An artist's depiction of NASA's Voyager 2 probe. (Image credit: NASA/JPL-Caltech) NASA just made an interstellar tweak to the Voyager 2 spacecraft, known as the "Big Bang", to keep its remaining 50-year-old science instruments running a little longer. Voyager 2 and its twin launched in 1977, called Voyager 1, rely on a form of nuclear battery known as a radioisotope thermoelectric generator that uses the heat produced by the decay of plutonium. But the supply of plutonium on each probe drops at about four watts a year on each spacecraft. To keep the probe running on this dwindling power supply, engineers recently reduced Voyager 2's power requirements by turning off a few non-science devices and using "lower-power alternatives" that are still effective enough to keep the spacecraft warm while it's so far from the sun, NASA officials said in a statement .…