# How to protect the Earth from the stellar evolution of the Sun?

Every day the Sun is closer to be a Red giant, making the live of the initial home of the humanity practically uninhabitable. Humans are not there anymore. It's a protected territory, but the Sun gonna end with that and we need to do something.

What humanity can do? There are a way to save the Earth, their flora and fauna from their own star? How much that solution gonna last?

Humanity is dispersed around the Universe, has acces to a really advanced technology (you can be creative here, but respect the physics as much as you can) and all the resources from closer stellar systems.

It's a maximum priority to preserve our history. Humanity need you.

• Can you move the planet? I don't think anything short of that is going to save it (and even that probably wouldn't save the flora/fauna). – Geobits Sep 22 '16 at 13:46
• It's a possibility, but I can't imagine how. – Malkev Sep 22 '16 at 13:50
• Malkev, is there anything specific you want to see in an answer? There are clearly many techniques you could use if we assume that humanity's much more advanced several billion years in the future, and obviously many of them have already been covered. – HDE 226868 Sep 26 '16 at 19:58
• @HDE226868 yes, I know, but with only 216 views I think we can found something more. I love some of the answers too, so I want to give them a plus. ^_^ – Malkev Sep 26 '16 at 20:59
• Edited my answer to this post. I hope it helps – Yacomini Sep 28 '16 at 12:57

Since this is tagged as science-based, here's a scientific paper on the subject of moving the Earth away from an increasingly powerful Sun:

D. G. Korycansky, Gregory Laughlin, Fred C. Adams. "Astronomical engineering: a strategy for modifying planetary orbits." Astrophysics & Space Science, Vol. 275, No. 4, pp. 349–366.

The basic mechanism uses gravitational assists to (in effect) transfer orbital energy from Jupiter to the Earth, and thereby enlarges the orbital radius of Earth. This transfer is accomplished by a suitable intermediate body, either a Kuiper Belt object or a main belt asteroid. The object first encounters Earth during an inward pass on its initial highly elliptical orbit of large (~ 300 AU) semimajor axis. The encounter transfers energy from the object to the Earth in standard gravity-assist fashion by passing close to the leading limb of the planet. The resulting outbound trajectory of the object must cross the orbit of Jupiter; with proper timing, the outbound object encounters Jupiter and picks up the energy it lost to Earth. With small corrections to the trajectory, or additional planetary encounters (e.g., with Saturn), the object can repeat this process over many encounters. To maintain its present flux of solar energy, the Earth must experience roughly one encounter every 6000 years (for an object mass of 1022 g). We develop the details of this scheme and discuss its ramifications.

Other interesting quotes from the paper:

A great deal of energy must be expended to implement this migration scheme. However, the energy needed to move Earth is relatively modest compared to that needed for interstellar travel. ... The energy requirements and overall ease of implementation also compare favorably with various terraforming projects.

...

As for the Moon, reasoning by analogy with cases of stellar binaries and third-body encounters suggests that the Moon will tend to become unbound by encounters in which O passes inside the Moon’s orbit. (As well, there is the non-zero probability of collisions between O and the Moon, which must be avoided.) Again, detailed quantitative work needs to be done, but it seems that the Moon will be lost from Earth orbit during this process. On the other hand, a subset of encounters could be targeted to “herd” the Moon along with the Earth should that prove necessary.

...

The fate of Mars in this scenario remains unresolved.

...

An obvious drawback to this proposed scheme is that it is extremely risky and hence sufficient safeguards must be implemented. The collision of a 100-km diameter object with the Earth at cosmic velocity would sterilize the biosphere most effectively, at least to the level of bacteria. This danger cannot be overemphasized.

• Alternately, you might be able to plant an immense solar sail a bit closer to Earth than the L2 Lagrange point, where the solar pressure on the sail would balance out the force of gravity from Earth. Gravity from the sail would slooooowly pull the Earth away from the sun. I haven't run the numbers to see how big the sail would need to be, but if they add up, sailing might be a safer means of moving the planet. – ckersch Sep 28 '16 at 15:02
• I saw this question and was dying to answer it...and then here is the correct answer with paper links and all. There is only one way to move a planet, and that is a series of orbital energy transfers. – kingledion Sep 30 '16 at 2:12

# Move the planet

Ultimately, shielding or adapting to the increased heat will not be sufficient once the red giant phase gets underway. So skip half measures such as moving the planet, as described by this question and others.

# Fix the sun

One use of star lifting is stellar husbandry. More generally, take over from the natural process of the star’s lifecycle. Reduce mass or find a way to stir up the remaining material. Again, see other questions asking this.

Moving the Earth is the only way with plausible, known physics. (I am going to assume that for various reasons, Earth cannot simply be shunted through a wormhole to another star).

Much like spacecraft use momentum transfer to "slingshot" around Jupiter, you can also "slingshot" asteroids or comets around the Earth. If the orbital vectors are such that the comet or asteroid loses velocity, Earth will gain a corresponding amount of velocity. Given the vast disparity in masses, it will obviously take a lot of asteroids to do this. Realistically, you would attach a solar sail or similar device to the asteroid and use the solar energy to add velocity after the Earth crossing encounter and bring it into another Earth crossing orbit to exchange momentum again. XKCD describes the mechanics of the process here

Assuming super science, the Earth could also be moved by warping space and allowing the Earth to "fall into" the new depression in space-time. Given it takes an entire solar mass to generate the dent in space-time we orbit in, this would be an astro engineering problem requiring huge amounts of mass or energy to do.

Regardless of the method, the Earth needs to be moved gently. Even 5 billion years from now as the Sun is rapidly expanding into a red giant, suddenly imparting momentum to a planetary body would involve depositing huge amounts of energy and could cause earthquakes and other natural disasters. Slowly shifting the Earth out to perhaps the orbit of Neptune would probably provide protection when the sun is at its peak expansion, and then the same processes can be reversed to gradually move the Earth inwards to the newly formed white dwarf star which marks the remains of the Sun.

Of course, now you have to erect some sort of shield that will screen out the violent ultraviolet radiation the white dwarf will emit while bringing the Earth in to a much closer orbit in order to maintain the needed insolation for life.

• Other questions here have asked about moving the orbit specifically. – JDługosz Sep 22 '16 at 15:04
• Wouldn't we need to move the other planets as well as to avoid running into stuff? – Morrison Chang Sep 22 '16 at 15:05
• With enough computing power and active guidance of the asteroids in flight, that might not be a problem. Every extra planet you want to move means more time, effort and energy is needed for the project. – Thucydides Sep 22 '16 at 15:16
• Space is huge so you probably won't need to move other planets. The distance between Earth and Venus is 0.28 AU, Earth - Mars 0.5 AU. The distance between Mars a Jupiter is 3.5AU, so plenty of space to park a planet between them. – ventsyv Sep 22 '16 at 16:26
• Since the outer mostly hydrogen envelope is kicked off from the Sun after the red giant phase anyway, and it will likely be at least 10% of the mass of the current sun. Why not collect most of it for a Jupiter turned sun? (You can also collect the other gas giants hydrogen, a tiny amount of what you need I know, and collect the solar wind near the end of the Sun's red giant phase which is expected to have increased significiantly before the planetary nebula phase.) Then move the Earth there instead, though the moon and tidal issues will be a problem. – Brooks Nelson Aug 3 '17 at 18:35

# Short answer? We cannot save Earth

Saving Earth from it? I don't think theres a possible way of doing that.

The reason that stars swell in size after exhausting their hydrogen cores is that the stars begin fusing helium, according to the University of Michigan. The helium releases more energy during fusion than the hydrogen releases during the process. The amount of energy produced by the helium is greater than that needed to stave off gravitational collapse, which causes the star to swell greatly in size.

## Trying to slow down sun advance

Refuel the hydrogen core won't do nothing, even thought our sun still has a lot of it that would make nothing, let's not say that amount of hydrogen would be a lot.

Reducing the size of the sun? Well, I don't know if this is possible or not, if we can even have a machine that can do such task. Also humans can get near the sun, so we would need a machine to operate from distance or a machine controlled by robots that won't melt being near the sun.

Also, what would this machine do? If a machine like that is possible.

Of course I'm using the perspective view of a 21th century man, we really don't know what we may develop in the future. But in terms of what we know right know there's no possible way of slowing down or avoiding our star to devour us.

But, that would take time, around 1.75 billions years according to scientists, so...

## Traveling to another planet

If you want to save flora and fauna people has always come with the expectation that we can find another habitable planet where we can land our already know flora and fauna. But I always wonder if that would be possible due to the fact that would be like introducing a new specie to an environment, and that has not always had the best results, but it may be possible if the new planet has the condition the flora and fauna needs to survive.

## Moving Earth

Eventhought there are a lot of post about moving the planet we need a tremendus force to achieve that. We are not lifting a plane, we are moving a dense rock that wieghts around 5,972 × 10^24 kg. If we can achieve a source of energy capable of doing such task then we would need to figure out how to create a machine capable of moving earth.

So, in my opinion, we have around 1.75 billions years (if we don't destroy ourselves before) to figure a way out of this planet, because I think is the most viable method. Slowing the sun seems impossible and moving earth seems out of reach.

An arxiv paper in astrophysics investigated that point: https://arxiv.org/abs/0801.4031

Their idea is that the sun will lose some of its mass at the end of its life, about 1/3 in 8 billions years, causing the earth path to extend and giving us a "short" break. This mass loss would not save the Earth from being swallowed, except if:

• the Earth can be moved to a radius of 1.15 AU from the Sun
• the mass loss by the Sun can be increased

A bit of elaboration about fixing the sun by star lifting

• actually you can preserve Sun and solar system indefinitely (until heat death of universe, or until it makes sense), given Humanity is dispersed around the Universe resources.

wiki Sun,Life_phases

the Sun has so far converted around 100 times the mass of Earth into energy, about 0.03% of the total mass of the Sun.

Which cause makes red giant from our star? Products of reaction, products of hydrogen fusion - which is Helium.

So one way is to remove this product from sun, it is about 1.1931e+17kg per year and replace it with Hydrogen from Jupiter as example. Jupiter mass should be enough for next 15 billion years. Sun produces more then enough energy for such operation, so energy of the process is not an issue.

speed of migration matter from Sun core is not a fast process , I guess, if it is like energy migration from core to upper layers of sun, but should work.

Just as notice, removing carbon also might affect speed of energy production, but eventually Helium fusion will dominate, so it is less efficient way in therms of indefinite prolongation, but more productive way in therms of getting useful materials from sun.

1.1931e+17kg of helium is something around 120km diameter sphere of liquid Helium. ($\text{125-145 }kg/m^3$ helium density in liquid form)

Maybe not the answer you are looking for, but worth challenging. Human redundancy is our current answer to this issue...get off the planet and out of the star system before our sun dies so that any galactic calamity can only wipe out a portion of us.

What humanity can do? There are a way to save the Earth, their flora and fauna from their own star?

Humanity can provide the same redundancy to the flora and fauna of earth...IE, get it off that planet and go find another 1 (or 2 or 2000) to put it on. But I somewhat have to question the why portion here...this event is several billion years in the future:

a) most of the life you are saving will be unrecognizable to todays standards. Much evolution takes place across this time scale

b) most of the earth will be unrecognizable to todays standards. This is billions of years and the world will heavily change. In 250 million years, it's likely that America will collide with Asia creating Pangaea Ultima. In another 200 million after that, they break up again forming continents, before reforming together once more. The globe will look completely alien. When you are talking such a large time frame, nothing is constant...why bother conserving anything but this changing nature?

This point in particular:

It's a maximum priority to preserve our history. Humanity need you.

No it isn't. Preserving an unrecognizable rock that we may have developed once upon a few billion years ago is anything but maximum priority and I'm sure humanity needs you for many other things beyond resisting inevitable change.