Space rock 'on collision course'

It has been called the most threatening object in space

By Dr David Whitehouse BBC News Online science editor

An asteroid discovered just weeks ago has become the most threatening object yet detected in space.

A preliminary orbit suggests that 2002 NT7 is on an impact course with Earth and could strike the planet on 1 February, 2019 - although the uncertainties are large.

Astronomers have given the object a rating on the so-called Palermo technical scale of threat of 0.06, making NT7 the first object to be given a positive value.

From its brightness, astronomers estimate it is about two kilometres wide, large enough to cause continent-wide devastation on Earth.

Many observations

Although astronomers say the object definitely merits attention, they expect more observations to show it is not on an Earth-intersecting trajectory.

This asteroid has now become the most threatening object in the short history of asteroid detection

Dr Benny Peiser

It was first seen on the night of 5 July, picked up by the Linear Observatory's automated sky survey programme in New Mexico, US.

Since then astronomers worldwide have been paying close attention to it, amassing almost 200 observations in a few weeks.

Could it be deflected?

Dr Benny Peiser, of Liverpool John Moores University in the UK, told BBC News Online that "this asteroid has now become the most threatening object in the short history of asteroid detection".

NT7 circles the Sun every 837 days and travels in a tilted orbit from about the distance of Mars to just within the Earth's orbit.

Potential devastation

Detailed calculations of NT7's orbit suggest many occasions when its projected path through space intersects the Earth's orbit.

Researchers estimate that on 1 February, 2019, its impact velocity on the Earth would be 28 km a second - enough to wipe out a continent and cause global climate changes.

However, Dr Peiser was keen to point out that future observations could change the situation.

He said: "This unique event should not diminish the fact that additional observations in coming weeks will almost certainly - we hope - eliminate the current threat."

Easily observable

According to astronomers, NT7 will be easily observable for the next 18 months or so, meaning there is no risk of losing the object.

Observations made over that period - and the fact that NT7 is bright enough that it is bound to show up in old photographs - mean that scientists will soon have a very precise orbit for the object.

Dr Donald Yeomans, of the US space agency's (Nasa) Jet Propulsion Laboratory in California, told BBC News Online: "The orbit of this object is rather highly inclined to the Earth's orbit so it has been missed because until recently observers were not looking for such objects in that region of space."

Regarding the possibility of an impact, Dr Yeomans said the uncertainties were large.

"The error in our knowledge of where NT7 will be on 1 February, 2019, is large, several tens of millions of kilometres," he said.

Dr Yeomans said the world would have to get used to finding more objects like NT7 that, on discovery, look threatening, but then become harmless.

"This is because the problem of Near-Earth Objects is now being properly addressed," he said.