Mashtar, the Red Earth.

[Enio]

In my own system called Somaris, I made a planet called Mashtar.
Mashtar orbits a K2VI star, it has a circular orbit and the distance is 0.55 AU. The radius of this big world is 8635 Km and the day have a duration of 18 hours. The size of star is 0,82 Rsun.
Mashtar have two moons: The first is a big asteroid with a radius of 436 Km called Brooklix and the second moon is Anshtar with planetary size of 2674 Km.
Anshtar have a thin atmosphere of sulphur. Part of the sulphur that scape to the space go to the asteroid and to the planet.
Mashtar atmosphere is 10x dense, the sky is red with many big clouds, clear sky in nights are rare, and is more humid. Because of the dense atmosphere, is rains a lot and the differences of temperatures are small.
The gravity is 2x the gravity on Earth. If you weight 50 Kg here, there you will weight 100 Kg.
There are some avians, because of the dense atmosphere and is more easy to fly there.
The beings of this planet are small and fat because of the gravity. But this doesn't mean that they are weaker than beings on our planet. They are stronger, more resistant and have a more compact body.
There are a lot of species of animals and plants on air, earth and sea.
The plants and trees are orange instead of green.
The intelligent specie of Mashtar are smaller ( about 1,30 meters ), stronger, more resistant, not so beautifull and intelligent than humans.
The society in there is more organized, because the government of Mashtar is not Capitalism, is a kind of Socialism world. But this Socialism is much better and organized than on Earth. In Mashtar, money not exist. All people in this world have some job, the only unemployed people are people that don't want to work. All people travel in buses and trains. Only people that work in government have cars. All parts of the cities have information posts, mini hospitals, free restaurants and gratuit services. BUT ONLY PEOPLE THAT WORK HAVE THE RIGHT TO HAVE ALL OF THESE SERVICES FOR FREE. PEOPLE THAT DON'T WORK DON'T HAVE THE RIGHT FOR NOTHING, EXCEPT FOR GO TO HOSPITALS. They have a kind of card that prove that they have a job.
Living on this society is much better than our society, because they are much more organized than us and don't exist money. I'ts all for free.

[Evil Dr Ganymede]

Assuming you're posting this here to reality-check it... there are some major realism problems.

First, its primary is a K2 II star. Which means it's very evolved. I think at best it would have started off as a mid-F V star, which would make it about 5 billion years old. It's probably younger than that and even more massive, given it's a K2 II star and not an M2 II star.

More to the point, K2 II stars can be pretty huge, and they are very luminous. Assuming you mean the planet is at 0.75 AU from the surface of the star (if you mean that it's that far from the centre of the star, then the planet is well inside the star), the surface temperature is going to be obscenely high.

Also - assuming off the top of my head that the star actually has a radius of say 4 AU - then the planet would, while the star was in its main sequence stage, have been in a similar situation to Mars today. Or it might even have been beyond the frost line in which case it would have probably been icy in composition, like Ganymede or Callisto. As such, the world's density seems rather high considering how far it is from the star. That's assuming the planet could even form around a star that massive of course...

You could solve most of these problems by making the primary a Main Sequence (size V) star instead. Probably a late F or early G would be OK - that'd let it keep its moons too, since a habitable world would most likely be tidelocked around a K V or M V star.

[Enio]

Look above, I corrected the text.

[Evil Dr Ganymede]

Well, it's definitely better now, but a size VI star is a subdwarf with low metallicity... which makes it rather unlikely that it can have such a dense planet orbiting it. A V star wouldn't have that problem.

Speaking of which, the density is really rather high - 8100 kg/m3 to get a world that big with twice the gravity of earth. That seems a little extreme to me - it must have a huge iron core. You'd be hard-pressed to find a world like that around a star with a normal amount of metallicity, let alone a subdwarf.

Plus it's now close enough to the star to be tidelocked due to solar tides. If it's tidelocked, it has no moons. If it starts off with a rotation period of about 10 hours, then it doesn't have to be tidelocked unless it's more than 2.5 billion years old.

I make a K2 VI to have a luminosity of 0.12 Sols and a mass of about 0.58 Sols, so at 0.55 AU your world has a blackbody temperature of 220 K (about -53 C). A bit cold. It'd need a very strong greenhouse effect and a lower albedo than earth to be even habitable at that distance, let alone warm.

Plus right now it's massive enough to hold onto hydrogen in its atmosphere .

[Enio]

The problem is that Celestia only have the albedo and distance to star to modify the temperature of a planet. It would be better if it could have greenhouse value code.
I corrected it again, and it's now a G8IV star with a diameter of 2.00 Rsun.
The planet now is at a distance of 1.46 AU, with an albedo of 0.30, the temperature is about 283K and the rotation period is 36.14 hours.
And what you think of the beings of this planet and it's society written in the test?

[Evil Dr Ganymede]

The problem is that Celestia only have the albedo and distance to star to modify the temperature of a planet. It would be better if it could have greenhouse value code.
I corrected it again, and it's now a G8IV star with a diameter of 2.00 Rsun.
The planet now is at a distance of 1.46 AU, with an albedo of 0.30, the temperature is about 283K and the rotation period is 36.14 hours.
And what you think of the beings of this planet and it's society written in the test?

Man, you like the wacky star types don't you... We've hopped from II to VI to IV now. If the next try is a White Dwarf, I'll scream!

G8 IV is better, but it's a subgiant. It's a very old system (at least 8 billion years old, I reckon), so this world was probably about where Mars was relative to its primary when it was a main sequence star (probably an early G V like the sun, or a late F V). Again, we have a problem explaining the very high density of the planet. But at least now you can have your satellites.

When it was a main sequence star the world would have been very cold with no oceans (like Mars) - so life probably wouldn't have evolved on it, unless it had a very strong greenhouse effect (not sure whether your dense atmosphere is thick enough for that). But the problem then is that as the star warms up to become a subgiant, the greenhouse effect would increase the temperature even more and you're going to end up with a runaway greenhouse effect (like Venus).

You sure you don't want to just put it around a late F or G V star?

As for people/society... well, this isn't really the forum for it (plus I don't know what this world is being written for - a roleplaying game? scifi background? or just for fun?).

[Enio]

When the system was still forming, there were three stars, two of them were red and the other was yellow. The two red stars had a collision and the only star that survived was the yellow star. The explosion of the other two stars and the dust disk around the yellow star formed the planets. The red stars were rich in metals, that's why it explains the high density of this planet and the sitellite.

[selden]

Enio,

As The Evil One pointed out, this really isn't intended as a fantasy forum. It would help a lot if you would explain what you're trying to accomplish with your postings.

While imaginary situations can be entertaining, your postings are confusing because you are writing your fantasies as if they were factual.

It might be more appropriate if you were to post questions instead -- asking how likely some of your ideas might be and what conditions would be necessary for them to happen.

Although many of the people who are responding to you are highly knowledgable about the current scientific theories about planetary formation, or may even be doing professional research on them, many of your readers are not so familiar with planetary astrophysics.

[Enio]

Sorry.

[Enio]

I'm sorry. In reality, i'm trying to make a fantasy system formed with a medium yellow star with some planets rich in heavy elements.

[Evil Dr Ganymede]

I'm sorry. In reality, i'm trying to make a fantasy system formed with a medium yellow star with some planets rich in heavy elements.

Why not just use a high metallicity G V star then? There are plenty of stars that have a higher metallicity than Sol (but not *too* high). You don't need to have stellar collisions to get those

As for who's into planetary astrophysics, well obviously I am - hell, I'm building planets while I'm at work. Slartibartfast is my hero! Plus I've made more worlds than I can count for the Traveller scifi roleplaying game. and my main area of interest is worldbuilding anyway.

Plus there's Dollan and eburacum45 who have made lots of worlds for the Arcbuilder and Orions Arm scifi universes.

Selden's right though - if you can phrase things more as questions rather than as statements then it'll make it easier to figure out what you want to know .

[Enio]

Yes, but in my Somaris system, the collision of the two red stars happened and the material of the two stars formed a kind of dense ring with the material of the yellow star that formed dense planets. Again, the planet now have a radius of 7235 km and orbit a G5V star with a distance of 0.76. The star now have a radius of 0.93 Rsun. I put many artificial satellites in orbit and night light cities to show that the planet have much intelligent beings.