Here's a fairly astounding fact: The entire history of the United States has unfolded in the time it's taken Pluto to orbit the Sun once.

The United States has been around for 238 years. A year on Pluto is 248 years. (Thanks to Corey Powell for pointing out this map, recently published by the New Horizons team.)

NASA's New Horizons probe is now closing in on Pluto, due to reach it on Tuesday after a nine-year journey. And though that might seem like a long time, the truth is that Pluto has been traveling towards this rendezvous for much, much longer.

The last time Pluto was in its current position — in 1768 — humans were totally unaware of its existence (it was discovered in 1930). At the time, humans still hadn't figured out how species evolve, how germs transmit diseases, or how the Earth's tectonic plates slide around. Aviation was still decades away — and spaceflight wouldn't happen for nearly 200 years.

All of which is to say: it's pretty amazing that, this time around, Pluto will be visited by a tiny robot sent by a curious species of apes three billion miles away. A lot can change in a single orbit.