The twin Voyager probes are the ultimate spaceflight overachievers, but everyone knows their run can’t last forever.

Right now, it’s looking like the grizzled spacefarers have about five years before they fall silent, when they’ll be no longer able to send word of their adventures back to the humans who have eagerly awaited their telegrams for 42 years and counting. The Voyagers’ journey will continue indefinitely, but we will no longer travel with them.

“It’s cooling off, the spacecraft is getting colder all the time and the power is dropping,” Ed Stone, the mission’s project scientist and a physicist at Caltech, said during a news conference held Oct. 31 in conjunction with the publication of a handful of new scientific papers. “We know that somehow, in another five years or so, we may not have enough power to have any scientific instruments on any longer.”

Their success is unprecedented, even by NASA standards; the mission has lasted for two-thirds of the agency’s existence. “We’re certainly surprised but also wonderfully excited by the fact that they do [still work],” Stone said. “When the two Voyagers were launched, the Space Age was only 20 years old, so it was hard to know at that time that anything could last over 40 years.”

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