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" he added.

NASA has also revealed in radar imagery of object that it has several dark surface features, which suggest large concavities. It also has it's own moon - with the preliminary estimate for the size of it at approximately 2,000 feet - or 600 meters -wide.

Radar data of the asteroid show a small, moving white dot which is its moon, or satellite.

And for those who fear an asteroid strike on Earth, these instances are pretty rare. Alan Fitzsimmons of the Astrophysics Research Centre at Queen's University in Belfast explains.

"Luckily objects of this size or larger only hit us about once every four million years. Radar observations of 1998 QE2 will let us check it's not coming near us for a long time to come" he said.

But David Moore - editor of Astronomy Ireland magazine - is warning more research is needed to assess the threat to Earth from future asteroids. A rock of a similar size to this asteroid wiped out all dinosaurs and 75% of all species thousands of years ago.