Sci-Fi catastrophe halp.

[Silux]

Oh herro.

So, need a little help, you wonderful, creative people who are totally willing to help me with my problems!

I'm doing a bit of writing / world building for a pretty serious sci-fi setting I am working on. I'm not going to detail the plot, but I need help determining a certain aspect of the story.
I need a catastrophe that could befall Earth that would force Humans to relocate. Bear in mind this is a setting in which Humans can terraform and regenerate environments, so events like global warming are not really relevant as they could be resolved in this setting. Ideally, it would be great if somebody could stimulate an idea that wasn't too 'just-so', and didn't feel like it was added in simply to facilitate this exodus of Humans. Any ideas?



Much <3

[Lupus]

Aliens(Ridley Scott)

- - - Updated - - -

And when ya gonna finish Rise? :P

[Silux]

Rise... Whenever Asuras gets free time. It's a scary ass world to build. There is so much documentation.

back on topic, though. No aliens in this setting
Also war is unlikely. Humans are just recovering from a huge civil war, and are in a new-found state of hippy love.

[Lupus]

I would say world ending event, like asteroid, super volcano, megaquake.

Or if nature isn't useful, human created event. Said civil war could have been nuclear. Or we could have pollution causing huge destruction. Or, by trying to change the climate, humanity makes a Cat 7 Hurricane. It won't be a lose in resources, we have the Asteroid Belt and could harvest water from Mars and comets.

[Silux]

It was nuclear. Lots of people died quite horribly.
The problem with standard natural disasters is that they are possible to recover from when the Humans have the ability to regenerate environments. Ideally he event would require a certain degree of finality about it. My current idea was for development of an FTL Alcubierre drive would causes a particle backlash (That is what theoretically happens upon an Alcubierre FTL slowdown) that has the equivalent explosive force of several quadrillion megatons - enough to throw Earth from it's orbit around the sun and veering off into deep space.

But... meh.

[Kagamine]

Nuclear war you say? Well that's easy. The radiation could be making the planet too dangerous- unless that falls under the "fixing the environment" piece.

In which case, you're probably just making this harder than it needs to be for yourself with that terraform thing.

[ultimateplay91]

Alien invasion, nuclear war, gray goo (look it up on tv tropes), earth blowing up (like krypton), and robot uprising.

[Goldmarble]

Easy: Scattered Disc object (asteroid/comet) of sufficiently large diameter with such a large elliptical orbit, that it is just coming into the solar system for the first time in 10,000+ years.

Is this possible?
http://en.wikipedia.org/wiki/90377_Sedna

Sedna is a 1000km in diameter long period object in space. It takes 11,400 years to make a single orbit in theory.

It is easily possible, and plausible to have such an object come hurtling out of the Oort cloud at us. Though it would have to be suitably massive, such as a Dwarf Planet or a Proto-Planet, to prevent the possibility of us being able to deflect it with any possible technology we could come up with. It would be heralded by vastly increased meteor showers and meteorite strikes, if it plowed through the Kupier belt or the Asteroid belt as well.

Otherwise, you are looking at humanity fucking up the world with some kind of Earth Shattering Kaboom!™
The problem with this scenario, is how does humanity have enough time to basically savagely rape the planet of all resources, to build the colony ships necessary to GTFO?

Either would render massive changes in the inner sphere of our solar system due to mass ejection of the Earth, the Moon, and the colliding object itself.

[Ommanipadmehum]

Try this calculator for destructive fun-times that don't destabilize the solar system. Here's what happens on the opposite side of Earth when a 100 km wide, metallic asteroid hits the Earth head on, while moving at twice the speed of the Sun's orbit around the galaxy. All-around massive death and destruction. Sounds implausible? There's at least 200 asteroids of that size in just the main belt, and a supernova could easily accelerate such an asteroid to high speeds.

EDIT: If an asteroid that big sounds unlikely, one a tenth that size, of which there's at least 100,000 in our main belt, would still royally screw the planet. The global ecology would be hurting bad, and the climate would be thrown way out of balance by the tons of fallout from the blast.

EDIT 2: I know you said no aliens, but if you're open to changing your mind, here's a thought. Rather than invading with motherships and laser cannons, they could devastate the biosphere by shooting asteroids at 1% light speed at Earth, timing the launches so that they strike in the most ideal spots over the course of a day. By the time we'd see the asteroids coming, there'd be no way to stop them. We'd realize this was no freak of nature and scramble to colonize space as quickly as possible, even if Earth didn't become an apocalyptic wasteland. As to why the aliens did it, they calculated incorrectly on whether we'd be space-capable by the time the impacts would occur, and planned to physically invade way after.

[Turtlicious]

Humans decide to try Nuclear power once again, yeah they're all crunchy granola, but those plants are only dangerous when they catastrophically fail. Suddenly fault lines start to pull apart causing huge earthquakes, causing every nuclear reactor on earth to melt down, washing the earth in radiation. While terraforming is a possibility, the UN decided to write off Earth as a lost cause, leaving nothing but a barren wasteland filled with mutants and food too irradiated to eat behind. You could even bring up a plot point later where humans left behind mutated quite a bit (not the good kind of mutation,) and got really pissed for being abandoned.