One day in the future, Earth's oceans will boil, destroying all life on the planet's surface and rendering it completely uninhabitable. This global warming is in some sense inevitable: the gradual warming experienced by the Sun occurs due to the gradual burnout of the fuel inside the star. However, there is a way to keep the Earth habitable if we develop a long-term solution: the migration of the entire Earth. Is it possible?
We need to figure out how hot it will get and how fast it will happen in order to move the Earth at a pace.
The way any star gets its energy is by fusing 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; at the very heart of the core, the temperature reaches 15,000,000 degrees. This speed is almost always constant. Over time, the percentage of hydrogen to helium changes, and the interior heats up a little more over billions of years. And when the warm-up occurs, we observe the following:
- luminosity increases - more energy is emitted over 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.
It all boils down to one inconvenient fact: the amount of energy that reaches the Earth slowly increases over time. For every 110 million years, the solar luminosity increases by about 1%. This means that the energy reaching the Earth also increases by 1% in about 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 nothing, significant problems will form on Earth. At some point, the surface temperature will rise to 100 degrees Celsius. That is, the oceans will evaporate.
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How can we mitigate this? There are several possible solutions:
“We can install a series of large reflectors at the L1 Lagrange point to prevent some of the light from reaching Earth.
“We can geo-engineer 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 methane and carbon dioxide molecules from the atmosphere.
“We can leave Earth and focus on terraforming outer worlds like Mars.
In theory, everything can work, but it will take tremendous effort and support.
However, the decision to migrate the Earth to a remote orbit may become final. And although we will have to constantly move the planet out of orbit to keep the temperature constant, it will take hundreds of millions of years. To compensate for the effect of a 1% increase in the Sun's luminosity, the Earth must be moved 0.5% away from the Sun; to compensate for the increase of 20% (that is, over 2 billion years), the Earth must be moved 9.5% further. The Earth will no longer be 149.6 million km from the Sun, but 164 million km.
The distance from the Earth to the Sun has not changed much over the past 4.5 billion years. But if the Sun warms up and we don't want the Earth to roast completely, we will have to seriously consider the possibility of planetary migration.
It takes a lot of energy! To move the Earth - all of its six septillion kilograms (6 x 1024) - away from the Sun would significantly alter our orbital parameters. If we move the planet 164,000,000 km away from the Sun, there are obvious differences:
- The Earth will revolve around the Sun 14.6% longer
- to maintain a stable orbit, our orbital speed must drop from 30 km / s to 28.5 km / s
- if the period of the Earth's rotation remains the same (24 hours), the year will not be 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 quite compensated; The sun will appear smaller from the Earth.
But in order to bring the Earth this far, we need to make very large energy changes: we will need to change the gravitational potential energy of the Sun-Earth system. Even taking into account all other factors, including the slowing of the Earth's motion around the Sun, we will have to change the Earth's orbital energy by 4.7 x 1035 joules, which is equivalent to 1.3 x 1020 terawatt hours: 1015 times the annual energy costs incurred humanity. One would think that in two billion years they will be different, and they are, but not much. We will need 500,000 times more energy than humanity generates around the world today, and it will all go into moving the Earth to safety.
The speed at which the planets revolve around the sun depends on their distance from the sun. The slow migration of the Earth at 9.5% of the distance will not disrupt the orbits of other planets.
Technology is not the hardest question. The tricky question is much more fundamental: how do we get all this energy? In reality, there is only one place that will satisfy our needs: the sun itself. Currently, the Earth receives about 1500 watts of energy per square meter from the Sun. To get enough power to migrate the Earth in the right amount of time, we will have to build an array (in space) that will collect 4.7 x 1035 joules of energy, evenly, over 2 billion years. This means that we need an array of 5 x 1015 square meters (and 100% efficiency), which is equivalent to the entire area of ten planets, like ours.
The concept of space solar energy has been in development for a long time, but no one has yet imagined an array of solar cells measuring 5 billion square kilometers.
Therefore, to transport the Earth to a safe orbit further away, a solar panel of 5 billion square kilometers, 100% efficient, will be needed, all the energy of which will be spent on pushing the Earth into another orbit within 2 billion years. Is it physically possible? Absolutely. With modern technology? Not at all. Is this practically possible? With what we know now, almost certainly not. Dragging an entire planet is difficult 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 actions. Until we figure out how to collect and use this amount of energy, we will need other strategies.
Ilya Khel