Pioneer 10 is one of the space program's robotic heroes. Launched in 1972, it was the first spacecraft to fly by the outer planets and into interstellar space. Now, nearly 7 billion miles from Earth, the probe may be nearing the end of its illustrious career -- or maybe not.

"As an engineering feat, it's marvelous," says Larry Lasher, Pioneer 10's project manager at NASA's Ames Research Center. "It's lasted over 27 years -- and it was designed to last 21 months." (The latter was the period of time needed for the probe to get to Jupiter.)

Pioneer 10's funding was ended formally in 1997 but the probe has continued to operate under the control of the Lunar Prospector team. Although technically Pioneer 10 has become a "training mission" for controllers, the probe has continued to gather scientific data, its instruments powered by a trickle of energy from a plutonium battery.

Now even the current arrangement is near an end, since the Lunar Prospector team will be disbanded in September. (The lunar probe was crashed deliberately into the moon July 31 in an effort to verify that water exists there.) Even so, says Lasher, there's a "fair chance" that Pioneer 10 will remain in contact past September, with controllers of other missions checking in on the old probe on a "voluntary basis."

And even if Pioneer 10 does lose touch with Earth, its usefulness may not be at an end. The probe carries a gold plaque containing information for possible extraterrestrial readers in the distant future. Included are drawings of a human male and female, and diagrams indicating the time and place of present-day Earth.

"If the plaque is ever found -- science fiction, perhaps -- it would tell whatever found it where we are, when we are and who we are," says Lasher.