Asteroid 2015 FS passed by the Earth at a distance of 16 620 000 km (43.4 times the average distance between the Earth and the Moon, or 11.1% of the average distance between the Earth and the Sun), slightly after 11.40 pm GMT on Saturday 14 March 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented minor threat. 2015 FS has an estimated equivalent diameter of 31-99 m (i.e. it is estimated that a spherical object with the same volume would be 31-99 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 47 megatons of TNT (about 2800 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater about 1.2 km across.
The calculated orbit of 2015 FS. JPL Small Body Database.
2015 FS was discovered on 16 March 2015 (two days after its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2015 FS implies that it was the eighteenth asteroid (asteroid S) discovered in the second half of March 2015 (period 2015 F).
While 2015 FS occasionally comes near to the Earth, it does not actually cross our orbital path. It has an elliptical 611 day orbit, at an angle of 8.12° to the plane of the Solar System, that takes it from 1.09 AU from the Sun (1.09 times the average distance at which the Earth orbits the Sun), slightly outside our orbit, to 1.72 AU from the Sun, (1.72 times the distance at which the Earth orbits the Sun and more than the 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 also means that 2015 FS has fairly frequent close encounters with the Earth, with the last one calculated to have occurred in March 2010.
See also...
Asteroid 2015 EU passed by the Earth at a distance of 9 359 000 km (24.7 times the average distance between the Earth and the Moon, or 6.26% of the average distance between the Earth and the Sun), slightly after 2.40 am GMT on Thursday 12 March 2015. There was...
Asteroid 2015 EO6 passed by the Earth at a distance of 109 400 km (0.3 times the average distance between the Earth and the Moon, or 0.07% of the average distance between the Earth and the Sun), slightly after 0.30 am GMT on Thursday 12 March 2015...
Asteroid 2015 FD passed by the Earth at a distance of 4 212 000 km (11.0 times the average distance between the Earth and the Moon, or 2.82% of the average distance between the Earth and the Sun), slightly before 2.10 am GMT on Wednesday 11 March 2015...
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