http://news.bbc.co.uk/2/hi/science/nature/2147879.stm
Tuesday, 23 July, 2002, 22:50 GMT 23:50 UK
Space rock 'on collision course'
An asteroid could devastate Earth
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 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 2km wide, large
enough to cause continent-wide devastation on Earth.
Although astronomers are saying the object definitely merits attention,
they expect more observations to show it is not on an Earth-intersecting
trajectory.
It was first seen on the night of 5 July, picked up by the Linear
Observatory's automated sky survey programme in New Mexico, in the
southern US.
Since then astronomers worldwide have been paying close attention to it,
amassing almost 200 observations in a few weeks.
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 its 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 28km 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
astronomers will soon have a very precise orbit for the object.
Dr Donald Yeomans, of Nasa's 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 kms," he said.
Dr Yeomans told BBC News Online that 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.
