Terraforming a gas giant by freezing the "gas" and "liquid" and removing it by huge impacts

Question

In my setting, humans want to colonize Jupiter, so as to establish an outpost in the outer Solar System, but cannot due to a barrage of reasons.

• Jupiter's gravity is really high and would prove to be hazardous to any astronaut who stays there long term.
• Jupiter has no surface to land on—this point is most stressed on by many scientists and engineers upon the concept of a Jupiterian outpost
• Even the humble airship is disastrously inefficient on Jupiter—due to the lack of a solid surface to land on, Zeppelins and cloud cities have been proposed as an alternative for colonizing Jupiter. However, even these zeppelins provide really little lift in Jupiter's atmosphere, as Jupiter's atmosphere's density is only about 0.16 kg/m³, just twice that of hydrogen

So scientists come up with a solution.

A giant solar shade is installed in orbit in the Lagrangian point between Jupiter and the Sun. The solar shade itself doesn't need to be really thick. It is really just a few micrometers thick. This causes Jupiter's surface atmosphere to cool considerably.

Meanwhile to remove Jupiter's zenothermal heat/internal heat, large quantities of copper powder are sprayed into the planet by reusable probes that carry the powder. When the particles fall into the planet, they are heated up by the intense heat inside and are lifted up again. The copper particles radiate this heat into space, and then again fall back into the planet. This creates a runaway convection-cycle, that ends up radiating most of the heat into space. This results in the gas giant freezing into a solid ball of solid hydrogen. This hydrogen is then blasted out into space by impacting asteroids into it, leaving behind a rocky core. I computed the gravity of the core, which is 32,000 km wide and 20 earths-masses, and it is merely that of Neptune, i.e. the gravity is just 11 m/s², just a bit more than Earths, but manageable.

What are the advantages and disadvantages of this terraforming technique?

Answer 1

There are a number of problems.

First, Jupiter has it's own heat source. So cooling it is a challenge. Cooling it to solid hydrogen temperatures, about 14K, is pretty much not going to happen.

The sun shade is an issue as well. It has to be big enough to cover Jupiter. Plus it has to be in orbit. I'm having a hard time thinking how to get coverage with anything less than a tubular shell of some kind. This is a mega structure, a sleeve for Jupiter. It has to stand up to the radiation around Jupiter, the various things the moons are jetting into the area (one of them has a sulphur volcano) and the tides they produce. It would certainly be millions of tonnes of material. If you can produce such a thing you probably don't care very much about Jupiter.

Even if that worked, the time for the atmosphere to cool as much as you want would be inconvenient. There is a calculator for that based on thermal radiation. I will leave that for your homework. But as a hint, it is going to be a lot longer than you will find convenient.

And the idea of knocking the solid atmosphere off is not going to be very practical. You would need to provide enough kinetic energy to get that mass off Jupiter. Such collisions are not very efficient means of producing what you want so they will transfer large quantities of heat to the planet. To get a kilogram off the planet you would need a projectile significantly more massive than that kilogram. So you would either need to reuse projectiles, which means you have to go collect them, redirect them, and send them to collide again. Or you need several times the mass of Jupiter as projectiles.

Now supposing all that really could work. What you will have left is a core that is heated to molten-magma temperatures from impacts. Cooling from that takes many thousands of years just to get a solid surface. Remember that you have been pounding from space with projectiles going 10's of km/s. It will churn up and heat up the rock to 10's of km deep. So even if all the problems could be fixed, you would get a lava planet that was not much good for anything.

So it would not work the way you suggest. And if you could produce the results you would be able to make mega-structures that were far more useful than retro-fitting Jupiter. So it's a no-go.

Answer 2

Good enough for a video game. Or a Star Wars movie. But practicalities: aside from the amount of heat you would need to dispense with to freeze J into a solid ball, I wonder about /When the particles fall into the planet, they are heated up by the intense heat inside and are lifted up again./

Why would metal particles that got heated start to rise? Particles, even atoms of copper will never be less dense than the gaseous atmosphere around it. They will never float. Dense particles (e.g. metal) of any temperature will make their way through the gas atmosphere down to the chewy center of the planet. You will move the heat not to the outer atmosphere to be radiated away, but down to the depths where all the heat is anyway.

Answer 3

Frame Challenge: Your scientists want any outpost in the outer solar system

And that being the case, why does it need to be Jupiter? If you have enough rocket fuel and raw materials to do anything on a planetary scale, let alone on the scale of the largest planet in the solar system, you have plenty enough to build a truly massive space station.

Make a large satellite - or more practically, a cluster of reasonably close satellites with varying functions - orbiting around Jupiter. It still occupies the same general area, and it can be gradually built over successive generations instead of waiting millennia for those terraforming processes to take place