Let's say I have a terrestrial planet superficially like earth, except that it rotates much slower (about 10-15 days per rotation) and its atmosphere is ideally several times thicker. If I want this planet to have a substantial magnetic field (3/4 of Earth's as a minimum, though higher is better), what factors can I play with to plausibly provide it that field strength? What approximate values would I need to give these factors to accomplish this?
Here are some ideas I'm toying with (please vet for plausibility):
- Large metallic core
- Tidal Heating: Interactions with the planet's star can generate internal heat and keep a dynamo active. (Would that work?)
- Increase radius: The larger the radius, the faster (m/s) the spin for a given rotation period. The faster the spin the more potential for a strong magnetosphere?
- I read somewhere that Venus's small (non-core generated) magnetosphere can be attributed to some interesting physics happening within its dense atmosphere. Is there a way to take advantage of this phenomena? I presume my planet's atmosphere isn't dense enough nor the phenomena significant enough.
Giving the planet a bigger metal core (and hence making it denser) AND giving it a larger radius would seem to be a good recipe for increasing field strength. [Edit: Removed gravity considerations. Planet can be a Super Earth]
It's not clear to me what variables are the most critical. Is rotation rate more important than core size/composition, or vice-versa? Is internal heating (whether from tidal stress, radioactive decay, or leftover formation heat) as critical as the above two variables? I'm not versed enough in this domain to know.
My understanding is that the exact parameters behind terrestrial magnetic fields haven't 100% been worked out. From what I've read there are no 100% reliable models for taking in a set of variables (planet size, density, etc.) and spitting out a simple value for the strength of a magnetosphere. If this is the case, then all I need to aim for is plausibility. As long as it's credible I can use the wiggle room to our advantage.