Instead of a barren ice ball, Pluto featured vast plains of nitrogen ice, jagged mountains made of water ice, and intricate networks of frozen canyons. Its heart-shaped region, informally called ...

(Correction: An earlier version of this story misstated how far Pluto is from the sun. The correct number is 3.7 billion miles.) What was discovered in Flagstaff, Arizona, and killed off in Prague?