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Another benefit, stemming from wobbles in Pioneer's flight path, may be the detection of a long-suspected tenth planet or perhaps even an unseen nearby star. Both possibilities have been suggested as the source of the gravitational tugging that is causing the strange perturbations in the orbits of Uranus and Neptune. Scientists are even speculating that by carefully following Pioneer's movements they may detect effects of long-sought gravity waves. Postulated by Einstein's general theory of relativity, these waves are thought to be the carrier of the gravitational force, just as the photon, or light particle, is the transmitter of the electromagnetic force.
As the nuclear-powered spacecraft continues its probings of deep space, its findings will be awaited "with intense excitement," says the University of Iowa's James Van Allen, who utilized Explorer I a generation ago to discover the earth's radiation belts. Says Van Allen: "No one dreamed we would still be hearing from Pioneer today." The scientists, however, will have to be patient. At its present distance, radio messages take 4 hr. 20 min. to reach the earth from Pioneer. And the length of time is steadily increasing.
*Ordinarily, Pluto is the outermost planet, but because of its lopsided pathway, it will be traveling inside Neptune's orbit for the next 17 years.