Pluto is a dwarf planet because it has not cleared its orbital neighborhood. Under the International Astronomical Union’s definition for our solar system, a planet orbits the Sun, is massive enough for gravity to make it nearly round, and has cleared its orbital neighborhood. Pluto meets the first two conditions. The third is where it differs from the eight planets. The reclassification in 2006 changed how scientists grouped Pluto. Its surface, orbit and moons did not change when the decision was made.

Clearing the neighborhood describes gravitational dominance over a region, not a completely empty path. A planet can still have small objects nearby, including companions trapped in stable orbital patterns. Pluto belongs to the Kuiper Belt, where many icy bodies orbit beyond Neptune. It has not become the dominant object across that region. Think of the test as a question about what an object’s gravity has done to the other bodies around its orbit over time. A photograph showing a round surface cannot answer that orbital question by itself.

A dwarf planet can have moons and a complex landscape. Pluto has five known moons, and its largest, Charon, is unusually large relative to Pluto. NASA’s New Horizons spacecraft flew past in 2015 and returned close views of a surprisingly varied surface. If you are labeling a solar system model, put Pluto beyond Neptune in the Kuiper Belt and give it a dwarf planet label. That keeps it visible in the model and makes the category distinction clear without suggesting that it is a moon or an asteroid.