Sciency Thoughts: Asteroid 2015 FX284 passes the Earth.

Saturday, 11 April 2015

Asteroid 2015 FX284 passes the Earth.

Asteroid 2015 FX284 passed by the Earth at a distance of 18 250 000 km (47.5 times the average distance between the Earth and the Moon, or 12.2% of the average distance between the Earth and the Sun), slightly after 10.40 pm GMT on Tuesday 7 April 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented only a minor threat. 2015 FX284 has an estimated equivalent diameter of 26-82 m (i.e. it is estimated that a spherical object with the same volume would be 26-82 m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) in the atmosphere between 18 and 0.5 km above the ground, with only fragmentary material reaching the Earth's surface, although since an object at the upper end of this range would be expected to release an amount of energy equivalent to about 27 megatons of TNT (roughly 1600 times the energy released by the Hiroshima bomb), then being directly underneath it might be fairly unpleasant.

The calculated orbit of 2015 FX284. JPL Small Body Database.

2015 FX284 was discovered on 28 March 2015 (four days before its closest approach to the Earth) by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2015 FX284 implies that it was the 7123rd asteroid (asteroid X284) discovered in the second half of March 2015 (period 2015 F).

While 2015 FX284 occasionally comes near to the Earth, it does not actually cross our orbital path. It has an elliptical 507 day orbit, at an angle of 8.61° to the plane of the Solar System, that takes it from 1.03 AU from the Sun (1.03 times the average distance at which the Earth orbits the Sun), slightly outside our orbit, to 1.46 AU from the Sun, (1.46 times the distance at which the Earth orbits the Sun and slightyl less than the average distance at which the planet Mars orbits the Sun). As a Near Earth Object that remains strictly outside the orbit of the Earth it is classed as an Amor Family Asteroid. This means that close encounters between 2015 FX284 and the Earth are quite common, with the next predicted for July this year.