An artist's impression of an asteroid near the Earth. However, it will sail safely past at 4.6 lunar distances - about 1.8 million kilometres away. Scientists in the US have nicknamed the asteroid "The Rock" either in honour of action hero Dwayne Johnson or after the Rock of Gibraltar, depending on who you ask. Professor Tim Bedding, head of the school of physics at the University of Sydney, said: "If an asteroid this size hit Earth, it would be catastrophic. "If it hit an ocean, the tsunamis it would raise could wipe out coastal cities. If it hit land, it would be a different scenario but in both cases completely catastrophic."

People look at what scientists believe to be a chunk of the Chelyabinsk meteor, which exploded over Russia in 2013. Credit:AP Dr Tucker said: "In the grand scheme of things, yes it is close because space is big. If it hit, its impact would be on the order of 10,000 megatons of TNT." But the asteroid poses no threat to Earth. "The Rock", Dwayne Johnson. Dr Tucker said: "Our real worry is not something a kilometre long, that's easy to spot. We know where most of these are.

"Something much smaller, such as the one that exploded over Chelyabinsk in Russia three years ago is more of a threat. That could come out of nowhere. That was about 10 or 20 metres - and that can cause enough damage if it hits the right place. Those, we know only a very few per cent." The Rock of Gibraltar. Credit:Getty Images Dr Tucker said: "We are still undoing all the damage that Armageddon did. Bruce Willis destroyed 10 years of science communication efforts in one poorly made movie. "We're just not going to have a rogue asteroid that comes out of nowhere to destroy the Earth." Professor Bedding said: "The most important thing is to detect big asteroids early so you can measure accurately their orbit. And if there is a chance they might intersect with Earth you have - hopefully - years or even decades to do something about it."

Dr Tucker said: "Yes, we are going to have something that hits the Earth eventually. That is inevitable. But the planet has been around for 4.5 billion years and we only know of a few rare instances of very large impacts, so they are not common." Frequency of small asteroid impacts in the Earth's atmosphere, 1994-2013. NASA said 556 objects were destroyed in the Earth's atmosphere in that 20-year period. Credit:NASA/JPL NASA tracks asteroids as part of its Near Earth Object program. The object that poses the greatest impact threat to Earth is asteroid 29075, which is 1.3 kilometres long. NASA estimates it will come close to Earth on March 16, 2880. The probability of impact is one chance in 8300. This means there is a 99.988 per cent chance the asteroid will miss the Earth. Next month in Japan, NASA is holding a "Planetary Defence Exercise", simulating how agencies would react to the approach of an asteroid between 100 and 250 metres wide. The simulation will assume a possible impact 10 years later, in 2027.

Dr Tucker said: "Every 100 million years or so you could expect one of these kilometre-sized asteroids to hit and release 10,000 megatons worth of energy - that's about half a million atom bombs the size of which destroyed Hiroshima in 1945." The asteroid that triggered the mass dinosaur extinction events 66 million years ago was 10 times the size of "The Rock". The robotic telescope service Slooh will be screening a live fly-by of the asteroid, which will be closest to the Earth at 9am on Thursday. Professor Bedding said: "There are few clever ideas about how to move asteroids if any become a serious threat to Earth. You could paint one side of an asteroid black so it heats up in a particular way and the solar heat causes it to move out of harm's way. "Breaking it up into pieces like in Armageddon won't help as the pieces all come and hit the Earth anyway."

Other proposed methods do involve using nuclear weapons to deflect an asteroid's trajectory, or using lasers over time to push the object off a collision course, or pushing the object using ion thrusters or other engines.