Editing Pioneer 10 (section)

===Encounter with Jupiter===
On November 6, 1973, the ''Pioneer 10'' spacecraft was at a distance of {{convert|25|e6km|sp=us|e6mi|abbr=unit}} from Jupiter. Testing of the imaging system began, and the data were successfully received back at the Deep Space Network. A series of 16,000 commands were then uploaded to the spacecraft to control the flyby operations during the next sixty days. The orbit of the outer moon [[Sinope (moon)|Sinope]] was crossed on November&nbsp;8. The [[bow shock]] of Jupiter's magnetosphere was reached on November 16, as indicated by a drop in the velocity of the [[solar wind]] from {{convert|451|km/s|abbr=on|sp=us}} to {{convert|225|km/s|abbr=on|sp=us}}. The [[magnetopause]] was passed through a day later. The spacecraft instruments confirmed that the magnetic field of Jupiter was inverted compared to that of Earth. By the 29th, the orbits of all of the outermost moons had been passed, and the spacecraft was operating flawlessly.{{sfn|Fimmel|van_Allen|Burgess|1980|pp=79–93}}

Red and blue pictures of Jupiter were being generated by the imaging photopolarimeter as the rotation of the spacecraft carried the instrument's field of view past the planet. These red and blue colors were combined to produce a synthetic green image, allowing a three-color combination to produce the rendered image. On November 26, a total of twelve such images were received back on Earth. By December 2, the image quality exceeded the best images made from Earth. These were being displayed in real-time back on Earth, and the Pioneer program would later receive an [[Emmy award]] for this presentation to the media. The motion of the spacecraft produced geometric distortions that later had to be corrected by computer processing.{{sfn|Fimmel|van_Allen|Burgess|1980|pp=79–93}} During the encounter, a total of more than 500 images were transmitted.{{sfn|Fimmel|van_Allen|Burgess|1980|p=170}}

The trajectory of the spacecraft took it along the magnetic equator of Jupiter, where the [[Particle radiation|ion radiation]] was concentrated.{{sfn|Fimmel|van_Allen|Burgess|1980|p=93}} Peak [[flux]] for this electron radiation is 10,000 times stronger than the maximum radiation around the Earth.{{sfn|Fimmel|van_Allen|Burgess|1980|p=126}} Pioneer 10 passed through the inner radiation belts within 20&nbsp;''R''<sub>J</sub>, receiving an integrated dose of 200,000 [[Rad (unit)|rads]] from [[electrons]] and 56,000 rads from [[protons]] (in comparison, a whole body dose of 500 rads is fatal to humans).<ref name=radiation/>  The level of radiation at Jupiter was ten times more powerful than Pioneer's designers had predicted, leading to fears that the probe would not survive. Starting on December 3, the radiation around Jupiter caused false commands to be generated. Most of these were corrected by contingency commands, but an image of [[Io (moon)|Io]] and a few close-ups of Jupiter were lost. Similar false commands would be generated on the way out from the planet.{{sfn|Fimmel|van_Allen|Burgess|1980|pp=79–93}} Nonetheless, ''Pioneer 10'' did succeed in obtaining images of the moons [[Ganymede (moon)|Ganymede]] and [[Europa (moon)|Europa]]. The image of Ganymede showed low [[albedo]] features in the center and near the south pole, while the north pole appeared brighter. Europa was too far away to obtain a detailed image, although some albedo features were apparent.{{sfn|Fimmel|van_Allen|Burgess|1980|p=121}}

The trajectory of ''Pioneer 10'' was chosen to take it behind Io, allowing the [[Refraction|refractive effect]] of the moon's atmosphere on the radio transmissions to be measured. This demonstrated that the [[ionosphere]] of the moon was about {{convert|700|km|sp=us}} above the surface of the day side, and the density ranged from 60,000 electrons per cubic centimeter on the dayside to 9,000 electrons per cubic centimeter on the night face. An unexpected discovery was that Io was orbiting within a cloud of hydrogen that extended for about {{convert|805,000|km|sp=us}}, with a width and height of {{convert|402,000|km|sp=us}}. A smaller, {{convert|110,000|km|mi|sp=us|adj=mid}} cloud was believed to have been detected near Europa.{{sfn|Fimmel|van_Allen|Burgess|1980|p=121}}

It was not until after ''Pioneer 10'' had cleared the asteroid belt that NASA selected a trajectory towards Jupiter which included a [[Gravity assist|slingshot effect]] to send the spacecraft out of the Solar System. ''Pioneer 10'' was the first spacecraft to attempt such a maneuver, a model for future missions. Such an extended mission was not in the initial proposal, but was planned for prior to launch.<ref name=salina_1983/>

At the closest approach, the velocity of the spacecraft reached {{Convert|132000|km/h|mph m/s|abbr=unit}},{{sfn|Fimmel|van_Allen|Burgess|1980|p=79}} and it came within {{convert|132,252|km|sp=us}} of the outer atmosphere of Jupiter. Close-up images of the Great Red Spot and the terminator were obtained. Communication with the spacecraft then ceased as it passed behind the planet.{{sfn|Fimmel|van_Allen|Burgess|1980|p=93}} The [[radio occultation]] data allowed the temperature structure of the outer atmosphere to be measured, showing a temperature inversion between the altitudes with 10 and 100&nbsp;[[mbar]] pressures. Temperatures at the 10-mbar level ranged from {{convert|-133|to|-113|C|lk=on|K F}}, while temperatures at the 100&nbsp;mbar level were {{convert|-183|to|-163|C|K F}}.{{sfn|Fimmel|van_Allen|Burgess|1980|p=135}} The spacecraft generated an infrared map of the planet, which confirmed the idea that the planet radiated more heat than it received from the Sun.{{sfn|Fimmel|van_Allen|Burgess|1980|p=141}}

Crescent images of the planet were then returned as  ''Pioneer 10''  moved away from the planet.{{sfn|Fimmel|van_Allen|Burgess|1980|p=90}} As the spacecraft headed outward, it again passed the bow shock of Jupiter's magnetosphere. As this front is constantly shifting in space because of dynamic interaction with the solar wind, the vehicle crossed the bow shock a total of 17 times before it escaped completely.{{sfn|Fimmel|van_Allen|Burgess|1980|pp=123–124}}

<gallery class="center" caption="Jupiter encounter images">
File:Pioneer10 Image a51.jpg|Jupiter as imaged by ''Pioneer 10''
File:Pioneer 10 image of Jupiter (image A5).jpg|Jupiter close up as imaged by ''Pioneer 10''
File:Pioneer 10 - Ganymede - P102a.jpg|[[Ganymede (moon)|Ganymede]] as imaged by ''Pioneer 10''
File:Pioneer 10 - p102b.jpg|[[Europa (moon)|Europa]] as imaged by ''Pioneer 10''
File:Pioneer 10 - p158.jpg|Crescent Jupiter as imaged by ''Pioneer 10''
</gallery>