Astronauts warn of ‘city killer’ asteroids

Ball of fire: The Chelyabinsk asteroid, 20 metres wide, which exploded over Russia in 2013.

A group of scientists and former astronauts claim that humankind is dangerously unprepared for a calamitous strike from space. Should we be worried or does Earth have more pressing problems?

As gigantic pterosaurs soared above a lumbering T. rex chasing prey, a dot appeared in the sky. It was a six-mile-wide chunk of rock hurtling towards the ground at 50 times the speed of a bullet. Its impact had over a billion times the energy of an atomic bomb. The dust it threw up blotted out the sun, reducing the planet’s temperature so drastically that three-quarters of life on Earth was wiped out.

It has been 65 million years since this catastrophic comet struck and so far the cosmos has not hurled anything else so devastating at us. However, a group of experts and former astronauts called the B612 Foundation warn that it is only ‘blind luck’ that a ‘city killer’ asteroid has not yet struck our planet.

They have released data showing that 26 major comets and asteroids have collided with the Earth since 2000, which is three to ten times more often than earlier estimates. Only one of these was detected in advance. The group is raising funds to place an $250m telescope in orbit around the Earth to provide advance warning of approaching danger.

Every day more than 100 tonnes of dust and sand-sized particles bombard Earth’s atmosphere and around once a year a car-sized rock burns up before reaching the surface.

In 2004, astronomers discovered an asteroid they named Apophis. It is bigger than a football stadium and in 2029 it will come closer to Earth than orbiting satellites. While experts say it will not hit the planet, if a collision did occur it would release the energy of 100 nuclear bombs.

Experts are confident that new technologies would allow us to push any dangerous Earth-bound asteroids or comets off course. But B612 warns we can only do this if they are spotted early, and our current detection rate is woefully inadequate.

Yet other scientists say the chances of a large asteroid hitting a populated area are minute, and we have plenty of other things to worry about.

Back down to Earth?

B612 warns we are too complacent about this very real risk. In 1908 a comet exploded seven miles above Siberia, yet it still sent out a shockwave that flattened 80 million trees over 2,000 square kilometres. They ask us to imagine the same thing happening over a city. The investment required for protection is tiny when compared to the possible destruction of all life on Earth.

But others are not impressed by this disaster scenario. There are almost 20,000 nuclear weapons in existence, some of which could easily fall into the wrong hands. And global warming may devastate our planet by the end of the century if we do not change the way we live. Our resources would be better spent dealing with issues closer to home than dealing with a once-in-a-million-year event.

You Decide

  1. Should we be more worried about asteroids and comets hitting the Earth?
  2. ‘There is never any use in worrying.’ Do you agree?


  1. In pairs, list five calamities that worry you. Then for each one, think of three ways they might be prevented from happening.
  2. Using the links in ‘Become an Expert’, find five examples of comet and asteroid collisions. List when they happened and how much damage they caused.

Some People Say...

“The risk of destruction from outer space should remind us of how small we humans really are.”

What do you think?

Q & A

Are comets and asteroids really so dangerous?
The collisions with Earth recorded by B612 all unleashed between 1 and 600 kilotons of energy. For comparison, the atomic bomb which the US dropped on the Japanese city of Hiroshima at the end of World War ll was 16 kilotons. Yet most of the Earth’s surface is water and a large percentage of the land is uninhabited, so the odds of anything hitting a city are small.
What could we do if one is on course to hit Earth?
One option is to land a probe on the asteroid or comet, which was first achieved in 1995. Then it could ignite thrusters to change the object’s course. A relatively small amount of force can easily alter the direction of an object travelling through space.

Word Watch

These are relatively small, icy objects in orbit around the sun. When they come close to the sun the ice vaporises, forming a tail of dust and gas. There are 5,000 known comets, but this can only be a fraction of the total.
These are rock or metallic objects in orbit round the sun. They can be considered as minor planets.
B612 says its telescope would be placed in a wide orbit around the Earth. It could track 90% of objects larger than 100m across heading towards the Earth, and would provide decades of notice for anything that was a danger.
Burns up
Objects colliding with the Earth are travelling incredibly fast and when they enter the atmosphere, the friction creates huge amounts of kinetic energy and heat.
The comet is named after the ancient Egyptian demon of chaos and darkness.


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