"I would argue that in any habitable zone that doesn't boil or freeze, intelligent life is going to emerge because intelligence is convergent." -Simon Conway Morris
Someday, in the far distant future, the evolution of the Sun will cause it to heat up and emit so much energy that the Earth’s surface will reach a terrible threshold: 100 degrees Celsius (212 degrees Fahrenheit). When this happens, the oceans will boil away, rendering the surface completely uninhabitable and inhospitable to even the most extreme known forms of life.
While there are many potential solutions, perhaps the most intriguing is to migrate the entire planet farther away, buying our world additional billions of years of potential habitability. However, the energy costs are huge, and the amount of power required is much larger than anything humanity has ever known. Is it physically possible? Yes. But from a practical perspective? There are, shall we say, challenges.
Still, if we want to save the Earth, far down the road, we need to know what it takes! Find out on this edition of Ask Ethan.
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Not wanting to sound pessimistic, but don't think we'll be there for that. Cockroaches might be.. but humans.. unlikely.
It will take billions of years for the sun to enter the red giant stage where this question becomes relevant. But the largest asteroids.. several kilometers large (like the dinosaur-wiping-ones) are on the frequency of several million years.
That gives them the chance to wipe all the mammals on Earth several thousand times over, before anything/anyone notices the sun. Ahh.. time.. though art the cruelest mistress of them all.
Even given all that energy (for the sake of argument, let's grant it from solar panels in space), what are you going to do with it to move the Earth? I guess you'd have to increase our orbital velocity, so as to lead to a higher orbit, and you'd have to do that by... throwing away mass from whichever side of the earth happens to be "trailing" at that particular time of day? Maybe we could build launch sites in each of the 24 time zones, timed to launch mass away from us every day at the appropriate time. What could we eject from the earth that we have enough of to spare, and how would we manage the ejection efficiently? What about orbital safety afterwards: if we eject stuff from the "back" of the earth to make us move forwards faster, are we going to pollute our orbit with crap we're just going to be colliding with, one year later?
Maybe you could also accomplish the same by a series of millions of gravity assists: send something smaller towards Earth so the smaller body gets a slingshot effect and the Earth will get the opposite effect, scaled down enormously because of relative mass. This just shifts the problem to generating orbital changes for millions of smaller bodies--which start out all around the solar system--and delivering them extremely precisely to our vicinity. Sure, each smaller body is easier to nudge than our entire earth, but you have to do it millions of times, without any single one of them being nudged catastrophically *into* the earth instead of just behind it. I'd love to see a description of how we'd do it, even magically granted as much energy as we want.
I think if humanity still exists by the time Sun gets much hotter, surely there would be enough technology by that time to move all humans (and lots of water) to Mars (which is much farther away from the Sun).
How about a different problem:
Can we move Mars (which is too cold today) closer to Sun to make is more hospitable for human life?
Could we slowdown orbital speed of Mars (to get it closer to Sun), by slowly changing orbits of selected asteroids(and comets?) to make them collide with Mars in a controlled way? (And if we continue doing that for hundreds of years.)
Colliding asteroids with Mars would also increase its mass, which is a good side effect because Mars is significantly smaller than Earth.
Colliding comets is even better because they would increase (surface) water content of Mars.
Right, but we have two billion years to do it. That works out to an increase in our orbital radius of 7.2 m/year, or 2.28E-7 m/s. If we can give the earth a 'kick' then we don't have to apply a force the entire time (do we?). We just need to impart that velocity to it and let it coast outward over time. Taking our outward velocity to be zero right now, the work required is 1/2*(6E24)*(2.28E-7^2 - 0^2) = 3.1E11 kg m^2/s^2.
How to apply that energy to 'kick' the Earth into an outward motion...is a different story.
Can we cheat and transfer orbital energy from other solar system bodies via gravitaional interactions. One suggestion is to manipulate the orbits of asteroids, so that they repeatedly have gravitational encounters with the earth, which transfer some energy and angular momentum from the asteroid to the earth. I suspect this could be potentially much more energy efficient, as we are essentially stealing orbital energy from other objects. I.I. we hack the solar systems orbital mechanics to migrate some planets sunward while out own planet migrate outward?
Even better, would it be possible to set up an asteroid in an elliptical orbit such that it gravitationally scatters off both the earth and say Venus, transferring orbital energy from Venus to the earth? If so we could "sacrifice" Venus in order to save our planet.
BTW, its not the boiling of the oceans that we need to fear, somewhere around a global surface temp of 50C, the greenhouse effect from water vapor reaches a runaway point. But, we would already be dead by that point.
Another issue, is that we could keep the temperature in check for quite a while by scrubbing greenhouse gases, but as the CO2 concentration drops too low for plant life, then we have a problem.
Since we know that Sun will get gradually hotter and bigger as it aged, here is an utterly insane long term plan to ensure distant future of humanity, assuming we will have the power to modify orbits of asteroids and comets such that
we can make any of them collide with any planet in a controlled way so that we can increase or decrease size of the orbit of the planet (we would be also keep increasing the mass of the planet we bombard; also we could use available comets to provide extra water to target planet):
Imagine first we could bombard Mars until its climate and water content is good enough for humanity.
Then move humanity to Mars (or as much as we can),
then we could bombard Earth to increase the size of its orbit as much as we want/need.
And afterwards as the Sun keeps getting bigger/hotter,
we could keep moving humanity back and forth between Earth and Mars, and each time after we moved humanity to one of the planets, we could bombard the other planet to increase the size of its orbit as much as we want/need.
Potential problems would be, can we keep the orbits of all other planets still stable for long term,
and what are the limits of keep increasing the mass (and water) content of a planet we want to live in?
Also after how many times we moved humanity, we would run out of asteroids to use (and only can use comets)?
Could we still continue by using comets?
If so when we would run out of comets?
And if we also run out of comets,
what would be the final mass (and water content) of Earth/Mars?
What would be the size of the orbit of Earth/Mars,
and would there be any chance of moving humanity to any planet in any nearby star?
Another potential problem is, even if we added lots of water to Mars, how we would get a suitable atmosphere?
Assuming we have no elektrical power production problem, maybe we could separate lots of water to oxygen and hydrogen gas,
and release hydrogen gas to space.
But then can we live in a almost pure oxygen atmosphere?
Are the common rocks on Mars have enough nitrogen we could release to atmosphere?
Or is there any other suitable inert gas we could produce enough from the rocks?
But also how we could modify the orbits of almost any asteroid or comet?
I don't think any kind of rocket fuel would be enough.
But assuming we can produce portable fusion power generators that can generate maybe something like megawatts for decades,
it maybe possible to produce enough thrust in space using only electrical power in different ways.
One way I was thinking could be to create giant rotating electrical and/or magnetic fields around a spacecraft
to swim thru sea of cosmic rays around (positive and negative charged particles) like a submarine.
Of course if we had technology to easily modify asteroid and comet orbits, it would also be useful for protecting humanity from any unwanted asteroid or comet impacts anywhere.
These all sound like futile attempts in the long run. I mean, sure.. it will buy another billion years or so.. But if we are pondering those timescales... then it's futile in the end. I mean, the sun won't stop expanding. In the red giant stage it will encompass both earth and mars orbits. The "safe" areas will be Neptun and beyond. If we have the technology to move comets, asteroids and such and have the ability to move whole planets, then we'll probably have the tech to build enormous space stations and habitats. We might not be able to settle other worlds beyond our solar system, but by that time it might be more efficient to focus the resources in building new habitats, then moving planets more and more away from the ever growing sun, which is in the end a lost battle.
I think it is not necessarily a lost battle in the end.
That is why I had asked what would be the size of orbit of Earth/Mars when we run out of asteroids and comets.
Because I think if the size of the orbit is big enough, it could make it possible to come close to a suitable planet in a nearby star. Keep in mind we would prefer to save all humanity if possible.
Also can any space habitat would be viable way to live for humanity indefinitely?
Wouldn't it keep getting damaged by cosmic rays?
Could we always repair and protect it?
How about another crazy idea:
Could we build lots of giant towers on Earth where their tops are above the atmosphere of Earth?
If so and we also have tech to create efficient and powerful pure electric drives for space, maybe we could turn Earth itself to a mobile planet. :-)
This maybe the craziest idea:
What if we turn Earth to a mobile planet and also bombard Mars with asteroids and comets and get it closer to Earth and also make Mars have similar amounts of water and oxygen atmosphere, and later also turn Mars to a mobile planet?
Then we would have two mobile planets to live and move anywhere, maybe even to nearby stars.
Then maybe we could keep creating more mobile planets everywhere we go in the universe. :-)
I really like your work Ethan. can I call you that?
It seems others are not so pessimistic; see eg
where Kuiper belt objects are proposed as angular momentum adjusters.
@RobinBecker fite me TRYIN TO IMPRESSE MY ETHANU WITH YOUR SPACE TALKS. FITE ME. ETHANU IS MINE!