Help with a fictional Star System

[SargeRho]

So, I'm currently working on a game that takes place on a planet in another Solar System. The planet is called Tenorra, and while the star system it resides in has no effect on the gameplay, I would like to make it believable. The planet itself is 1.2 Earth Radii, but less dense, and thus has close to 1G of surface gravity, and is currently under siege by an armada of alien murder-bots from outer space programmed to seek out and destroy technological civilizations. Gone slightly awry. There are 2 major superpowers on Tenorra - the Tenorran Defense Union and the Coalition of Populist Socialist Nations, both are still recovering from a short-lasted dark age after the troublesome settlement of the planet, but are already I guess 40-50 years more advanced than us, much more than that in some areas.

The star system consists of two Stars - an Orange K2V class main sequence star somewhat heavier than the Sun orbited by 3 asteroid belts and 14 planets, and an M8 class Brown Dwarf companion orbiting at about 120 AU from the main star, orbited by 5 planets/moons.

The K2V star has an inner asteroid belt, then 2 small rocky planets - Roasted and Toasted, that are well "inside" of the Habitable Zone, and are exactly as their names imply, roasted and toasted.

Followed by a "gas dwarf" - a gas planet about 8-9 times the size of Earth, made mostly of Hydrogen, Helium and Methane. It orbits well inside of the habitable zone. It's used by the Tenorrans as a source of Anti-protons via orbiting magnetic traps. No exceptional moons.

Then comes Tenorra as 4th planet. Tenorra is as described above, has 9 continents that are all much smaller than Earth's, also it has a Moon about as big as Mars with a relatively thick Argon atmosphere, which is was used as a fuel source prior to the invasion.

It also has 3 moons - Thor, Ares and Prometheus, all of them about as big as Charon, except Ares, which is half as big. There are laser cannons built onto the surface of each of them, in addition to smaller laser satellites orbiting Tenorra itself.

Then comes another asteroid belt.

The 5th planet is an Ammonia planet, with Ammonia based animal-plant hybrid life on it.

The next 9 planets I haven't really worked on yet. There are 3 Gas Giants, 4 Ice Giants and 2 rocky planets.

The M8 Dwarf has a small rocky companion not bigger than Pluto, but with an unusually strong mangetic field and a tenuous hydrogen atmosphere "siphoned" off from the star's outer atmosphere.

The next one is a semi-habitable planet about as big as Earth, tidally locked to the Dwarf that formed at the inner edge of the habitable zone, which has since moved inwards, with primitive microbial life on it, as well as a space station and some surface outposts established recently. These were the first things to be destroyed by the ICES armada - Interstellar Civilization Eradication System is what they were called by their creators, obviously in their language. And yes, that is an ISIS pun.

The other 3 companions of the dwarf are fairly boring rocks with equally boring rocks orbiting them.

-

So the question is: How physically viable - not probable - is this system? I don't know enough about planetary formation and orbital mechanics to figure that out on my own.

I know that this system is unlikely to form in the first place, but that's not what I'm asking.

Edit: Graphical representation: http://i.imgur.com/7eKpWCD.jpg

Edited June 7, 2015 by SargeRho

[_Augustus_]

K2V star is orange, Mars-sized moons of Earth-sized planets don't make sense, everything else makes sense.

[SargeRho]

I thought Alpha Centauri B was a blue K2V?

[_Augustus_]

I thought Alpha Centauri B was a blue K2V?

Lol it's orange.

[SargeRho]

Ok, clear case of "Didn't do enough research". Fixed it in the original post.

I was going off of this image: http://themeridianijournal.com/wp-content/uploads/AlphaCen.jpg

[Starwhip]

I used this to make a star system for one of my novel ideas:

Gravity Simulator

EDIT:

I also had this. Might have helped. XD

Aurrera
Orbital Period: 436.91 Days
Rotation Period: 25 Hours 16 Minutes
Altitude: 1.197 AU
Mass: 7.53181 x 10^24 Kg
Diameter: 8,123 Miles (13,080 Km) (Earth is 7,918 Miles, and this planet has more gravity)
Density: 6442.951 Kg/m^3
Gravitational Force: 1.2 G’s (11.76 m/s^2)
Earth Masses: 1.2603
Orbital Eccentricity: 0.01
Orbital Inclination: 0.02
Asteroid Moons: 83, 230,700 m  - 1,000 Km

Arreba
Orbital Period: 245.28 Days
Rotation Period: 31 Hours 9 Minutes
Altitude: 0.672 Au
Mass: 3.564952 x 10^24 Kg
Diameter: 7797 Miles (12,556 Km)
Density: 1,146.515 Kg/m^3 (Made of light elements and is entirely cold, massive cave formations)
Gravitational Force: 0.6 G’s (6.03 m/s^2)
Earth Masses: 0.59693
Orbital Eccentricity: 0.03
Orbital Inclination: 0.05

Zaharra
Orbital Period: 200.02 days
Rotation Period: 40 Hours 31 Minutes
Altitude: 0.548 Au
Mass: 6.9905164 x 10^23 Kg
Diameter: 2,548 Miles (4,103 Km) Volume: 108,498,673,344,8767 Km^3
Density: 6442.951 Kg/m^3
Gravitational Force:
Earth Masses: 0.11697
Orbital Eccentricity: 0.03
Orbital Inclination: 0.2
Asteroid Moons: 3, 30,000-60,000 m









Erraldoi
Orbital Period: 106.22 days
Rotation Period: 5 Hours 3 Minutes
Altitude: 0.291 AU 
Mass: 2.360568 x 10^27 Kg
Diameter: 90,237 Miles (145,303 Km)
Density: 1469.587 Kg/m^3
Gravitational Force: 3.04 G’s (29.83 m/s^2)
Earth Masses: 395.2329
Orbital Eccentricity: 0.02
Orbital Inclination: 0.05
Asteroid Moons: 15, 300,000 - 450,000 Km

Average Asteroid
Diameter: 7 Km
Volume: 250,000 m^3
Mass: 1,610,500,000 Kg
ECC: 0.1
INC: 0.25
Distance from E-2: 200,000 Km
Density: 6442.951 Kg/m^3
Countless asteroids in Aurrera’s orbital path




Simulation of the orbits. Green is Erraldoi, red is Zaharra, White/Gray is Arreba, and Blue is Aurrera

Gravity (mâ„s^2 )=  ((Gravitational Constant)(Mass of Planet))/〖(Radius of Planet (meters))〗^2 

Conversion From Miles to Kilometers (Miles * 1.6102 = Kilometers)
Geosynchronous Orbit:
Altitude (m)= ∛(((Gravitational Constant)(Mass of Planet) (Rotational Period)^2)/(4À^2 ))-Radius of Planet

[Drunken Hobo]

I don't think it's possible for an orange star to be more massive than the Sun.

I'm also not entirely sure how possible a hot gas dwarf would be, as the atmosphere would be stripped away by the Sun. Even with an intense magnetic field, free hydrogen & helium would still reach escape velocity just because of temperature.

If you want to mess around with orbits, then Universe Sandbox is a fun tool. Steam sale is likely to start up soon and it often becomes ridiculously cheap.

[SargeRho]

The gas dwarf is within the habitable zone, so it's temperate, I should have stated that in the OP. Fix'd that too.

[Drunken Hobo]

The gas dwarf is within the habitable zone, so it's temperate, I should have stated that in the OP. Fix'd that too.

You've got to get quite far out for hydrogen & helium to remain in an atmosphere. They still escape from Earth and even Mars.

[SargeRho]

Hmm. Could it be a former gas giant, that has lost a portion of its atmosphere?

[ChrisSpace]

A visual representation would be nice.

[SargeRho]

Done. Warning: Huge-ass picture:

Also linked it in the OP.

[Drunken Hobo]

Hmm. Could it be a former gas giant, that has lost a portion of its atmosphere?

I suppose it could still be losing its atmosphere - there's no reason it has to be stable.

I have no idea how long it would take to strip away significant quantities of hydrogen from a planet. Venus has lost the equivalent to about 1 Earth atmosphere over its lifetime, but it just happens to have about another 94 Earth atmospheres to compensate. If your hypothetical planet has a large supply of hydrogen then it could last for millions or even billions of years, especially if it used to be significantly larger. (There is a hypothetical class of planets called "chthonian planets" where all of the atmosphere of a gas giant has been stripped away, so logically there must be an intermediate stage).

This is sort of where my knowledge breaks down though - I was just going by the physics that dictates how quickly small molecules travel.

[Aanker]

Venus also doesn't have the same degree of magnetic shielding that Earth has, maybe as a result of its very slow rotation.

[PB666]

K2V star is orange, Mars-sized moons of Earth-sized planets don't make sense, everything else makes sense.

I agree, if a mars sized planet orbited the earth the tides in many areas would be 30 meters high. If you moved it further away it would be plucked from its orbit by the gas giant. Even tideless areas you would expect the daily tides to be a couple of meters. Not much sea faring going on in those cultures. The claim is that the moon is the remnant of an ancient collision where crustal material coalesced into the moon and a much closer orbit than present (presumably with much greater tides). But a Mars size planet would not be so easily accelerated into higher orbit, it would remain relatively close to earth and the tides would pretty much erode the continents into shallow seas.

It can exist, its just not so favorable to sentient life forms.

Venus's atmosphere is not equivocal to Earths atmosphere, most of what comprises Venus's atmosphere is what we find in our oceans (oxides of carbon, sulfur the like are dissolved in water). Remove 2/3rds of the radiation hitting Venus for a millennium and Venus's atmosphere would change considerably.

[RuBisCO]

There would be no tides if the two worlds are tidal locked, and considering the closeness in mass that is likely to happen. Consider Pluto and Charon as examples, or Duna and Dress: Binary Planetary Systems with both worlds tidal locked and center of gravity outside of either.

It is even possible to have them orbit about each other to have earth long days, though you will need to check the Roche limit to make sure such a thing is stable, I would say 2-6 earth day long days to be on the safe side.

[Scotius]

There would be no tides if the two worlds are tidal locked, and considering the closeness in mass that is likely to happen. Consider Pluto and Charon as examples, or Duna and Dress: Binary Planetary Systems with both worlds tidal locked and center of gravity outside of either.

It is even possible to have them orbit about each other to have earth long days, though you will need to check the Roche limit to make sure such a thing is stable, I would say 2-6 earth day long days to be on the safe side.

And both bodies would be noticeably oblate Generally, Earth-sized planets with too many big moons would be a rough place to live because of cumulative effects of their gravitation on the planet. High, irregular tides, weather disturbances and increased quakes galore...i suggest you prune those not relevant to the story out.

[Drunken Hobo]

Venus also doesn't have the same degree of magnetic shielding that Earth has, maybe as a result of its very slow rotation.

Having a magnetic field doesn't help much against stripping away of hydrogen & helium. Just due to to the temperature of the atmosphere, an average H_{2 molecule on Venus travels at about 1/3 escape velocity. Obviously due to collisions not all molecules in a gas travel at the same speed and some will reach escape velocity, never returning to the planet. For Jupiter, hydrogen only travels about 1/40 escape velocity, hence it can hold on to it easily.}

_{It's simply a matter of temperature vs. gravity. A very hot body like the Sun can hold onto hydrogen easily due to its gravity, whilst a very cold body like Titan still can't keep a hold of hydrogen due to its low gravity.}

_{There would be no tides if the two worlds are tidal locked, and considering the closeness in mass that is likely to happen. Consider Pluto and Charon as examples, or Duna and Dress: Binary Planetary Systems with both worlds tidal locked and center of gravity outside of either.}

_{It would still be possible to have tides if the orbit of the moon was eccentric. I think two tidally locked bodies would have a tendency to have a circular orbit, but if there are other moons in the system it could prevent them from doing so.}

Edited June 7, 2015 by Drunken Hobo

[SargeRho]

What would the upper limit be for the moon? How about one the size of Titan, at a distance slightly further than our moon?

[Dispatcher]

Given the length of time that any planetary system exists, the odds do not favor another planet in another system having a civilization which only differs technologically from us by a mere 50 years or so. In fact, the Drake equation seems to restrict our own technological level (in terms of electromagnetic spectrum communication) to a small sliver of time relative to the lifespan of a civilization; and restricts the span of multi celled life on a planet to a fraction of the planet's existence.

That said, good luck on your game!

[SargeRho]

The Tenorrans are humans, that have settled the planet some 5-6 centuries ago, and are recovering from a short-lasted dark age after the settlement didn't go quite as planned.

[RuBisCO]

And both bodies would be noticeably oblate Generally, Earth-sized planets with too many big moons would be a rough place to live because of cumulative effects of their gravitation on the planet. High, irregular tides, weather disturbances and increased quakes galore...i suggest you prune those not relevant to the story out.

I think a binary planetary system is a great idea for atmosphere and plot purposes, I've seen it done before to great effect. Really you and Drunken Hobo are picking on nits, tides would be minimal, weather: unknown, tectonics: who knows, there is enough scientific uncertainty to build a story,

[Bill Phil]

You've got to get quite far out for hydrogen & helium to remain in an atmosphere. They still escape from Earth and even Mars.

Gas planets have a lot more mass. It would stay attached for a longer period of time.

See: Hot-Jupiters

[Scotius]

I think a binary planetary system is a great idea for atmosphere and plot purposes, I've seen it done before to great effect. Really you and Drunken Hobo are picking on nits, tides would be minimal, weather: unknown, tectonics: who knows, there is enough scientific uncertainty to build a story,

Well, apparently we read different books A series by Anne McCaffrey i've read described a habitable planet, Earth-like and with two (or three, i do not remember now) hefty moons orbiting it. Everytime there was a conjunction of two (or stars forbid three) moons, surface of the planet became a hell hammered by hurricanes non-stop until conjunction ended. It was so bad everyone were forced to evacuate to underground bases or orbital stations - and any stragglers caught on the surface were considered as good as dead.

[Armchair Rocket Scientist]

So, I'm currently working on a game that takes place on a planet in another Solar System. The planet is called Tenorra, and while the star system it resides in has no effect on the gameplay, I would like to make it believable. The planet itself is 1.2 Earth Radii, but less dense, and thus has close to 1G of surface gravity, and is currently under siege by an armada of alien murder-bots from outer space programmed to seek out and destroy technological civilizations. Gone slightly awry. There are 2 major superpowers on Tenorra - the Tenorran Defense Union and the Coalition of Populist Socialist Nations, both are still recovering from a short-lasted dark age after the troublesome settlement of the planet, but are already I guess 40-50 years more advanced than us, much more than that in some areas.

All righty. A planet bigger, but less dense than Earth implies it has a smaller core, which could mean issues with the magnetic field. Humans should be able to live comfortably in 1.2 gs, but it could make spaceflight challenging.

The star system consists of two Stars - an Orange K2V class main sequence star somewhat heavier than the Sun orbited by 3 asteroid belts and 14 planets, and an M8 class Brown Dwarf companion orbiting at about 120 AU from the main star, orbited by 5 planets/moons.

K-class main sequence stars heavier than the sun do exist, but they're pretty rare. And IIRC they will usually have low metallicity (high-metallicity stars are hotter for the same mass), which is bad news for forming lots of rocky planets. You may want to make your central star a bit smaller; look at the masses of real K2V stars.

The K2V star has an inner asteroid belt, then 2 small rocky planets - Roasted and Toasted, that are well "inside" of the Habitable Zone, and are exactly as their names imply, roasted and toasted.

The inner asteroid belt may be a problem. In our solar system, we have found ZERO asteroids that are entirely inside the orbit of Mercury. You may want to do a bit more research on this. The small rocky planets are fine.

Followed by a "gas dwarf" - a gas planet about 8-9 times the size of Earth, made mostly of Hydrogen, Helium and Methane. It orbits well inside of the habitable zone. It's used by the Tenorrans as a source of Anti-protons via orbiting magnetic traps. No exceptional moons.

Ignore what others have told you, a "gas dwarf" is completely plausible. Kepler-11 has three of them orbiting well inside the HZ, and it's 8.5 Gy old, so the planets didn't migrate there recently. However, replace "no exceptional moons" with "no moons at all." Planets far inside the HZ of a K-class star will be tidally locked, and this goes double for low-density planets like gas dwarfs which develop larger tidal bulges. Moons of tidally locked planets are unstable: because they orbit faster than their parent rotates, tidal interactions will cause them to spiral inward (instead of outward like our moon is doing) and eventually impact the planet. In our solar system, we can see this happening to Phobos, Deimos, and Triton, which will eventually impact Mars and Neptune respectively.

Then comes Tenorra as 4th planet. Tenorra is as described above, has 9 continents that are all much smaller than Earth's, also it has a Moon about as big as Mars with a relatively thick Argon atmosphere, which is was used as a fuel source prior to the invasion.

Moon as big as Mars? That should be possible ON ITS OWN. Naturally it will be tidelocked to Tenorra, and should thus orbit pretty close in if you want a reasonable day length.

Thick Argon atmosphere? Hell no. Not happening. Argon isn't a common element, it's mostly produced by radioactive decay. Earth and Venus only have a few millibars, Mars has about 0.1 millibars. Not to mention I'm not sure what you'd be fuelling with Argon, besides a VASIMR.

It also has 3 moons - Thor, Ares and Prometheus, all of them about as big as Charon, except Ares, which is half as big. There are laser cannons built onto the surface of each of them, in addition to smaller laser satellites orbiting Tenorra itself.

Do an N-body on this, considering the size of Tennora's hill sphere. Those three moons on their own are, compared to Tennora, in the size range of the Galilean moons relative to Jupiter (a bit bigger), so on their own they could be stable, but the big moon will have a huge effect on the system, and may destabilize the smaller ones.

Then comes another asteroid belt.

The 5th planet is an Ammonia planet, with Ammonia based animal-plant hybrid life on it.

This seems reasonable. However, looking at the graphics you should move the ammonia planet farther out: it needs to be at 200-240 K average surface temperature, and ammonia planets are likely to have a strong greenhouse effect due to atmospheric methane.

The next 9 planets I haven't really worked on yet. There are 3 Gas Giants, 4 Ice Giants and 2 rocky planets.

That's a lot of planets to fit within 10-20% of the M8 dwarf's periastron distance. You may want to move the companion out to 1200 AU.

The M8 Dwarf has a small rocky companion not bigger than Pluto, but with an unusually strong mangetic field and a tenuous hydrogen atmosphere "siphoned" off from the star's outer atmosphere.

Nope. A magnetic field won't do anything: a hot, pluto-sized object simply does not have the gravity to hold on to hydrogen.

The next one is a semi-habitable planet about as big as Earth, tidally locked to the Dwarf that formed at the inner edge of the habitable zone, which has since moved inwards, with primitive microbial life on it, as well as a space station and some surface outposts established recently. These were the first things to be destroyed by the ICES armada - Interstellar Civilization Eradication System is what they were called by their creators, obviously in their language. And yes, that is an ISIS pun.

Define "semi-habitable." However, M8V is on the border between a star and a high-mass brown dwarf. It would barely even have a habitable zone worth mentioning. Here's an example of an M6V: http://en.wikipedia.org/wiki/Kepler-42. Note in the graphic the HZ is probably about 1.5-2x as far from the star as Callisto is from Jupiter.

I would go with an M3V to M5V if you want a habitable planet.