One day in the future the oceans of the Earth will boil, destroying all life on the surface of the planet, and make it completely unsuitable for life. This global warming is in some sense inevitable: the gradual warming experienced by the Sun is due to the gradual burning out of the fuel inside the luminary. However, there is a way to keep the Earth habitable if we develop a long-term solution: the migration of the whole Earth. Is this possible?
We need to find out how hot it will be and how quickly it will happen to move the Earth at a pace.
The way any star receives its energy is to fuse the lighter elements into heavier ones in the core. Our Sun, in particular, synthesizes helium from hydrogen in regions where the core temperature exceeds 4,000,000 degrees. The hotter, the faster the synthesis rate; In the heart of the core the temperature reaches 15,000,000 degrees. This speed is almost always constant. For a long time, the percentage ratio of hydrogen to helium varies, and the inner part heats up slightly more over billions of years. And when there is a warm-up, we observe the following:
- luminosity increases – more energy is radiated with time
- the luminary slightly increases in size, the radius increases by several percent for every billion years
- its temperature remains almost always constant, varying by less than 1% per billion years.
All this boils down to one uncomfortable fact: the amount of energy that reaches the Earth slowly grows with time. For every 110 million years, solar luminosity increases by about 1%. This means that the energy reaching the Earth also increases by 1% around the same time. When the Earth was four billion years younger, our planet received 70% of the energy it receives today. And in another one or two billion years, if we do not do anything, on Earth there are significant problems. At some point, the temperature on the surface will rise to 100 degrees Celsius. That is, the oceans evaporate.
How do we mitigate this? There are several possible solutions:
- We can establish a series of large reflectors at the Lagrangian point L1 in order not to allow part of the world to reach the Earth.
- We can change by geoengineering the atmosphere/albedo of our planet so that it reflects more light and absorbs less.
- We can save the planet from the greenhouse effect by removing molecules of methane and carbon dioxide from the atmosphere.
- We can leave the Earth and focus on terraforming external worlds like Mars.
In theory, everything can work, but it will require tremendous effort and support.
However, the decision to migrate the Earth to a remote orbit may become final. And although we will constantly have to take the planet out of orbit in order to keep the temperature constant, it will take hundreds of millions of years. To compensate for the effect of a 1% increase in the luminosity of the Sun, it is necessary to take the Earth 0.5% of the distance from the Sun; To compensate for the increase of 20% (that is, over 2 billion years), it is necessary to take the Earth 9.5% further. The earth will no longer be 149,600,000 km from the Sun, but at 164,000,000 km.
The distance from the Earth to the Sun has not changed much over the past 4.5 billion years. But if the Sun is warming up and we do not want the Earth to be fried definitively, we will seriously consider the possibility of migration of the planet.
This requires a lot of energy! To shift the Earth – all its six septillion kilograms (6 x 10 24 ) – away from the Sun – means significantly to change our orbital parameters. If we take the planet away from the Sun by 164,000,000 km, there will be obvious differences:
- The Earth will make a revolution around the Sun by 14.6% longer
- to maintain a stable orbit, our orbital speed should drop from 30 km / s to 28.5 km / s
- if the rotation period of the Earth remains the same (24 hours), in the year will be not 365, but 418 days
- The sun will be much smaller in the sky – by 10% – and the tides caused by the Sun will be weaker by a few centimeters
If the Sun swells in size and the Earth moves away from it, these two effects are not completely compensated; The sun will seem smaller from the Earth
But in order to bring the Earth so far, we need to make very large energy changes: we need to change the gravitational potential energy of the Sun-Earth system. Even taking into account all other factors, including the slowing down of the Earth’s motion around the Sun, we will have to change the orbital energy of the Earth by 4.7 x 10 35 joules, which is equivalent to 1.3 x 10 20 Terawatt-hours: in 10 15 times more than the annual energy costs that are borne by mankind. One might think that in two billion years they will be different, that is, but not much. We will need 500,000 times more energy than mankind generates today in the whole world, and all this will go to the movement of the Earth to a safe place.
The speed at which planets revolve around the Sun depends on their distance to the Sun. Slow migration of the Earth by 9.5% of the distance will not disturb the orbits of other planets.
Technology is not the most difficult question. A complex question is much more fundamental: how do we get all this energy? In reality, there is only one place that will satisfy our needs: this is the Sun itself. At present, the Earth receives about 1500 watts of energy per square meter from the Sun. To get enough power to migrate the Earth in the required time interval, we will have to build an array (in space) that will collect 4.7 x 10 35 joules of energy, evenly, over 2 billion years. This means that we need an array of 5 x 10 15 square meters (and 100% efficiency), which is equivalent to the entire area of ten planets like ours.
The concept of cosmic solar energy has been developed for a long time, but no one has imagined an array of solar cells measuring 5 billion square kilometers.
Therefore, to transport the Earth to a safe orbit further away, we need a solar panel of 5 billion square kilometers of 100 percent efficiency, all of whose energy will go to pushing the Earth into another orbit for 2 billion years. Is it possible physically? Absolutely. With modern technology? Not at all. Is this possible in practice? With what we know now, almost certainly not. It is difficult to drag an entire planet for two reasons: first, because of the gravitational pull of the Sun and because of the massiveness of the Earth. But we have just such a Sun and such an Earth, and the Sun will heat up regardless of our deeds. Until we figure out how to collect and use this amount of energy, we will need other strategies.