This ELW is a moon and has a moon with a moon?

[GunnerBill]

Jinkies Moon-a-rama!

Actually I'm not sure how to describe the orbital arrangement here...

Is the ELW a moon to the Y Brown Dwarf or is it a binary with it? Can a Y Dwarf have moons as it is a "star" urrrrghhh MY HEAD HURTS!

 

[Saool]

THe ELW look like it is a pair with the Brown Dwarf. The last planet is totally separate with it's own moon.

 

[Vasco Sapien]

Maybe the ELW and the moon/moon are a system that combined create a barycentre realtionship with the Brown dwarf which has its own moon system?

 

[dognosh]

ELW & Dwarf in binary, the other planet is just another in orbit round the star, not hard but can be confusing

 

[soddish]

Earth-Like and Y Dwarf are in binary orbit, Earth Like has no moons but the dwarf seems to have plenty of orbital bodies (moons? planets?), including some that are in binary orbit with each other.

TL: DR that's no moon, it's a binary orbit.

 

[Vasco Sapien]

THe ELW look like it is a pair with the Brown Dwarf. The last planet is totally separate with it's own moon.

Yup, i think thats correct.

 

[Sysmon]

Looks to me like the ELW is a binary with the brown dwarf, as it is not in the list of moons below. It will probably look like it is orbiting the brown dwarf, as the barycentre will be deep within the brown dwarf. The ELW has no moons, but the next planet out does.

So maybe not that exciting, although the brown dwarf system will look exciting with several landables and an ELW to dance with.

S

 

[GunnerBill]

OK The next planet is not a moon because it's a horizontal line going to the right? And not a vertical line dropping down?

Is it orbiting the main star or the ELW or the Brown Dwarf? Basically I am confused how the "bridge" link to the dwarf changes things.

 

[Winterwalker]

OK The next planet is not a moon because it's a horizontal line going to the right? And not a vertical line dropping down?

Is it orbiting the main star or the ELW or the Brown Dwarf? Basically I am confused how the "bridge" link to the dwarf changes things.

The horizontal line represents bodies orbiting around the main star (off screen).

Every planet has a center of mass, and it's that single point that orbits the star (imagine the weight of the whole planet shrunk down onto a single point of influence).

Conbining the ELW and Y Dwarf, they travel around each other (as a binary) and between these two centres there is also a third centre of mass, around which the binary planets orbit.

It's this 'virtual' (shared) centre of mass that orbits the main star.

[up]

edit: a good way to get to grips with this in game, is to turn obit lines on (right panel) and you can compare the orbital lines with the system map, to see how things are moving.

 

[Flimley]

That's even more awesome then button moon. !

Flimley

 

[Corbin Moran]

But isn´t the real puzzle here how an ELW is able to be in a binary arrangement with a star... Im not a physicist but my understanding is that a binary orbital arrangement is only possible if the difference in mass between the two objects are not too great. If one object has much larger mass than the other, the shared center of gravity will be located somewhere within that object - and then its not a binary arrangement...

Can anyone explain what is wrong with my reasoning or the stellar forge here?

 

[Winterwalker]

But isn´t the real puzzle here how an ELW is able to be in a binary arrangement with a star... Im not a physicist but my understanding is that a binary orbital arrangement is only possible if the difference in mass between the two objects are not too great. If one object has much larger mass than the other, the shared center of gravity will be located somewhere within that object - and then its not a binary arrangement...

Can anyone explain what is wrong with my reasoning or the stellar forge here?

I think you're right but would have to have a good look at the stats. The actual comparative masses, of gaseous Y-Dwarf (not quite a star) versus rocky planet, might be different sizes but different densities might reduce the mass difference .. and orbital period and distances, the Y might move slowly around the centre of gravity, the ELW much faster, throwing it further from the centre? Could be a captured planet and - worst case - might also depend where you draw the line on 'binary' (ie. how much wobble constitutes a binary orbir)

 

[iain666]

But isn´t the real puzzle here how an ELW is able to be in a binary arrangement with a star... Im not a physicist but my understanding is that a binary orbital arrangement is only possible if the difference in mass between the two objects are not too great. If one object has much larger mass than the other, the shared center of gravity will be located somewhere within that object - and then its not a binary arrangement...

Can anyone explain what is wrong with my reasoning or the stellar forge here?

Binary planets vs one planet with a moon isn't a law of physics, it's an arbitrary human label (and there is not currently one single definition that's accepted by the IAU according to wikipedia....).

So whatever arbitrary rule FDev have implemented in their 'drawing the lines on the system map' function says this is a binary pair and that's pretty much that.

Most of us would probably go for something based on relative sizes (which would also imply a barycentre not contained within either body) but there's currently no authoritative way to say that anything is right or wrong.

I don't recall ever seeing a big (0.1EM+) moon so maybe FDev's arbitrary rule is just based on the absolute body mass rather than the relative masses of the bodies...

 

[Sapyx]

With every object that is generated by the stellar forge in orbit around a primary object, the game calculates where the barycentre for that pair of objects would be. If the barycentre is inside the primary, then the object is a "moon" and the orbit of the is a simple ellipse around that primary, with the primary considered to be stationary with respect to the object. If the barycentre is calculated to be outside of the primary, then the object is a "co-orbiting planet" and the orbits of both the object and the primary are calculated to be going around the barycentre. This is a simplification of the many-body problem, necessary because the procedurally-generated nature of the ED universe can't handle dynamic, multiple-body orbital mechanics that could make a planet's orbit unstable.

The barycentre is not a physical, selectable object but the game treats it as such, for orbital calculation purposes; the barycentre of two co-orbiting planets is considered to orbit the star, just like a planet. You can then have additional stars/planets/moons that this barycentre orbits or co-orbits around.

 

[iain666]

With every object that is generated by the stellar forge in orbit around a primary object, the game calculates where the barycentre for that pair of objects would be. If the barycentre is inside the primary, then the object is a "moon" ... If the barycentre is calculated to be outside of the primary, then the object is a "co-orbiting planet"

Is that a thing you know from empirical evidence or a statement to that effect from FDev or a thing that you suspect which seems to hold true?

If you know that that'll save me looking up the details of the system I found with an ELW/Y-Dwarf pair....

 

[Sapyx]

I'd classify it as a "reasonable hypothesis based on observational evidence": I've never seen a pair of objects the game classifies as a co-orbiting planet which has a barycentre inside the larger object. Of course, correlation does not imply causation. I'm not familiar with the inner workings of the stellar forge, and FDev are normally tight-lipped about the mechanism.

 

[Winterwalker]

Of course, correlation does not imply causation. I'm not familiar with the inner workings of the stellar forge, and FDev are normally tight-lipped about the mechanism.

That's right. I think the inner workings of stellar forge aren't really for us to reason why probably because all that really matters is it generates plausible body orbits, from system to system. These might not always fit with natural planetary formation because the example of wandering Jupiter means we shouldn't always expect planets to stay where they formed and modelling erratics like that, is both more realistic and makes life more interesting.

What's interesting about the planet in the OP for me is it does look like an odd place for an ELW to be and, given that I think it must have a fairly eccentirc orbit to be there, because atmosperic worlds aren't being fully simulated yet, I wonder if the planet might have mini ice ages during it's binary year, not shown (because not modelled yet) at the moment water looks liquid on the surface, year long.

As mentioned, for me it could have been captured by the Y Dwarf. Perhaps having formed closer to the main star, giving any plant life a chance to get going, pulled the planet out of it's formation orbit by Orbital Resonances, for capture by the Y?

 

[[VR] optimal_909]

That's right. I think the inner workings of stellar forge aren't really for us to reason why probably because all that really matters is it generates plausible body orbits, from system to system. These might not always fit with natural planetary formation because the example of wandering Jupiter means we shouldn't always expect planets to stay where they formed and modelling erratics like that, is both more realistic and makes life more interesting.

What's interesting about the planet in the OP for me is it does look like an odd place for an ELW to be and, given that I think it must have a fairly eccentirc orbit to be there, because atmosperic worlds aren't being fully simulated yet, I wonder if the planet might have mini ice ages during it's binary year, not shown (because not modelled yet) at the moment water looks liquid on the surface, year long.

As mentioned, for me it could have been captured by the Y Dwarf. Perhaps having formed closer to the main star, giving any plant life a chance to get going, pulled the planet out of it's formation orbit by Orbital Resonances, for capture by the Y?

I think this particular ELW is being kept warm by the main star and not the Y dwarf, so no eccentric orbit is necessary.
Quite the opposite, tidal forces, the magnetic field of the dwarf, collosions with asteroids of its ring system and stuff like that would make it rather unlikely to allow a habitable place.

 

[marx]

@ GunnerBill: If the ELW is sufficiently heavy and its binary partner dwarf star (or gas giant) sufficiently light, then sure, it should be possible. If an ELW then had moons of its own, they would be below the ELW, not next to it. (It's very rare, but it can happen.) If said moon had a moon, it would be to its right: the system map's zig-zagging it. However, I'm fairly certain that the last scenario would be impossible, as an ELW's moon would be too light to have a moon of its own.

Also, even larger stars can orbit another star. For example, a class K star orbiting a black hole.


@ Winterwalker: Stellar Forge models all stars heating the planets, so this one would be heated by its primary too, not just the dwarf star. This is why it's possible to have Earth-likes orbiting a class M dwarf far outside what its habitable zone would be in its own, if for example there is a neutron star sufficiently close by.

 

[GunnerBill]

Thanks to all for the really cool info!