Both plumes have been active throughout the Galileo tour of the Jovian system which began in 1996. Zamama, however, is considerably larger and brighter in these images from the spacecraft's eleventh orbit of Jupiter than when imaged previously. Prometheus was also active during 1979 flybys of NASA's Voyager spacecraft. There are two other much fainter plumes that can be detected on the bright limb of the third and fourth images. See if you can find them by changing the brightness levels of the images to enhance the dark regions.
North is to the top of the picture.
To make the plumes easier to see, the colors have been enhanced by increasing the brightness at the blue end of the spectrum. The ASU Planetary Geology Group is under the direction of Dr. Ronald Greeley.