Impacts with space debris are truly spectacular events, as the size of the object belies the devastation they can wreak. Not only does an impact event obliterate the the area around it, rock can also be thrown high into the air and particularly large ones can change the very evolution of life.
History
After the birth of the solar system 4.6 billion years ago, its planets saw many planet-sized collisions. Mercury was hit by an object that formed the 1550km Caloris basin. Venus suffered a glancing blow that was enough to make it spin the other way. Mars saw an impact that created a crater the size of half the planet's surface.
Earth was not spared from this violent game of billiards; it itself collided with Mars-sized Theia. The energy from the collision remade the Earth's fragile crust and ejected enough material into orbit so as to form the Moon.
65 million years ago, a 10km long asteroid hit the Earth. Hitting what is now the Gulf of Mexico, the crater has been buried under the ocean. However, it created monstrous tsunamis and threw material into space. It caused the extinction of the dinosaurs, as well as many other species, when the resulting temperatures roasted the Earth's surface. Many burrowing mammals, as well as sea creatures, manage to escape the searing heat and, in the aftermath, enjoy the worldwide barbeque.
In 1908, a large meteorite exploded over a remote area of Siberia. It caused the flattening of forests; however, since it was not near any population centre, it caused very few or no casualties.
Sol's belt
There are several objects floating around in space that are left over from the solar system's creation. Most of them either in the Asteroid Belt (asteroids) between the orbits of Mars and Jupiter and the Oort Cloud (comets) well beyond Pluto. Occasionally, some of them do travel in a path that will cause them to hit Earth. As comets randomly release jets of gas, their paths are very difficult to predict.
Ripple in temperature
When a large object hits, the energy contained in its motion will release explosively. Not only will the impact obliterate the immediate vicinity, it will also throw large amounts of rock into the air. In the case of a major impact event, like the one that killed the dinosaurs, this rock can even be thrown out into space, where it hangs in a temprary orbit around the Earth. Eventually this material will fall back down. As they burn up in the atmosphere, they can raise the surface temperature to cooking temperatures, and any life caught unsheltered will be burnt.
Once the hail of rocks ends, there still persists the finer particles in Earth's atmosphere. Much like in the case of a volcanic eruption or nuclear explosion, this matter will block out the Sun's radiance and create an unseasonal winter.
As the dust settles, there still persists carbon dioxide from the burning of plant and animal matter, and due to the scale of the previous wildfires, there will be lots of it. This will push up global temperatures in a global warming event that causes, among other things, wilder weather. This will continue until plants and algae manage to remove the excess carbon dioxide in the air.
Air burst
Given the enormous friction against the air, the object's leading face may flatten out while streaking through the atmosphere. This further increases the friction it faces, and if the object itself is too weak, it can explode before it hits the ground.
Dancing with the stars
The largest collisions occur between two galaxies. Given that a galaxy is almost entirely empty space, it is almost certain that no two stars will collide. Instead, gravity will act to push and pull the two galaxies into streams of stars and dust. If they do not simply pass by each other, tidal forces will eventually stabilise and a new, larger galaxy will form.
The Milky Way is on track to collide with the Andromeda galaxy in 4 billion years. It is probable that the solar system will be slung away from the core, and Earth's observers will be able to see (from a safe distance) the entire event unfold over millions of years.
Taking out the rubbish
Given the risk that even a metre-sized object poses, there have been devised several ways to deal with the problem of an incoming asteroid or comet:
- Disintegrating the object with a nuclear explosive. Given the risk that several smaller objects poses, this would be pursued only as a last resort.
- Nudging it with a fast-moving spacecraft (being used as a kinetic impactor). This will cause the object to suddenly turn a different direction, and given enough lead time, the object will deviate considerably from its original path.
- Peeling it away with a gravity tractor. A gravity tractor is an object with mass that is used to move something else with mass. As long as the tractor can stop itself from falling into the object, the object will move with the tractor and its path will change. This will also need a few years of lead time with a ton-weighing spacecraft and kilometres-long object.
- In the case of a comet, a high-powered laser or large parabolic reflector (reflecting the Sun's light) can be used to vaporise some ice and force an outgassing.
Consequences of an asteroid or comet collision
- Immediate obliteration of impact zone
- If on an ocean, tsunamis
- Shower of space debris
- Searing hot temperatures, then impact winter, then global warming
Conclusions
- 2012-compatible? No
- Will the world end with a bang or whimper? Bang in impact zone, whimper elsewhere
- Armageddon or Ragnarok? Armageddon
Bibliography
- 24 Hours Later: Asteroid Impact (2009), television program, National Geographic Channel.
- Bad Universe: Asteroid Apocalypse (2010), television program, Discovery Channel.
- Dean, Tim (2008), 'Doomsday', Cosmos, no. 22.
- Earth: Making of a Planet (2010), television program, National Geographic Channel.
- Prehistoric Disasters: Birth of the Planet (2008), television program, Discovery Channel.
- The Known Universe: Collision Course (2009), television program, National Geographic Channel.
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