Moon-packing around an Earth-mass Planet

[Thineboot]

Moon-packing around an Earth-mass Planet in Monthly Notices of the Royal Astronomical Society, 01 August 2022

Abstract
All 4 giant planets in the Solar System host systems of multiple moons, whereas the terrestrial planets only host up to 2 moons. The Earth can capture small asteroids as temporary satellites, which begs the question as to how many moons could stably orbit the Earth, or an Earth-mass exoplanet. We perform a series of N-body simulations of closely-spaced equal mass moons in nested orbits around an Earth-mass planet orbiting a Sun-like star. The innermost moon begins near the host planets Roche radius, and the system is packed until the outermost moon begins near the stability limit for single moons. The initial spacing of the moons follows an iterative scheme commonly used for studies of compact planetary systems around single stars. For 3-moons system, we generate MEGNO maps to calculate periodic and chaotic regions and to identify the destabilizing MMRs. Our calculations show that the maximum number of moons depends on the assumed masses of the satellites (Ceres-, Pluto-, and Luna-mass) that could maintain stable orbits in a tightly-packed environment. Through our N-body simulations, we find stable configurations for up to 7 ± 1 Ceres-mass, 4 ± 1 Pluto-mass, and 3 ± 1 Luna-mass moons. However, outward tidal migration will likely play a substantial role in the number of moons on stable orbits over the 10 Gyr stellar lifetime of a Sun-like star.

While this is only the abstract you may get a better feeling for how many moons you'll add on creation day. Note that it's a paid article. So if you wanna dig deeper and read the paper itself you will have to spend money. But for the devs it may be worth spending.

[mordachai]

Very cool. Too many of the moons are too large for their parent bodies in this game.

Would be cool to have a "more realistic" galaxy gen. mode.

[Buio]

But for the devs it may be worth spending.

Asking for devs to pay for paywall article, because you don't think the moons are done realistically enough in the game?

[rxnnxs]

Before the devs read this (and do some math, well, would be nice..) and we talk about the possibility of a moon that big that orbits earth stable (which is something very very special), why don't they give them all an orbit with a "spin" to it?

Otherwise they would, maybe.., come together..?

[Radamanthe]

Very cool. Too many of the moons are too large for their parent bodies in this game.

Would be cool to have a "more realistic" galaxy gen. mode.

TBH, if they had to be realistic about it, we would hardly see even the biggest planets at system zoom level in the first place.

[Thineboot]

But for the devs it may be worth spending.

Asking for devs to pay for paywall article, because you don't think the moons are done realistically enough in the game?

Well, I know that I know only a tiny fraction of the knowledge that is available to humanity. And with each passing second I know less, not because I'm losing my mind, but because as I keep forgetting things, which is a mechanism of the human brain to stay sane, new knowledge is emerging on a scale that no human being can keep up with. At the same time, I am always eager to learn new things of all kinds, especially those that interest me. Building and playing a game about stars, worlds, near and distant, seemed like a reasonable thought to share this abstract with all of you. Pointing out that it is only an abstract and that the article is behind a paywall seemed only fair. If I were to develop a game like this, I would be interested in gathering as much new knowledge as possible that could help me develop an even better version of my vision. Note the difference between may and is. It's up to them to decide whether it's worth spending £12 or not.

That said, putting words in my mouth or fingers, we're in a forum, not the Forum, is one thing. In addition, to claim to know what I think is something else. Good luck with that mocking attitude in life.

Very cool. Too many of the moons are too large for their parent bodies in this game.

Would be cool to have a "more realistic" galaxy gen. mode.

TBH, if they had to be realistic about it, we would hardly see even the biggest planets at system zoom level in the first place.

That's called artistic freedom and without it we wouldn't playing any exploration game

[Radamanthe]

Very cool. Too many of the moons are too large for their parent bodies in this game.

Would be cool to have a "more realistic" galaxy gen. mode.

TBH, if they had to be realistic about it, we would hardly see even the biggest planets at system zoom level in the first place.

That's called artistic freedom and without it we wouldn't playing any exploration game ;)

Not really. Exploration is far from just being able to see planets at system level. Talking about dimensions and proportions realism related to exploration, playing Elite:Dangerous gave me that realism (and at least those ones) with the best exploration experience I could dream of since decades ;) Granted it's not the same game at all...

[Thineboot]

KSP involves also exploration, so you're right, not any exploration game. Let's put it this way: If you were sitting in a spaceship and looking at your NAV monitor, you would also expect to see more than just a fraction of a pixel Never played Elite:Dangerous, but I'd guess they also zoom in the bodies while being far away.

[Radamanthe]

Never played Elite:Dangerous, but I'd guess they also zoom in the bodies while being far away.

Precisely not. I'm quite aware of the dimensions involved, so I'm a bit picky about this. To put it simply, until you're close enough, planets and moons in the system just look like stars in the field. E:D is unrealistic in many ways (to my great despair), but not about dimensions and proportions. That's the main reason I stick with it, because so many games of its kind don't care at all. Now, that's not something that has to be done in all kinds of space games, at least I guess we agree with it.

[Thineboot]

I have meant in terms of navigation, unless navigation is solely text based, there has to be a visible spot on the nav-screen, no? But besides that, I love "realism" in space games, too.

The more I come back to this thread, the more I remember the discrepancies in scaling.
DW2's Earth has a diameter of about 6K, it varies with each game (4,000-6,500). Our Earth has a radius of about 6K km (6,371 km). So let's say 1K ~ 2,000 km.
According to beam weapons, light travels at 5,000/sec ~ 300,000 km/sec in our universe. That's 1K ~ 60,000 km.
The average main sequence star is 30K-36K in diameter. Our sun yields 1,393,000 km. That's 1K ~ 40,000 km.
With all those very different scales we can assume that everything in DW2 is more on the side artistic freedom than a mapping of reality.
Which doesn't mean, that it can't be done in a more realistic way, even with a static galaxy, where no body is moving around their respective center of mass. It wouldn't harm gameplay. Still, it's another universe and that could have other universal constants. What drives me more crazy is that all ships have handbrakes

But all that wasn't the goal of this thread. It was simply pointing to new discoveries related to Moon-packing around an Earth-mass Planet

If it helps making the game a bit more realistic, great. If not, you can never know enough, and I appreciate sharing knowledge with others and vice versa.

[Radamanthe]

I have meant in terms of navigation, unless navigation is solely text based, there has to be a visible spot on the nav-screen, no?

Of course there is, we call it HUD :) Think augmented reality somewhat holographically projected in the cockpit (not just on the helmet glass). Nothing really magic, that's quite hard SF at this point. Target destination is represented by a static circle around it on the HUD so we don't get lost when we are too far away to see the target, but we can get rid of the whole HUD with a simple shortcut to see things as they are supposed to be, that's obviously what I talked about. Realistic scales are a thing in E:D, and I wouldn't talk about that otherwise (realistic from our familiar macro scales to galaxy scales... quite impressing when you realize it).

According to beam weapons, light travels at 5,000/sec ~ 300,000 km/sec in our universe.

Which is wrong as light always travels at ~300K km/sec in the vaccum of space, no more no less. In fact, photons always travel at ~300K km/sec anywhere (ie. light is slower in water, not photons), but let's focus... I guess it's convenient enough to argue that beam weapons in DW2 are probably not only photon based, and it's fine to me.

What drives me more crazy is that all ships have handbrakes :shock:

Ships designs should include forward reactors to "break" anyway (in Newton's space), but I know what you mean. Now, about this epic and hilarious sequence from Spaceballs you linked, that's not completely absurd to stop promptly with a hypothetic hyperspace technology since in the theory (from Alcubierre drive, mainly), travelling FTL by contracting and expanding space does not involve usual Newton's physics at all. Hence, no inertia to project you (well... crush all of the molecules of your body at such speed) into the cockpit on the stop. Sorry Mel, but "Star Anything" precursors were somewhat right about this :)

I know I know, I'm not always funny... but believe me, I can sometimes!

But all that wasn't the goal of this thread.

I know, pardon me.

If it helps making the game a bit more realistic, great. If not, you can never know enough, and I appreciate sharing knowledge with others and vice versa.

I would not be worried at all if the number of moons around planets respected what we know about that. At least, it would not impact gameplay.

[Buio]

But for the devs it may be worth spending.

Asking for devs to pay for paywall article, because you don't think the moons are done realistically enough in the game?

Well, I know that I know only a tiny fraction of the knowledge that is available to humanity. And with each passing second I know less, not because I'm losing my mind, but because as I keep forgetting things, which is a mechanism of the human brain to stay sane, new knowledge is emerging on a scale that no human being can keep up with. At the same time, I am always eager to learn new things of all kinds, especially those that interest me. Building and playing a game about stars, worlds, near and distant, seemed like a reasonable thought to share this abstract with all of you. Pointing out that it is only an abstract and that the article is behind a paywall seemed only fair. If I were to develop a game like this, I would be interested in gathering as much new knowledge as possible that could help me develop an even better version of my vision. Note the difference between may and is. It's up to them to decide whether it's worth spending £12 or not.

That said, putting words in my mouth or fingers, we're in a forum, not the Forum, is one thing. In addition, to claim to know what I think is something else. Good luck with that mocking attitude in life.

I held back on the mocking of your ridicilous post. That post is straight out of entitlement land.

You can suggest changes and wish for additions in the game, but if you don't understand why your post was bad you need to take a few steps back and think about it for a while.

[rxnnxs]

Never played Elite:Dangerous, but I'd guess they also zoom in the bodies while being far away.

Precisely not. I'm quite aware of the dimensions involved, so I'm a bit picky about this. To put it simply, until you're close enough, planets and moons in the system just look like stars in the field. E:D is unrealistic in many ways (to my great despair), but not about dimensions and proportions. That's the main reason I stick with it, because so many games of its kind don't care at all. Now, that's not something that has to be done in all kinds of space games, at least I guess we agree with it.

I have to say that, so my two cents to elite is, they did a good job for the vastness of space, but why the heck do every, every place I fly into, has instantly someone there?
It is not like I go into the wild and I find a coca cola bottle, I want to find unexplored stuff.
And in such a big universe, it is impossibe, that when I fly to a random star, fly into a belt, huge like saturn, fly into some asteroids and... hello.. some unfriendly ships are already there and some miners..
Hello.. not my game from that time on..

[rxnnxs]

I have meant in terms of navigation, unless navigation is solely text based, there has to be a visible spot on the nav-screen, no? But besides that, I love "realism" in space games, too.

The more I come back to this thread, the more I remember the discrepancies in scaling.
DW2's Earth has a diameter of about 6K, it varies with each game (4,000-6,500). Our Earth has a radius of about 6K km (6,371 km). So let's say 1K ~ 2,000 km.
According to beam weapons, light travels at 5,000/sec ~ 300,000 km/sec in our universe. That's 1K ~ 60,000 km.
The average main sequence star is 30K-36K in diameter. Our sun yields 1,393,000 km. That's 1K ~ 40,000 km.
With all those very different scales we can assume that everything in DW2 is more on the side artistic freedom than a mapping of reality.
Which doesn't mean, that it can't be done in a more realistic way, even with a static galaxy, where no body is moving around their respective center of mass. It wouldn't harm gameplay. Still, it's another universe and that could have other universal constants. What drives me more crazy is that all ships have handbrakes

But all that wasn't the goal of this thread. It was simply pointing to new discoveries related to Moon-packing around an Earth-mass Planet

If it helps making the game a bit more realistic, great. If not, you can never know enough, and I appreciate sharing knowledge with others and vice versa.

Space Engine is, when you filter only for "known" (in reality existing) objects, a really awesome tool to make yourself an idea of how the scale of the universe is in reality.

And on the other hand, to get the realism into a space ship game, Children of a dead Earth must be a good game.
But, you can imagine, being that realistic, it is not for casual gamers
I alsoy love to explore the universe but want also to relax.
I am still very hopeful DW2 is that game, when some things are taken care of.

Realism is something we do not need that excessive, but when you can have a planet and a moon side by side and fleets from moon and planet are so close that they can shoot at each other, it is not only unrealistic, but kills my imagination.

This is what I mean. Moon and Planet, generated from the game itself, I just placed with the galactic editor the stations to show the weapon range.
I wrote this in the forum months ago, but I guess they do have other goals.

ms.jpg (87.32 KiB) Viewed 1043 times

And when planets would have a realistic (i mean just moving) orbit, even planets could shoot at each other, stations from both planets would even collide..
Maybe a mod could tear those orbits a bit outside.

[Thineboot]

And now for something completely different aka off topic, once more

[...]

Currently, there are 26 cosmological constants that describe our universe - not entirely. DW2 includes breaches to at least another universe. Therefore, they do not necessarily have to have the same cosmological constants.

You would think that electromagnetic waves always travel at the speed of light or ~300K km/sec. And you're right, Beam weapons are not only photon based. Since Laser Cannons include Laser and they only have a speed of 1000/sec, Beam weapons have to be more like a Scotty weapon, transporting their energy through another sub-space, which makes FLT weapons possible. I was blinded by the light of many 5000/sec weapons while there is also the Super Laser [X] with 9000/sec. As long as Plasma means plasma it's sending charged particles from A to B at 1100/sec. But we don't even know laser in a pre-warp start, only missiles and kinetic weapons, travelling at 350/sec.

So our physics are not directly comparable to DW2 physics and that's fine, it's a game we enjoy - most of the time

As for Mel, at 1:04 they make a clear statement about breaking and they are accelerating for the next 18+ seconds when they hit ludicrous speed - and I'm pretty sure nothing was meant serious in his film, except for where Dark Helmet's brain was going

While there are several references to Skip drives the homage to Star Trek's Warp drive bubble is undeniable. And Alcubierre has put forward a theory that may one day come true 41 years from now


@ Buio, have fun in life

[...]
It is not like I go into the wild and I find a coca cola bottle, [...]

[Thineboot]

[...]

Space is a vast emptiness any we keep blocking our way into it more and more at an even more increasing speed by doing the same to our lower orbit the same way we're trashing our one and only living space. Seems too few are even caring about getting an idea about how the scale of the universe is in reality

Just checked out Children of a dead Earth at Scott Manley's channel. Looks like a military KSP that did never care much about graphics. Still, the ratings are impressive for a game that had it's last patch in 2017. I'm not a casual player, guilty as charged
Looking up The Expanse, with did many things right on the screen, I just run into Solar Expanse, which shall be released before Mars landing

Without hope for DW2 I wouldn't be here. They have shown that they can deliver over a six year period patches and upgrades. So they were no quitters and we're just at the beginning of a hopefully successful journey over many years to come.

They have put many details into OrbTypes.xml, including ChildCountMaximum, which is nothing else but Moon-packing around an orb - there are no explicit moons in DW2, they all are planets orbiting a sun or planet. There are also OrbitalDistanceFromSunRationMinimum and OrbitalDistanceFromSunRationMaximum. So hopes are high that they'll manage sort out these much too close distances between planets and moons. It's more or less a scaling problem.
As for orbs (planets, moons, asteroids) revolving around orbs (suns, planets, asteroids), that would mean a lot more work and probably changes in game design, too. But it would be great to see

[Radamanthe]

Never played Elite:Dangerous, but I'd guess they also zoom in the bodies while being far away.

Precisely not. I'm quite aware of the dimensions involved, so I'm a bit picky about this. To put it simply, until you're close enough, planets and moons in the system just look like stars in the field. E:D is unrealistic in many ways (to my great despair), but not about dimensions and proportions. That's the main reason I stick with it, because so many games of its kind don't care at all. Now, that's not something that has to be done in all kinds of space games, at least I guess we agree with it.

I have to say that, so my two cents to elite is, they did a good job for the vastness of space, but why the heck do every, every place I fly into, has instantly someone there?

[OFF_TOPIC]

Honestly, I can only guess 2 possibles answers to your question. Either:

1° You only scratched the game.
2° We don't talk about the same game.

I'm quite confident at this point that the answer is 1°.

But let's develop my point a bit. In E:D lore, humanity colonized roughly thousands of systems around Sol. This is known as "the bubble". A bubble which represents a tremendously tiny portion of a simulated Milky Way of ~4 billions systems (of course, this is mostly procedural generation at work).

When you start the game, you're in the bubble. Getting out of it takes time (most players don't have that time, I'm ok with it), especially if you don't take the time to improve your warp drive to make bigger jumps. Then you have to jump from systems to systems until you get out of the bubble. That's where what we can call "exploration" begins. Most of the player base stays in the bubble because there are many things to do there, while outside, except in the very few outposts humanity dared to settle a bit, there is only exploration to do (let's not develop on the many things exploration is all about here, this post is long enough).

Even so, even if you stay in the bubble, most of the planets are not inhabitable (ie. could not be terraformed yet, or not terraformable at all). So, even in that tiny bubble, you're plainly wrong stating that every place you fly into are occupied. I can only conclude that you only visited planets which are occupied, that even there, you only landed on places which are occupied (usually by outposts) because maybe you don't see the point of landing onto a inhabited planet as there are probably (in your mind) nothing much to do there (like missions any NPC human could give you). Even less in a system with no planet at all, or simply a system with absolutely 0 population (which we find easily, even in the bubble). That's fine too as it is up to you.

Still wrong about exploring call, as true exploration, besides the fact that you're alone somewhere in space without any station nearby (in the order of lightyears distances) to support your needs in "social activities", is about... well... exploring things nobody explored before, and contributing so to map such a galaxy. It can be boring to some (and a bit stressful too because you're alone far away from other human beings), it's marvelous to others.

Now, to make it clearer, here's an interesting video of what this is all about as of today:

https://edastro.com/mapcharts/video.html

There are many videos behind this link, but let's just focus on the first one. As you can see, this is a video of the progression of the systems which at least someone entered since the game started years ago. Even at full resolution, that video does not pay tribute to the vastness of that galaxy, as even only one pixel represents many systems. In the end (~today), you can see that only 0.018955% of the whole galaxy has been explored, and this is taking into account the fact that a system only has to be entered (not even taking the time to explore it's planets, if any) to be marked as "explored", hence higlighting (a tiny bit) the pixel which it pertains to. You can easily see that the bubble (in red) is a very tiny portion of the whole thing.

Given that number, that's 99,981045% of unexplored systems where, obviously, you won't find anyone, and even more because an already "entered" system in the past, probably for a few seconds, does not mean in any way there is someone there at the time you visit it. During my last trip, in the order of "only" 5000 light years away of the bubble, I did not encounter anyone, players or NPC, during weeks, back-and-forth (except of course near the bubble, or in that isolated station in a system in a nebula that I used as a relay to break a bit with my sought-after loneliness, and of course, that same station I did not found by chance, but by consulting the database).

Finally, needless to say, in this regard, that the player base will unlikely explore the whole galaxy until centuries (in the unlikely event that the game, which is online, continues for centuries...).

It is not like I go into the wild and I find a coca cola bottle, I want to find unexplored stuff.

Looks like there's a hole between wanting it and doing it. But TBH, I don't think you really want as it's easier to do in E:D than just getting out of the bubble. As I said, most places, even in the bubble, are not occupied.

And in such a big universe, it is impossibe, that when I fly to a random star, fly into a belt, huge like saturn, fly into some asteroids and... hello.. some unfriendly ships are already there and some miners..

In a colonized tiny portion of the galaxy, a colonized "bubble" where humanity spread in the order of gazillions of souls, undoubtedly you'll find someone in any hot spot where most people go. Looks like you did not have the will to wander (like me who appreciate loneliness) in spots not considered hot. I'm also fine with it.

Hello.. not my game from that time on..

Looks like it resumes it all. Can't blame you.

And buddies, don't take me wrong: I'm not here to sell E:D. There are many aspects of that game that I blame too. But definitely not the exploration aspect. Now, like you, I also love conquering a galaxy the 4X way, even if it's only made up of a hundreds of systems ;)

[/OFF_TOPIC]

[rxnnxs]

Thank you all for the input. Here we can see that we all are different - in taste and thinking.
Where we come together: DW2.
Elite, in my eyes, and I am not putting 50+ hours in it to get to a place where there is no npc auto generated mining ship or hostile ship nearby. They made the game with many things in mind that annoy (sure not only) me. It goes a bit, a tiny bit, in the direction where this robert space stuff still is doing a great job (in writing more than doing anything - and people believe in them..).
Therefore, I play Star Ruler 2, MOO3, Polaris Sector and DW2 And every month or so, my rating of those games is shuffled somehow again.. meanwhile, the "real thing" is doing twists, noone dared to dream about..

[Radamanthe]

taste and thinking

This was not about taste and thinking. This was about facts.

Where we come together: DW2.

True. Nice to see you can sometimes speak some truth...

Elite, in my eyes, and I am not putting 50+ hours in it to get to a place where there is no npc auto generated mining ship or hostile ship nearby.

This is getting insanely ridiculous in the bad faith register. I first though that you managed to make me laugh more loudly than Mel Brooks and Monty Python combined. Well, after recovering from my emotions, not that much, but still... congratulations :)

Now, more seriously: few minutes are enough to get to a place with nobody around, and this with the slighest will. Maybe an hour the first time you play, given the time needed to learn how to handle things. Facts.

Anyway, I guess I did what I had to do to contradict what I know to be complete non-sense.

Long life to DW2 (to me, one of the best space 4X game I had the pleasure to enjoy).

[rxnnxs]

taste and thinking

This was not about taste and thinking. This was about facts.

Where we come together: DW2.

True. Nice to see you can sometimes speak some truth...

Elite, in my eyes, and I am not putting 50+ hours in it to get to a place where there is no npc auto generated mining ship or hostile ship nearby.

This is getting insanely ridiculous in the bad faith register. I first though that you managed to make me laugh more loudly than Mel Brooks and Monty Python combined. Well, after recovering from my emotions, not that much, but still... congratulations

Now, more seriously: few minutes are enough to get to a place with nobody around, and this with the slighest will. Maybe an hour the first time you play, given the time needed to learn how to handle things. Facts.

Anyway, I guess I did what I had to do to contradict what I know to be complete non-sense.

Long life to DW2 (to me, one of the best space 4X game I had the pleasure to enjoy).

While downloading 19 Gigabyte for Elite, I read through the comments, and only 76% of the game think positive about it. If you read the negative, and i read only some of them and from those that play the game over hundreds of hours, they all say:
The npc take you out of your jump and fight you, the game is mostly a grind and it is getting worse than before.
So please, accept my opinion on that, I stop the download, that is not worth my time. Shoot, they got my money very long time ago and just can not make happen what i wrote at the beginning: just mining in peace is not possible and to get there kind of, is a looong grind. and maybe I lose my cargo many times before I even get there.. Nope, I do not know how you play, but.. I play different. I do not like it to be kicked in the butt.
But you know what, I keep downloading it, and may I PM you later?