I have some research I want to do about a planet for a novel I'm writing. It is a fiction/science fiction novel, but I do wish to actually have some parts of the world correct in the scenes I depict.

So, basically this planet is situated in an entirely different solar system, with a similar star to Sol, but much more standard galaxy-wise. i.e. a Star roughly the same size, but component-wise, and light-wise, it is as average as can be.

The planet has about 4 times the surface area of Earth but is not tidally locked. It has its own perfect spot where it is able to rotate around its sun in about 320 days, and 'around itself' in about 20 hours - yes I know that is quite fast.

The Solar System has about 4 planets the size of Jupiter, and with this particular planet, there are only 2 other planets, each very small in comparison. You can think of them in any order, but they are at least partially visible as stars with the naked eye.

The moon orbiting this planet is about twice the size of our Moon, and is habitable, but yet uncolonized by the dominant species. Only normal life exists there, thus no external light sources on this moon. It is far enough away from the planet to regarded as equivalent in size to our Moon.

The plants on this planet should, theoretically, be able to operate at about 60% efficiency but are much rather red, and blue in colour with green scarcely found, but still found in the older species of the planet.

I figured to add this point since, from what I know, even if this might be wrong, larger planets have higher chances of being tidally locked depending on how close they are to the Star in question. Thus it should be pretty far out to not be tidally locked, but at such a distance where light is not exactly the same quality as on Earth, forcing the plants to be much more efficient.

The temperatures should also then be colder, but I figured with high enough amounts of greenhouse gasses it should be possible to at least make it somewhat livable. Specifically, I am talking about the more effective greenhouse gasses - whatever they may be at this point (I will do more research on this at a later point. The answers here should probably change the atmospheric constituents somewhat)

The atmosphere make-up is around 80% nitrogen, 8% hydrogen, 2% other gasses, and 10% oxygen.

So, I have a question about what one would experience on this planet close to the sea.

Would it be safe to assume that the sky would be a similar colour as found on Earth during sunset, sunrise, noon, and night around sea level?

Thank you for any and all help provided.

Edited: Removed unnecessary questions to follow the one-post-one-question rule. Explained Certain points in more detail.

  • $\begingroup$ Welcome to worldbuildin, please take the tour and visit the help center to better understand how this community work. Since we adhere to the model of "one post-one question", your post is at risk of being closed since, as you state, there are a lot of questions in it. Please rework it. $\endgroup$
    – L.Dutch
    Feb 21, 2019 at 11:14
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    $\begingroup$ When you say that the other planet is 4 times the size of earth, what exactly do you mean? 4 times the radius, 4 times the surface-area or 4 times the volume? $\endgroup$ Feb 21, 2019 at 11:15
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    $\begingroup$ You give the composition of the atmosphere but not the pressure. 10% oxygen may or may not be enough for active animal life, depending on the pressure. And those 8% hydrogen will very quickly combine quite enthusiastically (see Hindenburg) with some of the oxygen, leaving 8% water vapor and 6% oxygen. And peak efficiency of photosynthesis on Earth is some 8%, with more typical leaf efficiencies around 5%; 60% is a massive stretch. $\endgroup$
    – AlexP
    Feb 21, 2019 at 11:18
  • $\begingroup$ I figured I'd use the surface area so that the surface is about 4 times that of ours. I know the efficiency of plants here is quite terrible, but I also figured I'd use a rather old planet, with far more life than ours. With this I simply mean life has had more time to adapt, and given where it might be for the planet to rotate in 20 hours the sun's rays would be quite weak, given the need for higher efficiency chloroplasts? The necessary cycles for the atmosphere to stay where it, percentage-wise, is present in its entirety, but I can change hydrogen to another greenhouse gas. $\endgroup$
    – GaryS
    Feb 21, 2019 at 11:27
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    $\begingroup$ "It has its own perfect spot where it is able to rotate in about 20 hours": what does this mean? The rotation of a planet does not depend on its distance from the primary. Do you mean "revolve around the star in 20 hours"? If so, consider that in our solar system a 20 hour orbit would be very very close to the Sun, so close and so hot that solar wind would strip the atmosphere in a geological instant. $\endgroup$
    – AlexP
    Feb 21, 2019 at 13:20

2 Answers 2


You may find this link useful: You assumed the atmosphere is the same as Earth's in composition but may have a different atmospheric pressure, and this may change the way the skies look. Also, the higher gravity (super-earth from your description) will give the appearance that the waves advance in a fast-forward mode: Gravity pulls the water down faster, and this pushes the water mass in front faster, therefore wave moves faster.

EDIT: Higher gravity means two things:

1- all objects fall faster, lighter-than-air balloons float faster as well,

2- Atmosphere is more compressed, having a higher refractive index at sea-level, causing greater distortions at the horizon, so sunrise/sunset will be more affected.

Atmospheric mass (the total amount of air above you), has another effect: Your view through a thick atmosphere resembles, somewhat, that of sunrise/sunset:

Another effect is the total amount of atmosphere. If there is no air at all then the sky will be black, as it is on the moon, since no light is scattered. It acquires more and more of whichever colours it would otherwise have as it thickens. This can be seen at high altitudes on Earth; the sky becomes a darker and darker blue until it becomes entirely black. What happens as the atmosphere thickens is something one can see at sunrise and sunset. If the sunlight goes through enough air then the blue and green light are so scattered that you start to see the reds and yellows, and the sky has a golden or yellow hue, pink, and then red.

You may find Terragen software by Planetside very informing. This link guides you through creating and simulating atmospheric effects.

  • $\begingroup$ Thank you. That actually helped quite a bit with the images I'll need for the scenes. Given the link you've given me, the sky should look quite a pale blue most of the time. The water effects will be brilliant to describe, but how would that affect falling droplets, if I can be so bold? $\endgroup$
    – GaryS
    Feb 21, 2019 at 11:55

One thing to note is that the high gravity will likely affect how most plants and animals are built. They will need to be thicker and sturdier to support themselves. Animals the size of horses may already need the body plan of an elephant to stay upright. Aquatic creatures would be unaffected, since they are supported by the water


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