Pluto Didn't Complete a Full Orbit Since Its Discovery

It's easy to imagine planetary orbits as swift, clockwork loops, but the reality for worlds in the outer solar system is a slow, epic journey. The farther a celestial body is from the Sun, the weaker the Sun's gravitational pull becomes. This results in a much slower orbital speed and a vastly longer path to travel. For the dwarf planet Pluto, this cosmic slowdown is extreme, stretching its "year" to a staggering length of nearly two and a half centuries.

When American astronomer Clyde Tombaugh discovered Pluto in 1930, it was just one point of light on a photographic plate. In the time since, humanity has lived through the Great (Review) Depression, fought a world war, landed on the Moon, and developed the internet. Throughout all of this rapid human history, Pluto has been patiently continuing the same single lap around the Sun that it was on when we first found it.

This incredibly long journey means that all of our observations of Pluto, from its initial discovery to the stunning close-up images from the New Horizons spacecraft in 2015, have taken place during the same Plutonian year. We will have to wait until March 2178 for Pluto to finally return to the same position in its orbit it occupied on the day of its discovery, completing its first full, observed revolution.