270m Asteroid Apophis to whiz past Earth today

Apophis, an asteroid with an estimated diameter of almost three football fields (270m), will make its close approach to Earth this week.

Slooh Space Camera will cover its near-approach on January 9, with several live shows on Slooh.com, free to the public, starting at 4 pm.

This is not the first time Apophis has whizzed past Earth.

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Apophis was discovered in June of 2004, observed briefly, and then lost until it was serendipitously recovered in December 2004.

It was immediately evident that the asteroid would make an unusually close approach to Earth in 2029, and initial calcluations placed the probability of an impact as high as about 3%.

Subsequent precovery optical observations showed that there was zero chance of impact in 2029.

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Radar observations at Arecibo in January 2005 revealed a bias in the precovery optical observations and showed and that the approach in 2029 would be significantly closer than previously thought -- only a few Earth radii -- but still too distant for an impact.

The 2029 approach will be close enough that terrestrial tides should alter the asteroid's spin state. In 2029, Apophis will still give Earth a very close shave as it will fly past at only 30,000 km.

In comparison, the Moon orbits the Earth at 385,000 km and communication satellites at 36,000 km. 

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There is still a tiny chance of an impact in 2036; the principal source of uncertainty is the acceleration due to the Yarkovsky effect, a non-gravitational effect that is a function of the asteroid's rotation period, pole direction, thermal properties, mass, shape, and dimensions. 

It's likely that radar astrometry in 2013 will shrink the uncertainties sufficiently to completely rule out an impact in the 2030s