Pluto Planet Coloring Page: Free Printable PDF Sheet

Pluto and Its Heart-Shaped Surface

A Dwarf Planet in the Outer Solar System

Pluto orbits far beyond Neptune in a distant region called the Kuiper Belt, a wide ring of icy bodies left over from the solar system's early formation. It is small even by dwarf-planet standards, measuring about 1,477 miles across, which is smaller than Earth's own moon and roughly two-thirds the width of the United States.

Pluto was classified as the ninth planet from its discovery in 1930 until 2006, when astronomers defined a stricter set of rules for what counts as a full planet and reclassified Pluto as a dwarf planet because it has not cleared other objects out of its orbital path.

The Famous Heart on Its Surface

The heart-shaped region shown in this scene is a real feature called Tombaugh Regio, named after Clyde Tombaugh, the astronomer who discovered Pluto. It is a massive plain of frozen nitrogen ice roughly 990 miles across, wide enough to stretch across several states, and it became the most recognizable marking on Pluto's surface once NASA's New Horizons spacecraft photographed it up close.

Scientists believe slow-moving nitrogen ice inside that heart-shaped basin churns in patterns similar to a lava lamp, driven by heat rising from below, which keeps the smooth icy plain looking almost crater-free compared to older, rougher regions nearby.

Charon, the Moon Almost as Big as Pluto

Charon, shown floating nearby in this scene, is unusually large compared to the dwarf planet it orbits, measuring about half of Pluto's own diameter. That size difference is so extreme that Pluto and Charon are sometimes described as a double dwarf-planet system rather than a typical planet-and-moon pair, since both bodies actually orbit a shared point of balance located between them.

Pluto has four smaller moons in addition to Charon, named Nix, Hydra, Kerberos, and Styx, all of which are tiny, irregularly shaped, and far too small to see without a powerful telescope. Charon itself carries a dark reddish cap at its north pole, thought to form from gases that escape Pluto's thin atmosphere, drift across space, and freeze onto Charon's colder surface.

New Horizons and the First Close Look

NASA's New Horizons spacecraft launched in 2006 and took more than nine years to reach Pluto, finally flying past it in July 2015 at a distance of about 7,800 miles. That flyby sent back the first clear photographs ever taken of Pluto's surface, revealing mountains made of water ice, nitrogen ice plains, and a thin, hazy blue atmosphere that surprised scientists who expected a duller, featureless world.

Pluto's average distance from the sun is roughly 3.7 billion miles, so far away that it takes 248 Earth years to complete one full orbit, meaning Pluto has not yet finished a single trip around the sun since its discovery nearly a century ago.

Pluto's thin atmosphere, made mostly of nitrogen gas, actually freezes and falls to the surface as frost each time Pluto swings toward the farthest point of its egg-shaped orbit, then thaws back into a light haze as it drifts closer to the sun again. New Horizons also spotted tall mountain ranges made of solid water ice, some rising more than two miles high, standing at the edge of the smooth nitrogen plains captured in this scene.