Nikolai Lofving Hersfeldt
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exoplasim updates
🕑 Added 2023-07-24 10:30:56 +0000 UTCSo recently I went digging around in the exoplasim code and put together a pull request to add some extra behavior for synchronous planets; you can find that here https://github.com/alphaparrot/ExoPlaSim/pull/5 but it's built against 3.3.0, which I've had a bit of trouble getting working myself; so if you want to try it out with an earlier version I've attached the necessary files here: Take a fresh install of exoplasim 3.2.4 (uninstall and delete any current install and add ==3.2.4 to the end of the "pip install" command), find the install directory (for openSUSE it's .local/lib/python3.6/site packages), place _init_.py in the exoplasim folder and radmod.f90 in exoplasim/plasim/src, then run a model and configure as normal.
With this update, any model that has synchronous=True should now show proper libration of the substellar point: it will move east and west based on eccentricity and north and south based on obliquity. I've also added the "soldaysperorb" parameter, which allows you to set a specific number of solar days per orbit for the synchronous case. By default it's 0.0, which gives you the standard tidal-locked behavior, but 0.5 would simulate 3:2 spin-orbit resonance, 1.0 would be 2:1 resonance, etc (be sure to still set rotationperiod to the proper sidereal day period).
I've also attached the output for a very quick run (T21, 30 years) I did of my "clock world" concept: 0.3 eccentricity, 30 degrees obliquity, and periapsis at southern summer solstice, such that the substellar point moves in a loop around the day side. I'll explore the concept in more detail another time but it gives you a sense of how this libration can significantly impact the global climate.
Comments
Nikolai Lofving Hersfeldt
Normally you do expect to lose obliquity during tidal-locking, but the influence of multiple bodies can induce a "Cassini state" where multiple types of precession coincide to create a constant effective obliquity. Our moon maintains about 7 degrees of tilt this way, but in principle it can be much higher.
Thanasis Kinias
This is exciting, and I can’t wait to try it! Are there cases where we’d see significant obliquity on a synchronous world? The tool I use to model locking (eqtide) always results in zero obliquity when a planet locks...
