Directions: The short passage below is followed by a question based on its content. Answer the question on the basis of what is stated or implied in the passage.
The little spaceships that could - Nasa's twin Voyagers - celebrate their 25th year on Tuesday by speeding towards the very edge of our solar system, carrying messages from Mozart, Bach and Chuck Berry. The first Voyager was launched on August 20, 1977, and was expected to take a quick four-year tour of Jupiter and Saturn, send back some data and retire. The other was launched on September 5, 1977 with a similar mission, but through a different route. Instead, the doughty robotic probes have kept going and going, snapping never-before-seen images of the outer planets, discovering volcanoes on Jupiter's moon 'Io' and a massive atmospheric storm on Neptune.
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