What was apparently the spacecraft's last signal was received Jan. 22 by the Jet Propulsion Laboratory's Deep Space Network. At the time, Pioneer 10 was 7.6 billion miles from Earth; the signal, traveling at the speed of light, took 11 hours and 20 minutes to arrive.
The signal and the two previous signals were very faint. The Deep Space Network heard nothing from Pioneer 10 during a final attempt at contact on Feb. 7. No more attempts are planned.
Pioneer 10 was launched March 2, 1972, on a 21-month mission. It became the first spacecraft to pass through the asteroid belt and the first to obtain close-up images of Jupiter. In 1983, it became the first manmade object to leave the solar system when it passed the orbit of distant Pluto.
Although Pioneer 10's mission officially ended in 1997, scientists continued to track the TRW Inc.-built spacecraft as part of a study of communication technology for NASA's future Interstellar Probe mission. Pioneer 10 hasn't relayed telemetry data since April 27.
"It was a workhorse that far exceeded its warranty, and I guess you could say we got our money's worth," said Larry Lasher, Pioneer 10 project manager at NASA's Ames Research Center.
Pioneer 10 carries a gold plaque engraved with a message of goodwill and a map showing the Earth's location in the solar system. The spacecraft continues to coast toward the star Aldebaran in the constellation Taurus. It will take 2 million years to reach it.