One of the most steady, unchanging properties in our cosmic history is Earth’s orbit. For the past 4.5 billion years, even as a whole slew of fantastic events have occurred — giant impacts, the formation of moons, the continued slowing of our planet’s rotation, and even the emergence of life — Earth’s orbital path around the sun has remained practically unchanged. Even with the gravitational influence of all the other objects in our solar system and galaxy taken into account, there’s greater than a 99% likelihood that Earth’s orbit will continue to remain unchanged in any appreciable fashion.
In the long-term, this will lead to an unmitigated catastrophe for the entire planet. Even the worst-case scenario for our present battle against global warming, where unchecked rises in the concentrations of greenhouse gases causes a severe temperature rise and the melting of all the polar ice on Earth, pales in comparison to what the sun will eventually cause. If nothing significant changes, then in 1-to-2 billion years, the sun’s ever-increasing energy output will boil the entirety of Earth’s oceans, leading to the likely death of all life on Earth.
Is there any way to save Earth from this fate? Migrating our planet to a different location in the solar system, by changing Earth’s orbit, might be our last best hope. Here’s how a giant thruster at the South Pole could wind up saving the entire planet.
The environmental problem
If you think the global warming we’re presently experiencing is bad, just you wait until you learn what the sun has in store for us. Today, the major cause of Earth’s changing climate and increasing temperatures has nothing to do with the sun, but rather is driven by the atmospheric changes brought on by human activity since the dawn of the industrial revolution. By adding greenhouse gases to the atmosphere, mostly carbon dioxide and methane, but also affected by feedback-driven changes in the long-term water vapor concentrations, Earth’s energy budget has changed dramatically over the past ~200 years.
Just as putting additional layers of clothing on yourself when you’re cold, or piling the blankets atop you, helps you better retain your own internal heat before it’s radiated away, putting additional concentrations of greenhouse gases in our atmosphere helps the Earth retain heat as well. As was established more than 50 years ago by new Nobel Laureate Syukuro Manabe, doubling the concentration of CO2 would increase Earth’s temperature by 2 °C (3.6 °F) or more, with worst-case scenario changes leading to a complete melting of all the polar ice on Earth within perhaps a few thousand years. An ice-free Earth wouldn’t be unprecedented, but it would be extraordinarily bad for humans on Earth.
But it won’t be nearly as bad as what the sun will gradually do as time goes on. Inside the sun, nuclear fusion occurs inside the core only: where temperatures exceed 4,000,000 K. In the very center of the core, temperatures can reach as high as 15,000,000 K, with the rate of fusion reactions rapidly increasing with temperature. Here’s the problem, however. As time goes on the following occurs:
- the sun’s core converts appreciable amounts of hydrogen into helium
- the helium gathers in the inner core, but cannot fuse any further at present
- which leads to gravitational contraction and causes the interior of the sun to heat up
- which raises the inner core’s temperature and expands the “4,000,000 K and above” region to a greater internal extent,
- which leads to a gradual increase in the sun’s rate of fusion,
- which increases the sun’s overall energy output.
With greater amounts of energy reaching the Earth, there are only so many defenses and feedback mechanisms our planet has at its disposal. Once the global average temperatures rise above 100 °C (212 °F), a scenario that will likely take place between 1-and-2 billion years from now, our oceans will boil away. For all intents and purposes, this will mark the inevitable end of the line for complex life on Earth.
The energy problem
If we can’t prevent the sun from heating up, then perhaps migrating the Earth farther away from the sun could provide the ultimate solution. There’s a straightforward, simple relationship between brightness and distance: every time you double your distance from a luminous source, the brightness that you experience is quartered. This is excellent news, as if the sun’s energy output were to increase by 10%, you’d only have to migrate Earth an additional 4.9% of the distance away from the sun to keep the energy we receive constant.
Given that the sun’s energy output is currently increasing by ~10% with every billion years that passes, this is a long-term problem that we’re going to have to address someday if we want our planet to remain habitable. Changing our orbit by a few percent might not seem like a particularly major task; after all, Earth orbits the sun in an ellipse, with our closest approach to the sun taking us within 147.1 million km (91.4 million miles) and our farthest distance clocking in at 152.1 million km (94.5 million miles). The difference in radiation received is about 6.5%, meaning that if we could simply replace Earth’s current orbit with one that constantly kept us at our aphelion distance, we’d keep Earth’s energy budget from increasing for more than 300 million years.
But that’s more than a major task; it’s an astronomically difficult one. The reason Earth orbits the sun in its present location is because that’s where our kinetic energy, or the energy of Earth’s motion around the sun, balances the gravitational potential energy at our current distance from the sun. If we managed to steal energy away from the Earth, we’d lose energy, causing us to sink towards a more Venus-like orbit but with greater speeds. Similarly, if we wanted to rise to a more Mars-like orbit, we’d need to pump energy into the Earth, leaving us with a net speed that’s currently smaller than our speed around the sun today.
The concept isn’t difficult, but the amounts of energy involved might seem like a dealbreaker. For example, over the next two billion years, we’ll have to push Earth’s mean distance from the sun out from its current value of 149.6 million km (93 million miles) to 164 million km (102 million miles) to keep the energy impacting our planet constant. But recall that Earth is incredibly massive: coming in at six septillion kilograms, or 6 × 1024 kg. To move us to a stable orbit that was that much farther away, we’d have to input an extra 4.7 × 1035 joules of energy into our planet: the equivalent of 500,000 times the cumulative energy generated by humanity for all purposes combined, continuously, for two billion years.
How a thruster can help
And yet, as tall an order as that seems, it’s not an impossibility in any sense of the word. There actually is enough energy out there, if only we choose to collect it: coming directly from the sun itself. Remember, the sun emits radiation omnidirectionally, where at the present Earth-sun distance, every square meter of area receives 1500 W of continuous power so long as nothing blocks its line-of-sight to the sun. That’s 1500 joules of energy every second, and we have two billion years (or about 6 × 1016 seconds) to:
- gather that energy,
- convert it into thrust,
- and use that thrust to change the momentum and kinetic energy of Earth.
Gathering the energy is one of the hard parts of this problem, but that’s where the idea of a solar collecting array in space can help tremendously. It might take an array that’s an astounding 5 × 1015 square meters in size to collect the necessary amount of energy from the sun, or about the surface area of ten Earths, but if that’s the energy we need, it’s available. More importantly, from a different point of view, it’s “only” 0.000002% of the sun’s energy that we need to harness: a large, but not impossible, amount.
The other big key, then, is to use that energy effectively to raise Earth’s orbit. That means, in physics terms, the same thing it means for any mass in a gravitational field: we have to apply an external force over a certain duration of time, creating an impulse that causes an acceleration and changes the mass’s momentum. The same physics that works for launching a rocket into space would work for launching Earth to a higher orbit. All you’d have to do is apply a thrust that changed Earth’s momentum in a positive direction, and it would boost us, eventually, to greater distances from the sun.
That always uses a thruster: some sort of device where the action (accelerating the Earth) is balanced by an equal and opposite reaction (expulsion of spent fuel) that you put to good use. Ideally, you’d always aim your thruster so that it pushed the Earth forward in the direction it’s already moving, but that’s very difficult to manage on a rapidly and continuously rotating planet. Instead, a superior strategy would be one where, assuming you could gather, control, transport, and convert that energy into usable work, you fired your planet-accelerating thruster continuously.
Why the South Pole?
That’s literally the reason why you’d choose the South Pole! Once all the ice melts on Earth’s surface, the continent of Antarctica will be exposed. Although it’s currently beneath an enormous, massive sheet of ice, there is a massive mass of land that rises far above the ocean; if we were to remove all of the ice from Antarctica today, the South Pole would sit at approximately 9,000 feet (almost 3,000 meters) above sea level. Install your massive thruster there and fire it continuously, and a tremendous number of positive things begin to happen.
- The Earth begins to accelerate, and will be boosted to a higher orbit.
- 100% of the thrust will be useful; none of it will be wasted countering Earth’s current direction-of-motion.
- The Earth will be “lifted” out of the current Earth-sun plane, but only slightly. After two billion years of thrust, we’ll then be orbiting only a few degrees out of our current plane.
But most importantly, as we increase our kinetic energy through continued thrusting, it helps dig us out of the Sun’s gravitational potential well. That takes us to a greater orbital distance, and would enable us to slowly decrease the flux of the solar radiation that strikes our planet.
As thousands and millions of years continue to pass, we’ll have to begin contending with continental drift. So long as the thruster gets periodically repositioned so that it stays at the south pole and points directly along Earth’s rotational axis, we won’t have to worry about changing Earth’s axial tilt in a catastrophic fashion. This is a huge concern, because the total amount of rotational kinetic energy that our planet has is “only” 2 × 1029 joules, or less than one-millionth of the energy we need to transfer to Earth to boost us to a higher orbit. Only by thrusting in line with our axial rotation will we eliminate the risk of messing our planetary rotation up.
It really is, when you think about it, the ultimate example of geoengineering. We’re not talking about changing the Earth through chemical or feedback processes, but rather through sheer brute force. Over long timescales, the meteor showers we experience will change, as our changing orbit moves us out of the path of certain long-period objects and into the paths of others. Yet the ultimate goal, of decreasing the amount of solar radiation that strikes our planet, and preventing the oceans from boiling due to our sun’s ever-increasing energy output, is an achievable one with the right technological developments and investment of resources.
It’s important to remember that there are some long-term changes that are going to happen to our planet regardless of human activity. The sun will burn through its fuel, its core will grow and heat up, and its overall energy output will increase. That, in turn, will increase the amount of radiation reaching Earth. These changes are extremely slow, but the lifetime of stars like our sun is long: we’re already receiving perhaps ~30% more energy than we were some four billion years ago, and that will continue to increase by about 10% with each subsequent billion years that comes to pass.
We cannot stop our sun from running out of hydrogen fuel and eventually entering the red giant stage of its life, but we could potentially buy a few extra billion years for life on our planet by migrating the Earth away from the sun. It would be the grandest project undertaken in the entire history of our world — perhaps in the entire history of the universe, for all we know — but it truly showcases the power that we possess as a species, if we choose to use it. The sun will boil Earth’s oceans and bring an end to life on our planet, if we do nothing, in just 1-to-2 billion years. But if we develop and implement the right technology, a South Pole thruster could literally be the one and only thing, after the ice melts, that truly saves our planet.