http://news.bbc.co.uk/1/hi/sci/tech/2147879.stm
Wednesday, 24 July, 2002, 02:29 GMT 03:29 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 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.
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.
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