Voyager Still Beams An 'Eye' on the Stars
VOYAGER 2 said "good bye" to the general public when it sent its last planetary picture show from Neptune two years ago. For scientists, however, it's still part of their working community.In fact, both it and its twin - Voyager 1 - now provide astronomers with a unique pair of observatories on the outer fringes of the solar system. Their picture-taking cameras are shut down. But their ultraviolet (UV) instruments can scan distant stars and galaxies. Considered in this context, these 14-year-old spacecraft can be said to have begun a whole new life. At a time when space-science budgets face curtailment in Europe, the United States, and the Soviet Union, the investment made in these spacecraft years ago continues to pay extraordinary dividends. That's an achievement in which the much-criticized US National Aeronautics and Space Administration (NASA) certainly can take pride. The Voyagers provide more than just another set of UV "eyes" to supplement UV satellite units. The positions of both the spacecrafts and the unique capabilities of their instruments allow them "to observe things at wavelengths that are, for the most part, unavailable to other spacecraft," according to Voyager UV team member Jay Holberg. He says these instruments are well suited for studying both the birth and death of stars. Stars are hot and emit a lot of UV radiation - especially at the more energetic UV wavelengths - during these two extreme phases of their life cycles. Dr. Holberg says Voyager observations are "helping us get a better handle on exactly how much energy these hot stars emit." Right now they are taking data on early blue stars and on white dwarfs, which are densely compressed stars near the end of their lives. These are time-consuming observations that the spacecraft managers couldn't afford when they were constrained by the demanding planetary exploration schedule. Now they can let a Voyager instrument observe an object for weeks at a time to build up a complete map of the object and the surrounding region. Other Voyager instruments also remain active. They can detect particles, radio waves, and magnetic fields. These instruments are sampling regions of space never probed before. Among other things, they likely will detect the heliopause - the boundary between the region dominated by the sun and interstellar space. The spacecraft are well on their way toward that encounter. Voyager 1 is nearly 7,000 million kilometers (4,347 million miles) away and traveling at 64,000 kilometers an hour relative to the sun. Voyager 2 is not quite so distant at 5,300 million kilometers and moving at nearly 60,000 kilometers an hour in an opposite direction. But the farthest spacecraft - and the one most likely to reach interstellar space first - is the 20-year-old Pioneer 10, already nearly 8,000 million kilometers away. The California Institute of Technology's Jet Propulsion Laboratory in Pasadena, Calif., which manages the Voyager program, expects to receive Voyager information for another two to three decades, if the spacecraft remain healthy. The UV instruments can operate only until the end of the century. But the other instruments have an indefinite life. Scientists of all nations can apply for time on the Voyager instruments. Its investment in this program has served the United States well. Now it has become a world resource.