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A distant Pioneer whispers to Earth
By Richard Stenger
(CNN) -- NASA engineers picked up a radio signal this month from the first spacecraft to fly beyond Pluto. Pioneer 10, now 7.5 billion miles (12.10 billion kilometers) from Earth, has been silent since March. Currently, a radio signal traveling at the speed of light takes more than 11 hours to reach Pioneer 10, which was launched in 1972. "The Deep Space Station near Madrid found the signal but could not lock onto the receiver," Pioneer 10 project manager Larry Lasher said in a mission status report this month. The radio receiver in Spain is one of several large dishes that comprise NASA's worldwide satellite network to communicate with spacecraft. Other radio dishes in Goldstone, California, and Arecibo, Puerto Rico, confirmed that the radio signal came from Pioneer 10. But the transmission was so faint that NASA engineers could not obtain any scientific readings from the craft, Lasher said. Pioneer 10 and its sister ship Pioneer 11, which took off in 1973, more than lived up to their names during decades of groundbreaking space exploration. Traveling in opposite directions, the two were the first to cross the asteroid belt, the first to explore the outer solar system and the first to send back images of the gas giant planets Jupiter and Saturn. Radio communications with Pioneer 11 ceased in 1995. In April 2001, Pioneer 10 surprised astronomers when it managed to send back a transmission to Earth as directed. In 1998, one of the newer, faster Voyager probes overtook Pioneer 10 to become the farthest man-made object in space. But Pioneer 10, now more than twice the distance from the sun as Pluto, continues to serve a valuable scientific function as it approaches the edge of the solar system. On the rare occasions when astronomers have coaxed even sparse data from Pioneer 10 in recent years, they have used the readings to investigate everything from cosmic rays to chaos theory to gravitational mechanics.
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