New Map Reveals How Many Fireballs Impact Earth's Atmosphere

You wouldn't think our planet experiences many close encounters from asteroids. Yet a new map shows exactly how often Earth's atmosphere is hit by small asteroids, called bolides. Now, scientists from NASA's Near Earth Object program have released a new map that reveals these small impact events are both frequent and random.

In this case, NASA used data gathered by U.S. government sensors from the years 1994 to 2013. Over this 20-year interview, U.S. government assets recorded at least 556 bolide events, or fireballs, of various energies. NASA then compiled the data into a map where blue represented nighttime events while orange dots represented daytime events.

The largest event recorded during this interview was the recent daytime Chelyabinsk event, which was recorded over central Russia on Feb. 15, 2013. During this event, a small asteroid exploded in the atmosphere over Russia, causing windows to shatter as a bright flash briefly lit up the sky. This asteroid was about 20 meters in size before it hit Earth, though the planet's atmosphere largely protected it.

"We now know that Earth's atmosphere does a great job of protecting Earth from small asteroids," said Lindley Johnson, NASA NEO Observations Program executive, in a news release. "How big is the population of larger asteroids we really need to worry about? We need to better understand that."

While these fireballs that light up in Earth's atmosphere aren't a threat, there are other, larger asteroids that could be a problem. That's why NASA's NEO program exists in the first place. Every day, Earth is bombarded with more than 100 tons of dust and sand-sized particles from space. And about once a year, an automobile-sized asteroid hits Earth's atmosphere and creates a spectacular fireball (bolide) event. Asteroids that are even larger, about the size of a football field, are the ones that NASA hopes to monitor and take preventative measures against.

"These newly released data will help NEO scientists construct a more complete picture of the frequency and scope of asteroid impacts with Earth," said Johnson.

For more information about Near Earth Objects, visit NASA's website.

The findings are published in the journal Nature.