30 Years and Counting for Voyager 2
It was thirty years ago today that the Voyager 2 spacecraft was launched from Florida for a grand tour of the outer solar system. (Voyager 1 was launched two weeks later; the details of their trajectories led Voyager 2 on a slower path to the outer solar system, so while launching later, Voyager 1 actually got to Jupiter and Saturn first.) At the time of launch it was not known if there would be funding for Voyager 2 to continue to Uranus and Neptune and become the only spacecraft (still) to explore those planets at close range. I have a special fondness for the mission because the data returned from the flyby of the outermost two planets in the solar system formed the core of my Ph.D. dissertation.
Voyager 2 is about 12 light-hours from Earth and is operating with about 300 Watts of power from its radio-isotope thermoelectric generators (RTGs). Its scientific mission continues with measurements of the magnetic field and charged particle densities as the spacecraft drifts across the boundary between the heliosphere and interstellar space. This is as good a definition as any for the edge of the solar system - the location where the background plasma is no longer dominated by streaming solar wind electrons and protons from the Sun but by the interstellar medium. There are comets gravitationally bound to the Sun much further away than Voyager 2 right now, but you’d have to go a fair way toward the nearest star to pass the Oort cloud of comets.