Project Orbiter Galaxy

[jedidia]

The amount of solid material available for it to form out of, and B: Its ability to hold onto Hydrogen and Helium, which would increase with mass and decrease with temperature.

Yeah, the relevant question for A) would then be how much dust can there possibly be. In accrete, the mass of dust seems proportional to the major bodies mass, but I don't know yet if this is really realistic , or if the formula that accrete uses is appliable to so massive stars. Will have to do some research into this.

B) is the reason I suspect why there are no Gas Giants formed around supermassive stars. I have not yet found the point in accrete where it processes the temperature, but they already used a very curious formula for calculating the luminosity, so I might have to do some corrections to the temperature-code, if only I'd find it... the code is 30 years old now, and I'm having my problems finding my way around it. Oh well, some more hours of looking at the screen and setting more or less random breakpoints and I'm sure I'll happen upon it...

 

[jedidia]

So far I could establish that the temperature code seems to work fairly well. When runing the numbers it turns out that a supergiant of 125 solar masses is far hotter than I imagined, resulting in temperatures well above 10,000 K even at a distance of over 2 AU, so it's not really that surprising that there are no gas giants around such a star. The question that pops up is if a planet formation at such temperatures is possible at all, or if I should implement an additional minimal distance for planet formation based on temperature.

The other remaining question is where accrete gets it's stupendious amounts of dust from to form planets that are not far from a small star, I'm still hunting for that in the code...

---------- Post added at 06:59 PM ---------- Previous post was at 04:17 PM ----------

And after another bit of analysis I seem to end up with the following cause: The more massive the central body, the more dense the dust closer to it. With a supergiant of 125 sm in the center, this gives an extremely dense dust-band, resulting in an extremely dense planet. My problem now is that I don't know wheather I should actually change that or not, since it all sounds very logical and I highly doubt I would come up with a more realistic model. So I'm trying to come up with possible solutions. Here's the basis:

So, let's assume there is an extremely dense dustcloud around a very large star, and it starts to form up to a ball of rock that has 3800 times the mass of earth (that's 0.01 solar masses), compressed down to 1.464 times the earths radius (that's a theoretical surface gravity of over 1700 G's, talk about navigation hazard...), orbiting it's star at a distance of 2.8 AU. It also has a surface temperature of around 10,000 K.

first question: Is this as imposible as it sound, or might there actually be such planets around supermassive stars? What do the current models predict?

second: At a temperature of 10,000 K, there wouldn't really be anything "solid" about this planet. It would practically be a liquid sphere of rock, very close to a HUGE gravitational well. I could imagine such a contraption would fall victim to tidal disruption and absorption by the star pretty fast?

third: taking into account the huge gravity and heat provided by the star, would it be more likely that dust in a certain range gets absorbed by it faster than a planet can form?

or, with other words, should I just go with the current model and wipe out all planets that occur in a certain high-temperature high-gravity environment (meaning under a certain radius depending on heat and mass of the star). That would most certainly be easiest, and maybe even most realistic for all we currently know. The trouble would then be figuring out the properties of the "radius of destruction".

So, what's your thoughts about this? any other ideas?

 

[jedidia]

For now, I terminated all dust that is hotter than 2000 K for planet formation. That leaves supermassive stars effectively without planets, but does produce reasonable results. Now I'll have to put in some code to add some moons, which seems rather tricky because there seems to be some unclarity about the formation of moons under different circumstances. I guess it will be a random generator that produces believable results rather than an actual formation model.

 

[Linguofreak]

first question: Is this as imposible as it sound, or might there actually be such planets around supermassive stars? What do the current models predict?

Current models predict that massive central stars will blow away not only their own protoplanetary disks before planets can form but those of nearby lower-mass stars within several *light years*. It not only has to do with the amount of light they're putting out, but also the average wavelength. I think it also may have something to do with the stellar winds of such stars (which can have very high velocities). It has pretty much nothing to do with the gravity of the central star, though.

"Photoevaporation" is the term you're looking for here.

---------- Post added at 19:51 ---------- Previous post was at 19:24 ----------

For now, I terminated all dust that is hotter than 2000 K for planet formation. That leaves supermassive stars effectively without planets, but does produce reasonable results. Now I'll have to put in some code to add some moons, which seems rather tricky because there seems to be some unclarity about the formation of moons under different circumstances. I guess it will be a random generator that produces believable results rather than an actual formation model.

Being that you're using Accrete, I think you may also have to add some code to do planetary migration, since Hot Jupiters won't form without it. Something that makes this even trickier is the fact that migration happens while planets are still forming, rather than afterward, so you can't just tack on a migration phase after formation.

It does seem though, that you may be able to simulate Jovian formation and migration first, and then do terrestrial formation/migration, since some reading on the subject, as well as my own prior knowledge, seems to indicate that terrestrials probably form late. (Terrestrials apparently migrate much more rapidly than Jovians if they form early, and thus would probably end up dumped into the central star). But be careful with that, I'm not sure.

 

[jedidia]

I've allready thought about the migration thing, but have not yet worked on it. Trying to get sensible moons right now, doesn't quite work yet. But for the little time I spent so far on reworking stargen, I have already achieved more than expected. If things continue to go so well, I might even get to a release in early spring. Oh well, let's not praise the day before the evening...

 

[tgep]

" should I just go with the current model and wipe out all planets that occur in a certain high-temperature high-gravity environment (meaning under a certain radius depending on heat and mass of the star). That would most certainly be easiest, and maybe even most realistic for all we currently know. The trouble would then be figuring out the properties of the "radius of destruction". "

In a situation like this, I think it's much more likely for a second star ( or more depending on the ammount of remaining gast and dust after the first star forms ) to form giving rise to a double or multiply star system. That would jibe with the large numbers of multiple sytems observed like those found in the Pliedes.

 

[jedidia]

uff, I'm kind of sick lately, so my activity is a bit reduced.

In a situation like this, I think it's much more likely for a second star ( or more depending on the ammount of remaining gast and dust after the first star forms ) to form giving rise to a double or multiply star system. That would jibe with the large numbers of multiple sytems observed like those found in the Pliedes.

Problem is, how am I going to do multiple solar systems for Orbiter? it just doesn't seem practical (besides the fact that writing a system generator that produces reasonable results for multiple solar systems would be a major undertaking, and probably quite a bit out of my league...)

 

[goop]

I'm currently tinkering on something that basically should become a much more sophisticated version of Msss-MFD, if I ever get it finished. I'm not too far yet, and I'm known for dropping things, so I won't make too much of a hype here. I'd like to use this thread for general advice-seeking on my part, because else I'll spam the boards with too many different questions over time.

So far I have rigged up StarGen to output solar systems for Orbiter, So I have quite a powerfull generator for systems with Sun-like stars. It will be a lot of work to get this working realistically with any other type of stars, but that's a thing for the future.

What I'm currently engaging is the actual starmap. I plan to have a full procedural galaxy in the end with the possibility to throw in pre-defined starclusters, but for now I just want to get going with the HYG-Catalogue to have fairly realistic surroundings of sol (50 Parsec radius, about 120,000 stars).

Now what I'd like some input on is how I should implement the actual starmap. Easiest for programming would be an MFD, but ithen it will be a pain to handle, because it's so small and labeling stars might prove difficult. Also, a lined-up preview of the planets in a system would get quite cramped and rather hard to read.

I'm playing with the thought of creating a Form that could be accessed via the custom functions in the F4-menu.
This would seem easiest to create a starmap in the style of first encounters (which had a rather good one, allthough still somewhat twodimensional), but I assume that I'd have to use Win-GDI functions to draw the thing in the form, which would make it incompatible with the OGLA-client...
a third way would be doing it all in a seperate programm alltogether and alt-tabbing between Orbiter and the Map programm, but I fret all the work that would thrust uppon me. (then again, I would be able to use Irrlicht, which might make the whole task actually easier...).

I'd appreciate your thoughts about this, which version of these three you would find best, if you can think up another one, and how to best realise it. Thanks all.

I came across something earliear that could help you,
http://www.shatters.net/celestia/
Good luck!

 

[Linguofreak]

Looking at this project, one thing that concerns me (and indeed is also a problem in something I have ambitions to do myself), is the problem of getting a good blend between real and generated regions. The brightest stars you can detect at intergalactic distances, but the dimmer ones are barely visible when you're a few light-decades away from them. So we can be certain we have all the information on bright stars for quite a great distance, but as you go to dimmer and dimmer stars the radius in which we can be sure we have them all shrinks. In fact, there's a fair number of dim stars which we know of only by their gravitational effects on stars they're in a binary system with. The problem is with joining a generated map with real stars in such a way that the distribution looks natural, smooth, and realistic.

---------- Post added at 18:51 ---------- Previous post was at 18:38 ----------

uff, I'm kind of sick lately, so my activity is a bit reduced.



Problem is, how am I going to do multiple solar systems for Orbiter? it just doesn't seem practical (besides the fact that writing a system generator that produces reasonable results for multiple solar systems would be a major undertaking, and probably quite a bit out of my league...)

Well, you should be able to get reasonable results by simulating close binaries as single stars with an inner limit on how close planets can be (planets that go inside that limit either get ejected, eaten, or migrate back out). Far binaries (which are a fairly good fraction of all binaries), can be simulated as separate stars, and mid separation binaries as a combination of the two (with an outer limit for planets of either star and an inner limit for the combination). Getting close/mid binaries to work well as Orbiter solar systems would remain a problem. Even using a planet as a stand-in for one star, IIRC there are bugs in how Orbiter handles a planet orbiting the pair (it ends up orbiting as if it were just orbiting one star).

 

[jedidia]

Getting close/mid binaries to work well as Orbiter solar systems would remain a problem. Even using a planet as a stand-in for one star, IIRC there are bugs in how Orbiter handles a planet orbiting the pair (it ends up orbiting as if it were just orbiting one star).

I wouldn't call it a bug, Orbiter just wasn't made with the possibility to simulate binaries in mind. So, the center of gravity of a system remains fixed at its center. The only possibility around that I could see is defining the epicenter of the two stars as the "sun" without a texture, and making the stars as well as the planets orbit that epicenter. That's a very poor excuse for a binary system though.

Otherwise, if one would only want to make ONE system (or maybe two) he could write a dll for the planets. That's not an option for my project, of course.

Looking at this project, one thing that concerns me (and indeed is also a problem in something I have ambitions to do myself), is the problem of getting a good blend between real and generated regions. The brightest stars you can detect at intergalactic distances, but the dimmer ones are barely visible when you're a few light-decades away from them. So we can be certain we have all the information on bright stars for quite a great distance, but as you go to dimmer and dimmer stars the radius in which we can be sure we have them all shrinks. In fact, there's a fair number of dim stars which we know of only by their gravitational effects on stars they're in a binary system with. The problem is with joining a generated map with real stars in such a way that the distribution looks natural, smooth, and realistic.

Well, Once there is a beta (still a far way of), everyone can evaluate the results, and we'll see if it's a big issue and if yes how to correct it.

Anyways, I'm still bothering with the moons currently. I knew this would be a challenge, since the only way stargen produces moons is to check weather two planets collide, which is not the case very often. Another problem is that moons form not on the basis of a single model, but have several means of creation.
Gas Giants manage to hold their own accretion discs, and many moons condense out of that disc. I am currently playing with re-using the accrete algorithm to simulate the accretion of moons around gas giants. Considering that, I have two questions:
Is the planets SOI a viable outer limit for a moon being formed, or is it impossible for a moon to form at the SOI's edge?
What would be a sensible inner limit? Obviously no moon will form within the radius of the planet, but the dust in too close an orbit usually get's condensed to rings, not to moons. Got something to do with gravity and tidal disruption I hear, but what would be a sensible inner limit for a moon being formed?

Then there's the other two models by which moons get usually formed, impact and capture. While impact with other planets is simulated by stargen, capture is not. I'd love to create a few randomly generated objects and see if they get captured, but it's a bit above my head. Instead, I guess I'l just calculate how probable it is for a planet to capture an object and then assign a few moons based on those probabilities (that is for anything not being a gas giant, of course). However, I'm not quite sure what properties deserve consideration in this. Obviously, the planets mass and that of nearby planets (i.e. the radius of a planets sphere of influence and the strength of the influence). Are there other things that should be taken into account for such a calculation?

Also, I'm still running after a few "bugs" in accrete (seems not quite fair to call them bugs, since everything works fine in the scope accrete was created for), one of them being that the density of a planet seems to be calculated only by it's mass. leaves my with some very small "rocky" planets whose rocks seem to be less dense than air... :blink: Oh well, I'll be getting there.

 

[Linguofreak]

Well, Once there is a beta (still a far way of), everyone can evaluate the results, and we'll see if it's a big issue and if yes how to correct it.

It will almost certainly be a big issue unless specific plans are made to counter it.

Anyways, I'm still bothering with the moons currently. I knew this would be a challenge, since the only way stargen produces moons is to check weather two planets collide, which is not the case very often. Another problem is that moons form not on the basis of a single model, but have several means of creation.
Gas Giants manage to hold their own accretion discs, and many moons condense out of that disc. I am currently playing with re-using the accrete algorithm to simulate the accretion of moons around gas giants. Considering that, I have two questions:
Is the planets SOI a viable outer limit for a moon being formed, or is it impossible for a moon to form at the SOI's edge?

I don't know

What would be a sensible inner limit? Obviously no moon will form within the radius of the planet, but the dust in too close an orbit usually get's condensed to rings, not to moons. Got something to do with gravity and tidal disruption I hear, but what would be a sensible inner limit for a moon being formed?

You're looking for the Roche Limit. It's determined by the radius and mass of the moon, and the mass of the primary. It can be calculated in terms of the radius of the primary simply from the densities of the two objects.

It's also something you may need to take into account for the dimmer stars, which can be very dense. Planets will not be able to form within the Roche Limit, and in some cases this will prevent the star from having any planets within its habitable zone. (There's also some debate as to whether tidally locked planets could be habitable).

Then there's the other two models by which moons get usually formed, impact and capture. While impact with other planets is simulated by stargen, capture is not. I'd love to create a few randomly generated objects and see if they get captured, but it's a bit above my head. Instead, I guess I'l just calculate how probable it is for a planet to capture an object and then assign a few moons based on those probabilities (that is for anything not being a gas giant, of course). However, I'm not quite sure what properties deserve consideration in this. Obviously, the planets mass and that of nearby planets (i.e. the radius of a planets sphere of influence and the strength of the influence). Are there other things that should be taken into account for such a calculation?

I'm not entirely sure, but my impression is that, generally, captured moons are small enough that they can be ignored. Then again, there is the example of Neptune's Triton.

Also, I'm still running after a few "bugs" in accrete (seems not quite fair to call them bugs, since everything works fine in the scope accrete was created for), one of them being that the density of a planet seems to be calculated only by it's mass. leaves my with some very small "rocky" planets whose rocks seem to be less dense than air... :blink: Oh well, I'll be getting there.

Well, there's going to be a base density for the material in question, and then you've got gravitational compression. I've tried in vain to find a good equation for it.

 

[jedidia]

I don't know

just looked at the gas giants in our solar system, and all the moons seem to be very deep inside the SOI. I'll have to do some research on what a sensible limit might be...

You're looking for the Roche Limit.

Great, thanks!

I'm not entirely sure, but my impression is that, generally, captured moons are small enough that they can be ignored.

would still be nice to have some as a small touch of detail. Oh well, by far no priority right now. I'm currently hunting the reason why half of my moons come out of accrete with funny properties like a mass of -300 xillion earth masses :lol:

---------- Post added at 05:08 PM ---------- Previous post was at 01:23 PM ----------

Made some decent progress today, playing around with the dust-density coefficient I'm finally getting some reasonable results. Now all I need is a sensible outer limit. I'm experimenting, but am not satisfied yet. making the outer limit SOI dependable leads to outer planets having much more moons in unreasonable distances. I'll have to link the outer limit to mass somehow, but not sure how exactly.

 

[Linguofreak]

I couple errors in my above post: One from not paying attention to quote tags, the other to not thinking about what I was saying or what you were asking.

The first was just a comment that the border between existing and generated stars will almost certainly be problematic unless specific steps are taken to deal with it.

The second is that there is an outer limit as far as the gravitational stability of orbits, but I don't think it gives a good boundary for the accretion disk of a forming gas giant. It can actually be much *bigger* than the SOI, because Orbiter's SOI calculation really doesn't tell you anything (The moon for instance, orbits outside Earth's orbiter SOI). This outer limit is called the Hill sphere. http://en.wikipedia.org/wiki/Hill_sphere

Apparently even the outer regions of the Hill sphere are rather unstable, and typical orbits will be within 1/2 to 1/3 the HS radius.

 

[jedidia]

The second is that there is an outer limit as far as the gravitational stability of orbits, but I don't think it gives a good boundary for the accretion disk of a forming gas giant.

Well, I can specify the boundary for the accretion disk as well as an outer limit for planets to be formed, so this might come in very handy. Will try it out this evening, thanks.

 

[tgep]

uff, I'm kind of sick lately, so my activity is a bit reduced.



Problem is, how am I going to do multiple solar systems for Orbiter? it just doesn't seem practical (besides the fact that writing a system generator that produces reasonable results for multiple solar systems would be a major undertaking, and probably quite a bit out of my league...)

No , no ..... not Multiple solar systems ....... multiple STAR systems. I'm talking about double and triple stars in orbit about each other .... planetary formation would be VERY unlikely in star systems such as this

 

[T.Neo]

Why?

I'd imagine if the stars were close enough or far out enough, planets should form fine.

Barring other planets and/or metallicity issues.

 

[tgep]

Why?

I'd imagine if the stars were close enough or far out enough, planets should form fine.

Barring other planets and/or metallicity issues.

Your forgetting about the effects of of the solar wind as well as the blast wave from the innitial ignition of the star itself .... put two or three stars like that in close proxcimity and they will clear out a lot of the remaining gas and dust in a hurry.

 

[jedidia]

Hmmm, the hill sphere suffers a similiar problem as does soi: it is much bigger for planets that are further away, so taking it as a basis for an outer limit for moons that are formed leads to outer gas giants having much more moons than inner gas giants, a fact that I do not see reflected by our solar system. I guess I'll just play around with a gravity limit until I guet results that I like...

I'm talking about double and triple stars in orbit about each other

I understood you correctly, but misformulated. But as I said, Orbiter doesn't seem to a very practical platform for systems with more than one star.

 

[Nemoricus]

Are you sure that that effect is not present in our solar system? The outer planets are harder to observe and may have many more moons than we currently know of. Especially moons of the barely-more-than-debris kind.

 

[Linguofreak]

Your forgetting about the effects of of the solar wind as well as the blast wave from the innitial ignition of the star itself .... put two or three stars like that in close proxcimity and they will clear out a lot of the remaining gas and dust in a hurry.

There is no "blast wave" per se from the ignition. There is a sharp increase in brightness, but it still occurs over the course of many years (it's sharp compared to the lifetime of the star, which is many, many, many, many, many years). Also, if the stars are of different masses, the ignitions will happen at different times and last for different amounts of time (big stars ignite earlier and faster than little stars).

And any given collection of stars is *less* bright than a single star of the same mass.

The primary obstacle to planetary formation in multiple star systems is the gravitational influence of the stars.

---------- Post added at 01:47 ---------- Previous post was at 01:35 ----------

Hmmm, the hill sphere suffers a similiar problem as does soi: it is much bigger for planets that are further away, so taking it as a basis for an outer limit for moons that are formed leads to outer gas giants having much more moons than inner gas giants, a fact that I do not see reflected by our solar system. I guess I'll just play around with a gravity limit until I guet results that I like...

In fact, the problem is actually worse for the Hill Sphere than for the SOI. It's a good limit for capture moons, but not for co-formed moons, and *certainly* not for impact moons (whose orbital radius will depend on the age and angular momentum of the planet-moon system).

Neptune has a pair of moons (capture moons I think, but am not sure), that have *very* wide orbits (SMa's around a third of an AU, apoapses even further out). The total Hill sphere radius is .775 AU.