Twenty years after demotion, Pluto's planetary status faces renewed scientific debate

Twenty years ago, a gathering of astronomers in Prague drew a line through the solar system and left Pluto on the wrong side of it — not out of malice, but out of necessity, as the discovery of hundreds of similar icy bodies forced science to define what it had long assumed. Since then, a spacecraft's revelations of glaciers, mountains, and moons have made that line harder to hold, and now a mixture of national sentiment, political will, and genuine scientific reconsideration is pressing the question again. The debate over Pluto is, at its heart, a debate about how human beings draw boundaries