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You are an intelligent species whose sun is very near expiring. When your sun expires your world will be engulfed by it. You are evacuating your planet as fast as possible but you don't yet have enough resources to evacuate the whole planet. As a backup plan you have given every being a space suit and keep them all on the far side of the planet (the side facing away from the sun) at all times. If the sun explodes you plan to use the piece of your planet where everyone is residing as a vehicle of sorts. You explode the planet while, very carefully, accelerating the side of the planet that you are currently on away from the sun. You plan to out run the expanding sun and rescue as many of your fellow aliens, and supplies, off of your floating planet chunk as possible.

Possible complications:

  • The G forces from the explosion could kill the alien inhabitants
  • The inhabitants wouldn't be able to survive on a floating planet chunk
  • There wouldn't be enough gravity to keep everyone secured
  • all sorts of other complications

Possible solutions:

  • The species has a very flexible / strong skeletal system
  • They build shelters that are secured to the ground, have shock absorbents, have air supplies etc. ( This is not an ideal solution because most of them will be gathering supplies and won't be able to make it to their shelters in time )

What would have to be true to make this possible?

Edit: Any solutions are valid—the planet could be a dwarf planet, they could use the core of the planet to fuel the explosion, etc...

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  • $\begingroup$ For that level of effort they might try stellar engineering instead. Converting the star into a stable red dwarf will extend the lifetime of the sun by billions of years,,,,, $\endgroup$
    – Thucydides
    Commented Jan 13, 2016 at 2:46
  • $\begingroup$ Isn't there a logic hole in this kind of circumstances? When star expires it does not do this from normal to bang in a matter of years; you will have between one and one thousand million years of giant-phase. When your civilization was inside the habitable zone before, they will get scorched (or eaten by the corona) long time before that star could explode. Even the change to a giant is a slooow process. Or is there another explanation for that star going ((hyper)super)novae? oh, Please tell us what kind of star this might be by the way. $\endgroup$
    – Confused Merlin
    Commented Jan 13, 2016 at 6:13
  • $\begingroup$ One thing you might be able to achieve by blowing up your planet, is to reduce escape velocity. This way, Spacecraft built and manned before the explosion might be able to escape the gravity of the remaining chunk. $\endgroup$
    – Burki
    Commented Jan 13, 2016 at 11:59

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Exploding the planet is kind of pointless, since you will need it later.

A planet can be accelerated or decelerated to a new orbit by the process of "momentum exchange". Consider that when a spacecraft does a slingshot past a gas giant planet, it accelerates to a higher velocity and changes direction. What is usually overlooked is the giant planet is actually losing the same amount of momentum as the spacecraft has gained, although when you consider Jupiter vs the Voyager spacecraft, the effect on Jupiter is probably not measurable by our current instruments.

Sending a stream of asteroids or comets to do close flypasts of your planet will provide the momentum that is needed to drive your planet outwards from the expanding sun. Each asteroid or comet will be losing momentum, and in an "open" system, probably fall inwards into the sun itself. Since we generally don't have enough asteroids or comets in the right orbits, we should recycle them. Once the asteroid or comet passes the planet and gives up its momentum, it will be falling towards the sun on a much closer orbit. At that point, a solar sail should be unfurled and solar energy used to "boost" the asteroid or comet into a new orbit with much more energy. With some clever orbital mechanics it can be set on a crossing orbit to deliver more momentum, while the sail is furled for another pass.

Once the sun passes its maximum expansion in the red giant phase, the process needs to be reversed and the planet brought back inwards to huddle close to the white dwarf that remains. You now have a few hundred million years to consider your next step until the white dwarf cools below a temperature that can sustain life.

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  • $\begingroup$ Wait... did you just lay the groundwork for a cosmic bucket brigade from a gravity well? $\endgroup$
    – user8827
    Commented Feb 6, 2016 at 20:30
  • $\begingroup$ Well, yes .. ;-) $\endgroup$
    – Thucydides
    Commented Feb 6, 2016 at 22:03
  • $\begingroup$ Jupiter does't lose momentum, it actually gains a little. The orbit drops towards the sun slightly due to the increased gravity of the planet(still not measurable) increasing the orbit speed. This hurls the spaceship outwards which in turn lowers the planets gravity causing it to return to its original orbit with a temporary boost of speed. $\endgroup$
    – Bellerophon
    Commented Feb 11, 2016 at 21:48
  • $\begingroup$ @sam... momentum in the system has to be conserved. If i slingshot out of Jupiter's gravity well, i have taken some of that momentum. If I use it to brake, I have added some. $\endgroup$
    – user8827
    Commented Feb 12, 2016 at 2:51
  • $\begingroup$ No its more like rolling down a cliff I pick up speed but no one loses any. $\endgroup$
    – Bellerophon
    Commented Feb 12, 2016 at 16:17
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Perhaps they built a giant, resilient complex into the surface of their planet chunk. They then create a machine that would harness the core of the earth, and use it to propel them away from he planet. It slowly accelerates, gaining speed. The energy shot back at the planet builds up in the center, until it all releases and boom! The planet explodes! Perhaps the aliens made the planet explode to release it's gravitational hold on your planet chunk.

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  • $\begingroup$ What happens when they get to far away to harness energy and get pulled into orbit around another planet? $\endgroup$
    – Bellerophon
    Commented Feb 11, 2016 at 21:51
  • $\begingroup$ @Sam They calculate it beforehand so that doesn't happen. $\endgroup$
    – Xandar The Zenon
    Commented Feb 11, 2016 at 21:53
  • $\begingroup$ the problem is when they start drifting without power, they will freeze, if they have heating the will eventually run out of power as they will have few fossil fuels no solar(obviously) and no geothermal, hydroelectric for a while maybe but that will run out as they have no evaporation. $\endgroup$
    – Bellerophon
    Commented Feb 11, 2016 at 21:57
  • $\begingroup$ @Sam Well, they are obviously aiming for their version of Mars, and are prepared to get there. They have just enough fuel to heat their planet chunk until they get there. They also have enough food, and have calculated everything. Their Mars will then be habitable, because it will now be warm enough, but not too hot. $\endgroup$
    – Xandar The Zenon
    Commented Feb 11, 2016 at 22:00
  • $\begingroup$ Yeah, sorry for doubting you, it sounds like a good answer, tbh they could probably meet up with the other evacuees there and the chunk would be good to bring oxygen generators, and greenhouse gas generators, along with other start up materials. +1 $\endgroup$
    – Bellerophon
    Commented Feb 11, 2016 at 22:03
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Well since first you must have figured out how to stop the rotation of your planet, since if you take earth, it rotates every face toward the sun every 24 hours. Being able to keep the entire population on the night side of the planet would take huge resources better used to getting them OFF the planet.

With this kind of tech to stop a planets rotation or at least make it tidally locked with it's star. They might also be able to create a solar sail for the planet to move the planet out of orbit by using the sun's solar winds to push it.

Since getting the whole planet moving away from the sun would be your best bet. When good ol' Sol decides to go super nova, it is going to completely consume/obliterate most if not all of the planets in this system. Meaning that not even 'chunks' of earth will exist to push survivors on. They need to be out of the blast radius or speeding up to escape velocity on something before the sun goes boom. Or they will cease to exist in a fiery flash when the pressure wave shows up.

If the solar sail gets the planet moving fast enough earlier enough, it might provide enough protection and extra surface area to help the planet survive the 'push'.

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The resources required to accelerate half a planet are enormously larger than what it would take to evacuate by more conventional means.

What you are trying to do is achieve escape velocity. If their planet is earthsized, you are looking at needing to reach 25,000 mph from an explosion. That should give you a sense for what they are in for. The structures to survive that (shock absorption) would be sufficient for virtually any other evacuation scheme.

Maybe if they lived on a dwarf planet...

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  • $\begingroup$ I edited my post. Anything goes. $\endgroup$
    – Tyler Davis
    Commented Jan 13, 2016 at 1:19

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