Target earth: Waiting for the tumbling stone
By Vishnu Vardhan Reddy

Worried about getting killed by an asteroid
strike?
Well you better be.
You are more likely to die in an asteroid
impact than in an airline crash.
The odds are that there is a one in five
thousand chance of this happening during your lifetime. Thats four times
higher than that of getting killed in a 9/11-type air crash!

On a daily basis, about a hundred tonnes of cosmic debris rain down our
atmosphere and burn up. But some biggies manage to reach our "pale blue
dot" and hit us hard enough to make an impact. A majority of this space
junk originates from the asteroid belt - solar systems only ghetto.
Deep inside the asteroid belt,lurk the "cosmic Bin Ladens." These rogue
asteroids or NEOs run amok during their yearly pilgrimage to the inner
solar system. Occasionally, they get romantic with the earth making
close encounters, even closer than our moon at times.
Astronomers estimate that there are about 2,000 near-earth asteroids with
a diameter bigger than 1 km that are capable of destroying all traces of
humanity.

The last such catastrophe, 65 million years ago, led to the extinction of
dinosaurs and the chances are that the next one can happen anytime without
an invitation.
"Such an impact could literally kill billions and us back to the Dark
Ages," says Dr Clark R. Chapman, an asteroid researcher at the Southwest
Research Institute, San Antonio, Texas. Making a statement before the
US Congress, Dr Chapman said: "The impact would loft so much debris
into the atmosphere that we would be deprived of sunlight for years. No
nation would be unscathed, no nation could assist others."
Astronomers call this the global killer. Nothing survives, not even
bacteria deep on the abyss.
The last time we had a close shave with a "space bullet" was in 1908
when a large chunk of Comet Encke annihilated vast tracks of the Tundra
at Tunguska, Siberia.
To know how much damage an impact can cause, astronomers have devised
the Torino Scale, something similar to the Richter scale used to measure
earthquakes.
The scale runs from one to 10. An asteroid with a value of zero or one
will virtually have no chance of hitting the earth; a 10 means a global
catastrophe.

So, how do we detect such a cosmic attack?
After the spectacular collision of Comet Shoemaker-Levy 9 with Jupiter
in 1994, the United States government formed a task force to deal with
similar collisions on earth.
The task force, called the Spaceguard Survey, aims at discovering the
2,000-odd NEOs that might hit us within the next 10 years. Currently, there
are about half a dozen professional surveys scanning the skies for
these space rocks. Apart from such surveys, a handful of dedicated
amateur astronomers also track these NEOs.
According to the Sky and Telescope magazine, the closest unexpected
visitor we have had in recorded history was on December 9, 1994, when an
asteroid passed less than 100,000 km from our cloud tops.

For that matter, the Nineties were graced with many such uninvited guests.
Of the 18 asteroid approaches recorded since 1937, 12 of them took
place during the Clinton presidency. In fact, the White House was
reportedly alerted on February 1, 1994, following an impact of an object
the size of a small house observed by US surveillance satellites over
the South Pacific.
For many years, astronomers have been debating ways to mitigate a
possible impact. Nuclear option has been a popular one. A nuclear explosion
can be used either to deflect the approaching asteroid or destroy it.
But recent studies have shown that this only-known option may not just
work. "Even if we know today that an asteroid might hit us in 2010, we
just dont have the technology to destroy or deflect it," says Prof.
Tom Gehrels of the Spacewatch. Prof. Gehrels was one of the first astronomers
to look for NEOs at the Spacewatch telescope on Kitt Peak,Arizona.
"Our only option is to search the whole sky and make sure that we don't
have any surprises in the near future," he says. But more countries need
to participate in this eliminating threat. "We must realise that even a
small event like the January 2001 Gujarat earthquake can kill
millions of people in India. Such highly-populated countries must
take the lead and support NEO surveys. At present, there are no
professional NEO-tracking observatories in India. But a small private
observatory - the first in the subcontinent - is expected to come online
during the first half of 2002. Astronomers feel that the governments
around the world have not taken the impact
threat seriously.
"As it took with the terrorism business, it takes a nasty event(September 11)
to bring people to their senses. One of these days well get another Tunguska,
and then people will think about putting some money into this,"
Brian Marsden who is a world authority on asteroids at the Minor Planet
Centre at Cambridge in Massachusetts, told the Independent. Till then,
our best chances are to wait and watch!

CHART
Chances of dying

Cause of Death Chances
Motor vehicle accident......................1 in 100
Homicide...............................................1 in 300
Fire..........................................................1 in 800
Firearms accident...............................1 in 2,500
Electrocution........................................1 in 5,000
Asteroid/comet Impact.......................1 in 20,000
Passenger aircraft crash...................1 in 20,000
Flood......................................................1 in 30,000
Tornado.................................................1 in 60,000
Venomous bite or sting.....................1 in 100,000
Diwali accident.....................................1 in 1 million
Food poisoning....................................1 in 3 million

(Source: C.R. Chapman & D. Morrison, 1994, Nature 367, 33-40.)