How Much Is Too Much Space Junk?

If you’ve ever walked through a swarm of gnats at a picnic, you have some idea of what it’s like to navigate the mass of debris that circles our planet in low-Earth orbit. Space planners have long warned that the growing belt of cosmic junk would eventually lead to collisions, and on Tuesday it happened, when an American satellite and a defunct Russian satellite totaled one another 500 miles above Siberia.