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Old 08-12-2022, 08:45 PM   #21
Fred Brackin
 
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Default Re: Number of habitable worlds within170 light years?

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Originally Posted by Pursuivant View Post
IMO, something that Fermi didn't consider was the unique nature of Earth's formation - a massive interplanetary collision which not only provided a huge "nurse moon" but also gave the planet an extreme axial tilt.

"
It's not shielding from asteroids so much or action on the molten core. It's tidal drag. Tidal drag has slowed even Mars to a slower rotation than Earth and nevermind what it's done to Venus and Mercury.

This is because tidal drag has acted on the Earth-Moon system as a whole and not either body individually. The Moon moves farther away from the Earth as a consequence. The Moon is beleived to have formed _much_ closer.

Even without any tidal effects Venus still seems to ahve a molten core.

Without a relatively large companion moon I'd expect a planet in Earth's position to have a much longer day that might be a signioficant problem.

The msot common habitable planet-type mnight be a sort of "Super-Mars". This would be a planet in Mars relative position that has maintained a moltent core through its' larger size and a day of reasonable length through its' distance from its' star. Then youu have a thick atmosphere and geothermal heat combining to keep your Super-Mars above the freezing point of water at its' surface.
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Old 08-12-2022, 11:20 PM   #22
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Default Re: Number of habitable worlds within170 light years?

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The thing is with no particular evidence leaning in any particular direction, you can pick whatever you want for the game.

Want a space opera like universe with a thousand shirtsleeve planets - life is common and the oxygen cycle is universal.

Want a setting where there are thousands of planets where you could set up habitation domes with some effort but the two known oxygen worlds are prizes of immense value worth fighting over, life is rare but the oxygen cycle is normal.

Want a setting where there are thousands of worlds with alien biospheres but none of the have breathable air and the dozen different alien species in campaign flee for their lives if the Terran's airsuits spring a leak and start spewing horrible war grade chemical weapons into the atmosphere. You can do that too.
The intention is to do a simple write up of every world (!!!) and so need to keep it manageable, but still have enough to make the universe feel full.
The intention is to fill the area with approximately 200 lightly detailed places most of which will be habitable worlds than if they leave the play area have some extra worlds to plop down in their way as needed

The issue is more to do with it feeling full since this is more of a space opera type place. I can also detail many ruined worlds as well since this is a universe where interstellar civilization has collapsed (far future apocalyptic?)
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Old 08-13-2022, 01:15 AM   #23
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Default Re: Number of habitable worlds within170 light years?

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The intention is to do a simple write up of every world (!!!) and so need to keep it manageable, but still have enough to make the universe feel full.
Bear in mind that there's something like a million star systems in that distance.
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Old 08-13-2022, 01:43 AM   #24
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Default Re: Number of habitable worlds within170 light years?

A useful tool you might consider is the article at the Atomic Rockets site on Interstellar Empire Math. It lays out the details of how the numbers were developed so that you can work with your own assumptions, too. Really, the whole Atomic Rockets site is an incredibly useful resource, but those formulas are particularly useful for the purpose you have here.
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Old 08-13-2022, 03:25 AM   #25
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Default Re: Number of habitable worlds within170 light years?

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More than a thousand if you set the bar low and just settle for liquid water. Actual breathable air without many centuries of terraforming? I suspect the number would be more like a hundred.

Given that people are kicking around various possibilities, perhaps the OP would define "habitable" for the purposes of argument. Just-like-Earth, temperate zone? 100 degrees in the shade, requires supplemental oxygen, 1.75 G?
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Old 08-13-2022, 02:05 PM   #26
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Default Re: Number of habitable worlds within170 light years?

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Given that people are kicking around various possibilities, perhaps the OP would define "habitable" for the purposes of argument. Just-like-Earth, temperate zone? 100 degrees in the shade, requires supplemental oxygen, 1.75 G?
Variety of worlds humans could visit and breathe, with hoth-like North pole planets , all the way to sahara tatooine desert planetsó- but all breathable oxygen worlds.
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Old 08-13-2022, 02:07 PM   #27
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Default Re: Number of habitable worlds within170 light years?

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Bear in mind that there's something like a million star systems in that distance.
Everyone gives different numbers. A million worlds wouldnt work at all obviously, so might bring it down to a smaller area in order to reduce it
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Old 08-13-2022, 02:09 PM   #28
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Default Re: Number of habitable worlds within170 light years?

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A useful tool you might consider is the article at the Atomic Rockets site on Interstellar Empire Math. It lays out the details of how the numbers were developed so that you can work with your own assumptions, too. Really, the whole Atomic Rockets site is an incredibly useful resource, but those formulas are particularly useful for the purpose you have here.
Amazing thx!
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Old 08-13-2022, 03:02 PM   #29
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Default Re: Number of habitable worlds within170 light years?

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Everyone gives different numbers. A million worlds wouldnt work at all obviously, so might bring it down to a smaller area in order to reduce it
Most star systems are going to be total garbage ones with M class primaries and can be discounted.
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Old 08-13-2022, 05:03 PM   #30
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Default Re: Number of habitable worlds within170 light years?

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Everyone gives different numbers. A million worlds wouldnt work at all obviously, so might bring it down to a smaller area in order to reduce it
My campaign universe has a livable planet on most systems. Some almost earth-llke and some colder or hotter then comfortable. On some the atmosphere is not quite right (too heavy or too rare; tainted, things like that).

You see, one of the first FTL ships from Earth misjumped and landed around 5,000,000 years in the past with everybody and everything pretty much smashed. The aliens (methane breathers, long gone by the time of the game) decided that in thanks for the secret of the FTL drive, they would terraform the galaxy for us (it was a religious obligation to them). They didn't get more than a few percent done but it was enough to really confuse the human scientists when we go out there.

And most of the planets held life that was sort-of earth-like. The aliens (the forerunners) have been gone for about 4,000,000 years now. There are so few traces of them that we know almost nothing about them.
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