Pioneer 10: the preliminary results

Pioneer 10 reached the point of closest approach to Jupiter (2.86 Jupiter radii or R/sub j/) at 02:25.19 GMT on 4 December 1973. Pioneer 10 has now become the first spacecraft to travel beyond the orbit of Mars, through the asteroid belt, and through the intense Van Allen radiation belts which surround Jupiter. The large amount of information which has been reaching Earth from Pioneer 10 has revealed many facts previously unknown and opened new speculations about Jupiter and its rich satellite system, Characteristics of the Jovian environment which have become evident from this experiment and which are discussed here include the strength of the magnetic field, the radiation belts, which are regions where protons and high-energy electrons are trapped by the planet's magnetic field, and the effect of the radiation belts of the Jovian satellites. The fact that helium has been positively detected for the first time in Jupiter's atmosphere by dayglow observations recorded by Pioneer 10's ultraviolet photometer is considered. The infrared radiometer used measured a brightness temperature of 145 K for Jupiter which, using a planetary albedo of 0.45, confirms that the planet emits more than twice the amount of energy it receives from the Sun. Themore » significance of this result is discussed. The images returned from Pioneer 10, providing the first closeup look at the planet, are considered. (UK)« less