Ask Ethan: Can we save the Earth by moving away from the Sun?

The NEXIS ion engine from NASA's Jet Propulsion Laboratory is a prototype of a long-acting engine capable of moving large mass objects at very long time intervals.

Someday, in the distant future, the oceans of the Earth will boil and destroy all life on its surface, turning it into an uninhabited planet. Not a single person can prevent such global warming: the Sun, which burns its fuel during life, is gradually to blame for it. But perhaps there is a way to keep the Earth habitable, if you plan a very long-term solution: move the whole Earth. But is it real in principle? This is what our reader wants to know:

I would like to dream: Do you think it would be physically possible to move the Earth's orbit, given our current scientific knowledge?

To find out, we need to understand how hot it will become and how quickly the temperature rises to move the Earth quickly enough to save it.


The section shows various parts of the surface and viscera of the Sun, including the core, in which nuclear fusion takes place.

Any star receives energy by synthesizing heavier elements from lighter ones in its core. In particular, our Sun converts hydrogen to helium in those parts of the nucleus where the temperature exceeds 4,000,000 K. The hotter the atmosphere becomes, the faster the synthesis proceeds; the very center of the core can heat up to even 15,000,000 K. This speed is almost perfectly constant - but not quite. Over long periods of time, the percentage ratio of hydrogen and helium in the nucleus changes, due to which the insides with the passage of billions of years heat up more and more. When warming up, three things happen:

• The star becomes brighter, that is, emits more energy per unit of time.
• It swells a little, significantly increasing the radius by a few percent every billion years.
• Its temperature remains almost constant, changing by no more than 1% per billion years.

The sun has increased the size, brightness and temperature, according to the curves, and these three characteristics will continue to increase in the future [red - brightness, blue - radius, green - temperature]

All this leads to an inconvenient fact: the amount of energy reaching the Earth grows very slowly with time. For every 110 million years, the solar brightness will increase by about 1%, which means that during this time the energy reaching the Earth will also increase by 1%. When the Earth was 4 billion years younger, our planet received hardly 70% of the energy that we have today. And after one or two billion years, if we do nothing about it, this increase will lead to serious problems for the Earth. At that time, the average surface temperature would reach 373 K (100 ° C / 212 ° F). In other words, at some point the Sun will become so bright that the oceans of the Earth will boil.


If the surface temperature rises too high, our planet will not be able to maintain the existence of liquid water on the surface.

How can we avoid it? There are several potential solutions:

• You can place several large reflectors at the Lagrange point L1, preventing part of the world from entering the Earth.
• It is possible, through geological engineering, to change the atmosphere and / or albedo of our planet in order to reflect more light and absorb less.
• We can reduce the greenhouse effect by removing molecules such as methane and CO ₂ from the atmosphere.
• We can throw the Earth and concentrate on the terraforming of outer worlds, for example, Mars.

Probable way of terraforming Mars towards Earth similarity

In theory, all this may work, but it will require a huge amount of work and support for results.

However, the decision to move the Earth to a more distant orbit would be permanent! And although we will need to expand the orbit quite strongly in order to maintain a constant temperature, time intervals of millions of years give us enough time for this. To neutralize the effect of increasing the brightness of the Sun by 1%, we need to move the Earth away from it by 0.5%. To offset the increase by 20% (expected in the next 2 billion years), we need to move the Earth back 9.5% from the Sun. Instead of being at an average distance of 149.6 million km from the Sun, we should aim for a value of about 164,000,000 km.


The distance from the Earth to the Sun over the past 4.5 billion years has not changed much. But if the Sun warms up and we don’t want the Earth to warm up, we need to seriously consider moving our planet out.

It takes a lot of energy! Having moved the Earth - all six septillions (6 × 10 ²⁴ ) kg - we will seriously change the parameters of our orbit. And if we increase the average distance from the Earth to the Sun to 164 000 000 km, we will notice several significant changes:

• The Earth will take 14.6% more time to complete a complete revolution around the Sun.
• To maintain a stable orbit, our orbital speed will have to be slowed down, from 30 km / s to 28.5 km / s.
• If the period of the Earth’s rotation remains the same (24 hours), we will have 418 days a year, not 365.
• The sun will appear slightly smaller in size - by about 10% - and the influence of the sun on the ebb and flow will decrease by a few centimeters.

If the Sun swells and the Earth moves away, these two effects do not quite level each other; The sun will appear slightly smaller in size.

But in order to push the Earth so far away, we need a serious energy change: we will have to change the gravitational potential energy of the Sun-Earth system. Even taking into account all the other factors, including slowing down the speed of the Earth around the Sun, we will have to change the Earth's orbital energy by 4.7 × 10 ³⁵ J, which is equivalent to 1.3 × 10 ²⁰ TWh: about 10 ¹⁵ annual energy needs of mankind. You can decide that this problem will help time in two billion years - and it will help, but not much. We will need 500,000 times more energy than humanity is creating today, which will have to be thrown into the task of moving the planet back to a safe, sustainable distance.


The speed of rotation of the planets around the sun depends on their distance from the sun. The gradual moving of the Earth outward by 9.5% should not disturb the orbits of other planets.

And energy conversion technology is the least of our concerns. The biggest problem is more fundamental: where to get all this energy? Realistically speaking, this amount of energy can be found only in one place - in the Sun itself. At present, the Earth receives about 1500 watts of energy per square meter from the Sun. In order to collect enough energy in order to move the Earth away at the right time, we will need to build a space array collecting 4.7 × 10 ³⁵ J of energy, constantly, for all two billion years. This means an array of 5 × 10 ¹⁵ m ² , 100% effective, or the equivalent of ten surface areas of the planet Earth.


The concept of a space solar power station has been around for quite some time, but no one conceived an array of 5 billion square meters. km

It turns out that in order to move the Earth to a higher, more stable orbit, we need a 100% efficient solar array of five billion square meters. km., all of whose energy will be spent solely on pushing the Earth into a more distant orbit for two billion years. Physically possible? Of course. With current technology? No options. Practically possible? Almost certainly not, at least based on data known to us. Moving the whole planet is difficult for two reasons: because of the very strong gravitational attraction of the Sun and because of the very large mass of the Earth. But this is our planet, this is the Sun, and the Sun will warm up, regardless of what we will do. Until we find a way to collect and utilize such a huge amount of energy, we will need other strategies for the survival of the final global warming apocalypse!

Ethan Siegel - astrophysicist, popularizer of science, blog Starts With A Bang! He wrote the books Beyond The Galaxy , and Treknologiya: Star Trek Science [ Treknology ].

FAQ: if the universe is expanding, why aren't we expanding ; why the age of the universe does not coincide with the radius of the observed part of it .