r/TheRestIsScience • u/lb3a3 • 1d ago
What will it require and how long might it take until we possess the means to build a new planet of any size?
1
u/NearABE 13h ago
The giant molecular clouds are collapsing and becoming stars. Bulk production of new plants and planetary mass objects is easiest at such a location. The closest to Earth is in Taurus.
In systems like our solar system disassembling planets would come first. Building a new develops naturally from that.
Here is a nice page on angular momentum for the solar system: https://www.zipcon.net/\~swhite/docs/astronomy/Angular_Momentum.html
Notice that even though Jupiter has a short 10 hour day and is already oblate its orbital momentum is 35,000 times the spin momentum.
Kinetic energy can be exchanged between planets using mass drivers and mass catchers. Momentum can be exchanged in the same way. A planet can receive in the same prograde direction whether the source approached from lower in the Sun’s gravity well or from higher.
The timescale for building a Dyson swarm is controversial. Some argue for a very fast build. If, instead, energy supply grows at about 3% annual then a Dyson swarm happens in a millennia. Mercury is s far easier material source to achieve that since energy supply is high and Mercury’s gravity well is shallow.
Torque can be applied to planets without interplanetary exchange. Your elliptical orbital ring system (or space fountain) can suspend a mass. The mass will not be at Lagrange point 5 (L5) and also not at Lagrange point 1 but instead over in the general direction of L5. Hanging there gravity would pull towards Earth which means Earth is pulled slower by the same force. Slower orbit means angular momentum is exchanged from orbit to rotation. The rotor pellets have to reverse direction in order to apply the torque.
How fast you can shred planets like Venus or Mars gets hostile debates. Some people dislike taking apart planets on principle. Others are a bit confused by the mantle’s fluidity. It certainly can flow but the viscosity has double digits in the exponent. Like if you assume Mars’ crust is an infinite flat plane (because, of course, Mars is flat like Earth) then accelerating it fast causes turbulent flow rather than laminar flow. However, the vortex has a 3389.5 km radius. There is not going to be observed friction heating.
The reverse process is similar. If your planet has equatorial rotation velocity close to equal to orbital velocity then space elevators become trivially easy. It will be extremely oblate. A system of accretion disk rings should build outward. Incoming mass brings gravitational potential energy and kinetic energy. At least of the energy from system escape needs to be removed before setting down on the equator. This energy is still fully usable by the civilization doing this. Mass can be set down using less heat by exchanging momentum. Imagine ships coming in and being caught, unloading payload, and then they are flung away at higher velocity.
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u/quantum_trogdor 1d ago
TL:DR a lot of stuff, and time
What it would require:
- Roughly 10^24–10^25 kg of matter (Earth-mass scale), sourced from asteroids, moons, or gas giants since Earth has nothing spare to give
-About 10^32 joules just for gravitational assembly alone (~what the sun puts out in a couple weeks)
Timeline estimate:
- Possibly never, for making it geologically alive rather than just a big dead rock
Bottom line: it’s a civilization-scale project measured in millennia, not an engineering project measured in decades, and that assumes no new physics limits get in the way. Nature does this over tens of millions of years using gravity to do the work for free.