What is 2012 TC4's background?
Discovery
2012 TC4 was discovered Oct 4, 2012 by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) located at Haleakala Observatory, Hawaii. It was observed for seven days (4-11 Oct 2012) when it approached to within ~15.5 Earth radii.
The seven days of observations provided a sufficient level of astrometry to produce a robust orbit solution that showed the asteroid would make a close approach to the Earth in Oct 2017. The solution was robust enough to determine that there is no chance of the asteroid striking the Earth during this event, but left a large uncertainty in the close approach distance.
Subsequent History
Since it was discovered, the conditions for observing 2012 TC4 were very poor. Because of its current 1.67 yr orbit, it makes three orbits for every five Earth orbits. Given this cadence, the asteroid was on the opposite side of the Sun over much of the last five years. In 2015, when it was on the same side of the Sun, it was near aphelion, and thus too far from the Earth to be detected.
2012 TC4 was recovered on Jul 27, 2017 (with confirmation observations on Jul 31 and Aug 5). At magnitude 27, this is the faintest near Earth asteroid ever recovered. Astrometry from these observations improved the orbital solution, showing that the asteroid will pass about 0.000335 AU (~50,000 km) from the Earth at 5:41 UT on Oct 12, 2017. (More accurate details can be found on the orbit page.)
Future Orbits
The 2017 approach to the Earth will alter the asteroid's orbit, increasing its orbital period to slightly over 2 years. Analyses are underway to investigate its future behavior. Additional astrometry between now and the close approach will help to reduce the uncertainty in the approach distance, which will in turn improve the predictability for future apparitions.
