Voyager 1 was launched in 1977 to study Jupiter and Saturn. It carried out its mission, but long since has traveled through the Kuiper Belt beyond Neptune and kept going. It's now 125 times as far away from the Sun as we are, some twelve billion miles from home.
It takes nearly eighteen hours for Voyager's signals to reach us. Yes, Voyager is still phoning home, which is how NASA is getting enough data to finally conclude that the little probe is now in interstellar space, the space between the stars.
But, of course, this wouldn't be the first time that scientists had decided that Voyager had left the Solar System, which, strictly speaking, it hasn't. It still hasn't passed through the Oort Cloud and will no longer be in touch with Earth by the time it has.
Voyager 1's twin, Voyager 2, is also headed towards the edge of the Solar System in a different direction. (I think it's a bit like Buzz Aldrin to Voyager 1's Neil Armstrong.)
Last edited by Mona - Astronomy; 09/19/13 11:25 AM.