SP-349/396 PIONEER ODYSSEY
 

8

Encounter with the Giant.

 

[138]

Artist view of Pioneer approaching Jupiter

 

[139] DURING THE MONTHS of November and December of 1973, Pioneer 10 sent back over 500 images of Jupiter. Most of these were taken from a comparatively large distance from the planet and show very little detail compared to pictures that have already been taken with telescopes based on Earth. However, those pictures that were obtained within 48 hours of the closest approach of the spacecraft to Jupiter are considerably better than any seen previously. Not only is the resolution greater, thereby revealing hitherto unseen details on the planet, but Jupiter has now been seen from viewpoints not available to observers based on Earth.

Because Jupiter is many times further from the Sun than the Earth, the angle subtended by the Earth and the Sun at Jupiter, i.e., the phase angle, never exceeds 11.5 degrees. Astronomers can see the planet only as a fully illuminated disc. From Earth, it is not possible to see Jupiter illuminated from the side or from behind as the Moon can be seen, with its crescent and half-moon shapes. Pioneer 10 provided the first opportunity to view Jupiter under varying illumination conditions, and this chapter presents some of the images obtained.

Figure 8-1 shows the trajectory of the spacecraft for 20 hours before and after its closest approach to Jupiter. As it approached the planet, the spacecraft was below the equatorial plane. Later it....

 


Figure 8-1. Phases of Jupiter as seen by the spacecraft from 20 hours before to 20 hours after closest approach.

Figure 8-1. Phases of Jupiter as seen by the spacecraft from 20 hours before to 20 hours after closest approach.

 


[
140]

Figure 8-2. (six black and white pictures of Jupiter).

Figure 8-2.


 

...crossed this plane and departed from the planet north of the plane. The lower part of the illustration shows schematically the change in the illumination of the disc of Jupiter, as seen from the spacecraft, at times corresponding to the positions of the spacecraft shown on the trajectory.

At 20 hours before closest approach, the dark limb is at the left of the planet. At 12 hours, it is under the planet as the spacecraft approaches below the equatorial plane. Just before closest approach, the dark limb slips around to the right side of the planet. Then the terminator rapidly sweeps across the view of the planet from the spacecraft, until the whole disc is dark as the spacecraft plunges into the planet's shadow. As Pioneer 10 emerges from the shadow, its images reveal a crescent Jupiter, the beginning of a unique series of pictures.

In the following pages, the images taken within four days of closest approach are designated with a code, such as A28 or B17. "A" images are before closest approach (periapsis) and "B" images are after closest approach. A fuller explanation of the code and a listing of the significant information about each image is given in Appendix 2. All dates and times used in this chapter are Universal Time (UT) which is the same as Greenwich Mean Time (GMT). DOY stands for day of year, i.e., January 1 is DOY 1, and December 31 is DOY 365.

The series of blue-channel pictures on this and the facing page was taken at two-day intervals, starting on DOY 321, 17 days before Pioneer 10's closest approach to Jupiter. None of these pictures has resolution as good as that which can be obtained from Earth. The scan lines, because they are so few, are quite evident.

The Great Red Spot and the banded structure are clearly visible even at these great distances, which range from 16 to 7.5 million km (10 to 4.7 million mi.). The terminator is on the west side of the disc of the planet and displaced slightly toward the south.

It is interesting to note that the detail, as seen by the IPP, is approximately the same as that which would be seen by the unaided human eye at [141] the same distance from Jupiter. All the pictures reproduced in this chapter show Jupiter as it might have been seen by an astronaut in a manned spacecraft, flying by Jupiter along the path of Pioneer 10.

The pictures on this and the facing page have all been reproduced to the same angular scale. The relative sizes are exactly as they would have appeared to an observer on the spacecraft as it approached Jupiter. These blue channel images have been selected to show Jupiter at approximately one day intervals, starting six days before periapsis. The last image shown in this series has a resolution comparable with that obtainable from Earth when the "seeing" conditions are good. Many of the pictures obtained over this period of time show satellites in the field of view. They are, however, too far away from the spacecraft to be resolved into detail and usually too far from the planet's disc to be seen in the pictures shown here. One satellite appears in the last frame of this series, slightly below and to the left of the disc of the planet.

 

Figure

Mid time

Distance

Phase angle degrees

DOY:hr:min

106 km

106 mi.

.

8-2(a)

321:01:36

16.0

10.0

37.3

8-2(b)

323:02:04

14.3

8.9

37.2

8-2(c)

325:04:07

12.6

7.8

37.0

8-2(d)

327:01:53

11.0

6.8

36.7

8-2(e)

329:06:46

9.1

5.7

36.1

8-2(f)

331:04:30

7.5

4.7

35.3

Figure

Mid time

Distance

Phase angle degrees

DOY:hr:min

106 km

106 mi.

.

8-3(a)

332:16:02

6.2

3.9

34.9

8-3(b)

333:01:44

5.8

3.6

34.4

8-3(c)

334:07:03

4.6

2.9

32.6

8-3(d)

335:12:53

3.4

2.1

30.0


Figure 8-3. (Four black and white pictures of Jupiter).

Figure 8-3.


[
142]

Figure 8-4. (Three color pictures of Jupiter)

Figure 8-4.


 

This spectacular series of consecutive pictures was taken over a period of four hours, between 44-1/2 and 40-1/2 hours before periapsis. The Great Red Spot is prominent, and the shadow of Io traverses the disc of the planet. Cosmetic enhancement as described in Chapter 7 was applied to all these images, especially to A49. A49 is shown before and after cosmetic enhancement in Figure 7-7.

 

Figure

Image no.

Mid time

Range

Phase angle degrees

DOY:hr:min

105 km

105 mi.

.

8-4(a)

A51

336:06:55

25.8

16.0

27.3

8-4(b)

A50

336:07:31

25.6

15.4

27.2

8-4(c)

A49

336:08:11

25.3

15,7

27.0

8-4(d)

A48

336:08:48

25.0

15.5

26.9

8 4(e)

A47

336:09:30

24.7

15.4

26.7

8-4(f)

A46

336:10:07

24.4

15.2

26.6

[143] The series of pictures, A39, A35, A31, and A28 on the next four pages shows one complete rotation of the planet. The final picture in the series is the last picture possible before the planet overfilled the field of view. Part of the data used to create A35 is missing. This results in the comb-like truncation of the northwest limb. This same effect occurs in several pictures in this chapter.

The gross morphology of belts and zones, with structures showing turbulence and convective cells in the middle latitudes of the planet, is clearly seen. The small white spots surrounded by dark rings, seen mainly in the southern hemisphere, indicate regions of intense vertical convective activity, somewhat similar to cumulonimbus or thunderclouds.

In places where the clouds are relatively featureless and have a bluish coloration, the IPP image provides a look down into the deepest and warmest parts of the atmosphere. These are called "blue festoons."

 

Figure

Image no.

Mid time DOY:hr:min

Range

Phase angle degree

105 km

105 mi

.

8-5(a)

A39

336:14:33

22.3

13.8

25.5

8-5(b)

A35

336:17:21

20.9

13.0

24.7

8-5(c)

A31

336:20:18

19.5

12.1

23.8

8-5(d)

A28

336:22:31

18.4

11.4

23.0

 


[144] Figure 8-6 (a).

Figure 8-5 (a).

[145] Figure 8-6 (b).

Figure 8-6 (b).

.

[146] Figure 8-6 (c).

Figure 8-6 (c).

[147] Figure 8-6 (d).

Figure 8-6 (d).

 

[148] At the head of this bright plume is a rising column of warm particles from a source deep within the clouds. The tail is to the left because the atmosphere moves more slowly at the upper regions than lower down. The southerly deflection of the plume, and the scalloped edges of the belt above the plume, support the theory that there is strong convective circulation between the lower and middle latitude belts and zones.

A color picture is shown together with the black and white images of the blue and red channels from which the colored image was constructed.

 

Figure

Image no.

Mid time

Range

Phase angle degree

DOY:hr:min

105 km

105 mi

.

8-6

A22

337:08:52

13.0

8.1

17.8


[
149]

Figure 8-6 (a). (b). Blue channel (c). Red channel. (photos of Jupiter).

Figure 8-6 (a). (b). Blue channel (c). Red channel.


 

[150] Red spots, other than the Great Red Spot, have been observed from the ground on previous occasions. This first close look at a northern hemisphere red spot shows convincingly the great morphological similarity between it and the wellknown and much studied Great Red Spot in the southern hemisphere. Ground-based observations indicate that this particular feature is very young- probably not more than 1 8-months old at the time of the passage of Pioneer 10.

Figure

Image no.

Mid time

Range

Phase angle degree

DOY:hr:min

105 km

105 mi

.

8-7

A-16

337:11:23

11.5

7.2

16.0


[
151]

Figure 8-7 (a). (b). Blue channel (c). Red channel. (photos of Jupiter).

Figure 8-7 (a). (b). Blue channel (c). Red channel.


[
152]

Figure 8-8 (a). (b). Blue channel (c). Red channel. (photos of Jupiter).

Figure 8-8 (a). (b). Blue channel (c). Red channel.

 

The pictures on this and the facing page are of similar areas of Jupiter and provide the best coverage of this enormously turbulent region. The "hooks" are several thousands of kilometers in extent. The belt structure is unstable at higher

latitudes. At the top of the pictures, a belt fragment, the darker elongated feature, can be seen in the transition zone between the belts and the relatively smooth looking polar region.

 


[
153]

Figure 8-9 (a). (b). Blue channel (c). Red channel. (photos of Jupiter).

Figure 8-9 (a). (b). Blue channel (c). Red channel

 

Figure

Image No.

Mid time

Range

Phase angle degrees

DOY:hr:min

104 km

104 mi

.

8-8

A9

337:14:47

95.4

59.4

13.4

8-9

A8

337:15:17

92.4

57.4

13.1



[
154]

Figure 8-10 (a). (b). Blue channel (c). Red channel. (photos of Jupiter).

Figure 8-10 (a). (b). Blue channel (c). Red channel

 

On this and the facing page is shown the type of fine detail revealed in the cloud photographs that will help scientists to unravel the complex behavior of the Jovian atmosphere.

In all the images, gross differences between the red and blue images are apparent. The fine repetitive wave-like structure discernible in the red channel image, which shows up as a bluish ripple on the colored image, is not real and should be ignored.

 


[
155]

Figure 8-11 (a). (b). Blue channel (c). Red channel. (photos of Jupiter).

Figure 8-11 (a). (b). Blue channel (c). Red channel

Figure

Image No.

Mid time

Range

Phase angle degrees

DOY:hr:min

104 km

104 mi

.

8-10

A7

337:16:19

86.1

53.6

12.4

8-11

A6

337:17:05

81.4

50.6

12.2


 


[
156]

Figure 8-6 (a).(photo of Jupiter).

Figure 8-12 (a).

 

The differences between the red and blue channel images are not only intriguing, but also important from the scientific analysis standpoint. This image shows again the plume conspicuous on Figure 8-6. But the detail is very much improved on this picture, which is one of the best close encounter pictures. Here features are seen that can be only glimpsed from Earth. Unfortunately, Pioneer 10 flew by so quickly that movements in the clouds cannot be detected between one picture and another. Even so, the nature of the detail enables inferences to be drawn concerning the dynamic properties of the Jovian atmosphere from these images.

 

Figure

Image No.

Mid time

Range

Phase angle degrees

DOY:hr:min

104 km

104 mi

.

8-12

A5

337:18:28

72.6

45.1

12.2

 


[
157] Figure 8-12 (continued)

Figure 8-12 (continued) (b) Blue channel. (black and white picture of Jupiter).(b) Blue channel.

.

Figure 8-12 (continued) (c) Red channel. (black and white picture of Jupiter).(c) Red channel.

 


[
158]

Figure 8-13 (a) (b). Two color pictures of Jupiter.

Figure 8-13 (a) (b).

 

While receding from Jupiter, Pioneer 10 showed Jupiter from a viewpoint never before seen by man: sunrise on a crescent-shaped planet. This series of images shows the northern hemisphere red spot, the Great Red Spot, and parts of the large plume. Contrast is lower in this crescent phase-a fact that can be explained in terms of the way in which the cloud particles scatter light. Irregularities in the profile of Jupiter are caused by a characteristic of the mechanism that drives the telescope.

The final picture in this series is the last one taken by the Pioneer 10 spacecraft on its epic journey, on New Year's Eve 1973.

 


[
159]

Figure 8-13. (c) (d) (e) (f) (Four black and white pictures of Jupiter).

Figure 8-13. (c) (d) (e) (f)

Figure

Image No.

Mid time

Range

Phase angle degrees

DOY:hr:min

105 km

105 mi

.

8-13(a)

B11

339:00:50

14.7

9.1

116.4

8-13(b)

B17

339:04:54

16.8

10.5

114,0

8-13(c)

B23

339:08:09

18.5

11.5

112A

8-13(d)

B39

339:21:25

24.9

15.5

108.2

8-13(e)

B69

341:17:08

43.7

27.2

102.5

8-13(f)

--

365:18:08

160.0

99 5

97.0



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