[Ammi]

An asteroid more than 1.7 miles long will speed past Earth this week.

The big rock - named Asteroid 1998 QE2 - will make its closest approach later tonight.

But it will be keeping a safe distance of 3.6 million miles, or 15 times the distance between Earth and the moon.

Astronomers will not be able to see the asteroid without a powerful telescope.

But for those with the correct gear it should offer an interesting insight into what the rock might do in the future.

"We expect to obtain a series of high-resolution images that could reveal a wealth of surface features," said radar astronomer Lance Benner, based at Nasa's Jet Propulsion Laboratory in California.

"Whenever an asteroid approaches this closely, it provides an important scientific opportunity to study it in detail to understand its size, shape, rotation, surface features, and what they can tell us about its origin.

"We will also use new radar measurements of the asteroid's distance and velocity to improve our calculation of its orbit and compute its motion farther into the future than we could otherwise."

And for those who fear an asteroid strike on Earth, Alan Fitzsimmons, of the Astrophysics Research Centre at Queen's University Belfast, told Sky News they are pretty rare.

"Luckily objects of this size or larger only hit us about once every four million years," he said.

"Radar observations of 1998 QE2 will let us check it's not coming near us for a long time to come."