Asteroid 2015 TB25 passed by the Earth at a distance of 3 658 000 km (9.51 times the average distance between the Earth and the Moon, or 2.45% of the average distance between the Earth and the Sun), slightly before 7.55 pm GMT on Sunday 11 October 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented only a minor threat. 2015 TB25 has an estimated equivalent diameter of 24-75 m (i.e. it is estimated that a spherical object with the same volume would be 24-75 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 about 3 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 18 megatons of TNT (roughly 1000 times the energy released by the Hiroshima bomb), then being directly underneath it might be fairly unpleasant.
The calculated orbit of 2015 TB25. JPL Small Body Database.
2015 TB25 was discovered on 10 October 2015 (the day before its closest approach to the Earth) by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2015 TB25 implies that it was the 627th asteroid (asteroid B25) discovered in the first half of October 2015 (period 2015 T).
2015 TB25 has an 531 day orbital period and an eccentric orbit tilted at an angle of 16.9° 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 1.55 AU from the Sun (i.e. 155% of the average distance at which the Earth orbits the Sun, slightly over 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). This means that close encounters between the asteroid and Earth are fairly common, with the most recent having occurred in October 1999 and the next predicted in March 2019.
See also...
Asteroid 2015 TC145 passed by the Earth at a distance of 16 710 000 km (43.4 times the average distance between the Earth and the Moon, or 11.2% of the average distance between the Earth and the Sun), slightly before 3.30 pm GMT on Saturday 10...
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...
Asteroid 2015 TC144 passed by the Earth at a distance of 3 255 000 km (8.47 times the average distance between the Earth and the Moon, or 2.18% of the average distance between the Earth and the Sun), at about 8.35 pm GMT on Thursday 8 October...
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