NASA shut off a Voyager instrument. Only these 4 remain.

Nuclear fuel lasts a long time. But not forever.

Both Voyager craft, launched in 1977, convert heat produced by the decay of radioactive plutonium-238 into electricity. Over the decades, NASA engineers have strategically shut off instruments to extend the life of Voyager 1 and 2, which are respectively well over 15 and 12 billion miles away. As their mission nears a half century, this fuel is dwindling, and the agency just turned off another gadget on Voyager 2, leaving it with four remaining science instruments.