Two NASA spacecraft jointly observing Jupiter's moon Io this winter captured images of a towering volcanic plume never seen before and a bright red ring of fresh surface deposits surrounding its source.
Combined information from images taken by the Cassini and Galileo spacecraft indicates the new plume is about the same size -- nearly 400 kilometers or 250 miles high -- as a long-lived plume from Io's Pele volcano. Pele's plume and ring are also seen in the new images.
The images and further information about them are available online from the websites of the Cassini Imaging Science team at the University of Arizona, Tucson, at this URL from the University of Arizona's Planetary Image Research Laboratory at this URL and from NASA's Jet Propulsion Laboratory, Pasadena, Calif., at this URL.
The new plume originates from a volcanic feature named Tvashtar Catena near Io's north pole. Scientists were astounded to discover so large a plume so near the pole, because all active plumes previously detected on Io have been over equatorial regions and no others have approached Pele's in size, said University of Arizona planetary scientist Dr. Alfred McEwen.
Galileo might pass right through the Tvashtar plume in August, if the plume persists until then. The spacecraft will be flying over that part of Io at an altitude of 360 kilometers (224 miles). Material in the plume is tenuous enough to present little risk to the spacecraft, and passing through it could give an opportunity to analyze the makeup of the plume, said Dr. Torrence Johnson, Galileo project scientist at the Jet Propulsion Laboratory in Pasadena, Calif.
It has been said that Io is the heartbeat of the jovian magnetosphere. The two giant plumes evidenced in these images may have had significant effects on the types, density and distribution of neutral and charged particles in the Jupiter system during the joint observations of the system by Galileo and Cassini from November 2000 to March 2001.
These Cassini images were acquired on Jan. 1 and Jan. 2, 2001. The Galileo images were acquired on Dec. 30 and 31, 2000. Cassini was about 10 million kilometers (6 million miles) from Io, ten times farther than Galileo.
Cassini is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages Cassini and Galileo for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena.
(Editor's Note: More information about the Cassini and Galileo joint observations of the Jupiter system is available online at this URL.)
[Contact: Alfred S. McEwen, Carolyn Porco, Laszlo Keszthelyi ]