Asteroid 2004 XK14 passed by the Earth at a distance of 14 720 000 km (38.3 times the average distance between the Earth and the Moon, or 0.84% of the average distance between the Earth and the Sun), slightly after 7.40 pm GMT on Friday 28 November 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented a genuine threat. 2004 XK14 has an estimated equivalent diameter of 62-200 m (i.e. a spherical body with the same mass would be 62-200 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 261 megatons (about 15 350 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater about 3 km across, and resulting in global climatic problems that could last for decades or even centuries.
The calculated orbit of 2004 XK14. JPL Small Body Database.
2004 XK14 was discovered on 10 December 2004 by the Massachusetts Institute of Technology's Lincoln Near Earth Asteroid Research Laboratory in Socorro, New Mexico.
The designation 2004 XK14 implies that it was the 360th asteroid
(asteroid X14) discovered in the first half of December 2004 (period 2004 X).
2004 XK14 has a 237 day orbital period, with an elliptical orbit tilted at an angle of 3.10° to the plain of the Solar System which takes in to 0.42 AU from the Sun (42% of the distance at which the Earth orbits the Sun, slightly outside the average distance at which Mercury orbits the Sun, but closer to the Sun than Mercury at the furthest part of its orbit) and out to 1.07 AU (7% further away from the Sun than the Earth). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in March 2014 and the next predicted in August 2017. Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2004 XK14 spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid.
2004 XK14 is also thought to have occasional encounters with the planets
Mercury and Venus,
with the most recent encounter with Mercury thought to have happened in January 2012 and the next predicted for June 2021, and the last close
encounter with Venus thought to have happened in January this year and the next
predicted for November 2023. Asteroid
orbits that have close encounters with multiple planets are considered
to be quite unstable, as any perturbations can quickly become magnified,
throwing the asteroid onto a new orbital path.
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