After twelve years and more than seven billion kilometres, Voyager 2 arrived at Neptune within 100 kilometres of where it had been aimed — a margin NASA compares to sinking a golf putt 3,630 kilometres long

A hundred kilometres of error over seven billion kilometres traveled is a miss of about fourteen parts per billion. After Uranus, Voyager 2 made its largest midcourse correction on February 14, 1986, firing its hydrazine thrusters for 2 hours and 33 minutes. The whole flyby was a geometric bet refined over twelve years and seven billion kilometres. At Neptune, Voyager 2 found six new moons and four rings, along with the Great Dark Spot and the deep cold of Triton. We aimed a machine across seven billion kilometres and delivered it within 100.