With asteroid 2012 TC4 about to pass between Earth and the moon, NASA is gearing up for its much-anticipated live test of its warning system.
Back in July, the approaching rock caused a brief flurry of speculation that an impact was imminent, before the European Space Agency issued a “calm down” statement.
With error bars still in the asteroid's orbit calculations, there's the chance it could get as close as 42,000 km – just above the roughly 36,000 km altitude of geosynchronous satellites – and that could make the pass visible to amateur astronomers.
NASA, which is coordinating the radar and optical observations to test its planetary defences, says amateurs will need to be on their toes: “the asteroid will be very difficult for backyard astronomers to see, as current estimates are that it will reach a visual magnitude of only about 17 at its brightest, and it will be moving very fast across the sky.”
The closest approach will happen at 0142 Eastern Daylight Time on October 12 (sorry, Australians, that's during daylight hours).
2012 TC4 is estimated to be around 15 metres across, is probably an elongated shape, and is moving at around 7.6 km/second relative to Earth.
Sky and Telescope notes its approach is close enough that the rock's orbit will get a small deviation from Earth's gravity. Its 12.2 minute spin rate might also change.
A previous pre-test of NASA's defence system, watching Asteroid Florence in early September revealed a rock dragging a surprising two moons along with it. ®