Home: a world in an eccentric orbit with climate challenges

[Vareck Bostrom]

In the long march to 5 forum posts, I'll elaborate on my introduction post.

Home started as a world set in a Traveller universe but was subsequently moved out, and in fact the entire Traveller universe done away with.

The star is the same mass and luminosity as the sun, and Home has the same mass and atmosphere as Earth. The world is about 55% land mass. There is no moon.

The inner solar system started out looking like this:



Silvernight as an inferior planet, with a superior rocky planet and dwarf planet. There is, in addition, a large gas giant in the outer system.

Home started as a reasonable place to live. About 1.06 AU, 31 degree axial tilt, and a year just over 405 days long. Eccentricity was about 0.01 and the seasons were more or less equal length. Perihelion occurred just before the northern hemisphere spring equinox.

I ran the initial configuration of the solar system forward 20,000 years. About 4000 years into the run, and lasting about 2000 years, Home and Silvernight (the inferior planet) underwent a gravational interaction. Home's eccentricity was boosted significantly to about 0.15, inclination was boosted to about 5º, and semi-major axis was slightly reduced. I had placed Silvernight too close to Home - normally this sort of thing would have happened early in the evolution of the solar system but I decided to leave things as they were, mistake and all.



Here's a time lapse of the orbit interaction. Note that the orbits are projected onto the fundamental plane, thus it looks like Home's perihelion is much closer than its actual 0.98 AU - the inclination is causing that distortion. The orbit wobbling / vibration is caused by the system's gas giant inducing an oscillation in the sun's position.

(oops, only one video per post)

Consequently, Home is a much less hospitable world now. The seasons are not of equal length: in the northern hemisphere, Summer is 93.935 days long, Autumn is 113.565 days long, Winter is 104 days long and Spring is 90 days long. Perihelion now is quite close to the summer solstice (about 5 days before):



As an illustration, this is daily integrated energy at each latitude, at about 65% of the way from summer solstice to autumnal equinox (in the northern hemisphere):



As can be seen by the snow coverage / glacier plot, though it's only late summer, much of the world is covered with ice and snow:



Thanks to the timing of aphelion and Home's eccentricity, the Southern Hemisphere is icebound throughout the year. The northern hemisphere is habitable, though the short growing season likely makes that difficult.

[Azélor]

day just over 405 days long

That's almost 4 Venusian days!

I was wondering what inferior and superior planet referred to.

The simulation is pretty cool but if I understand correctly, the Silverlight/Home planets are still unstable. I don't know what you used for the simulation: is in Universe Sandbox?
If the system is still unstable, there might be a cataclysm looming ahead. Or the system could remain like that for a very long, it could be cyclical without incident for a very long time but I don't have enough knowledge to help on this.
But I know that using softwares have limits. For example, simulating gravity at a too great speed results in inaccuracies that could wreck the system apart. Not sure if this is what happened but it's a consideration.

[Vareck Bostrom]

That's almost 4 Venusian days!

I was wondering what inferior and superior planet referred to.

The simulation is pretty cool but if I understand correctly, the Silverlight/Home planets are still unstable. I don't know what you used for the simulation: is in Universe Sandbox?
If the system is still unstable, there might be a cataclysm looming ahead. Or the system could remain like that for a very long, it could be cyclical without incident for a very long time but I don't have enough knowledge to help on this.
But I know that using softwares have limits. For example, simulating gravity at a too great speed results in inaccuracies that could wreck the system apart. Not sure if this is what happened but it's a consideration.

Oops, that should have read a year is 405 days long (and just over 403 days long now).

For simulation the equations of motion are defined and evaluated in Mathematica, usually. I use the BDF method of NDSolve. Accuracy is one of the reasons I prefer to use Mathematica over something like Universe Sandbox - I can use an equation evaluator that I know has error control. (In addition, my equations of motion are more complex than what I think universe sandbox uses, and I change them from time to time too. )

[Vareck Bostrom]

That's almost 4 Venusian days!

I was wondering what inferior and superior planet referred to.

Inferior planet is an astronomical term to mean a planet on a closer orbit to the sun. Mercury and Venus are Inferior Planets to Earth. Superior planet has the opposite meaning.

The simulation is pretty cool but if I understand correctly, the Silverlight/Home planets are still unstable. I don't know what you used for the simulation: is in Universe Sandbox?

I believe they are stable now, but I’ll run the simulation forward for a million years or so to verify that.

If the system is still unstable, there might be a cataclysm looming ahead. Or the system could remain like that for a very long, it could be cyclical without incident for a very long time but I don't have enough knowledge to help on this.
But I know that using softwares have limits. For example, simulating gravity at a too great speed results in inaccuracies that could wreck the system apart. Not sure if this is what happened but it's a consideration.

Now that I have more time to answer, in normal ODE solvers, the step size varies and is bounded by error control. If the independent variable is time, for example, you don’t just say each timestep is 10 seconds and leave it at that, you shrink the timestep until the result becomes stable. The advantage is that the timestep can expand greatly too when appropriate, which will accelerate the evaluation.

Universe Sandbox (for whatever reason) seems wedded to fixed timestep solutions. I don’t know what method it uses but it could be something as direct as Euler or Runge Kutta.

I’ve had stable results from simulating the (real) solar system over millions of years.

In terms of an upcoming cataclism - even if there is, it’s likely to occur very slowly, just like the last one did. Perhaps a few thousand years of season length changing which would give enough time for adaptable species to adapt, unless it does something like further boost the eccentricity of Home.

[Ilanthar]

Interesting! Always amazed by the details some of us are putting in their fantasy world(s).

[Vareck Bostrom]

And, I had intended on adding this in the first post, but here is the 10k year progress of the gravitational interaction - the wobble due to the gas giant inducing an oscillation on the sun:

https://youtu.be/kNeg29jdjSY