feat(content): Add new uninhabited landable planets to existing systems in Human space

[Quantumshark]

Content

This PR does help somewhat with the problems described in issue #4628

Summary

Adds four new uninhabited landable planets to existing systems in Human space - specifically, in Gacrux, Alpheratz and Nocte.

This both adds rewards to exploration, in the form of interesting things that can be found (sort of like #8274 did, though in this case they can be found while still flying a human ship), and provides safeish stopovers that pirate players can use without needing to give the spaceport authorities a cut of their hard-earned plunder.
And now there's actually a reason to check out at least some of those uninhabited dead end systems.

Screenshots

In pink are the three existing uninhabited landables I remembered when I made this image: Hope, Watcher and Mutiny. In yellow are the four new ones: Asphodel, Neriene, New Kola and Asterus.

Testing Done

None whatsoever.

Save File

This save file can be used to test these changes:
Any in human space, pretty much.

[MasterOfGrey]

If the air pressure is broadly tolerable, so is the gravity.

[Quantumshark]

I'll admit I'm not particularly well-versed in planetary geography, but what I'm trying to say here is that the air pressure is only tolerable on high mountain peaks, not at ground level.
To the best of my knowledge though, there's quite a large degree of variability in atmospheric pressure relative to gravity - see Earth vs Venus, or Titan vs Ganymede, and I've seen discussions of Earth-like (in size) exoplanets being projected to have thin or no atmospheres in some circumstances too.

[MasterOfGrey]

Air pressure is proportional to gravity. If there is a place where you can land and tolerate the air pressure pretty well (without also needing protective gear because it's corrosive or whatnot), then at that place you can also tolerate the gravity pretty well.

Titan has similar pressure to earth because it's atmosphere is made up of much heavier stuff, and is super cold.
Venus atmosphere has much greater pressure than earth because it's made of of much heavier stuff, and is super corrosive.

If you can safely step outside with just oxygen gear at a particular level in the atmosphere, you can also tolerate the gravity at the same level as well.

[Quantumshark]

Air pressure is proportional to gravity. If there is a place where you can land and tolerate the air pressure pretty well (without also needing protective gear because it's corrosive or whatnot), then at that place you can also tolerate the gravity pretty well.

I don't think that's right. At the top of Mount Everest, the atmospheric pressure is about one third of that at sea level, and the gravity is almost exactly the same as at sea level. To take a more extreme example, the gravitational pull experienced at the altitude of the ISS' low earth orbit (400km) is less than 10% less than at sea level, but the atmospheric pressure is zero. To experience half the gravitational pull, you need to travel 2,600km above Earth's surface.
As far as I can tell, atmospheric pressure is the result of the weight (i.e. mass times gravity), of all the atmosphere above a particular point, so it would be increased by increasing the mass of the atmosphere or by increasing the strength of gravity. But as you move up, an increasing portion of the atmosphere is now below you rather than above, and hence isn't weighing down on the atmosphere where you are.

[MasterOfGrey]

And at the top of Everest you need more than just oxygen gear because it's cold enough to kill you, and quite quickly.

If you can safely step outside with JUST oxygen gear at a particular level in the atmosphere, you can also tolerate the gravity at the same level as well.

[Azure3141]

Air pressure is proportional to gravity. If there is a place where you can land and tolerate the air pressure pretty well (without also needing protective gear because it's corrosive or whatnot), then at that place you can also tolerate the gravity pretty well.

This isn't right. Atmospheric pressure will depend upon a number of factors, such as the atmospheric density, the mass of atmosphere on the planet, the temperature, and the altitude. While pressure is proportional to gravity, the top of a mountain doesn't have lower air pressure because gravity is lower there (it barely changes compared to sea level), it's the elevation that reduces atmospheric pressure.

[MasterOfGrey]

For the love of god I don't have the time or the crayons for this, but at the very least you need some protection from wind chill to otherwise be there with only breathing gear.

[Hecter94]

Insulting people's intelligence isn't necessary, regardless of how much in the right you feel you are.

[roadrunner56]

Gravity and wind chill are two separate things though. If you want to argue that it would be too cold to step outside with only oxygen gear, that's one thing, but that's different from your previous argument that the air pressure would necessarily be intolerable.

[MasterOfGrey]

It's a combination of things. With the given combination as it stands, either the temp is cold and wind chill will freeze you, or the temp is warm and the wind will suck the moisture from you and you'll die of dehydration quicker than the gravity will be an issue.
And even that possibility is falling into an extremely narrow range of only hypothetically plausible possibilities.

air pressure would necessarily be intolerable.

And I didn't say it would necessarily be intolerable, I said that either the pressure would be intolerable, or the atmosphere would kill you other ways - which remains consistent with my point.

[bene-dictator]

Nice! I may do the same myself. Later.

[bene-dictator]

Added new landing pictures in Quantumshark#3. I'll do the copyright and @2x later. Done in Quantumshark#4 and endless-sky/endless-sky-high-dpi#398.

Previews:

[bene-dictator]

I think most of the scenes are unused, we can leave that for another PR.

[LorenzoBolla]

Lovely stuff!

[bene-dictator]

ziproot didn't provide a link for snow23 (though perhaps because a similar image exists ingame). Everything else looks alright.

[ziproot]

ziproot didn't provide a link for snow23 (though perhaps because a similar image exists ingame). Everything else looks alright.

The link would be in PR #9459, which was just merged. As the same image is used in both cases, I think the two files should be combined into one entry, as follows:

Files:
 images/land/snow23*
 images/scene/iceplains3*
Copyright: Daniel Frank
License: Unsplash
Comment:
 Taken from https://archive.is/xK5Wu. This image was
 uploaded to unsplash.com after June 2017, so it is subject
 to the Unsplash License. It was also uploaded after
 February 2018, so it is subject to an additional restriction
 limiting the sale of unaltered copies.

The entry would have to be below images/scene/iceplains*, though.