27-megaton Asteroid Apophis to fly by Earth tonight

An artist's rendering of the asteroid Apophis.Not that you'll be able to see it as it goes by, but there's a massive asteroid flying past the Earth tonight, named 99942 Apophis.

99942 Apophis was discovered on June 19th, 2004, by astronomers Roy Tucker, David Tholen and Fabrizio Bernardigot, who were working at the Kitt Peak National Observatory. It originally caused quite a stir as initial plots of its orbit showed a significant chance of an impact with the Earth in 2029 and 2036, and it climbed to the top of NASA's list of threatening asteroids, ranking as a 4 on the Torino Impact Hazard Scale — the highest level reached on that scale by any object so far.

As a result of this, Tucker, Tholen and Bernadigot named it Apophis, after what the Ancient Greeks called the Egyptian god Apep, the Uncreator (and apparently also inspired by a villain in their favourite TV show, Stargate SG-1). Truly, if this 270 m long, 27-megaton hunk of rock slammed into our planet, it would likely not be an 'extinction-level event', but it would certainly cause tremendous devastation to the region of the planet it hit.

[ Related: Life may have existed on Mars, shows meteorite study ]

With further observations, and thus further refinements to the plot of its orbit, a 2029 impact was ruled out, but there was still a possibility that it would fly though a 'gravitational keyhole' — a tiny region of space where Earth's gravity could disturb the asteroid's orbit enough that an impact in 2036 would be far more likely. This kept the asteroid on the list of threatening asteroids (as a 1 on the Torino Scale) until 2006, when astronomers determined that the chances of it passing through that 'keyhole' were very small, and an impact was ruled out.

Currently, the chance of an impact with Apophis in 2036 stands at around 1 in 233,000, or in other words, there is a 99.99957% chance that the asteroid will miss us. That's as 'good' as it gets for Apophis for the next 90 years, so we can rest easy that particular hunk of space rock won't be any danger to us (although astronomers are still watching it, and some thought has been put into how to deal with it, should it prove to be a greater threat at some point in the future).

[ Related: NASA considers towing an asteroid into orbit around the Moon ]

If you want to see the asteroid as it makes its fly-by, check out the Slooh Space Camera website at midnight Greenwich Mean Time, which is 7pm Eastern Standard Time or 4pm Pacific Standard Time.