New Horizons (Pluto Flyby)

Launched in 2006—before Pluto's demotion—New Horizons traveled 5 billion km to reach the dwarf planet in July 2015. The first close-up images revealed a geologically active world with nitrogen glaciers, the heart-shaped Tombaugh Regio (1,000 km wide), and water-ice mountains as tall as the Rockies. It then flew past Arrokoth in 2019, the most distant object ever visited at 6.6 billion km. This mission produces 50% more data per kilometer than #7 (the ISS) for comparative cost, proving Pluto is one of the solar system's most dynamic bodies.