The end of NASA’s Voyager probes is near

Saturn as captured by Voyager.

Smith Collection/Gado/Getty Images

When the Voyagers’ planetary journeys were completed, a new phase of the mission could begin. After their final planetary stops, both probes reached Solar System escape velocity. For Voyager 2, they’ve gone interstellar. since after those dates the sensors of the probes showed that the charged particles from the Sun became less abundant and energetic than those detected from the galactic environment.This was a golden opportunity to study the boundaries of the Solar System and the environment beyond it.

Voyager 1 and 2 carried the Golden Records, recordings of sounds and images intended to show aliens life and culture on Earth.

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The secret of a long life

Reaching such a distance is possible only with the right energy source. Many probes use solar panels, but if they travel too far from the sun, they become useless (the farthest probe that uses them is Juno orbiting Jupiter). Voyagers’ secret lies in their atomic hearts. both are equipped with three radioisotope thermoelectric generatorsor RTGs, small power generators that can produce power directly on board.Each RTG contains 24 plutonium-238 oxide pellets with a total mass of 4.5 kilograms.

Plutonium-238 is an unstable isotope, which means it undergoes radioactive decay. The plutonium atoms in RTGs emit alpha particles, which consist of two protons and two neutrons, and these hit the RTG element, heating it up heat is converted into electricity.

An RTG built for the Voyager program.

NASA/JPL/Voyager

But over time, the plutonium on board is depleted, and thus the RTGs produce less and less energy, so the Voyagers slowly die.

To conserve the probes’ remaining power, the mission team is gradually turning off the probes’ various instruments that are still active. The same device on Voyager 1 was disabled in 2007 due to a malfunction. These instruments were used to study charged particles in the sun’s magnetic field, and it was this detector that determined in 2018 that Voyager 2 had exited the heliosphere and become interstellar.

Four active instruments remain, including a magnetometer and other instruments used to study the galactic environment with its cosmic rays and interstellar magnetic field. But these are in their last years. In the next decade, it’s hard to say exactly when, the two probes’ batteries will run out forever.

This story originally appeared on WIRED Italia: and translated from the Italian.