Asteroids may have brought life-forming chemicals to the early Earth

They say that there is a one in 909,000 chance of asteroid 2003 QQ47 impacting our planet.

The chances of a catastrophe are likely to become even slimmer once more measurements of the asteroid's orbit have been made.

The current odds are based on 51 observations made since the giant rock was spotted by a US programme in New Mexico on 24 August.

2003 QQ47 has been ranked one on the Torino scale.

Zero on the scale is for objects where the chances of collision with Earth are virtually nil.

The top of the scale, 10, is reserved for certain collisions capable of causing a global climatic catastrophe.

2003 QQ47 is likely to drop down to zero on the Torino scale once more observations have been made.

Torino scale one objects are deemed worthy of careful monitoring.

The BBC's science correspondent Christine McGourty says that 2003 QQ47 merits observation due to its sheer size and velocity.

Fast-moving rock

The rock is said to measure approximately 1.2 kilometres (less than a mile) across - only one tenth of the size of the impactor thought to have wiped out the dinosaurs 65 million years ago.

It is travelling at a speed of about 30 km (approximately 20 miles) per second.

"In theory such an asteroid could cause devastation across an entire continent," Christine McGourty says.

The odds are very, very low... We have to keep some kind of perspective Sara Russell Natural History Museum

The asteroid is estimated to weigh 2.6 billion tonnes and would deliver the same energy as detonating 350 billion tonnes of TNT in the extremely unlikely event of it hitting Earth.

Dr Sara Russell, a meteorite researcher at London's Natural History Museum, told the BBC that she was not worried that 2003 QQ47 would be a danger.

"The odds are very, very low... We have to keep some kind of perspective," she said.