Melting the core

Question

I have suggested that you could use antimatter to melt the core of Mars and restart the magnetic "dynamo", but it occurs to me that I never really considered exactly "how" you could do this. Melting the core of medium sized planets might actually be part of a far future tool kit to terraform worlds, so this is the sort of technology a space faring civilization would have.

Digging a shaft to the planet's core is out of the question, since the static pressure would collapse any conceivable tunnel long before you reach the core. So the question is "how would you go about melting the core of a planet". Antimatter is a convenient energy source, but I won't constrain any answers to just using antimatter, if you have a plausible, non magical means of melting the core of a Mars sized planet.

The Melting the Core question does seem similar, but most of the answers there either involve destructive heating of the entire planet or creating an artificial magnetic field without changing the composition of the core. I am looking at the idea as a way to solve several terraforming problems at once: generate a magnetic field, restart plate tectonics and the carbon cycle, recharge the atmosphere via volcanic outgassing and restarting the hydrological cycle as the crust warms up and the permafrost melts. The other difference is what technology or technique is needed to actually inject the energy to the core, something which is usually hand waved.

Answer 1

I'd ram the planet with another, smaller, planet.

So long as the smaller planet was sufficiently large, and not moving fast enough to completely destroy Mars, this would deliver enough kinetic energy to liquefy the entire planet, including the core. This would also both increase the mass of Mars enough for it to support an atmosphere, and create one as a result of the increased volcanic activity.

Of course, inhabiting the planet in the immediate aftermath of this procedure may be a bit challenging, given the liquid nature of the surface, but the colonists are resourceful. I'm sure they'll figure it out.

Answer 2

Make a micro black hole and drop it in the planet.

A black hole has such high density that it can sink through iron as if it were a stone in water. The black hole will oscillate around the center of the planet and, after what may be several months (if ever), finally settle at the center (it'll be best to dig as deep as possible before dropping it in).

The black hole will be emitting Hawking radiation. Heating the planet. Some speculation exists on whether this is already happening in our solar system:

And if a black hole gets inside your planet? You get additional heat. This might account for unusual temperatures seen on Saturn and Jupiter, which are hotter than they should be from solar heating alone. A black hole inside the Earth might actually raise temperatures on the surface enough to sustain animal life long after the Sun dies out.

A power source that would last for eons, providing the most efficient possible conversion of matter to energy.

This research details the power output and lifetime of micro black holes. A black hole of about 200k tonnes will output around 1,527 petawatts in the beginning of its projected month long lifetime. That's over 20 times the solar radiation hitting the upper atmosphere of the Earth. You can drop in multiple black holes at different points in the planet to increase the power and energy distribution.

The black hole would not grow. It's only 0.6 attometers in diameter; that's subatomic in size. This means it doesn't fall into the Bondi accretion regime. A black hole must have an effective radii larger than atomic size for it to be able to capture more mass.

Several articles have discussed what would have happened if the LHC had accidentally created and released a black hole into the Earth.

The researchers point out that the slower the black hole, the less mass it accretes; so although it might pop out of the LHC and sink into our planet, it will suck up very little mass.

If it does evaporate, then near the end of its life, it will either explode or turn into a white hole, releasing any remaining matter in the center of the target planet. Alternatively, if it does grow, it'll happen very slowly (billions of years) and you won't have to replenish the core with black holes.

Answer 3

If you don't want to wreck the planet with an impact crater, I'd go with tidal heating: put Mars in a close orbit around Jupiter for a few million years and let gravitational flexing do the work for you.

Answer 4

Neutrinos. Specifically, neutrino-antineutrino annihilation. Direct two stream of particles straight down towards the core, one of neutrinos, another of antineutrinos. The streams will barely interact with the matter in the planet, but once the two streams converge, they'll annihilate each other. The resulting release of radiation provides the energy the liquefy the core.

This even lets you localize the heating, by controlling the angles of the streams.

Answer 5

When an earth quake happens shock waves propagate through the planet. On earth it is thought to be possible to trigger earthquakes by building a dam and adding a lot of water to the wrong place

How this would apply to a geologically inactive planet like Mars I am not sure but given you have said we have anti matter to play with a Mars-quake or powerful shock wave machine needs to be built. Actually several. On opposite sides of the planet. The quakes/pulses will be timed so the shock waves from all the machines will meet in the core of the planet in such a way that they cause compression of the material there. This compression will cause heating.

If each shock wave can raise the temperature of the core by a small fraction of a degree this will accumulate over time and many shock waves. The shock waves will want to be as powerful as possible but not so powerful they destroy what ever machine is making them or do too much damage to the surrounding landscape. Though you could make that part of the world if you want.

Enough Mars quakes to bring the core up to the required temperature then you can move your colonists in. It would probably be pretty unpleasant being on the planet while the machines are running.

Answer 6

Disclaimer: melting planetary cores is expensive, widely considered rude (by the locals), and hazardous to your health.

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OK, so you still want to melt it? This is going to be a big job, but you can make large quantities of antimatter, so you're probably capable of doing this.

Make a breeder reactor–a big one. You're going to want to gather all the uranium on the planet. You might need all of earth's uranium too, or you could synthesise lots of it, since you apparently have great enough mastery of physics to make planet melting quantities of antimatter. Dig a huge pit and place the uranium in it. Add a carefully calculated (left as an exercise for the reader at home) quantity of Pu-239 to get things going, then sit back and wait.

The Pu-239 will convert U-238 to Pu-239, generating more fuel than is consumed. This will eventually get hot enough to melt, then start melting its way through the rock. The reaction rate will increase as it descends because it's breeding more and more fuel. Eventually, you'll have a molten iron core with a load of radioactive materials keeping it warm, just like on earth.