Could it be possible for two planets to collide and not kill everything?
Before we begin, two things. This question was inspired by this one. I definitely don't want this to happen.
So, I have two very close tidally locked planets, each fills up about 2/3 of the sky of the other. They both have about .75g of gravity. There is also a moon orbiting the two planets at some distance (where it is stable). One planet is predominantly ocean with scattered topical islands, small forested islands, and some swamps. The other is mostly desert, in that it has little water.
Note - Assume these aliens have interstellar travel, and are able to travel just under the speed of light. If you think they'd have other kinds of technology as well, then feel free to include it. These alien races would like to help the planets come together gently, let them help if you can. (They can't stop the planets from colliding.)
Now, is there a way for the two planets to collide and not wipe out each other?
You can change some factors about the planets, but their sizes must be between Mars's and Earth's. As a last resort, the inhabitants can flee the planets, but I want to avoid this if possible.
This post was sourced from https://worldbuilding.stackexchange.com/q/34583. It is licensed under CC BY-SA 3.0.
1 answer
Everyone will burn to death.
This NASA page shows temperature changes during the collision between Earth and Theia in the Giant Impact Hypothesis. The temperature is on the x-axis, in Kelvin:
Your people are going to die at temperatures worse than hellish. This will be an inferno never before seen on Earth, or any terrestrial planet not subject to such an impact. Temperatures may be lower because the impact velocity will be slower than in the Earth-Theia collision, but they will still be very high.
So, I don't think that people can survive, unless they
- Escape somewhere else.
- Go to the orbiting moon, which is hopefully far away. The collision between the planets may eject material into an orbit around the resulting body (if there is one), so there's a chance the moon may be adversely affected.
If not, the intense temperatures will kill them, and even the oceans can't stop that.
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