Can we start a colony on a passing rogue planet?
A rocky planet, similar to Earth in mass and composition, is set to pass through the solar system in one year's time. It has frozen oceans of water ice and a thin atmosphere of unknown composition. It's traveling at 50 kilometers per second, almost tangent to Earth's path around the sun. At its closest point it will be ten million kilometers away.
Physicists calculate that it will destabilise Earth's orbit and send Earth heading straight into the sun. The calculations aren't yet precise enough to find out what will happen to the planet.
Given current technology, and the fact that we have a year to plan, do we have a chance of surviving by starting a colony on the planet?
This post was sourced from https://worldbuilding.stackexchange.com/q/28493. It is licensed under CC BY-SA 3.0.
1 answer
Like other answers so far, I don't think that we have any chance of establishing a colony on that planet. I would like to add another reason, however, for why this is not possible with current technology.
You state that the planet is a year away and moving at 50 km/s at a right angle to the solar system ecliptic, heading for us. This puts its current distance at about 10.5 AU from the ecliptic and presumably a very similar distance from the Earth.
Uranus' orbit around the sun has a semi-major axis (distance along the greatest diameter) of about 20.1 AU. Since Earth's distance from the sun is about 1 AU, this means that the rogue planet is currently about as far away from Earth as is Uranus at closest approach. (This isn't very far at all in astronomical terms, but it is still quite a distance.)
We don't have the ability to go to Uranus in any way that would allow us to establish a colony around those parts of the solar system. Heck, we can't even do it to Mars, which is practically next door in comparison.
But wait -- it gets worse! This rogue planet is moving toward our solar system at those same 50 km/s, to within rounding error. Excluding solar probes like the HELIOS probes, the fastest spacecraft that have been launched from Earth move at about 15-20 km/s relative to the sun. Let's be generous and call it an even 20 km/s. Let's also be very generous and say we could get to this velocity without spending a lot of time doing fancy gravity slingshots, which almost certainly would be required in practice. Let's also say that we put all that effort into getting a spacecraft moving toward the rogue planet. Forget about the specifics of the spacecraft, let's just get it on the quickest possible intersecting trajectory at 20 km/s relative to the sun.
The relative speed of the two are now on the order of 70 km/s. The rogue planet is approaching the ecliptic at 50 km/s, and our spacecraft is moving away from the ecliptic (and toward the rogue planet) at an additional 20 km/s relative to the ecliptic.
In order to survive landing, we need to bring the relative speed down to effectively zero. In other words, for landing, we need to somehow come up with a delta-v (velocity change) budget of 70 km/s.
The way rockets work is by bringing mass (fuel), which is pushed in one direction to cause a resultant velocity change in the other direction. (Newton's third law of motion.) This lowers the mass of the rocket, which means we need less mass the next instant for the same velocity change. Conversely, going backwards, we need to bring enough mass with us to apply the change in velocity not just to the rocket itself and its payload, but also to the remaining mass of the fuel. This is known as the tyranny of the rocket equation.
When Apollo went to the Moon, after the TLI burn (translunar injection, which raised the spacecraft's orbit such that it went from a low-Earth orbit into an orbit that intersected the Moon, whether or not in a free return manner depending on the specific mission), the spacecraft was moving at about 11 km/s relative to the Earth. For any significant payloads, this is about the best we have been able to do so far. Besides the fact that this would be needed on the outbound leg of the trip, this left the Apollo CSM with very little additional delta-v budget; the LM had a bit to spare, for a soft landing on the Moon, but we are talking nowhere near the amounts that would be needed.
Even given maximum generosity and taking the velocity change from takeoff from ground to after TLI, your delta-v budget is now short only a measly 59 km/s. (In reality, it would be short a lot more.) Since lithobraking from even the slow and gentle 59 km/s to 0 km/s relative to the ground tends to be a bad idea, and because of the rocket equation's exponential nature, this is very bad news.
TL;DR: Even if we could figure out a way to establish a colony that would be able to survive, given current technology, we have no realistic way of getting there in the first place.
TL;DR;DR: In your scenario, humanity is doomed.
0 comment threads
0 comment threads