Asteroids of about a meter and larger in size invade our planet’s atmosphere every other week, a study released by NASA shows. According to data gathered over the past 20 years, at least 556 such asteroids collided with Earth over this period.
According to the study, small impact events – also called fireballs or bolides – happen “all the time.”The asteroids hit the atmosphere and disintegrate at a frequent and random rate, according to the data gathered by US government sensors and based on infra-sound detections.
“We now know that Earth’s atmosphere does a great job of protecting Earth from small asteroids,” said Lindley Johnson, executive of NASA’s Near Earth Object (NEO) Observations Program.
The asteroids, marked on the NASA map, do not include smaller impacts, but – according to the study – our planet is bombarded with more than 100 tons of dust and sand-sized particles from space every day.
The observation program’s aim is “to find potentially hazardous asteroids before they find us,” according to Donald Yeomans, manager of NASA’s NEO Program Office at the Jet Propulsion Laboratory.
This diagram maps the data gathered from 1994-2013 on small asteroids impacting Earth’s atmosphere to create very bright meteors, technically called “bolides” and commonly referred to as “fireballs”. Sizes of red dots (daytime impacts) and blue dots (nighttime impacts) are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy, and show the location of impacts from objects about 1 meter (3 feet) to almost 20 meters (60 feet) in size. (www.nasa.gov)
About once a year, a larger asteroid the size of a car hits Earth’s atmosphere without reaching its surface, creating a spectacular fireball event while disintegrating – sometimes explosively. In September, one such fireball whistled across Spain, lighting up its skies and leaving a trail of smoke through many of its regions. The largest impact recorded in the recently published study was the Chelyabinsk meteor of about 20 meters in size, which hit the atmosphere with the equivalent impact of 440,000–500,000 tons of TNT and fell in Russia’s Urals region in February 2013. Scientists later found out the meteor that exploded above the Russian city – which injured over 1,000 people and shocked millions – was formed by a space collision. The world’s largest existing crater, which marks the biggest known cosmic intruder’s hit, is the Vredefort crater in South Africa. It has an estimated radius of 118 miles (190 kilometers) and is some two billion years old.
An ice hole in Lake Chabarkul, Chelyabinsk Region, where pieces of a meteorite could allegedly fall December 15, 2013 (RIA Novosti)
Other known asteroid impacts include the Popigai crater in Russia’s Siberia – which is said to be one of the largest diamond deposits in the world – and the 53-mile-wide (85 kilometer) Chesapeake Bay crater in the US state of Virginia. Both craters are said to date back some 35 million years.
An object the size of a football field hits Earth approximately every 5,000 years and causes significant damage, studies of Earth’s history indicate. The impact from an asteroid about half a mile in diameter could temporarily change global climate and kill millions of people. A space rock big enough to cause a larger global disaster impacts Earth every few million years on average.