[kabacha]

The instant question this title raises: how hard would it be to move a planet into close orbit of the sun?

Weirdly enough I never came up to a similar scenario in countless sci-fi books. I'd imagine it would be so expensive that if we were capable of it we would probably wouldn't need/want it as other alternatives would be much more efficient, right?

The thought of designed solar system is interesting - what if we FTL is an unbeatable barrier - we might just be stuck here and populate our system with hundreds of rogue passerby planets!

[peeters]

Napkin math: Earth orbits at ~30 km/s, escape velocity is ~42 km/s. So to get Earth to leave the solar system (the inverse of capturing a planet under the most optimal circumstance), you would need to give it 12 km/s. Earth is ~6 * 10^24 kg, so that represents ~4.3 * 10^32 joules. The sun gives out around 3.8 * 10^26 joules per second (i.e. watts).

So with perfect efficiency, working just from conservation of energy, this would require around 13 days of the entire energy output of the sun. Or around a trillion years at Earth's current energy consumption.

[ngold]

Napkin math, my favorite kind of math. Love the days of the sun output part. Sure why not...only 13 days.

[kabacha]

Honestly that doesn't sound so much for a late civilization.

[m4rtink]

Yeah, nothing complicated for an advanced Dyson swarm - getting the energy there and propelant (unless you somehow acquired a reactionless drive) would be the main problems.

[maxerickson]

Aliens in Ring World do it: https://en.wikipedia.org/wiki/Pierson%27s_Puppeteers#Homewor...

[taotau]

Aside from the logistics and energy requirements of controlling the trajectory of something that weighs 10^24 kg, I wouldnt trust anyone alive on earth to be able to work out a stable orbit that wouldnt impact the delicate existing balance of our solar system. Something that massive would change the orbits of earth, mars, venus, even jupiter to a certain extent, not to mention all the asteroids and comets. The current stable configuration of the solar system was surely a significant contributor to the evolution of life, and it probably just came about as a freak accident. No way I would vote to allow anyone to mess with it on this scale.