A question about very near planets

[kikinho]

Look at this:



Is it possible to this happen in the real universe? These are only a very few planets of my Sheron'nish Cluster project. This is a small part of my HIP 1000001 system that have a K0V star. This system i'm doing is divided in three groups: Hot giants, Earth-like and outer cold planets.

What is your opinion?

[Rassilon]

Planets that pass the Roche limit will eventually tumble into the parent planet/star it orbits or break apart due to the massive tidal forces and generate rings or just be engulfed...as in the case of your orbits above...The first two planets would if not first be vaporized by the sun...eventually collide with each other...Orbits generally have a span...Based on both the radius of the parent and the child/moon...That is of course in the simplest fashon...

[kikinho]

In my system, the first two planets won't collide, because:

"Mini Hell" "HIP 1000001"
{
Color [ 1 0.2 0 ]
Texture "HotPlanet.dds"
NightTexture "HotPlanet-night.dds"
Radius 23615
Oblateness 0.03265
Atmosphere {
Height 1000
Lower [ 1 0.2 0 ]
Sky [ 1 0.2 0 ]
Upper [ 1 0.2 0 ]
}
EllipticalOrbit {
Period 0.034
SemiMajorAxis 0.034
Eccentricity 0.006
Inclination 7
}
Albedo 0.01
Obliquity 10
}

"Jereminguara" "HIP 1000001"
{
Color [ 1 0.2 0 ]
Texture "HotPlanet.dds"
NightTexture "HotPlanet-night.dds"
Radius 18262
Oblateness 0.07342
Atmosphere {
Height 1000
Lower [ 1 0.2 0 ]
Sky [ 1 0.2 0 ]
Upper [ 1 0.2 0 ]
}
EllipticalOrbit {
Period 0.042
SemiMajorAxis 0.042
Eccentricity 0.524
Inclination -44
}
Albedo 0.01
RotationPeriod 5
Obliquity 90
}

"Loriscra" "HIP 1000001"
{
Color [ 1 0.2 0 ]
Texture "HotPlanet.dds"
NightTexture "HotPlanet-night.dds"
Radius 27632
Oblateness 0.01725
Atmosphere {
Height 1000
Lower [ 1 0.2 0 ]
Sky [ 1 0.2 0 ]
Upper [ 1 0.2 0 ]
}
EllipticalOrbit {
Period 0.068
SemiMajorAxis 0.068
Eccentricity 0.350
Inclination 6
}
Albedo 0.01
RotationPeriod 16
Obliquity 30
}

"Gambicandra" "HIP 1000001"
{
Color [ 1 0.2 0 ]
Texture "HotPlanet.dds"
NightTexture "HotPlanet-night.dds"
Radius 25725
Oblateness 0.12784
Atmosphere {
Height 1000
Lower [ 1 0.2 0 ]
Sky [ 1 0.2 0 ]
Upper [ 1 0.2 0 ]
}
EllipticalOrbit {
Period 0.092
SemiMajorAxis 0.092
Eccentricity 0.415
Inclination 27
}
Albedo 0.01
RotationPeriod 3
Obliquity -50
}
You see now that in Celestia they won't collide. The second planet don't pass exactely in the orbit of the first. I modofied the size of the planets.

[tony873004]

What are the masses of your planets?

Your first two planets might be saved from collision in the very short term because of their 3:2 resonance (similar to Neptune and Pluto).

But that outermost planet looks pretty massive. I'd guess that it would cause major instability throughout the entire region, quickly pulling the first two planets out of their resonance, and pulling them and the other planets into chaotic orbits, causing them to be quickly ejected from the star system or sent on a collision course with the parent star or the other planets.

[kikinho]

I've updated the text above about 4 planets of my system. Have a look.

[kikinho]

Ah, and my HIP 1000000 system have a G6V star with 40 planets! What do you think? Yeah..., it's too much planets for a G6V star, but I doubt that anyone here did a system with 40 or more planets. The bigger system I saw at now in Celestia have 17 planets.

[Spaceman Spiff]

Hello kikinho,

Going back to your original question:

Is it possible to this happen in the real universe?

... the answer would be "yes, but...". The "yes" is because it is physically possible to have some planets in orbits as you displayed at a particular instant in time. The "but" is that it is very unlikely to occur, and also if it did, it wouldn't last long on a time scale relative to the typical orbital periods of those planets. The planets are so close to each other that even though the mass of the star still dominates, the planets would pull each other and change their orbits (and I'm assuming planet masses of a 10th to 10 times that of Jupiter, which is a 10,000th to a 100th of a solar-type star mass).

Your 'hot Jupiters' would have periods of days to hours, so after a week, all their orbits would have changed. After a year, I would expect at least two, maybe three of the four planets would be on their way out of the hot, inner system altogether. You could try having fun with a proper gravity simulator to see how planets fly off away from their star when they pass each other closely.

The real problem for you and many other Celestia users is that there is no way for you to tell that this would happen from Celestia - it uses a 'kinematic' model for orbital motion, not a dynamic model. That is, 'kinematic' means 'considers motion, but not forces', while 'dynamic' means 'considers both forces and motion'.

Celestia restricts us to specifying 'Keplerian' orbits (the blue loops it draws for orbits), which obey a specific kind of motion that is true when there are only two masses to consider. That's for our 'ease of use' of Celestia. In the Solar System, because planets and moons are often so spaced apart that each is governed only by one other body, the sun or the parent planet, Keplerian orbits worked very well for a limited time. It's like a 'clockwork' model: it won't tell you how orbits evolve due to third bodies, etc. You have to use the xyz traces to get a different motion from Keplerian, and even then it should have been computed to agree with Newton's law of gravitation.

If things were ideal, Celestia would include a sophisticated dynamic model, and if it should draw the instantaneous and equivalent Keplerian orbit of each planet, you would see the shape of the orbits suddenly change for any two planets that came sufficiently close to each other (this is called "perturbation of orbits"). It would be fun, and it would happen quickly and often for your system.

In the meantime, there is no easy answer to you for what would actually happen - that's a lot of mathematics and calculations.

Still, I think an important rule for Celestia is: Have fun!

Spiff.