Asteroid Close Calls

Under the right circumstances, asteroids just 20 meters wide can destroy a city. So far, humans have discovered 266 asteroids with possible diameters of this size that have passed or will pass closer to Earth than the Moon. This chart shows each flyby at its relative distance from Earth. The asteroids are not to scale; in reality they would be too small to see. See the end of this page for more details.
Design by Josh Worth, data NASA CNEOS, last updated May 2021
Before 2010
2010 — 2020
Beyond 2020
What does "average estimated diameter" mean, and why are some asteroids on here smaller than 20 meters?

It's tough to nail down the exact size of a small asteroid speeding through space. NASA's close approach database lists diameters as a probable range, such as 11 to 23 meters. We included all asteroids with possible maximum diameters greater than 20 meters but for brevity display an average. In some cases, the average is less than 20 meters.

Why do some asteroids have the exact same flyby distance?

Just as it's tough to determine the exact size of a small asteroid, it's hard to calculate the exact distance at which it passed Earth. NASA's close approach database estimates flyby distances as "nominal lunar distances" where one LD equals the average distance between the Earth and the Moon. Nominal LDs are only estimated to two decimal points, giving some asteroids identical flyby distances.