Voyager spacecraft beyond the solar system, illustration. In 1977, NASA's Voyager 1 and 2 spacecraft began their pioneering journeys across the Solar System to visit the outer planets. Now, the Voyagers have left the Solar System and are travelling through unexplored territory. Along the way, they are measuring the interstellar medium, the environment between stars. The NASA/ESA Hubble Space Telescope is measuring the material along the probes' trajectories. Hubble data, combined with that from the Voyagers, have provided new insights into how our Sun travels through interstellar space.