent particles; monitoring of the Galilean satellites (and some as they become eclipsed by Jupiter) to understand the nature of their surfaces and their interactions with the Jovian magnetic field; and searching for new, previously undetected satellites in the Jovian inner satellite region.
Other Cassini scientific instruments, able to see in regions of the electromagnetic spectrum not accessible to the cameras, have equally impressive plans. And the Cassini spacecraft, with its monolithic high gain antenna, is capable of returning much more information on the Jupiter system than was the Galileo spacecraft. Finally, Cassini will swing through the Jupiter system while Galileo is still operational, making for a truly historic event in which both spacecraft will make simultaneous observations of the Jovian magnetosphere, atmosphere, rings and satellites.
By the time Cassini's encounter with Jupiter and its rendezvous with Galileo are over in the spring of 2001, we will have amassed the most comprehensive data set on the Jupiter system ever collected. This is one event you won't want to miss.
And you won't have to. Over the course of the next five months, the Imaging Team will be periodically posting select images and short movie sequences of the planet, its rings, and satellites to this website, accompanied by our initial scientific interpretations and commentary. Please feel free to visit, and ride along with us, as we enter the Jupiter system, make our closest approach on December 30, bid Galileo hello and goodbye, and then swiftly depart for the final journey to Saturn.
Carolyn Porco Cassini Imaging Team Leader University of Arizona Tucson, AZ