© AFP/NASA
The asteroid, named 2004 BL86 by scientists, is estimated to be between 440-1,000 meters in diameter. 1.2 million kilometers is approximately three times the distance from the Earth to the Moon.
According to astronomers, there is no threat of the object colliding with our planet. The Goldstone Observatory, located in California's Mojave Desert, will observe the asteroid during its approach.
2004 BL86 was discovered on January 30, 2004, by the Lincoln Near-Earth Asteroid Research (LINEAR), responsible for the majority of asteroid discoveries from 1998 until 2005, when it was overtaken by the Catalina Sky Survey (CSS). As of mid-September 2011, LINEAR had detected some 231,082 new objects, of which at least 2,423 were near-Earth asteroids and 279 comets.
A space object is considered potentially dangerous if it crosses the Earth's orbit at a distance of less than 0.05 AU (approximately 19.5 distances from the Earth to the Moon), and if its diameter exceeds 100-150 meters. Objects of this size are large enough to cause unprecedented destruction, or generate a mammoth tsunami in case they fall into the ocean.
When a meteorite burst above the city of Chelyabinsk in February 2013, the impact was estimated to be equivalent to 440-500 kilotons of TNT. But the Chelyabinsk meteorite was relatively small, about 17 meters in diameter. It disintegrated with a blast at an altitude of over 20 kilometers.
If the Chelyabinsk object was 17m in diameter before impact, and the flyby object is from 440m to 1000m, then the incoming asteroid has a diameter that is anywhere between 25.9 and 58.8 times the size of the Chelyabinsk object. And if the composition and density are the same in the new asteroide and the Chelyabinsk object, then one could expect the volume and therefore the mass of the new object to have from 17400 to 203000 times the mass of the Chelyabinsk object, since 25^3=17400 and 58.8^3=203000
In terms of energy, this new object can hold a lot more than the Chelyabinsk object. Consider the impact of 17400 bombs each with a load of 440 kilotons of TNT hitting one place on Earth!