Fictional Exoplanet creation

Linguofreak

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Those would be most conveniently specified as 'at L4 (or L5)' and placed using a Lagrange point finder (surprise, I have one of those as well...)

I'm interested in things like the effect of librational dynamics on climate, so I'm interested in arbitrary orbits in the vicinity of the L4/L5 point (thus the word approximately in my previous post).

I've never heard that you can have planets developing there though... it seems kinda hard to accumulate enough mass, usually it's just debris that's been captured

The literature seems to be undecided on whether Trojan planets can actually form (highly sensitive to modeling assumptions and things like grid resolution, cartesian vs. cylindrical coordinates, etc) and fairly confident that they can remain stable over gigayear timescales once formed or captured. The possibility is taken seriously enough that empirical searches are being performed.

Meanwhile, the giant impactor that whacked Earth to form the moon is believed to have formed as a Trojan and been perturbed into a collision with Earth by Jupiter and/or Venus (in that case it wasn't stable for gigayears).

Those you already asked and I answered - they're interesting and can be done.

(In fact, you can cheat a bit and specify a 'star' with the temperature and luminosity of a gas giant, let that orbit your companion star and you get the results with the existing code and interface)

But temperature and luminosity for a gas giant are dependent on climate, and different on the day vs. night side. Depending on if and at what lattitudes water clouds form, albedo can be markedly different (if you're too warm for clouds, you end up with a dark blue color from Raleigh scattering). So being able to model them as planets will be useful.

I guess for me the point is - of course there's all sorts of weird situations where orbital dynamics is interesting. But most of these cases would be rare and exotic. Whereas what is a major influence and not rare at all is... atmosphere. So I'm actually more interested in spending my time with improving the atmosphere simulation and see whether one can tease some gross weather patterns out for instance (like the (non)-existence of a jet stream) than coding an interface for arbitrarily weird situations (also with extending the solver to 3d - the issue isn't so much the solver, 3d is easy there, the issue is interface and analysis tools, they become much more complicated and messy without providing much more insight - most systems would be near-planar problems..)

The jury is still out on Trojan configurations, and the fact that so many hot jupiters show up suggests that gas giants migrate aggressively, which means we can anticipate a fair number of terrestrial planets captured into resonances. Resonant configurations will tend to pump up eccentricity, which will affect climate, and the Kozai mechanism will then tend to drive up inclination and drive the longitude of periapsis to +/- 90 degrees, which will then be vital to keeping the resonance stable if eccentricity gets high enough for the orbit of the terrestrial planet to approach or cross that of the gas giant. Even in the Solar system, the 2/3 resonance with Neptune defines the Plutinos, and a significant fraction of them have significant eccentricities and inclinations.

And then there's all the red dwarfs with multi-planet resonance chains, and the solar system has the Galilean moons in their 1:2:4 chain, and not just any 1:2:4 arrangement will work, it depends on particular phase relationships for stability.

Point being, I'm not sure that interesting configurations that depend on orbital phases or non-planarity are as rare as you think. And even for the circular, non-resonant, near-planar case, inclinations of less than a degree are sufficient to cause significant seasonal changes in binary-star eclipses, and for moons, to give a worked example, the angular diameter of Jupiter is about 13 degrees at 2 light seconds (a bit less than the orbit of Europa). A coplanar eclipse in this configuration can be expected to last roughly 1/27th of the orbit, which works out to about an extra 2 hours and 30 minutes of darkness in a 70 hour day for the planet-facing side of the moon (assuming that the planet has the mass of Jupiter and the moon is tidally locked), or an hour of darkness in a 27-hour day, (for a more massive planet of the same radius*). In such a configuration, an inclination of five degrees to the ecliptic would be sufficient to cause significant variation in the length of eclipses with the seasons.

*We can assume that the radius is about equal to Jupiter because a planet twice as massive as Jupiter is only very slightly larger, and 2 Jupiter masses of hydrogen has the largest radius that any object can have without significant support from thermal pressure, so the smallest red dwarves are actually slightly smaller than Jupiter, and then get larger with more mass as heat from fusion puffs them up.
 

Thorsten

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Point being, I'm not sure that interesting configurations that depend on orbital phases or non-planarity are as rare as you think.

It's charming in a way, but...

Are you by any chance confusing my hobby with an NSF grant review?

I don't propose to provide a tool to simulate 'most' 'interesting' exoplanets (as for 'most', since finding them is significantly biased by the finding methods which prefer large and heavy objects, we don't really know how 'most' look like, as for 'interesting', different people are interested in different things - some may search for edge cases like Helliconia because the orbital dynamics/climate interaction is really interesting, others may find open water more interesting, yet others water under ice layers,...).

I'm not doing an academic project, I'm not getting academic funding or any academic credits for it, so what would be of relevance in academia doesn't really apply here. Apart from being a toy for me, I suppose this could be illustrative for school or study introductory projects and science-minded SciFi writers - certainly none of these groups needs an exhaustive treatment of Lagrange point objects and their climate or cares much in particular how common the different arrangements in the universe really are.

I've licensed it under GPL, which means that you get full access to the code and full rights to use it (sell the program even...) - if you're interested in a particular application that's not covered, you can add a particular set-up to the solver - that's usually less than 30 lines and run that.

A coplanar eclipse in this configuration can be expected to last roughly 1/27th of the orbit, which works out to about an extra 2 hours and 30 minutes of darkness in a 70 hour day for the planet-facing side of the moon (assuming that the planet has the mass of Jupiter and the moon is tidally locked), or an hour of darkness in a 27-hour day, (for a more massive planet of the same radius*). In such a configuration, an inclination of five degrees to the ecliptic would be sufficient to cause significant variation in the length of eclipses with the seasons.

Again, I think you're kidding yourself as to the relative importance of that when you compare to something as simple as cloud formation on the planet (that's currently not at all covered by the atmosphere code).

Clouds and atmosphere make the difference between a scaldingly-hot Venus and the high-albedo iceball that could be in the same orbit - but isn't.

The eclipse example is a bit forced (three of Jupiter's Galilean moons actually orbit slower than 70 hour orbit, and even a day-long stellar eclipse in the simulation isn't really felt 24 hours later any more), can be understood by comparing a run with and without eclipse finder without a 3d framework and basically is a correction to a situation without eclipss - an atmosphere usually is not a correction to the situation without atmosphere, it really is a lot different.
 
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Thorsten

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I'm happy to announce the version 0.3 which now includes support for some of the issues we had discussed. In particular, it is now possible to set up the simulation of gas giant moons - here is an example of temperatures on Io

world10_io.png

This includes the (optional) effect of eclipses and reflected and IR radiation from the planet (which both are, as I predicted, pretty small).

Also there is now support for writing time series of observables and to avoid lengthy orbital computations, also for saving and resuming orbital states.

Here is an example of sun elevation angle on Mercury for different longitudes:

world12_mercury.png

Download and tutorials still here.
 

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there is a direct competitor to the Orbiter "SpaceEngine" there outer space is made infinite planets are randomly generated (outside of those studied)
since the planetarium is popular in the Russian segment, there may be problems with the Russian language
 

donatelo200

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there is a direct competitor to the Orbiter "SpaceEngine" there outer space is made infinite planets are randomly generated (outside of those studied)
since the planetarium is popular in the Russian segment, there may be problems with the Russian language
I wouldn't call SE a direct competitor to orbiter yet. Orbiter is focused on space flight mechanics while SE is focused on the universe/planetarium aspects. It's more of a competitor to Celestia imo. I do love SE though and actually helped create the default planet colorings for it.
 

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I'm happy to announce the version 0.4 of the simulation tool which now can do some stuff on atmosphere and hydrosphere transport and has a simple weather and climate code for Earth-like worlds (there's more to come, but it's already fun to play with what is there).

Here's a quick view on simulated weather on a simple Earth model over a year in tropical jungle

world15_T_jungle.png

Compare with the climate chart of Hanoi (different hemisphere, therefore seasons shifted by half a year...) this doesn't look too bad:

world15_hanoi.png


Here's an interesting piece of dynamics - increasing high cloud cover increases albedo and lowers temperature. For a range of cloud fraction this is all that happens - but eventually snow doesn't melt any more and the simulation is driven into an Ice Age with rapidly dropping temperatures:

world16_iceages.png

Download and tutorials still here.
 

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Here's some work in progress - the Chapman mechanism (UV light dissolves O2 -> O+O, part of that forms ozone, ozone has a strong absorption cross section at longer wavelength UV and leads to a pronounced heating of the upper atmosphere, giving rise to the temperature increase in the stratosphere).

After computing the ozone production rate, here's the heating curve that's obtained with it...

earth_atmosphere_heating.png

... and using a heuristic model for how that translates into temperatures (basically it ain't really blackbody radiation exactly, but must be subject to similar scaling) I get the following temperature distribution for Earth atmosphere in altitude when I combine that with the radiative average temperature and adiabatic lapse rate from the surface upward:

earth_atmosphere_T.png

Now, the interesting thing is that all of this hinges on the presence of short-wavelength UV to split up the oxygen. It seems no other molecule can easily take the role of ozone, so... if there is no real short wavelength UV because the star is cooler than the Sun, there's no ozone, so there's no absorption of longer wavelength UV, there's no heating of the upper atmosphere, there's no stratosphere really...

... which (and this is why I absolutely wanted to have a code to compute this) has profound implications for the weather on such a world, because then convection (Cb clouds mostly) are not confined within a low troposphere and reach only 10 km in altitude, but can potentially tower much higher. There might be worlds for which weather is happening all the lowest 100 km or so - just because there is little short wavelength UV radiation from the star.
 

Linguofreak

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Now, the interesting thing is that all of this hinges on the presence of short-wavelength UV to split up the oxygen. It seems no other molecule can easily take the role of ozone, so... if there is no real short wavelength UV because the star is cooler than the Sun, there's no ozone, so there's no absorption of longer wavelength UV, there's no heating of the upper atmosphere, there's no stratosphere really...

Or if there's no O2 to break up in the first place (e.g, Venus).

The biochemistry of the local life (if any) will probably have a significant influence on what molecules are available to be photodissociated into what. O2 is unlikely to be present in significant quantities without life. You might consider some fairly exotic gasses as photodissociation precursors to stratospheric warming gasses, after all, the only reason we don't consider O2 to be an exotic atmospheric component is that the local plants happen to produce it and we happen to need it. Otherwise, O2 is far too reactive to stick around long. All you need is a plausible reason for life to be producing a particular gas.
 

Thorsten

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You might consider some fairly exotic gasses as photodissociation precursors to stratospheric warming gasses, after all, the only reason we don't consider O2 to be an exotic atmospheric component is that the local plants happen to produce it and we happen to need it.

I'm kind of limited by what the MPI UV/Vis spectral atlas offers in terms of cross sections... but yeah, there are quite a few lineshapes available.

As far as O2 is concerned, I agree - Earth history shows how heavily biosphere driven it is. However, it's much more interesting to simulate a world with life, open water and weather than a lifeless rock, and a highly exotic atmosphere has a chance to be too far from what we know to be simulated credibly (after all, to bridge all the gaps that can't be calculated either for lack of knowledge or computing power, Earth-based heuristics comes in...)
 

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The version 0.5 is now also out - with nice toys for looking into atmosphere structure:

Here is a case study of Brian Aldiss' Helliconia, a world that orbits its small sun Batalix while both in turn orbit hot and luminous Freyr,, leading to a summer at Freyr periapsis and a winter at apoapsis.

Here are spectra for summer and winter in space and after absorption by the atmosphere (note the strong UV component of Freyr close-by in summer):

world22_absorption.png


Here is the resulting heating profile of the atmosphere compared with Earth - basically the copious UV-flux causes the stratosphere to be much higher up and a correspondingly expanded troposphere:

world22_T.png

Much of the tutorials actually revolve around a somewhat detailed simulation of Helliconia (which unfortunately I believe does not really work as described in the novels, but of course in 1982 Aldiss hardly had the computers to look in any sort of detail into this...)
 

Linguofreak

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The version 0.5 is now also out - with nice toys for looking into atmosphere structure:

Here is a case study of Brian Aldiss' Helliconia, a world that orbits its small sun Batalix while both in turn orbit hot and luminous Freyr,, leading to a summer at Freyr periapsis and a winter at apoapsis.

Here are spectra for summer and winter in space and after absorption by the atmosphere (note the strong UV component of Freyr close-by in summer):

View attachment 32834


Here is the resulting heating profile of the atmosphere compared with Earth - basically the copious UV-flux causes the stratosphere to be much higher up and a correspondingly expanded troposphere:

View attachment 32835

Much of the tutorials actually revolve around a somewhat detailed simulation of Helliconia (which unfortunately I believe does not really work as described in the novels, but of course in 1982 Aldiss hardly had the computers to look in any sort of detail into this...)

Your second plot (the heating plot) only shows one curve for Helliconia, but your explanation of the dynamics, and the length of the secondary year, suggests that the tropospheric depth might shift between summer and winter. Is there such an effect?
 

Thorsten

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suggests that the tropospheric depth might shift between summer and winter. Is there such an effect?
Yes, there is - in winter the stratosphere moves down somewhat, although it still ends up being much higher than Earth (the hard photon flux is down by a factor 5 or so, but given that the density drops exponentially with altitude, that's not dramatic for things like O3 production rate).
 
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