Another Io-associated phenomenon searched for by Voyager was the Io flux tube. As a conductor moving through the Jovian magnetic field, Io generates an electric current, estimated to have a strength of about 10 million (10⁷) amperes and a power of the order of a million million (10¹²) watts. The region of space through which this current flows from the satellite to Jupiter is called the flux tube. Voyager 1 was targeted to fly through the Io flux tube. This was an important decision, since this option precluded the possibility of obtaining occultations by either Io or Ganymede. The event was to take place on March 5, just after closest approach to Io. The effects of the flux tube were clearly observed by the magnetometer, the LECP instrument, and other particle and field instruments; however, subsequent analysis indicated that the spacecraft had not penetrated the region of maximum current flow; it probably missed the center of the flux tube between 5000 and 10 000 kilometers. The flux tube is not the only connection between Io and Jupiter. Radio emissions from the atmosphere are triggered by Io’s orbital position, and the aurorae that illuminate Jupiter’s polar regions are the result of charged particles falling into the planet from the Io torus. Other charged particles can occasionally escape outward and be detected as far away as Earth. Io is unquestionably a remarkable world. The only planetary body known to be geologically more active than the Earth, it provides many extreme examples to test the theories of geoscientists. Its intimate interconnections with the Jovian magnetosphere and the planet itself provide a unifying theme to the complex processes taking place in the inner parts of the Jovian system. [Illustration: The Galileo Probe will make a fiery entry into the Jovian atmosphere, carrying a payload of scientific instruments for the first direct sampling of the atmosphere of a giant planet. Shown here is the moment, at a pressure level of about 0.1 bar, when the parachute is deployed and the still-glowing heatshield drops free from the Probe.] CHAPTER 10 RETURN TO JUPITER A Successor to Voyager The spectacular discoveries of the Voyagers did not exhaust our interest in the Jovian system. Both the giant planet and its system of satellites will almost certainly play a central role in any future program of solar system exploration and research. Thus, even as the two Voyager spacecraft directed their attention further outward toward Saturn, NASA had begun development of the next Jupiter mission, named Galileo.