Asteroid 2015 RM83 passed by the Earth at a distance of 15 580 000 km (40.5 times the average distance between the Earth and the Moon, or 10.4% of the average distance between the Earth and the Sun), slightly before 6.20 am GMT on Saturday 12 September 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented a considerable threat. 2015 RM83 has an estimated equivalent diameter of 68-220 m (i.e. a spherical body with the same mass would be 68-220 m in diameter), and an object towards the upper end of this range would pass through the atmosphere and directly impact the ground with a force of about 300 megatons (about 17 650 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater over 3 km across, and resulting in global climatic problems that could last for years or even decades.
The calculated orbit of 2015 RM83. JPL Small Body Database.
2015 RM83 was discovered on 15 September 2015 (three days after its closest approach to the Earth) by the Defense Advanced Research Projects Agency's Space Surveillance Telescope. The designation 2015 RM83 implies that it was the 2087th asteroid (asteroid M83) discovered in the first half of September 2015 (period 2015 R).
2015 RM83 has an 814 day orbital period and an eccentric orbit tilted at an angle of 19.6° to the plane of the Solar System that takes it from 1.09 AU from the Sun (i.e. 109 % of the average distance at which the Earth orbits the Sun) to 3.32 AU from the Sun (i.e. 332% of the average distance at which the Earth orbits the Sun, over twice the distance at which the planet Mars orbits). 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).
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