The fireball exploded over the southern part of the Atlantic Ocean on February 6 with a power that had not been seen since February 2013, when a similar “air explosion” injured more than 1,200 people in the Russian city of Chelyabinsk.
Last month, the fireball had an energy reserve of 13,000 tons (13 kilotons in TNT equivalent), but it exploded in a remote place, so no reports from eyewitnesses were received. (These events were added to the NASA report pages - Fireball and Car).
Meteors burn in the atmosphere of Earth every day, but most of them are too small and, therefore, fly completely under the radar. Fireballs, as in the case of the dramatic event of February 6, which was caused by an expert estimate of 16 to 23 feet (5-7 meters) wide, come to us about once every 2-3 years. So says Peter Brown, a professor at the University of Western Ontario in Canada and a member of the Western meteor physics group.
Brown added that on February 6, the fireball, while still powerful, probably would not have caused damage, even if it had broken into Earth above a populated area.
“The only way for us to get tangible damage is if the stones hit the ground and you would not be lucky to get hit by a shard,” he told Space.com. The object that exploded over Chelyabinsk three years ago was, according to experts, about 65 feet (20 m) wide, and an estimated explosive energy of 500 kilotons. The explosion destroyed hundreds of windows. Reported damage was almost all caused by fragments of flying glass.
The meteor terminology can be confusing, so here's a quick briefing. The asteroid is a space stone. A meteoride is a space stone that is about to hit the Earth. A meteor is a cosmic rock that burns in the Earth’s atmosphere, and a meteorite is a rock that has traveled all its way and appeared on the surface of the Earth. (And technically speaking, a fireball is a meteor that shines at least as brightly as the planet Venus in the sky).
Changing potential damage
Meteorids can come in several different forms. A small percentage of them (about 5%) consist of solid iron. Others look more like comets - a combination of ice and dust, and many more of rubble, rock pieces, dust and ice.
“If most of the meteorite is solid iron, then a part of the stone can survive the train through the atmosphere of the Earth and reach the Earth,” said Brown. But meteorides with a weak content often breaks up in the air.
Both the Chelyabinsk stone and the object on February 6 probably entered the atmosphere at a slight angle (about 20 degrees), thus undergoing a little heating and allowing themselves to go so deep into the atmosphere. Both rocks also exploded about 19 miles (30 kilometers) above the ground. A much more powerful explosion occurred over the Tunguska region in Siberia in 1908, hitting about 770 square miles (2000 square kilometers) of forest.
According to the best estimates, Brown said, the Tungus facility exploded with a force of 5 to 15 megatons, or about 10-30 times stronger than the energy of Chelyabinsk. Experts believe that the Tunguska meteorite was at least 100 feet (30 m) wide, and they suggest that it exploded at a distance of three times closer to the Earth than the object of Chelyabinsk. It is somewhere between 4.3-6.2 miles (7-10 kilometers) above the tops of Siberian trees.
NASA and other agencies have a robust asteroid tracking program that can detect objects approximately 16 to 32 feet (5-10 m) wide, depending on their proximity to Earth, lighting conditions, and other factors.
So far, researchers have discovered two asteroids of this size shortly before their impact with the Earth: TC3 in 2008, which passed over Sudan, and 2014 AA, which took place on the middle of the Atlantic Ocean on January 2, 2014.
Brown said the main observatories for this work are the Sky Survey at the University of Catalina in Arizona and the Panoramic Panorama Telescope and the Rapid Response System at Panstars University in Hawaii. Both Catalina and Panstars are constantly improving their capabilities, and will likely be able to detect more objects of this type in the coming years. Also in the next few months will be released online at the University of Hawaii the Last Asteroid Ground Alert Alert System (ATLAS). This asteroid detection system is optimized to search for asteroids affecting the Earth. She will scan the sky a couple of times a night in search of them. The goal is to carve out a few days before their invasion.
But such efforts relate, first of all, to potentially dangerous objects, and not to small bipods, like the one that caused the bang in the air on February 6.
“They are very difficult to detect before they crash into the atmosphere, and they bear almost no damage. And Chelyabinsk is just an exception to the rule, ”said Lindley Johnson, lead program manager for the newly created NASA Co-ordination Office for Planetary Defense.
“The object hit, and no one noticed,” Johnson added, referring to the February 6 event. “Except for the reports at NASA that made the event public.”