WATCH: The Stuff We've Left In Space

In 1957, humans launched a satellite into orbit, Sputnik-1.

The same mission also created our first piece of space junk: the rocket body that took Sputnik into space.

By the year 2000, there were hundreds of satellites in orbit — and thousands of pieces of space junk, including leftover rockets and pieces of debris.

And today? According to the Royal Institution in London, there are about 20,000 pieces of tracked space debris, ranging from larger than an apple to as big as a school bus. (There are far more objects smaller than that, including millions of pieces of debris too tiny to track, according to NASA.)

Stuart Grey of University College London created a visualization showing how those larger pieces of junk proliferated over time — and how single events, like a Chinese test launch in 2007 or the collision of two satellites in 2009, could create thousands of pieces of space trash.

You can see a short preview above, or try out the interactive version on the Royal Institution's website.