Asteroid (429094) 2009 SG2 passed by the Earth at a distance of 13 140 000 km (44.4 times the average distance between the Earth and the Moon, or 11.4 % of the average distance between the Earth and the Sun), slightly after 6.05 pm GMT on Saturday 28 March 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented a considerable threat. 429094) 2009 SG2 has an estimated equivalent diameter of 180-570 m (i.e. it is estimated that a spherical object with the same volume would be 180-570 m in diameter), and an object of this size would pass through the atmosphere and directly impact the ground with a force of about 200-1200 megatons (about 170 000-9 400 000 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater 5-15 kilometers across, and resulting in global climatic problems that could last for decades or even centuries.
The calculated orbit of (429094) 2009 SG2. JPL Small Body Database.
(429094) 2009 SG2 was first observed by Siding Spring Observatory in New South Wales on 3 September 2009. The designation 2009 SG2 indicates that it was the 57th asteroid (asteroid G2) discovered in the first half of September 2009 (peroid 2009 S). The longer designation, (429094), indicates that the asteroid was the 429 094th asteroid ever discovered. Asteroids are not given this longer designation immediately, to avoid duplicate or false sightings.
(429094) 2009 SG2 has a 434 day orbital period and an eccentric orbit tilted at an angle of 26.0° to the plane of the Solar System, which takes it from 0.93 AU from the Sun (i.e. 93% of the average distance at which the Earth orbits the Sun) to 1.31 AU from the Sun (i.e. 131% of the average distance at which the Earth orbits the Sun). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). This means that close encounters between the asteroid and Earth are extremely common, with the last having occurred in September 2009 this year and the next predicted in October this year. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, (90416) 2003 YK118 is also classified as a Potentially Hazardous Asteroid.
See also...
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