EARTH IS SET for an astronomical near-miss from a passing asteroid this November – when a rock measuring almost a quarter of a mile in diameter will come closer to the Earth than the moon is.

The asteroid, officially named 2005 YU 55, will approach the earth at 0.85 lunar distances – around 200,000 miles – making it the closest object to have passed by Earth since 1976.

Although the rock has been designated a “potentially hazardous asteroid” by the Minor Planet Centre in Massachusetts, David Moore of Astronomy Ireland says the asteroid should be seen as a mere reminder of how Earth is in a “shooting gallery” for asteroids.

Though the distance of 200,000 miles might seem close, Moore points out that Earth’s diameter is only about 8,000 miles – giving an illustration of how far away the asteroid would remain.

“This asteroid is nothing to worry about, but there are other asteroids that are more threatening,” Moore said. “In 2029, Apophis will come within 20,000 miles, which is only a couple of earth diameters away.

“That’s even closer to Earth than the geostationary satellites that give us satellite TV, telephones and the likes.”

But because Apophis still has “billions of miles to travel” before it reaches proximity with earth, trying to pin down exactly where it will travel is difficult – particularly because the gravitational fields of other objects could swerve its path.

“There’s one particular sweet spot that it might pass through – and if it passes through that spot in 2029, it’s going to come back and hit us in 2036,” Moore explains.

And with Apophis being “about the size of Croke Park”, the impact would result in what could only be described as “major devastation”.

“The country that it hits will be ruined,” Moore bluntly offers. “The earthquakes that would follow would devastate any larger area, while the volume of dust raised by it would block out the sun for months.”

Thankfully the chances of Apophis passing the gravitational ‘sweet spot’ are around 1-in-100,000 – though Moore said that other interstellar comets could pose a more short-term threat too:

There are comets coming from way beyond the planets, from halfway to the nearest star, and we get no warning of those because of their great distance – we might only get a few months’ warning that they’re coming.

Some of these comets, Moore suggests, could be over a mile wide: an object large enough to kill about a quarter of the Earth’s population on impact, while those who survive “will probably wish they hadn’t”.

So while 2005 YU 55 is worth noting from a statistical point of view – in that it’s coming 500 times closer to the Earth than we are from the Sun - there are other more pressing concerns that lie in the years ahead.

And is there anything we can do in the meantime? Moore’s advice is salient as ever: “Keep watching the skies.”