Asteroid (385186) 1994 AW1 passed by the Earth at a distance of 9 725 000 km (25.3 times the average distance between the Earth and the Moon, or 6.50% of the average distance between the Earth and the Sun), at about 2.20 pm GMT on Wednesday 15 July 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented a considerable threat. (385186) 1994 AW1 has an estimated equivalent diameter of 570-1800 m (i.e. it is estimated that a spherical object with the same volume would be 570-1800 m in diameter), and an object of this size would pass through the atmosphere and directly impact the ground with a force of about 10 000-1 500 000 megatons (roughly 588 000 to 8 820 000 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater about 8-20 kilometers across, and resulting in global climatic problems that could last for decades or even centuries.
The calculated orbit of (385186) 1994 AW1. JPL Small Body Database.
(385186) 1994 AW1 was discovered on 11 January 1994 by astronomers Kenneth Lawrence and Eleanor Helin at the Palomar Observatory in California. The designation 1994 AW1 indicates that it was the 47th asteroid (asteroid W1) discovered in the first half of January 1994 (period 1994 A), while the numeral 385186 indicates that it was the 385 186th asteroid ever discovered; asteroids are not given this numeric designation immediately, to avoid false or double sightings being given numbers, but rather wait until the existence of the body has been confirmed by multiple observations.
(385186) 1994 AW1 has a 424 day year orbital period and an eccentric orbit tilted at an angle of 24.1° to the plane of the Solar System that takes it from 1.02 AU from the Sun (i.e. 102 % of the average distance at which the Earth orbits the Sun) to 1.18 AU from the Sun (i.e. 118% of the average distance at which the Earth orbits the Sun). It is therefore classed as an Amor Group Asteroid (an asteroid which comes close to the Earth, but which is always outside the Earth's orbit). This means that close encounters between the asteroid and Earth are fairly common, with the most recent having occurred in February this year next predicted in December. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, (385186) 1994 AW1 Icarus is also classified as a Potentially Hazardous Asteroid (it comes no closer to the Sun than 102% of the average distance at which the Earth orbit's the Sun, but the Earth's orbit is not completely circular). (385186) 1994 AW1 is also thought to be a potential binary asteroid, i.e. it is thought likely that this body has a small moon orbiting it.
See also...
Asteroid (1566) 1949 MA Icarus passed by the Earth at a distance of 8 054 000 km (20.9 times the average distance between the Earth and the Moon, or 5.38 % of the average distance between the Earth and the...
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...
Asteroid (90416) 2003 YK118 passed by the Earth at a distance of 11 700 000 km (30.4 times the average distance between the Earth and the Moon, or 7.82 % of the average distance between the Earth and the...
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