Asteroid 2015 TJ238 passed by the Earth at a distance of 17 910 000 km (46.6 times the average distance between the Earth and the Moon, or 12.0% of the average distance between the Earth and the Sun), slightly before 11.10 pm GMT on Friday 9 October 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented a considerable threat. 2015 TJ238 has an estimated equivalent diameter of 49-160 m (i.e. a spherical body with the same mass would be 49-160 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 80 megatons (about 4700 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater about 2.5 km across, and resulting in global climatic problems that could last for years or even decades.
The calculated orbit of 2009 TJ238. JPL Small Body Database.
2015 TJ2388 was discovered on 14 October 2015 (five days after 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 TJ238 implies that the asteroid was the 5959th object (object J2389) discovered in the first half of October 2015 (period 2015 T).
2015 TJ238 has a 635 day orbital period and an eccentric orbit tilted at an angle of 5.8° to the plane of the Solar System that takes it from 0.71 AU from the Sun (i.e. 71% of the average distance at which the Earth orbits the Sun and roughly the distance at which the planet Venus orbits) to 2.18 AU from the Sun (i.e. 218% of the average distance at which the Earth orbits the Sun, considerably outside orbit of the planet Mars). 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).
See also...
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