Voyager probe trajectory, artwork. Artwork of the trajectory of one of the Voyager probes as it travels out of the solar system. NASA's two unmanned Voyager probes were sent to the outer planets in 1977. The probes beamed back the first close-up images of the outer gas giant planets. The probes have exceeded the solar system's escape velocity, and continue to beam back data as they head out into interstellar space. Voyager 1 reached the heliopause, the boundary between the heliosphere and interstellar space, in around August 2012. As of 2013, Voyager 1 is over 18 billion kilometres from the Sun.