New Horizons at Pluto (NASA, 2015)

New Horizons launched in January 2006 — before Pluto was reclassified as a dwarf planet — and reached it in July 2015 after a 9-year, 5-billion-km journey. No one expected much from a small, cold, remote world. The first close-up images showed a geologically active surface: nitrogen glaciers flowing into plains, mountains of water ice as tall as the Rockies, a surprisingly complex haze-layered atmosphere, and a heart-shaped nitrogen ice plain (Tombaugh Regio) 1,000 km across. Pluto, it turned out, is one of the most geologically dynamic bodies in the outer solar system. In 2019, New Horizons flew past Arrokoth, a contact-binary Kuiper Belt object 6.5 billion km from the Sun — the most distant object ever visited by a spacecraft.