dwarf planets

New Horizons passed 12,500 km above Pluto on July 14, 2015, the only spacecraft ever to do so. It found a nitrogen glacier churning in convection cells, water-ice mountains, layered blue haze, and a possible buried ocean, then spent 16 months sending the data home.

All 8 planets and 5 dwarf planets explained — sizes, atmospheres, moons, missions, and what makes each world unique in our solar system.

Pluto was reclassified as a dwarf planet in 2006, but the New Horizons flyby in 2015 showed a geologically active world with nitrogen-ice convection, water-ice mountains, hazy skies, and hints of a buried ocean. Beyond it, the Kuiper Belt holds the best-preserved leftovers of planet formation.