A small asteroid disintegrates in Earth’s atmosphere about every other week, and the distribution around the world appears to be random. That is the main message of a map released in November 2014 by NASA’s Near-Earth Object (NEO) observation program. The new data could help scientists refine estimates of the distribution of asteroids near Earth, including larger ones that could pose a danger.
The map above indicates the locations where small asteroids crashed into Earth’s atmosphere between 1994 and 2013. Each of these 556 events resulted in a very bright meteor—also known as a bolide or fireball. On the map, orange dots represent daytime impacts and blue represents nighttime. The size of each dot is proportional to the radiated energy of the fireball, measured in billions of Joules (GigaJoules).
The map includes asteroids/meteors ranging from about 1 meter (3 feet) to almost 20 meters (65 feet); it does not include objects smaller than a meter. Nearly all of them disintegrated in the atmosphere and were harmless to life on the surface. The notable exception was the February 2013 Chelyabinsk event over central Russia. That impact released the energy equivalent of 440,000 to 500,000 tons of TNT, and it was the largest meteor to hit Earth in this period.
Every day, Earth is bombarded by more than 100 tons of dust and sand-sized particles from space. About once a year, an automobile-sized asteroid hits Earth's atmosphere, creating a spectacular fireball as the friction of the atmosphere causes it to disintegrate. Studies of Earth’s history indicate that an object the size of a football field hits Earth and causes significant damage about once every 5,000 years. Once every few million years, Earth is hit by an object large enough to cause regional or global disasters.
NASA’s NEO program finds, tracks, and characterizes asteroids whose orbits bring them within 50 million kilometers (31 million miles) of Earth's orbit about the Sun. The public can help participate in the hunt for near earth objects through the Asteroid Grand Challenge. The goal is to create a plan to find all asteroid threats to human populations and to know what to do about them.
“We know that Earth’s atmosphere does a great job of protecting Earth from small asteroids,” said Lindley Johnson, leader of NEO. “How big is the population of larger asteroids that we really need to worry about? We need to better understand that.”
Map from NASA Planetary Science. Caption by Linda Billings (NEO program), Mike Carlowicz (Earth Observatory), and DC Agle (NASA Jet Propulsion Laboratory).