Main page: Predictions of future human civilization
Impacts are on a long time scale the greatest risk for future terraformed or inhabited worlds. Impacts occur with small meteorites (alone or in a meteor shower), with large meteorites or even with larger objects, like a dwarf planet.
We know the effects of the Tunguska Meteorite, that crashed in an unpopulated area of Siberia. If that rock were to fall in a populated area, it would have wiped out entire cities. But, this is nothing, compared with the meteorite or comet that wiped out the dinosaurs. Even more, in other solar systems, there might be the risk of collision with something far larger, like a dwarf planet.
The Risks Edit
There are many risks, but they depend on the size of the meteorite and the size of the planet.
Asteroid Size Edit
Depending on the size of the object, the risk is of local scale, continental scale, global scale or of total extinction.
A Local Scale Risk is of a meteorite around 10 meters. The impact can affect local communities, but it will not affect the planet as a whole.
The Tunguska Event was caused by a meteorite about 60 meters wide. Based on its effects, we can say that a celestial body with a diameter of 100 meters is of Continental Scale Risk. If it falls in ocean, it can cause a large tsunami.
For Earth, an impact with an asteroid larger then 1 km will affect the whole planet and will present a Global Scale Risk. At the impact point, consequences will be felt harder and some areas of the globe will not be so severely affected if the diameter is less then 2 km. But, if the asteroid is larger (like the one who killed the dinosaurs or even bigger), there will be no place on the Earth where you would be safe.
There is also another category, the Total Extinction Risk. In case of an impact between Earth and an object the size of Ceres or even larger, the impact will be so powerful, that the oceans will boil or even Earth's crust will liquefy. In this case, maybe some bacteria will manage to survive like in a miracle, but humans will have no chance.
Planet Size Edit
Earth is a large rocky planet. However, there are many other, smaller worlds. On a terraformed Moon, Mars or on the moons of Jupiter, the effects will be felt on a much larger scale. There is a strong correlation between planetary surface and the mass of the meteorite. If the surface is larger, then the planet will have more atmosphere to absorb gasses resulting from the impact (carbon dioxide and monoxide, sulfur dioxide and others). Also, a larger surface means that the planet will radiate heat from the impact faster. Surface increases with the square of diameter, while volume increases by the cube of the diameter. Based on these equations, one might argue that on a Super-Earth, the impact that killed the dinosaurs would not cause a mass extinction. Not the same can be said about a small world. A smaller asteroid can cause a mass extinction event on a terraformed Moon.
Terraformed worlds are far more vulnerable then Earth. This is because they are not in their natural equilibrium, but in an artificially maintained one.
An Outer Planet has greenhouse gasses in its atmosphere. The impact will pierce a hole in the gas layer. As shock waves propagate through the atmosphere, they will break the layer of protective gasses. This means that on one hand we will have holes in the gas layer, where temperature will drop dramatically, even below -100 C, while on the other hand, heat from the explosion will burn the surface. If greenhouse gasses survive the explosion, they can keep temperature high for many years. By opposite, if the greenhouse gasses are destroyed by the explosion, temperatures will permanently drop and the atmosphere will freeze.
In case of an Inner Planet, the greatest risk is a runaway greenhouse effect. These planets are already exposed to excess solar radiation and many of them (like Venus) were extremely hot before terraforming.
In case of a low mass planet, its gas layers are kept together by a weak gravity. They continuously need extra amounts of gasses to be sent to them. The impact might just have the power to blast away a significant amount of their atmosphere.
Probably the best place to survive a massive impact would be a Super - Earth.
If the impact target is an asteroid, the effects can also be catastrophic. Because of their small size, asteroids can be destroyed by the impact force. If not, the impact can send shock waves (felt probably like quakes), destroying foundations of existing colonies and breaking the walls of domes.
On a planet with only a tenuous atmosphere (like a not-terraformed Mercury), the effect will be different. Heat from the impact will not propagate throughout the entire planet. Gasses from the impact site will vanish in the vacuum. However, debris from the impact site will fall all over the planet. Without an atmosphere, there will be nothing to stop them.
The risk of a collision varies depending on many factors:
Planet Gravity is an important factor. We have seen Jupiter impacted by comet Shoemaker Levy 9 and recently by asteroids. Moons orbiting a gas giant share the risk of an impact with their planet. So, the risk of an impact is higher on Jupiter's moons then on Earth.
Stellar Gravity is another factor. Neptune is smaller then Jupiter, but further away from the Sun. The risk of a collision on Neptune is probably higher then the risk on Jupiter, because Neptune has a larger gravitational influence, since solar gravity is far smaller.
Asteroid Population is the third factor that limits the risks. Earth orbits far from the main asteroid belt. There are solar systems like Epsilon Eridani where huge Kuiper belts or asteroid belts exist. There, the risk of an impact is probably thousands of times higher. Even more, if a planet has an orbit that goes through an asteroid belt, then the risk of a collision is even higher.
Protection Methods Edit
It is obvious that there are places in the Universe where settlers will have to watch for asteroid or comet impacts. Epsilon Eridani has a Kuiper belt with an estimated mass of 100 to 1000 times that of our Kuiper Belt. So, the risk of an impact is 100 to 1000 times higher. Other stars, like Fomalhaut, have even larger Kuiper belts and even planets orbiting within. Those planets might be facing daily impacts with 100 meter asteroids and yearly collisions with asteroids or comets larger then 1 km. Settlers will have no way to terraform these worlds and to live there without a way of protection.
The best way to protect these worlds will be a global defense fleet. Even in solar System, since Jupiter got hit at least two times in modern history, we will need to have a defense fleet protecting the moons of Jupiter and Neptune.
Defense Fleet Edit
The defense fleet must have telescopes in orbit, continuously monitoring the sky. The number and power of each telescope differs based on the risk. The telescopes need to detect possible impacting objects within reasonable time.
Then, the fleet must have ships, able to divert impacting objects. If the risk is too high, ships will be stationed on an orbital base. If the risk is lower, then the ships can be located on the ground and detached when there is a risk of an impact. In case of a high collision risk, there should be always orbiting ships, ready for action. Large ships are needed to divert larger bodies. In case of small meteorites, the only solution would be an army of small, automated space drones. Rocky objects will be pushed away more easily. All we will need would be a ship to land on them and use their engines to change direction with a few degrees. In case of a fragile, fluffy object (like a contact binary or a pile of debris), ships will need to cover at least part of the object and gently push it away. The use of explosives might be the last solution. An explosion can transform an object with a global scale risk into small objects with continental scale risk or local risk.
Collision With Another Planet Edit
In case of a total extinction risk, a collision with a planet or a dwarf planet, a different approach is needed. In that case, the impacting planet needs to be discovered early enough. We still don't know exactly how can a planet be moved away. There are a few theoretical ways to do this:
- Repeated bombardment with diverted asteroids on a selected angle.
- Repeated large-scale nuclear explosions on a specified point (probably millions, billion times more powerful then the Tsar Bomba.
- Construction of giant engines on the surface, that will fire when in correct position, slowly pushing the planet away.
This way, if we have enough time, in hundreds or thousands of years, we would be able to divert a planet from an imminent collision.
Protection Shield Edit
This theory currently exists only in science - fiction. A powerful plasma, magnetic or gravitational shield could protect a planet from impacts.
Economical And Psychological Costs Edit
Maintaining a defense fleet is expensive. Settlers will permanently have to maintain telescopes in orbit, to search for possible impacting objects. On the same time, they will have to maintain a fleet of manned and unmanned ships operational. The costs implied are not small, at least for a little, young colony. The size of the fleet is in a strict correlation with the estimated impact risk.
There will be many costs: with the employed personnel, with sky surveying, with ship maintenance, fuel production, new ship production, drone creation and not the least with research for new, better technologies.
The risk of an impact has a great psychological effect. If there is not political stability, we might see situations like the following ones:
- . Because of an economic crisis, there is a lack of founding for the defense fleet. For a limited time frame, the colony can depend on existing ships and their fuel. Then, as time passes, ships will need to be repaired or replaced, telescopes will get old and in the end the risk of an impact will rise until at some point the inevitable will happen.
- . In a society governed by anarchy, the protection fleet detects an incoming asteroid. They will ask for massive founding, for political influence and will use the power of terror to rule the planet.
- . Even in a perfect society and with the best technology, there is a risk that an undetected asteroid will hit the planet. Settlers will always know that the risk exists, at least for small objects.
If the protection fleet fails, there still are ways of protection from the ground. A long-range atomic missile can be detonated close to the incoming asteroid. The impact might be enough to make the asteroid explode, diverting the highest amount of debris away from the planet. Still, there will be significant risk of a collision with remaining debris. However, this might reduce a global scale risk to a continental scale risk.
Preparations For Imminent Impact Edit
If the protection fleet fails, there still are things that are possible to be done to save settlements. These might include:
- Move to the safest location
- Get enough food, oxygen and electricity
- Build a good shelter
- Evacuate planet.
Asteroids and comets have hit the Earth and other planets and will do for sure. If we don't want to end-up like the dinosaurs, we need to be prepared.