Far Encounter Phase
By early February Jupiter loomed too large in the narrow-angle camera to be photographed in one piece; 2 × 2 three-color (violet, orange, green) sets of pictures were taken for the next two weeks; by February 21, Jupiter had grown too large even for that, and 3 × 3 sets were scheduled to begin. When these sets of pictures are pasted together to form a single picture, the result is called a mosaic.
By February 1, 1979, Voyager 1 was only 30 million kilometers from Jupiter, and the resolution of the imaging system corresponded to about 600 kilometers at the cloud tops of the giant planet. At this time, a great deal of unexpected complexity became apparent around the Red Spot, and movie sequences clearly showed the cloud motions, including the apparent six-day rotation of the Red Spot. [P-20993C]
One of the most spectacular planetary photographs ever taken was obtained on February 13 as Voyager 1 continued its approach to Jupiter. By this time, at a range of 20 million kilometers, Jupiter loomed too large to fit within a single narrow-angle imaging frame. Passing in front of the planet are the inner two Galilean satellites. Io, on the left, already shows brightly colored patterns on its surface, while Europa, on the right, is a bland ice-covered world. The scale of all of these objects is huge by terrestrial standards; Io and Europa are each the size of our Moon, and the Red Spot is larger than the Earth. [P-21082C]
While the imaging experiments were in the limelight, the other scientific instruments had also begun to concentrate on the Jovian system. The ultraviolet spectrometer had been scanning the region eight times a day; the infrared spectrometer (IRIS) spent 1½ hours a day analyzing infrared emissions from various longitudes in Jupiter’s atmosphere; the planetary radio astronomy and plasma wave instruments looked for radio bursts from Jupiter and for plasma disturbances in the region; the photopolarimeter had begun searching for the edge of Io’s sodium torus; and a watch was begun for the bow shock—the outer boundary of the Jovian magnetosphere.
On February 10, Voyager 1 crossed the orbit of Sinope, Jupiter’s outermost satellite. Yet the spacecraft even then had a long way to go—still 23 million kilometers from Jupiter, but closing in on the planet at nearly a million kilometers a day. A week later, targeted photographs of Callisto began to provide coverage of the satellite all around its orbit; similar photos of Ganymede began on February 25.
Meanwhile excitement was building. As early as February 8 and 9, delight with the mission and anticipation of the results of the encounter in March were already evident. Garry E. Hunt, from the Laboratory for Planetary Atmospheres, University College, London, a member of the Imaging Team, discussing the appearance of Jupiter’s atmosphere as seen by Voyager during the previous month, said “It seems to be far more photogenic now than it did during the Pioneer encounters; I’m more than delighted by it—it’s an incredible state of affairs. There are infinitely more details than ever imagined.”
The Voyager Project was operated from the Jet Propulsion Laboratory managed for NASA by the California Institute of Technology. Located in the hills above Pasadena, California, JPL is the main center for U.S. exploration of the solar system. [JB17249BC]
The Voyager TV cameras do not take color pictures directly as do commercial cameras. Instead, a color image is reconstructed on the ground from three separate monochromatic images, obtained through color filters and transmitted separately to Earth. There are a number of possible filter combinations, but the most nearly “true” color is obtained with originals photographed in blue (480 nanometers), green (565 nanometers), and orange (590 nanometers) light. Before these can be combined, the individual frames must be registered, correcting for any change in spacecraft position or pointing between exposures. Often, only part of a scene is contained in all three original pictures. Shown here is a reconstruction of a plume on Jupiter, photographed on March 1, 1979. The colors used to print the three separate frames can be seen clearly in the nonoverlapping areas. For other pictures in this book, the nonoverlapping partial frames are omitted. [P-21192]
The pictures from Voyager are “clearly spectacular,” said Lonne Lane, Assistant Project Scientist for Jupiter. “We’re getting even better results than we had anticipated. We have seen new phenomena in both optical and radio emissions. We have definitely seen things that are different—in at least in one case, unanticipated—and are begging for answers we haven’t got.” There was already, still almost a month from encounter, a strong feeling of accomplishment among the scientists and engineers; they had done a difficult task and it has been successful.
By the last week of February 1979, the attention of thousands of individuals was focused on the activities at JPL. Scientists had arrived from universities and laboratories around the country and from abroad, many bringing graduate students or faculty colleagues to assist them. Engineers and technicians from JPL contractors joined NASA officials as the Pasadena motels filled up. Special badges were issued and reserved parking areas set aside for the Voyager influx. Twenty-four hours a day, lights burned in the flight control rooms, the science offices, the computer areas, and the photo processing labs. In order to protect those with critical tasks to perform from the friendly distraction of the new arrivals, special computer-controlled locks were placed on doors, and security officers began to patrol the halls. By the end of the month the press had begun to arrive. Amid accelerating excitement, the Voyager 1 encounter was about to begin.
The smaller-scale clouds on Jupiter tend to be more irregular than the large ovals and plumes. At the lower right, one of the three large white ovals clearly shows internal structure, with the swirling cloud pattern indicating counterclockwise, or anticyclonic, flow. A smaller anticyclonic white feature near the center is surrounded by a dark, cloud-free band where one can see to greater depths in the atmosphere. This photo was taken March 1 from a distance of 4 million kilometers. [P-21183C]