| VOYAGER 1 BOW SHOCK (S) AND MAGNETOPAUSE (M) CROSSINGS | ||
|---|---|---|
| Boundary | Day | Distance (RJ) |
| Inbound | ||
| S | 2/28 | 86 |
| S | 2/28 | 82 |
| S | 3/01 | 72 |
| M | 3/01 | 67 |
| M | 3/02 | 59 |
| S | 3/02 | 58 |
| S | 3/02 | 56 |
| M | 3/03 | 47 |
| Outbound | ||
| M | 3/13 | 158 |
| M | 3/13 | 163 |
| M | 3/13 | 165 |
| S | 3/16 | 199 |
| S | 3/18 | 227 |
| S | 3/18 | 227 |
| S | 3/19 | 240 |
| S | 3/20 | 256 |
| S | 3/20 | 258 |
Accurate recording of the X-band data being sent from Voyager at 115 thousand bits per second required fairly clear weather at the tracking sites. The three Deep Space Network (DSN) stations in California, Spain, and Australia are located at normally dry sites. However, early in the morning, heavy rain at the Australian site interfered with reception of the Voyager signal for fourteen minutes. Fortunately, the loss occurred when the DSN tracking of the spacecraft was being switched from Goldstone, California, to the Australian station. Mission control was able to extend Goldstone coverage for several minutes so that only about three minutes’ worth of data was lost completely.
A more positive announcement was made at the press conference that morning by Donald Shemansky of the Ultraviolet Spectroscopy Team: the discovery of a high-energy torus of doubly ionized sulfur (S III) circling Jupiter in the region of Io’s orbit. “We were surprised out of our chairs to see a spectacularly bright emission in the 650-1100 angstrom region, immediately implying that we were looking at a plasma that had to be at a temperature of about 100 000 degrees.” The scientists estimated that the density of this torus must be at least 500 ions per cubic centimeter, and that the power needed to keep this plasma at such a high temperature must be in the neighborhood of 500 billion watts. As Al Hibbs mentioned on “Jupiter Watch” that night, 500 billion watts of power is the total amount of installed generating capacity of the United States.
Saturday, March 3.
(Range to Jupiter, 2.5 million kilometers). Early in the morning the final crossing of the magnetopause took place at 47 RJ, and Voyager finally joined the Jovian system. At the end of the day, the rapidly moving spacecraft crossed the orbit of Callisto, but that satellite itself was on the far side of the planet. Not until the outbound crossing of its orbit on March 6 would closeup views of Callisto be obtained.
During the preceding night, a severe summer thunderstorm in Australia again caused a loss of data. A line of storms over the tracking station blocked the high-rate, X-band science data for three hours and twenty minutes. Attempts were made to save a part of the data by commanding the spacecraft to slow its transmission rate, rather like speaking slowly to a partially deaf listener. But by the time the craft received the signal and responded, the storms had intensified, and no signal could get through. Closeups of the Great Red Spot and an extended series of observations of the glowing sodium cloud around Io were lost.
A black-and-white movie assembled from photos obtained in January and February was shown at the press conference. The movie was taken from observatory phase pictures photographed in blue light. From these pictures, the imaging team “put together this so-called ‘blue movie’,” said Brad Smith, introducing the film. The film showed changes taking place in Jupiter’s atmosphere over a period of about seventy Jovian days. Near the equator there were “bright plumes floating by—at high speed the plumes seem to wave around, something like a flag waving in the breeze.” Farther north, along the edge of the north temperate zone, one could see one of the dark ovals—“a rather fuzzy one would move up, catch up with the one just ahead of it, get stuck to the outside and roll around on it for a while, then get ejected a little later.” Dr. Smith also showed new closeup views of the region around the Red Spot, showing not only the anticyclonic features but filamentary “spaghettilike” material which was rotating in a cyclonic direction, indicating a low-pressure region. “The filamentary material still seems to be rather a mystery—very difficult to see the details of the motion.” But the photographs were already showing what seemed to be stream lines in the white ovals. “In appearance the white ovals seem to resemble the Red Spot. The stream lines are at least suggestive of divergent flow, that is, material in each of these spots which is upwelling in these areas and then moving out tends to go around in a counterclockwise anticyclonic motion but may, at the same time, be slowly diverging outward.”
At a resolution of about 100 kilometers a planetary surface just begins to reveal its personality. Io was photographed against the disk of Jupiter on February 26, from a distance of about 8 million kilometers. Such early pictures whetted the appetites of the Voyager scientists at JPL as they anxiously speculated about what they would find in closer views of the surface of this remarkable satellite. [P-21185 B/W]
The large white ovals are about forty years old. Dr. Smith explained how they formed: Between 1939 and 1940, “where those three white spots exist right now, was a rather bright band similar to the north temperate zone we see on Jupiter right now. In that time period of a year or so, three darkish spots formed. A dark cloud spread out at each one of those three locations and just kept spreading longitudinally until the white material condensed between them.” In the end, everything was dark except for the three ovals, which have persisted ever since.