SP-349/396 PIONEER ODYSSEY
 

9

The Giant Revisited.

 

[161] Pioneer 11, the second spacecraft to fly by Jupiter, returned approximately 460 images of Jupiter and its Galilean satellites during the period 18 November to 9 December 1974. As explained in earlier chapters the trajectory of Pioneer 11 past Jupiter was quite different from that of Pioneer 10. Not only did Pioneer 11 approach much closer to Jupiter's surface - to 0.60 Jovian radii compared with 1.82 Jovian radii for Pioneer 10, but also the spacecraft approached from south of the equator and left from above (to the north). This approach allowed the spacecraft to obtain many unprecedented images of the high latitude, near polar regions. And because the outgoing leg was highly inclined to the equator of Jupiter, several good images were obtained of the planet's north pole.

 


Figure 9-1. View of Jupiter from the spacecraft for the incoming (a) and outgoing (b) path.

Figure 9-1. View of Jupiter from the spacecraft for the incoming (a) and outgoing (b) path.

 


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Figure 9-2. The path of Pioneer 11 past Jupiter shown (a) from above the north pole of the planet, and (b) as seen from the equatorial plane.

Figure 9-2. The path of Pioneer 11 past Jupiter shown (a) from above the north pole of the planet, and (b) as seen from the equatorial plane.

 

To distinguish these Pioneer 11 images from those of Pioneer 10, a "C" and "D" notation is used with the image numbers being sequential in time starting at periapsis. "C" images were obtained before periapsis, "D" images after. Full details of these images are given in Appendix 2.

On the facing page the two images taken about a day before and after encounter show the attitude of Jupiter during approach and departure. Unlike Pioneer 10, no rapidly changing terminator position is seen. In all "C" images the terminator is in a position similar to that seen in C22 and all "D" images have the terminator in a position similar to that seen in D17.

The closeness of the approach, and the high relative velocity of the spacecraft over the surface meant that very close-in images could not be obtained; the data would have been gathered too sparsely for later reconstructing into an image. Four pictures on each side of closest approach (C4 through D4) were taken in the step inhibit mode of operation, in which the spacecraft motion alone provided the sweep to build up the picture. Four of this series are shown later in Figs. 9-11 through 9-14. At this close range only partial views of the planet could be obtained.

At about one day before periapsis, a malfunction affected the stepping function of the telescope and a few images were partially lost before a work-around could be effected. Images C16-C10 were affected in this manner. Following this radiation damage the University of Arizona observing team worked for many days and nights to make the necessary corrections to the command sequences to ensure that no more images would be lost.

 


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Figures 9-3 and 9-4. Typical views of Jupiter as Pioneer 11 approached (left) and departed from (right) the planet. Figure 9-3 (Image C22) was taken 33 hours before periapsis at a distance of 2,142,000 km (1,331,000 mi.). Figure 9-4 (Image D17) was taken 32 hours after periapsis at a distance of 2,085,000 km (1,296,000 mi.).

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Figures 9-3 and 9-4. Typical views of Jupiter as Pioneer 11 approached (left) and departed from (right) the planet. Figure 9-3 (Image C22) was taken 33 hours before periapsis at a distance of 2,142,000 km (1,331,000 mi.). Figure 9-4 (Image D17) was taken 32 hours after periapsis at a distance of 2,085,000 km (1,296,000 mi.).

Figures 9-3 and 9-4. Typical views of Jupiter as Pioneer 11 approached (left) and departed from (right) the planet. Figure 9-3 (Image C22) was taken 33 hours before periapsis at a distance of 2,142,000 km (1,331,000 mi.). Figure 9-4 (Image D17) was taken 32 hours after periapsis at a distance of 2,085,000 km (1,296,000 mi.).

 


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Figure 9-5. Image C9. Range 1,235,000 km (767,000 mi.), at 16 hours before periapsis.

Figure 9-5. Image C9. Range 1,235,000 km (767,000 mi.), at 16 hours before periapsis.


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Figure 9-6. Image C8. Range 1,144,000 km (711,000 mi.), about 14 hours before periapsis. This is one of the better pictures of the Great Red Spot. See also Figure 9-11 for a closer view.

Figure 9-6. Image C8. Range 1,144,000 km (711,000 mi.), about 14 hours before periapsis. This is one of the better pictures of the Great Red Spot. See also Figure 9-11 for a closer view.


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Figure 9-7. Image C7. Range 1,038,000 km (645,000 mi.), about 13 hours before encounter.

Figure 9-7. Image C7. Range 1,038,000 km (645,000 mi.), about 13 hours before encounter.


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Figure 9-8. Image C6. Almost two hours after Figure 9-7, this image was taken at 936,000 km (528,000 mi.).

Figure 9-8. Image C6. Almost two hours after Figure 9-7, this image was taken at 936,000 km (528,000 mi.). Great detail is now apparent in the belts and zones including many light and dark cells indicating convective activity in the south temperate zones. Also a small red spot is revealed in the northern hemisphere.


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Figure 9-9. Image C5. Range 765,000 km (475,000 mi.) at 8 hours before periapsis.

Figure 9-9. Image C5. Range 765,000 km (475,000 mi.) at 8 hours before periapsis.


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Figure 9-10. The picture is shown here exactly as it was received at the Ames Research Center.

Figure 9-10. The picture is shown here exactly as it was received at the Ames Research Center. No computer processing of any kind has yet been performed. This figure should be compared with Figure 9-9 (opposite) of which it is the blue channel data. The red channel problems were essentially identical. In producing Figure 9-9 four computer corrections were applied. First, the shape of the planet, distorted by the spacecraft's motion and viewing geometry was corrected. Second, the three bands of varying image intensity, a consequence of maximizing the scientific value of the data for photometric analysis of the clouds, were eliminated. Third, the black areas of missing data caused by problems at the receiving station, were filled in by interpolation between neighboring values (see Chapter 7). Fourth, two rolls of unsynchronized spacecraft data, showing as diagonal streaks, were correctly repositioned.


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Figure 9-11. Close up of Jupiter's Great Red Spot (Image C3). Obtaining this image of the Great Red Spot of Jupiter was one of Pioneer 11's most exciting prospects for planetary astronomers. The highest resolution image of the spot obtained by Pioneer 10 had been spoiled by radiation problems, but Pioneer 11 was successful in obtaining the unique image on the facing page (Figure 9-11a).

(a)

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Figure 9-11. Close up of Jupiter's Great Red Spot (Image C3). 
                                                      There is very little internal detail in the blue image (Figure 9-11b), the main feature being the dark border encircling the periphery. A break in this border seems to exist in the northeast part of the spot, where some intermixing of the red material into the South Tropical Zone appears to be taking place.
                                                      Much internal detail is revealed in the red image (Figure 9-11c), but perhaps most significant are two circular outlines which cross over near the center of the spot. This same feature was also seen in Pioneer 10 images. No clear suggestion of motions within the spot is evident from this image. The image does not show direct evidence of flow lines from any single region inside the spot which might be interpreted as a source or a sink of the red material.

(b) (c)

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Figure 9-11. Close up of Jupiter's Great Red Spot (Image C3). (Grid map)

 

Figure 9-11. Close up of Jupiter's Great Red Spot (Image C3). Obtaining this image of the Great Red Spot of Jupiter was one of Pioneer 11's most exciting prospects for planetary astronomers. The highest resolution image of the spot obtained by Pioneer 10 had been spoiled by radiation problems, but Pioneer 11 was successful in obtaining the unique image on the facing page (Figure 9-11a). The area covered on the planet is shown as the inset below the photograph.

This is the best view so far of the Great Red Spot of Jupiter. It was obtained at a range of 545,000 km (320,000 mi.) above the cloud tops.

The image contains more than 4000 individual pixels (see Chapter 7) of measurable data in the red area of the spot thereby providing a wealth of detail of the markings since each pixel represents an area of approximately 237 km (147 mi.) square.

Planetary scientists are deriving new interpretations of the Red Spot from this unique image. Despite the relatively high resolution obtained there is much less fine structure visible in the spot than in comparable images at other latitudes, for example, in Figures 9-12 and 9-14. The Red Spot appears to lie in the most quiescent zone of the planet, which may contribute to its stability.

There is very little internal detail in the blue image (Figure 9-11b), the main feature being the dark border encircling the periphery. A break in this border seems to exist in the northeast part of the spot, where some intermixing of the red material into the South Tropical Zone appears to be taking place.

Much internal detail is revealed in the red image (Figure 9-11c), but perhaps most significant are two circular outlines which cross over near the center of the spot. This same feature was also seen in Pioneer 10 images. No clear suggestion of motions within the spot is evident from this image. The image does not show direct evidence of flow lines from any single region inside the spot which might be interpreted as a source or a sink of the red material.

 


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Figure 9-12. The first image (D1) taken 3 1/2 hours after periapsis at a range of 375,000 km (233,000 mi.) shows the first view of the north pole of Jupiter.

Figure 9-12. The first image (D1) taken 3 1/2 hours after periapsis at a range of 375,000 km (233,000 mi.) shows the first view of the north pole of Jupiter. There is still great activity in the cloud forms at high altitudes, but the banded structure of the tropics changes to a random pattern of cells and turbulence down to the limits of resolution.

 


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Figure 9-13. This image (D2) would have been contiguous with Figure 9-12 but for a reconfiguration of the instrument to guard against radiation problems.

Figure 9-13. This image (D2) would have been contiguous with Figure 9-12 but for a reconfiguration of the instrument to guard against radiation problems. This image is further from the pole as shown in the inset. The time was 4 hours after periapsis, and the distance 435,000 km (270,000 mi.).


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Figure 9-14. This image (D4) is perhaps the most scientifically important image of Jupiter obtained by Pioneer 11. Figure 9-14a (opposite) is the computer processed image.

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Figure 9-14. This image (D4) is perhaps the most scientifically important image of Jupiter obtained by Pioneer 11.  Figure 9-14(b) and (c) above show smaller versions of the blue and red channel images, respectively.

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Figure 9-14. Grid map

Figure 9-14. This image (D4) is perhaps the most scientifically important image of Jupiter obtained by Pioneer 11. It covers an area of the planet from the equator to the north polar regions and provides details of the range of cloud features from bands to polar cells. Figure 9-14a (opposite) is the computer processed image. The colors are, however, probably less authentic than those of the images before periapsis because of an apparent change in the behavior of the instrument after passage through the intense radiation belts. Figure 9-14(b) and (c) above show smaller versions of the blue and red channel images, respectively. The comparatively large uniform area on the red-channel image is caused by detector saturation which resulted in loss of information. This was a result of having deliberately set the gain at a high level so that the darker regions near the north pole would be well imaged. The corresponding area in the colored image also lacks this information, which further affects the color balance. The range for this image was 610,000 km (379,000 mi.).


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Figure 9-15. Image D8. Range 1,079,000 km (671,000 mi.), 13 1/2 hours after periapsis.

Figure 9-15. Image D8. Range 1,079,000 km (671,000 mi.), 13 1/2 hours after periapsis.

 

The series of images Figures 9-15 through 9-20 shows Jupiter receding as Pioneer 11 leaves the giant planet and rises high above the ecliptic plane on its way to Saturn. Due to an anomaly which affected the rate at which the telescope swept across the planet the command sequence to obtain these pictures had to be changed day by day. Nevertheless all were obtained without any being lost, despite the fact that there was no time to verify the command sequence by computer simulations in advance.

 


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Figure 9-16. Image D10. Range 1,310,000 km (814,000 mi.). 17 1/2 hours after periapsis.

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Figure 9-16. Image D10. Range 1,310,000 km (814,000 mi.). 17 1/2 hours after periapsis.

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Figure 9-17. Image D11. Range 1,539,000 km (956,000 mi.), 21 1/2 hours after periapsis.

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Figure 9-17. Image D11. Range 1,539,000 km (956,000 mi.), 21 1/2 hours after periapsis.


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Figure 9-18. Image D12. Range 1,586,000 km (985,000 mi.), at 22 hours after periapsis.

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Figure 9-18. Image D12. Range 1,586,000 km (985,000 mi.), at 22 hours after periapsis.

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Figure 9-19. Image D14. Range 1,777,000 km (1,104,000 mi.), at 26 hours after periapsis.

 

 

 

 

 

Figure 9-20. Image D15. Range 1,847,000 km (1,148,000 mi.), at 27 hours after periapsis.

Figure 9-19. Image D14. Range 1,777,000 km (1,104,000 mi.), at 26 hours after periapsis. Figure 9-20. Image D15. Range 1,847,000 km (1,148,000 mi.), at 27 hours after periapsis.


 


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Figure 9-21. The best images of the four Galilean satellites obtained by the two Pioneer spacecraft are shown here.

Figure 9-21. The best images of the four Galilean satellites obtained by the two Pioneer spacecraft are shown here. Each column is for an individual satellite. The top image is the color composite, the next image shows this same color image as enhanced further by computer processing. Below this are shown the blue channel image followed by the red channel image. Finally, at the bottom of each column is a line drawing to identify the viewing aspect.

 

[181] With telescopes on the Earth, astronomers are afforded only the barest hints of what kind of markings appear on the Galilean satellites. Pioneers 10 and 11 recorded images of all four of these satellites which provide a much better idea of the albedo and color variations across the discs. Although all colors may not be represented properly since only red and blue data were recorded, it is certain that the yellow-orange regions are redder than white regions.

Only one good image of lo has been obtained. This is from Pioneer 11. The Pioneer 10 image of Io was missed completely due to the radiation environment of Jupiter. The Pioneer 11 image is a view from over the north pole of Io. From the Earth there have been observations suggesting that the polar regions of lo are reddish colored. On this Pioneer image there is orange coloration at the polar region, as contrasted with the whitish equatorial part of the satellite. lo is strongly affected by the radiation environment of Jupiter since its orbit is well within the radiation belts and the satellite sweeps up energetic particles from these belts. Also, its orbital motion affects the decametric radio emission of Jupiter. Although there is no indication of it in this picture, lo is the only Galilean satellite which is known to have an atmosphere although it is much less dense than that of the Earth or even that of Mars.

The single image of Europa recorded by Pioneer 10 has little color variation, but there is a broad dark region with some gross detail. Europa is among the brightest of satellites and is thought to have a crust of mainly water ice.

Two excellent images of Ganymede were recorded by the Pioneer spacecraft. These images show little color variation, but substantial albedo differences over the disc of this largest of the satellites. Ganymede's low density may be due to the presence of a high percentage of ices with some silicates from primordial material and from impacting material from space.

Several good images of Callisto show only small color differences and small albedo variations. The darkest of the Galilean satellites, Callisto has a low density which requires a high percentage of ices in its bulk structure. Two different views one a half-moon shape (reproduced here) and the other a gibbous shape-show the same prominent light region close to the terminator.

 

Satellite No.

Name

Image number

Midtime Year

DOY hr min

Range km

Pixel size km

Phase angle deg

Sub S/C,deg Lat

LCM

.

Jl

Io

D7

(1974) 337:17:33

756,000

376

67

+60

184

JII

Europa

A4

(1973)337:19:24

324,000

161

87

-24

290

Jlll

Ganymede

C51/2

(1974) 336:19:38

739,000

367

44

-29

46

JIV

Callisto

C12

(1974) 336:09:37

787,000

391

82

-34

33

Note: DOY: day of year

LCM: longitude of central meridian


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