Launched in 1977, the unmanned space probes Voyager 1 and 2 carried out an extensive survey of the planets and moons of the outer solar system. Visiting Jupiter, Saturn, Uranus, and Neptune, the Voyager program can only be called an unqualified success on virtually every level. The twin spacecraft returned thousands of photographs and reams of scientific data that fundamentally changed our understanding of our entire solar system. Currently in interstellar space, Voyager 1 is the farthest man-made object from Earth. Voyager 2 is near the edge of our solar system and will one day also enter interstellar space.
Many people are unaware that even after over 40 years, both probes are still actively generating scientific data and transmitting it to Earth. Although many of the instruments installed on Voyager 1 and 2 have been deactivated or have failed, several continue to function. Powered by nuclear radioisotope thermoelectric generators (RTGs), both probes should be able to continue to operate for several more years.
