The sun goes nova

[Swindle1984]

Your space civilization could have been screwing around with the sun, and fucked something up so badly, the solar system isn't habitable. Say, 'oops'.

Just make what they did, and the full effects 'classified', and all done. Maybe the sun is using up hydrogen x10's faster (with a x10 increase in radiation levels).

Try to avoid the 'alien fleet pursuing them' angle. To Battlestar Galactica

They're not being hunted down. They just have to get away before the aliens show up to stripmine the place and possibly wipe out the natives.

[Razor One]

Any alien species ruthless enough to genocide a different alien species out of its home system for resources is also going to make sure they mop up any survivors.

The last thing you want is a bunch of pissed off alien fanatics trying to kill your grandchildren for entirely justifiable reasons.

I've been considering a similar scenario lately as backstory to one of my projects where the inner system is relatively well developed while the outer system is still home to outposts and the like.

The idea was that people had to evacuate within five years of detecting an "anomalous threat"* to the solar system to a safety margin of ~50 LY, meaning the nearby systems are not safe either.

The main thrust was that 95% of humanity is screwed with the predictable "hell in a handbasket" results of quite a few billion people realising just how screwed they are. 90% of the survivors are probably screwed as well since five years leaves practically no time to properly prepare or stock up, and the survivors that do make it into relatively "Safe" space will probably have done so via generational methods with societies not optimised for long term high stress survival.

The ones that do cop all the breaks, find a safe planet with a compatible chemistry and make landfall have to wind up rebuilding the infrastructure and knowledge base that was lost with Earth, and that's assuming the social structure doesn't collapse into outright chaos from the word go.

*My current thinking for the "Anomalous Threat" is a Gamma Ray Burst. Unfortunately they don't quite last long enough to make the backstory plausible. The only workaround I could think of would be that this was either a new kind of interstellar object (not likely) or a remnant of technology left over from an alien species that went extinct a long, long time ago that activated spontaneously and started emitting gamma rays in the local group.

[Junghalli]

Suddenly, we've got a slow steamroller cruising into our solar system. There's no way to stop or deflect something that big, and, one by one, the planets and asteroids of the solar system wil find themselves pitched out of their customary orbits. Whether the body goes on a slow trip into interstellar space or a faster trip into the thermonuclear furnace of the sun, it's game over for that body. Either the brown giant ends its performance by smashing into the sun, prompting deadly flares, or it goes into a uselessly close orbit around Sol. Either way, our solar system suddenly becomes a lethally empty place.

It's unlikely that it would eject every body from the solar system (the Oort Cloud, for instance, is probably far too distributed), and it certainly wouldn't do it fast - just to touch the Kuiper Belt for instance it would need to take some pretty long orbits. A habitat-based civilization would be able to move ejected asteroids and habitats back into solar orbit (or simply away from orbits that take it close to the brown dwarf), and this would take a lot less delta V than reaching another star in a convenient timescale.

It's another one of those things that could screw up a planet-based society pretty easily but could be dealt with by easier means than moving to another solar system.

[Swindle1984]

Any alien species ruthless enough to genocide a different alien species out of its home system for resources is also going to make sure they mop up any survivors.

The last thing you want is a bunch of pissed off alien fanatics trying to kill your grandchildren for entirely justifiable reasons.

The species may or may not be ruthless enough to genocide humanity unless it can be done easily; if we're still here and still technologically inferior, they can just lob a bunch of projectiles at space habs and planets to devastate us so they can safely stripmine the system for resources before moving on. Or maybe the scout acted out of paranoia and without authorization and the main fleet is more amenable to trade and negotiation, especially since we've quite obviously expanded into space and become far more dangerous than before.

And which makes more sense, upon seeing the bulk of the population fleeing the system, pursuing them and getting into a generations-long war of attrition and genocide, or stripping their system of what you need and then hauling ass while they're still running away? How dangerous could the human fleet be, at its acceleration and the turn-around time needed to pursue the alien fleet?

Even if the aliens pursue the humans, it'll be after months or even years of resource extraction (and fighting whoever was left behind), so they can't catch up to the human fleet until it stops to do the same. And if the humans are leaving permanent settlements in each system they visit, that's a rearguard that can ambush the alien fleet as it enters the system, and warn the fleet that they're being pursued, giving them the opportunity to prepare for the aliens during the long, long voyage to the next system.

[Uncluttered]

Any alien species ruthless enough to genocide a different alien species out of its home system for resources is also going to make sure they mop up any survivors.

The last thing you want is a bunch of pissed off alien fanatics trying to kill your grandchildren for entirely justifiable reasons.

I've been considering a similar scenario lately as backstory to one of my projects where the inner system is relatively well developed while the outer system is still home to outposts and the like.

The idea was that people had to evacuate within five years of detecting an "anomalous threat"* to the solar system to a safety margin of ~50 LY, meaning the nearby systems are not safe either.

The main thrust was that 95% of humanity is screwed with the predictable "hell in a handbasket" results of quite a few billion people realising just how screwed they are. 90% of the survivors are probably screwed as well since five years leaves practically no time to properly prepare or stock up, and the survivors that do make it into relatively "Safe" space will probably have done so via generational methods with societies not optimised for long term high stress survival.
The ones that do cop all the breaks, find a safe planet with a compatible chemistry and make landfall have to wind up rebuilding the infrastructure and knowledge base that was lost with Earth, and that's assuming the social structure doesn't collapse into outright chaos from the word go.

*My current thinking for the "Anomalous Threat" is a Gamma Ray Burst. Unfortunately they don't quite last long enough to make the backstory plausible. The only workaround I could think of would be that this was either a new kind of interstellar object (not likely) or a remnant of technology left over from an alien species that went extinct a long, long time ago that activated spontaneously and started emitting gamma rays in the local group.

How bout a rogue gas giant, or brown dwarf? The brown dwarf especially because it's going to have it's own orbital bodies. It will be machine gunning Sol system with comets, asteroids, debries clouds and snew.

You won't have to reinvent the wheel, just abuse it a little.

[Razor One]

You missed the part where I wanted to render the local group unsafe for habitation for a radius of 50 LY. A Rogue planet or brown dwarf is excellent for throwing the solar system into chaos, 50 LY is a completely different monster.

Swindle, in the short term that's a viable strategy, but I'm thinking more long term, 30 - 1000 years after the fact. Humans will never forget genocide on that scale nor will they be likely to forgive it. The only thing that aliens do by taking such tactics would be to fill the desperate survivors of humanity with a hatred that will blaze across the generations.

Every effort, every thought, every action will be made to ultimately take back what was once ours and make the genocidal aliens pay for what they've done. I may not know exactly what the aliens would do but I know, somewhat, what we'd probably do, and any smart alien commander who's at least taken "Human Culture for Dummies 101" is going to realise that not completely annihilating us while we've still got all our eggs in one basket is just asking for retribution on a grand scale further down the track.

So yes, they'll be safe to stripmine the solar system to their hearts content. Meanwhile they'll merely have awakened a sleeping giant and filled it with a terrible purpose.

[Uncluttered]

.....devastate us so they can safely stripmine the system for resources before moving on.

The only problem I find with this, is that killing us for our resources is silly. If you can cross the interstellar void, you can cross to an uninhabited star system, and find pretty much anything you want, free for the taking. Also. If you stripmine a solar system, the Mass doesn't disappear. You have to move it somehow. The classic invasion plot doesn't really work.

(And so I followed this train of thought)
Moving all that mass....
I can imagine a scenario in which they invade us from a dyson swarm. The swarm moves their star using light pressure, balanced by gravity.
For example http://en.wikipedia.org/wiki/Stellar_engine
Use a small red or brown dwarf (or singularity) to explain why we don't see it already. BD will not have much light, but will have stellar wind. The swarm can use magsails.
They can't steer the star easily, so they have to grab matter from the nearest star system.
Lucky us.

The first thing they do might be to push a fleet with a particle stream. Electricity around a brown dwarf is cheap. The brown dwarf might have plenty of their own volatiles, so the swarm will want our womenheavy elements.
The fleet will appear to colonize our outer system, but in reality it's a little mining camp to them.
They will build solar sails, and slingshot guided matter around Sol, to rendezvous with the swarm.
They may use giant lasers, or Jupiters EM field to push a particle stream.

Their goals are not to kill us, we're just in the way. We're the aborigines, and they are esso.
They might even try to pay us with trinkets to strip mine our inner planets for them.
Trinkets may include:
1. Technology
2. Free ride to wherever with a push from their particle stream
3. The gospel of space Jesus
4. Admission to the united federation of swarms (This might be legit, and the swarm might actually be more than one civ)
5. Sex with green space babes
6. Space money
7. Sparing our puny earthican lives

They want our resources so they can:
1. Build onto the dyson swarm
2. Spawn a second swarm
3. Leave the milkyway altogether
3A. Because it's going to run out of hydrogen in a billion years
3B. Because the MW will crash into Andromeda in about 3 billion years
3C. Because they pissed off a bigger swarm
3D. Because they need to get to the post office on time.
4. Finish their galactic superhighway, a network of particle streams that cross the galaxy, allowing city sized clusters of ships to travel easily.
6. Build a massive matryoshka brain, and live forever on the edge of a black hole
7. Collect all the pokemon

A dyson swarm civ will have many different goals and factions, even one that is mostly AI minds. I can imagine a realistic scenario in which the plucky humans win the day...by suing them.

SpaceManLawyer to the rescue....OK..Time for bed for me.

[Uncluttered]

You missed the part where I wanted to render the local group unsafe for habitation for a radius of 50 LY.

I did miss that part. Sorry
50LY is a bit much IMHO.
Space is big. 1 lightyear is really really big, and with every LY you add, that sphere of space is growing exponentially. Unless something is eating the universe, there are few threats which can't be simply dodged.
They would have to be actively chased.

Even if your ragtag fleet is being chased, they have a good chance of hiding.

If they come from an Oneil culture, they won't be foolish to settle on a planet. They'll build out on any asteroid, comet, or handy body they find. They'll live like rats, and breed, and come back exponentially bigger. If I was Admiral Adama, I would've jumped into a asteroid belt, and never left until I built a fleet that could smash the Taiidani Cylons

[Swindle1984]

The only problem I find with this, is that killing us for our resources is silly. If you can cross the interstellar void, you can cross to an uninhabited star system, and find pretty much anything you want, free for the taking. Also. If you stripmine a solar system, the Mass doesn't disappear. You have to move it somehow. The classic invasion plot doesn't really work.

They didn't WANT to invade, they ran into us on accident. The scout ship was just passing through and lobbed the comet to wipe us out, or at least destroy enough infrastructure to keep us harmless, as it flew by. The main fleet behind it, however, HAS to stop to pick up more resources or simply because they can't change course without expending too much fuel/increasing travel time beyond what they can sustain, and now that we've spread out into space and are actively evacuating the system years before they arrive, they can't exterminate us without devoting their entire civilization to it.

And if we're traveling in a different direction and there's no faster-than-light travel, why bother pursuing us if they can just resupply and fly off in the opposite direction? Not only would it be an incredibly long time before we turned around and could chase after them for revenge, but the galaxy is a huge place; what are the odds that centuries, even millennia later, that we'd run into them again? And could you really hold a grudge for that long?

[sirocco]

Any alien species ruthless enough to genocide a different alien species out of its home system for resources is also going to make sure they mop up any survivors.

The last thing you want is a bunch of pissed off alien fanatics trying to kill your grandchildren for entirely justifiable reasons.

The species may or may not be ruthless enough to genocide humanity unless it can be done easily; if we're still here and still technologically inferior, they can just lob a bunch of projectiles at space habs and planets to devastate us so they can safely stripmine the system for resources before moving on. Or maybe the scout acted out of paranoia and without authorization and the main fleet is more amenable to trade and negotiation, especially since we've quite obviously expanded into space and become far more dangerous than before.

And which makes more sense, upon seeing the bulk of the population fleeing the system, pursuing them and getting into a generations-long war of attrition and genocide, or stripping their system of what you need and then hauling ass while they're still running away? How dangerous could the human fleet be, at its acceleration and the turn-around time needed to pursue the alien fleet?

Even if the aliens pursue the humans, it'll be after months or even years of resource extraction (and fighting whoever was left behind), so they can't catch up to the human fleet until it stops to do the same. And if the humans are leaving permanent settlements in each system they visit, that's a rearguard that can ambush the alien fleet as it enters the system, and warn the fleet that they're being pursued, giving them the opportunity to prepare for the aliens during the long, long voyage to the next system.

So
1- the initial asteroid impact was caused by a scoutship (or a scout-swarm of ships) that decided that we were a threat for their own space fleet.
2- In reaction, Earth started building O'Neill space habitats that evolved into space colonies which want to get more and more independant
3- As the aliens get closer to the Sol system, people start realizing that they should have a plan B involving those space habitats
4- They are converted into Rama style ships (or something as close as possible) then progressively positionned at the edge of Sol system
5- Finally they all depart for Alpha Centaury while people left behind will face the possible alien invasion
6- then?

Do you plan to write about both sides, space settlers and humans left behind or just the former? If this is about the settlers, I don't think you should start explaining what were the motivations of ET. Leave some mystery around what happened to Earth, make it a legend as people progress into the deep space, something that will bind them together or separate them.

Just think "the Iliad in space". And if you're bored, choose a hero to become the space Odysseus that will get back to Earth after a long trip and smite the monstrous invaders soiling his home. At that moment, you may even make some smart FTL if such thing does exist, so that he can get to Earth during his lifetime or some eugenics to (significantly) increase his lifetime.

Note: I had that idea once. Then nBSG happened...

Note2: If we finally act the same way as ET, the galaxy will end up with several space fleets full of people holding a grudge against a race they don't know anything about. Scary, isn't it?

[Uncluttered]

Not only would it be an incredibly long time before we turned around and could chase after them for revenge, but the galaxy is a huge place; what are the odds that centuries, even millennia later, that we'd run into them again? And could you really hold a grudge for that long?

The prosecution will now show exhibit B: Palestine....

[Junghalli]

Not only would it be an incredibly long time before we turned around and could chase after them for revenge, but the galaxy is a huge place; what are the odds that centuries, even millennia later, that we'd run into them again?

If we started systematically expanding through the galaxy at some point, pretty good. Even at low fractions of c you could colonize every star in the galaxy in an eyeblink compared to the universe's lifespan. It's the main thing that makes the Fermi Paradox a paradox.

[Swindle1984]

Any alien species ruthless enough to genocide a different alien species out of its home system for resources is also going to make sure they mop up any survivors.

The last thing you want is a bunch of pissed off alien fanatics trying to kill your grandchildren for entirely justifiable reasons.

The species may or may not be ruthless enough to genocide humanity unless it can be done easily; if we're still here and still technologically inferior, they can just lob a bunch of projectiles at space habs and planets to devastate us so they can safely stripmine the system for resources before moving on. Or maybe the scout acted out of paranoia and without authorization and the main fleet is more amenable to trade and negotiation, especially since we've quite obviously expanded into space and become far more dangerous than before.

And which makes more sense, upon seeing the bulk of the population fleeing the system, pursuing them and getting into a generations-long war of attrition and genocide, or stripping their system of what you need and then hauling ass while they're still running away? How dangerous could the human fleet be, at its acceleration and the turn-around time needed to pursue the alien fleet?

Even if the aliens pursue the humans, it'll be after months or even years of resource extraction (and fighting whoever was left behind), so they can't catch up to the human fleet until it stops to do the same. And if the humans are leaving permanent settlements in each system they visit, that's a rearguard that can ambush the alien fleet as it enters the system, and warn the fleet that they're being pursued, giving them the opportunity to prepare for the aliens during the long, long voyage to the next system.

So
1- the initial asteroid impact was caused by a scoutship (or a scout-swarm of ships) that decided that we were a threat for their own space fleet.
2- In reaction, Earth started building O'Neill space habitats that evolved into space colonies which want to get more and more independant
3- As the aliens get closer to the Sol system, people start realizing that they should have a plan B involving those space habitats
4- They are converted into Rama style ships (or something as close as possible) then progressively positionned at the edge of Sol system
5- Finally they all depart for Alpha Centaury while people left behind will face the possible alien invasion
6- then?

Do you plan to write about both sides, space settlers and humans left behind or just the former? If this is about the settlers, I don't think you should start explaining what were the motivations of ET. Leave some mystery around what happened to Earth, make it a legend as people progress into the deep space, something that will bind them together or separate them.

Just think "the Iliad in space". And if you're bored, choose a hero to become the space Odysseus that will get back to Earth after a long trip and smite the monstrous invaders soiling his home. At that moment, you may even make some smart FTL if such thing does exist, so that he can get to Earth during his lifetime or some eugenics to (significantly) increase his lifetime.

Note: I had that idea once. Then nBSG happened...

Note2: If we finally act the same way as ET, the galaxy will end up with several space fleets full of people holding a grudge against a race they don't know anything about. Scary, isn't it?

I plan on keeping what happens to Earth after the fleet leaves a secret. They keep sending laser and radio messages toward Sol, but after a few years in interstellar space they stop receiving messages. It could be for any number of reasons: the aliens destroyed the remaining humans, Earth is aiming their shit at the wrong place, natural interference, nobody knows. They just know they don't hear anything from Earth any more.

Also, at the point where people begin building space habs, nobody knows the comet was thrown at them deliberately; they think it was just an accident. It takes fifty years to get to the conflict between the colonists and Earth, and they don't find signs that the comet was a deliberate attack until a few years later; at roughly the same time, they start picking up the first signs of the approaching alien fleet. Humanity in general shits a brick, especially when someone openly suggests that the comet was a deliberate attack by a scout, at which point people put aside their petty bullshit and start organizing a response. They realize that even spreading out into the solar system isn't a guaranteed means of survival against a species that is technologically beyond them, so they start rushing as fast as they can to come up with a means of mass exodus so they can fly off in a direction the aliens aren't traveling in.

I think I'll include some planetary exploration later on in the series. I kinda liked The Legacy of Heorot and Beowulf's Children and wouldn't mind incorporating some their concepts into the story. Except I'll need to keep it somewhat scientifically plausible instead of "lol, this planet is perfectly suited to human settlement, it just has weird critters". What's a plausible way to have a planet people can explore and maybe survive on temporarily, but not permanently colonize? Biochemical incompatibility and atmospheric differences? What sort of conditions would exist to make life there biochemically incompatible?

[Junghalli]

What's a plausible way to have a planet people can explore and maybe survive on temporarily, but not permanently colonize?

Depends on what your criteria for a place you'd colonize is. You could theoretically colonize an airless ball of rock and ice orbiting a white dwarf star...

Biochemical incompatibility and atmospheric differences? What sort of conditions would exist to make life there biochemically incompatible?

I'm no biochemist but I suspect it'd probably be easier to get biochemically incompatible alien life than to get biochemically compatible alien life. It just needs to use different sugars, lipids, amino acids etc.

If you want something a bit more extreme, there are all kinds of unfriendly atmospheres you can imagine. For instance, the atmosphere might have 2-4X more nitrogen than ours so human explorers would suffer nitrogen narcosis, or there might be too little oxygen so bottled oxygen would be required, or the planet could have an average temperature of > 50 C and be inhabited by thermophilic life (e.g. something like this). For other ideas, you might want to check out this site.

[Swindle1984]

I was thinking mainly of having the flora and fauna on the planet based on right-handed amino acids instead of left-handed amino acids, but I was curious about what in the environment would make life select one or the other.

Theoretically, could something metabolize both left and right-handed amino acids?

[Junghalli]

I was thinking mainly of having the flora and fauna on the planet based on right-handed amino acids instead of left-handed amino acids, but I was curious about what in the environment would make life select one or the other.

Just looking it up on Google:

The origin of this homochirality in biology is the subject of much debate.[10] Most scientists believe that Earth life's "choice" of chirality was purely random, and that if carbon-based life forms exist elsewhere in the universe, their chemistry could theoretically have opposite chirality. However, there is some suggestion that early amino acids could have formed in comet dust. In this case, circularly polarised radiation (which makes up 17% of stellar radiation) could have caused the selective destruction of one chirality of amino acids, leading to a selection bias which ultimately resulted in all life on Earth being homochiral.

[Swindle1984]

I was thinking mainly of having the flora and fauna on the planet based on right-handed amino acids instead of left-handed amino acids, but I was curious about what in the environment would make life select one or the other.

Just looking it up on Google:

The origin of this homochirality in biology is the subject of much debate.[10] Most scientists believe that Earth life's "choice" of chirality was purely random, and that if carbon-based life forms exist elsewhere in the universe, their chemistry could theoretically have opposite chirality. However, there is some suggestion that early amino acids could have formed in comet dust. In this case, circularly polarised radiation (which makes up 17% of stellar radiation) could have caused the selective destruction of one chirality of amino acids, leading to a selection bias which ultimately resulted in all life on Earth being homochiral.

Which means... what? Theoretically, most life would use left-handed amino acids like us?

[Junghalli]

Which means... what? Theoretically, most life would use left-handed amino acids like us?

They don't know. If you want opposite chirality life, it's probably fairly safe to just go with it and not worry about how it got that way too much. Even if most life has the same chirality as us there's probably going to be the odd exception - it's a big universe out there.

[Swindle1984]

Theoretically, is it possible for a lifeform to process both chiralities?

[Junghalli]

I have no idea, sorry.

[Razor One]

I think I recall an article that stated that certain kinds of bacteria could process sugars and the like that normally couldn't be digested due to their chirality. Apparently they weren't directly consuming it, merely putting it through a conversion process before munching on it as normal.

I can't find the article so consider it apocryphal until I can find a link.

[Uncluttered]

What's a plausible way to have a planet people can explore and maybe survive on temporarily, but not permanently colonize?

I'd go with a red dwarf star. It's the wrong color for our monkey eyes, and gives off nasty radiation bursts.

If the live on Oneil/Ramas, skip the planet altogether. Have them colonize a belt.

[Junghalli]

I'd go with a red dwarf star. It's the wrong color for our monkey eyes, and gives off nasty radiation bursts.

Smaller stars emit proportionately less high energy radiation, not more (maybe you're thinking of a flare star? lots of red dwarfs are flare stars). If it's nasty radiation you want then you probably want to look at a star brighter than our sun. The papers I've read though suggest a habitable planet around a red dwarf would be stable (not in danger of atmosphere collapse due to the air freezing out on the tidally locked planet's permanent night side) with ~.1 bar partial pressure of CO2, which is way more than we evolved for; the air probably wouldn't be very healthy for us.

[bz249]

In case of an alien invasion, well they do not have to kill everyone to totally demolish us. They just have to kill enough to collapse civilization forever, which might not be that difficult as one first think. Since the more advanced the human civilization become, the more complex the logistics become. This means that we can not maintain even a current level society with just a few million men (note for example there is only two companies in the whole world which is capable of producing wide body aircrafts, for a market of billions... so for a human civilization of a few millions wide body aircrafts are not possible to produce, and most of the high-tech stuff is similar, only accessible with a reasonably big population) so the aliens can practically leave alone all the habitats if they are small and isolated.

So unless a yet unknown invention change the nature of manufacturing a scattered band of survivors pose no threat as they can only produce the most basic stuff by themselves. This also means that if they can not find a suitable location to restart the things they will forget all advanced knowledge (or at least the practical part of it) within a few generations. Advanced robotics might change the fact a bit, but robots have limited lifetime also (and the more sophisticated units tend to be the less damage prone), so without a proper support infrastructure they might degrade pretty soon too.

[Junghalli]

In case of an alien invasion, well they do not have to kill everyone to totally demolish us. They just have to kill enough to collapse civilization forever

Forever is a long time, and civilization could plausibly spring back in eyeblinks compared to galaxy-colonization timescales (since even 10-20 thousand years isn't that much time next to that, and in that time we went from cave men to a global industrial civilization). Leaving behind survivors on the logic that you've done enough just by knocking them back to the stone age strikes me as complacent.