One day in the year 1980 humans receive a message from an alien race. It reads a little something like this:

Hey guys, real sorry, but a weapon we launched in an excercise malfunctioned and is heading toward your solar system. When it arrives, all atomic particles within 5 astronomical units of the center of your sun will instantly and magically disappear, poof (no explosion or anything). We recommend that you evacuate the system. If you have not already detected the weapon, then your technology is far too primitive to deactivate or intercept it.

At the time of this message's writing, we are aware of several star systems near yours that may contain planets habitable to the majority of your planet's native lifeforms.

Some more details follow, from which we learn that:

  • The weapon will arrive and activate in March 2030
  • The weapon is coming from a specific direction (we can see it with many of our telescopes, it's clearly not natural, and it's still close to 50 light years away and traveling at very close to the speed of light, so it's clearly not manmade either). In other words it's pretty clearly not a hoax.
  • We truly don't have much hope of stopping it.
  • The message has traveled for about thirty million years at the speed of light, meaning the star systems it mentions were observed in the state they were in about sixty million years prior to year 1980 (if I got that right). The aliens are aware of this and adjusted their suggestions as best as they could.

The list of potentially habitable star systems is ranked by relative predicted livability. The aliens are not sure how livable they are, or even if any of them are livable. They also don't mention planets specifically, so it's possible they are making these calculations solely based on the characteristics of the stars themselves, but we don't know. All of the stars appear to us to be very much like our sun.

Star system A

Livability: 88

Distance: 24 light years

Star system B

Livability: 82

Distance: 19 light years

Star system C

Livability: 64

Distance: 8 light years

Star system D

Livability: 55

Distance: 12 light years

Star system E

Livability: 51

Distance: 36 light years

So... what do we do?

Keep in mind:

  • We have from 1980 to 2030 to (assuming there's political will) focus an intense international effort on solving this problem and potentially develop some technologies a bit more advanced than we would otherwise expect (or maybe not). For example it seems quite possible that we could find nearby planets and get some information about their atmospheres.
  • We don't necessarily need to save any human individuals, but rather provide for the long-term continuation of the human race.
  • You can make any assumptions you like about the question or about the historical / technological developments from 1980 - 2030, but more realistic is better. This question is mostly just for fun. If you'd like, after considering the 2030 deadline, feel free to consider what could happen with different deadlines.
  • We don't necessarily need to leave the solar system if there's a way we could survive without leaving. But leaving is preferred.


Instead of the particles in our solar system decaying they all just go poof as if they had never existed.

  • 1
    $\begingroup$ Thoughtful aliens, especially since they had to look into the future to know where to send the message, and in what language. $\endgroup$
    – AndreiROM
    Commented Mar 31, 2016 at 18:41
  • $\begingroup$ @AndreiROM you can assume that if you'd like, though neither is necessarily the case. $\endgroup$
    – Aurast
    Commented Mar 31, 2016 at 18:47
  • $\begingroup$ Given the year 1980 coincides with a growing interest in ufology, the message might get dismissed as another conspiracy by a good portion of the (US) population. It'd be hard to get funds for any appreciable space endeavor if constituents believed the request was based on a conspiracy. $\endgroup$
    – Frostfyre
    Commented Mar 31, 2016 at 18:57
  • $\begingroup$ @Frostfyre Good point, but that's boring, so let's pretend we can see this thing coming by space and Earth based telescopes once we're told where to look, and it's obviously neither natural nor manmade (much too far away to be manmade). $\endgroup$
    – Aurast
    Commented Mar 31, 2016 at 19:01
  • $\begingroup$ @Frostfyre: "One day in the year 1980 humans receive a message..." The message was probably received by all leading spacefaring nations. (as in, not just USA, but also USSR, China and India. just my thought after reading the question) $\endgroup$ Commented Mar 31, 2016 at 19:03

6 Answers 6


There's no way. Even if a crash space program was started, the ships would not be far enough away to escape a blast that size (as originally asked before the Q was edited in response to this note). Even though you stipulate that it won't hurt something 12ly away, it will certainly still bother someone a few decades outbound.

You wrote yourself into a corner. Perhaps the same message can contain instructions for constructing an advanced drive, or something like that.

(original question mentioned 30 million light years)

30 million light years is rather far for the aliens to be bothering one little star in a different group of galaxies. See this map.

edited question mentions...

If you see something travelling toward you at nearly the speed of light, it will be hot on the heels of the light, not 50 light years away. For the light to gain 50 ly on it during transit, it will have to have been travelling a long time.

  • $\begingroup$ Sorry to damage the relevance of your answer but I updated the question to get rid of the giant atomic blast problem as that was not intended to be an absolute limiting factor. $\endgroup$
    – Aurast
    Commented Mar 31, 2016 at 19:12
  • $\begingroup$ That's not nice. You should post updates after the original description rather than changing it seemlessly, once answers are posted. The answers you get might give you many improvements and changes to your scenario. $\endgroup$
    – JDługosz
    Commented Mar 31, 2016 at 19:22
  • 1
    $\begingroup$ Okay, I did that instead. Being not nice was also not my intention. $\endgroup$
    – Aurast
    Commented Mar 31, 2016 at 19:25
  • $\begingroup$ That's correct about the weapon traveling for a very long time. Both it and the message have been traveling for about 30 million years, and the message arrives just a little bit sooner, relative to that timescale. And yes, the aliens launched the weapon from a different galaxy cluster, or perhaps even from a void between them. The core question is how do we handle 50 years notice of the destruction of the inner solar system. The rest is just background. $\endgroup$
    – Aurast
    Commented Mar 31, 2016 at 19:31

IMHO, It would be awesome actually

I'll ignore all the flaws in your question, and go straight to the point: "There's a disintegration-bomb coming to earth, we've got 50 years, and the key word for the human success We are all dead no matter what country/group you're from".

That said, humans would focus on that one thing, survive, and let me tell you, we're quite good at it, all people would be involved in the project arcam de spe, we would gather all the resources, and all the brains for that one task, all our everyday lives would focus on keeping ourselves alive and building a spaceship or a fleet of spaceships to take as many people as we can.

We would build biospheres for keeping animals and humans alive, using algae and bacteria to recycle the CO², Methane, and other byproducts from living beings into O², H²O, we would also have a HUGE database containing all of our useful knowledge we have learned throughout all generations, we would keep copies of most people's and animals' DNA for future use, a lot of testing to make sure those biosphere-ships don't fail.

If the people take a stand...

Then when the day comes, we humans would send only the important people to keep those biospheres working even though they're automated, we would keep the elite out of the ships because one: they're not useful and two: it's unfair, we would have all cultures(countries) babies( male and female ) for future breeding, the babies would be fed by robots (not human-like ones, that type of robots we use to build cars), and they would have a screen for each race of baby with videos from their mother country, teaching them how to speak and everything else, a bunch of staff people to fix things in case of a problem, but they wouldn't have direct access to the babies (just in case we've got a psycho on board), because those babies are indeed the future of humanity.

Why did I choose babies to be in the ships?

Well, I chose babies to be in the ships because they're going to live longer, sure, however, the most important factor is purity, sure they're going to have violent instincts but given the right set of videos they would grow up peaceful, but they would have access to our database, therefore, giving them a choice, follow all of our legacies even the bad ones, or make the best out of it.

Where would we send them to?

Well, if we really want to keep humanity alive we would have to send the ships to different directions, we would scan the sky and carefully choose the nearest/best/livable earth-like-exo-planets we could find, and then after choosing a ton of them we would send ships to all of them, increasing our chances of success.


Forget the recommended stars, there's no way to go interstellar in the time available. You're looking for the most inhabitable bit of the solar system that's more than 5 AU from the sun, and will remain habitable with no sun.

So to start with, it depends exactly where Jupiter is in its orbit. Jupiter is an average of 5.2 AU from the sun, so should be safe, but its perihelion is 4.95 AU and so it would be destroyed if it happened to be near perihelion. Luckily, Jupiter will be at perihelion in 2023 and then not until 2033, so it should be safe.

In which case, I'd recommend Europa. Look to dig beneath the ice and establish underwater habitats. There's enough insulation above you that you will hardly notice the loss of the sun. Raw materials for future development will be a problem, so you should try to maintain a capability to travel around the Jovian system and mine smaller moons.

  • $\begingroup$ Of the nursery bots develop a problem, and they are segregated from the adult crew, what do you think will happen to the kids? $\endgroup$ Commented Apr 2, 2016 at 0:34

The only near term solution that would be possible in 1980 would be the ORION nuclear pulse drive, which was researched in the late 1950's and early 1960's.

The research and even a lot of the scientists involved in the initial rounds of calculations and experiments will still be around in the 1980's, so the project can be jump started then.

The problem, however, is that ORION, in all its variants, requires the use of nuclear devices to provide the high thrust/high ISP performance that the drive delivers, and lots of people are going to object to having a ship full of nuclear devices orbiting overhead (or the said nukes being transported to whatever space launch centre is being used to launch the devices to the ship). This will cause a huge amount of instability as people believe this is an attempt to dominate them from space, or try to hijack the nukes for their own purposes.

Problem 2 is that building one or more ORIONS is going to take a massive amount of resources, something like launching aircraft carriers into space. Much larger ORIONS were described in mathematical form by Freeman Dyson (including interstellar "Super ORIONS"

Freeman Dyson performed the first analysis of what kinds of Orion missions were possible to reach Alpha Centauri, the nearest star system to the Sun.[12] His 1968 paper "Interstellar Transport"[13] (Physics Today, October 1968, p. 41–45) retained the concept of large nuclear explosions but Dyson moved away from the use of fission bombs and considered the use of one megaton deuterium fusion explosions instead. His conclusions were simple: the debris velocity of fusion explosions was probably in the 3000–30,000 km/s range and the reflecting geometry of Orion's hemispherical pusher plate would reduce that range to 750–15,000 km/s.[14]

To estimate the upper and lower limits of what could be done using contemporary technology (in 1968), Dyson considered two starship designs. The more conservative energy limited pusher plate design simply had to absorb all the thermal energy of each impinging explosion (4×1015 joules, half of which would be absorbed by the pusher plate) without melting. Dyson estimated that if the exposed surface consisted of copper with a thickness of 1 mm, then the diameter and mass of the hemispherical pusher plate would have to be 20 kilometers and 5 million metric tons, respectively. 100 seconds would be required to allow the copper to radiatively cool before the next explosion. It would then take on the order of 1000 years for the energy-limited heat sink Orion design to reach Alpha Centauri.

In order to improve on this performance while reducing size and cost, Dyson also considered an alternative momentum limited pusher plate design where an ablation coating of the exposed surface is substituted to get rid of the excess heat. The limitation is then set by the capacity of shock absorbers to transfer momentum from the impulsively accelerated pusher plate to the smoothly accelerated vehicle. Dyson calculated that the properties of available materials limited the velocity transferred by each explosion to ~30 meters per second independent of the size and nature of the explosion. If the vehicle is to be accelerated at 1 Earth gravity (9.81 m/s2) with this velocity transfer, then the pulse rate is one explosion every three seconds.[15]


Dyson himself seems to have changed his mind:


I think that even with a crash program, starting with 1980 era technology, energy or momentum limited Super ORIONS are still going to be beyond the state of the art of human technology.

The final issue (which has no resolution even today) is that the science of creating closed cycle life support systems is in its infancy, and the crew of an ORION starship could end up dying between the stars as their closed ecologies crashed. Even if they were to arrive safely at Alpha Centauri, there is no garuntee that they would be able to successfully create colonies with closed life support systems capable of lasting the thousands of years needed to terraform any putative Mars or larger sized planet they find.

As an aside, if the device the aliens is sending is moving at just under the speed of light, then it does not have to have any sort of magical technology, a box of kitty litter can do an awesome amount of damage at that sort of speed: https://what-if.xkcd.com/20/

If there really was one way to identify and locate it (perhaps the aliens sent tracking information) the better plan would be to send an unmanned ORION directly into its path carrying warheads full of shotgun pellets (for a nuclear powered option, see: http://www.projectrho.com/public_html/rocket/spacegunconvent.php and look under "Nuclear shaped charges".

The point here is the closing speed is so great you must fill a large portion of the expected volume of space with fragments so at least one will collide with the incoming device well beyond the 5 AU limit from the Sun. The amount of energy released by the collision will be considerable (depending on how massive the object actually is), and we might have an issue with hundreds or thousands of comets suddenly disturbed out of their orbits in the Oort cloud, but this is presumably more in line with our capabilities than trying to flee the solar system.


Since evacuating Earth is something way above the possibilities (maybe you can launch a couple of ships, but I think not many more), if the weapon has not an active guidance system we can try to deviate it using a number of lead (or anything heavier) objects equipped with an active guidance system that control an array of ion drives. The goal it to try to hit the weapon to modify (slightly) its trajectory and velocity to miss the inner solar system.

The idea is that since you can see it, you know where to fire your "weapons" since you know the trajectory and you can calculate the position of the Earth in 50 years, so you can calculate how much you need to alter the course of the weapon to miss behind the inner solar system of about 3 AU, which while can give bigger problems, will also give us a lot more time to think about the possible solutions.

3 AU is about 450 million Km, so assuming you intercept the alien weapon in 2010, you need to be able to alter the trajectory of about 0.15 AU every year.

If you can fire your weapons in about 15 years an accelerate them for another 15 years, and if you aim well and are lucky, the impact (or multiple impacts) can probably be enough to alter the trajectory and slow it down. Of course the sooner you launch, the smaller is the "delta-v" required since you can intercept farther and it work on more years, but since you are basically firing a cube of lead with nothing more than a guidance system and some ion drives, a reasonable time frame for the launch is about 5/8 years.

Moreover, if you can launch them in the 5/8 years time frame, you have another 35/40 years to build a number of generational ships and to be sure to be beyond the orbit of Jupiter or Saturn (or on your way to the other stars) if your "weapons" miss and you need to evacuate earth, but in this case I really don't think you can evacuate more than a small rate of the Earth population.


I decided to do some research myself and here's what I found.

First Problem: Getting From Here to There, Wherever There is

In 1982, after a couple of years of bickering about the details, the United States, USSR, Japan, and various European countries agree to collaborate on a project to build an interstellar spaceship.

One potentially workable option is something along the lines of Project Daedalus. The Daedalus starship was designed in the 1970s and intended to rely on existing or near future technology. However much of that "near future technology" remains quite out of our reach today. But with all the funding a doomed world can provide, who knows?

The Daedalus ship was meant to accelerate to 12% of the speed of light but not to slow down. So perhaps the coalition of nations could double its already massive fuel requirements, or they could have it accelerate to only 6% of the speed of light.

The Deuterium/Helium-3 fuel may need to be mined from elsewhere in the solar system, which is a very daunting prospect in itself.

The machinery involved would need be robust far beyond what current engineering skill can achieve and still able to operate hundreds or thousands of years from now (though not all of it would need to operate for the entire trip).

It seems very unlikely to me that all this could be achieved by 2030. However, for the people starting in 1980, 50 years would seem to be fantastically far in the future, so they would try, though they would likely fail and we'd go extinct.

Another potential option would be massive solar sails. A 62 mile-wide sail could be used to make an interstellar trip in a thousand years. But the source didn't specify the payload size, so it may well need to be much, much bigger than even that. This is (as of 2010) tried-and-true technology, but has only been deployed on a small scale.

Second Problem: What do we Send

We could send some women, say, five, and a bunch of frozen female embryos (plus some males for the final leg) to implant in them and their children, but for a one-thousand year journey five people would require around 3.6 billion calories of food. Even with engineered, very calorie-dense food, this is likely to weigh over 700 tons. Project Daedalus was only meant to carry a 500 ton payload, but could perhaps be scoped to double the original size.

You would need to have at least a few of these surrogate mothers alive at any given time because they're probably going to be committing suicide at a rather high rate unless you can somehow prevent them from doing so.

Another option is just sending the frozen embryos and having automated systems on the ship raise them to, say, ten years old as the destination is approached. The food requirements here are more manageable, easily less than 100 tons for 20 children. How you get a ship to properly raise children is, of course, another very daunting challenge.

The best option, if it's technically possible, is to send frozen (and revivable) adults along with frozen embryos.

Third Problem: Where is There

We need some redundancy. Putting all of our hopes in one untested ship seems unreasonable. Let's build ten, and let's send two to each of the suggested star systems. If a system contains a perhaps-just-barely-inhabitable planet, then one of the ships will land there. If it lands successfully, then the other ship will continue on to another target (if it's made it this far and is able to continue).

If a planet looks particularly favorable, then both ships will land there.

If it's absolutely uninhabitable, then both ships will continue on.

Designing systems to automatically navigate foreign star systems, identify hospitable planets, and perform landings, will be quite a challenge, but probably easier than designing machines that can raise children!

While this all may well be possible at some point, doing it in 2030 seems very unlikely. Perhaps 2100, though I can hardly say what things will be like then.

Black Swan Possibility

An Alcubierre Drive could make this trip a piece of cake if a surprise scientific breakthrough leads to its development.


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