By Dr David Whitehouse
BBC News Online science editor
Astronomers have revealed how they came within minutes of alerting the
world to a potential asteroid strike last month.
No one was quite sure at the beginning where 2004 AS1 was
Some scientists believed on 13 January that a 30m object, later
designated 2004 AS1, had a one-in-four chance of hitting the planet within
It could have caused local devastation and the researchers contemplated
a call to President Bush before new data finally showed there was no
The procedures for raising the alarm in such circumstances are now
At the time, the president's team would have been putting the final
touches to a speech he was due to make the following day at the
headquarters of Nasa, the US space agency.
In it he planned to reset the course of manned spaceflight, sending it
back to the Moon and on to Mars, but he could have had something very
different to say.
He could have begun by warning the world it was about to be hit by a space
Bush would not have known where it would impact - only somewhere in the
Northern Hemisphere. Experts would have been bouncing radar signals off
the huge rock as he spoke in order to get more information about its
At about 30m wide, the asteroid was cosmic small fry, not the type of
thing to wipe out the dinosaurs or threaten our species, but still big
enough to cause considerable damage after exploding in the atmosphere.
Potentially, the loss of life could have been much worse than 11
In the end, Bush made no such announcement, but astronomers have
admitted they were on the verge of making the call.
Shall we call the President?
In a paper presented at this week's Planetary Protection conference in
California, veteran asteroid researcher Clark Chapman calls it a
He explains how word reached the astronomical community of an asteroid
that had just been discovered by the twin optical telescopes of the Linear
automated sky survey in New Mexico.
The Minor Planet Center in Massachusetts - the clearing house for such
observations - posted details on the internet requesting attention from
astronomers, one of whom noticed something peculiar.
Bush's Nasa speech might have taken a different turn
The object was expected to grow 40-times brighter in the next day - a
possible sign that it was getting closer, very rapidly.
But with data from just four observations available, the uncertainties
were large. There were many possible orbits the object could be on, and
the majority of them did not threaten the Earth.
What to do? Tell the world about the uncertain situation or wait for
For some astronomers, events reached a crescendo when Steven Chesley, a
researcher at Nasa's Jet Propulsion Laboratory, looked at the available
data and sent an e-mail saying the asteroid had a 25% chance of striking
the Earth's Northern Hemisphere in a few days.
It was then that astronomers Clark Chapman and David Morrison, chair of
the International Astronomical Union's Working Group on Near Earth
Objects, contemplated picking up the telephone to the White House.
'Jumped the gun'
But many astronomers did not agree that waking up President Bush would
have been wise.
"They completely misread the situation," said Benny Peiser of
Liverpool John Moores University in the UK. "There was plenty of time
to get other observers on the job."
Others also believe the call would have been premature.
"That would have jumped the gun before we knew much about the
object," said Brian Marsden, of the Minor Planet Center.
"I find it incredible that such action was contemplated on the basis
of just four observations. That is just not enough to yield a sensible
Chapman was close to raising alarm
"There was no need to panic as it was obvious that the situation
would have been resolved, one way or another, in another hour or
two," he told BBC News Online.
Fortunately for all concerned, shortly after the ominous Chesley
e-mail, an amateur astronomer managed to dodge the clouds and take a
picture of a blank patch of sky.
This was significant because if 2004 AS1 really was going to hit the
Earth, it would have been in the amateur's sights. The fact that it was
absent meant the rock would not strike us.
But Chapman says in his presentation that if it had been cloudy, and no
more observations could have been obtained at the time, he would have
raised the alarm.
Marsden disagrees. "If it had been cloudy and the call had been
made to the President it would have been disastrous."
Many astronomers recognise that they a false alarm could have brought
ridicule on their profession. They are calling for more planning and less
panic if it should happen for real next time.
And 2004 AS1? It turned out to be bigger than anyone had thought -
about 500m wide. It eventually passed the Earth at a distance of about 12
million km - 32 times the Earth-Moon distance, posing no danger to us