The Pioneer data confirmed the presence of a heat source in Jupiter and supplied a quantitative estimate of its magnitude. The global effective temperature was found to be -148° C, to a precision of ±3 degrees. This temperature implies that Jupiter radiates 1.9 times as much heat as it receives from the Sun. The corresponding internal heat source is 10¹⁷ watts. Surprisingly, the poles were as warm as the equator; apparently, the atmosphere is very efficient at transferring solar heat absorbed near the equator up to high latitudes, or perhaps the internal component of the heat comes preferentially from the polar regions. Helium in the Atmosphere. The Pioneer infrared experiment made the first measurement of the amount of helium on Jupiter. The ratio of the number of helium atoms to the number of hydrogen atoms was found to be He/H₂ = 0.14 ± 0.08. This is consistent with the known solar ratio of He/H₂ = 0.11. Measurements of helium in the upper atmosphere were also made by the ultraviolet experiment. [Illustration: One of the best Pioneer images of Jupiter was obtained at a range of 545 000 kilometers by Pioneer 11. Structure within the Great Red Spot and the surrounding belts and zones can be seen. There was much less turbulent cloud activity round the spot at the time of the Pioneer flybys than was seen five years later by the Voyager cameras.] [Illustration: Pioneer 10 confirmed theoretical models of Jupiter that suggest the planet is nearly all liquid, with a very small core and an extremely deep atmosphere. The liquid interior seethes with internal heat energy, which is transferred from deep within the planet to its outer regions. The temperature at the center may be 30 000 K. Since the temperature at the cloud tops is around -123° C, there is a large range of temperatures within the planet.] Distance (km) Visible clouds Hydrogen gas Cloud tops Ammonia crystals Ammonium hydrosulfide crystals Ice crystals Water droplets -123° C Transparent atmosphere Hydrogen/Helium gas 70 000 Transition zone 1980° C 60 000 Liquid hydrogen 50 000 11 000° C Transition zone 3 million atmospheres pressure 40 000 Liquid metallic hydrogen 30 000 20 000 Possible “sea” of helium 10 000 30 000 K Possible solid core 0 PIONEER SCIENCE INVESTIGATIONS Project Scientist: J. H. Wolfe, NASA Ames Investigation Principal Investigator Primary Objectives