36 votes
Accepted

How could a planet logically have green clouds but still be habitable?

Algae. You could simply state that on this planet there is some kind of micro- algae that lives in the tiny droplets of water that make up the fog and the clouds and that happens to be green.
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  • 2,546
29 votes

How can we make an alien atmosphere breathable, but uncomfortable?

Uncomfortable is a matter of tastes and culture, but I guess thiols make a good candidate for making an uncomfortable environment: proximity of rotting eggs, sewers, rotting algae are just few ...
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  • 237k
24 votes
Accepted

How can we make an alien atmosphere breathable, but uncomfortable?

Carbon dioxide. According to some tellings, Earth arose very near the inner limit of the "habitable zone" around the Sun. Earth life sucks up nearly every trace of carbon dioxide available ...
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  • 19.1k
18 votes

How can we make an alien atmosphere breathable, but uncomfortable?

There is a discussion about how much of various gases are necessary for humans to survive in Stephen H. Dole Habitable Planets for Man, 1964. https://www.rand.org/content/dam/rand/pubs/...
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16 votes

How can we make an alien atmosphere breathable, but uncomfortable?

Heavy Air 70% of Earth air is Nitrogen. This is nonreactive and harmless to your lungs. If you only breath Nitrogen you will asphyxiate. But it is not the Nitrogen that kills you. It is the lack of ...
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  • 38.6k
15 votes

Can a forest provide enough oxygen to breathe on a low oxygen planet?

Only if this forest is located in a "bowl" with low winds Our common deciduous trees are actually poor net producers of oxygen. By different estimates, it may take about an acre of trees to ...
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  • 40.7k
15 votes

How could a planet logically have green clouds but still be habitable?

Pollen. Planet has lush forests with plants spewing out green pollen year around. The pollen is carried by the winds and trapped inside water droplets and tint them green. The pollen on this planet ...
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  • 7,023
13 votes

How can we make an alien atmosphere breathable, but uncomfortable?

Simply humidity can make breathing uncomfortable. Humidity can make the air feel heavy. Figuratively, because actually humid air is lighter than dry air. The reason is that water vapor molecules are ...
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  • 1,239
12 votes

How can we make an alien atmosphere breathable, but uncomfortable?

Ozone. Ozone is formed by the action of UV radiation on oxygen and other atmospheric components. It is a normal and protective component of the upper atmosphere. It is also a normal minor component ...
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  • 273k
12 votes

How could a planet logically have green clouds but still be habitable?

Aerosols of iron rust could produce a green haze or green clouds. Aerosols of chromium oxide (Cr2O3) do the same but look nicer. It is used as pigment. Among gases the only one I can think of is ...
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  • 1,258
10 votes

Can a forest provide enough oxygen to breathe on a low oxygen planet?

Alien forest? https://www.botanyunbound.com/post/ocean-photosynthesis-what-a-plant-hears-discovery-drones-and-the-coolest-plant-on-earth An Earth forest lets its oxygen diffuse away. But you are not ...
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  • 273k
7 votes

Can a forest provide enough oxygen to breathe on a low oxygen planet?

Not only would the oxygen diffuse away, the forest would die. Trees photosynthesize complex organic molecules from sunlight, water, and carbon dioxide, but they also metabolize the molecules with ...
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  • 20.6k
5 votes

Can a forest provide enough oxygen to breathe on a low oxygen planet?

I am afraid it is totally impossible. The diffusion coefficient of oxygen in air (in your case it will be in pure nitrogen but it should be practically the same) is 0.2cm²/s to 0.3cm²/s depending on ...
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  • 179
5 votes

Is this an accurate environment for life on a super Earth speculatively?

There are a number of issues. It is possible to have a planet with twice the size of Earth and a lower gravity, but it requires the radius of the planet to be at least 1.45 the radius of the Earth. ...
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  • 2,920
4 votes

Is this an accurate environment for life on a super Earth speculatively?

Should be fine There was a time in the Earth's history where we had a lot of large animals. Look: Your world is like the prehistoric Earth. It is believable you have big animals too. There is no need ...
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  • 38.6k
4 votes

Is the following rogue planet's atmosphere setup possible?

Oxygen won't stay unbound for long. Without photosynthetic life you can't have free oxygen in the atmosphere, since oxygen will prefer to create compounds with other atoms rather than binding with ...
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  • 237k
4 votes

How can we make an alien atmosphere breathable, but uncomfortable?

I already upvoted one answer, but you said you wanted this galactic standard atmosphere to have a high oxygen level and that could in itself be the problem. Being so reactive, oxygen is toxic when you ...
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4 votes

If Earth was less massive, with 25% less gravity and an atmosphere scaled down proportionately, how would that affect climate?

If Earth had the same diameter and it's mass was reduced by 25 percent, its gravity would also be reduced by 25 percent, but it escape velocity would be 86.6 percent what it is now. To put that into ...
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  • 2,920
4 votes

How might a lower gravity planet sustain a warm, earth-like atmosphere?

More atmosphere https://www.coursehero.com/study-guides/astronomy/the-massive-atmosphere-of-venus/ ...as percentages, the proportions of the major gases are very similar for Venus and Mars, but in ...
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  • 273k
3 votes

Could a planet be cut in half and still sustain life?

Yes, but not immediately. After the split the two halves will merge again, unless the split has given each half escape velocity, and the merge will release a huge amount of heat, turning the planet in ...
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  • 237k
3 votes
Accepted

Could a planetary disk create a shared atmosphere?

A protoplanetary disk is, in astronomical terms, a violent and deadly place. It is not somewhere you want to live. Gravity has spun all of this debris from the birth of the star into a disk. ...
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  • 1,037
3 votes
Accepted

What would be the optimal atmosphere for Earth's life and humanity?

Hot and Humid The rainforest is full of life. Let's crank up the heat and humidity and go back to a planet covered in primeval jungle. Rainforests like the heat. Raise greenhouse gas levels to up ...
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  • 38.6k
3 votes

Can a forest provide enough oxygen to breathe on a low oxygen planet?

It would be perfectly possible for the forest to have the only sufficient concentration of oxygen on the planet - if the forest was at the bottom of the deepest canyon or trench on the planet, and if ...
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3 votes

What atmospheric pressure and temperature are reasonable to maintain water on a low gravity planet?

This is entirely dependent upon temperature. Here's the basic diagram, from Wikipedia: If there is enough light hitting the surface from the nearest star to melt it, and there is no available ...
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3 votes

Is the following rogue planet's atmosphere setup possible?

Short Answer. Depending on how long your world needs to maintain its breathable atmosphere in your story, you might need to change the parameters of the planet to enable it to retain the atmosphere ...
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3 votes

Can a forest provide enough oxygen to breathe on a low oxygen planet?

Perhaps. I figure that since you've pretty remarkable trees to begin with if they can survive at night time (assuming they need oxygen at all), then you can make-up your own rules to an extent. These ...
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2 votes

Can a forest provide enough oxygen to breathe on a low oxygen planet?

Without knowing the size of the forest weather conditions etc. I'd still have to say no. Any single mass of vegetation unless a great amount of time passes wouldnt be able to sustain the needed mix of ...
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  • 1,295
2 votes

For a planet with a given equilibrium temperature, what is the maximum pressure possible?

I'm going to answer the question of how to find the SURFACE pressure, not the MAXIMUM pressure, since you can always just get a higher pressure by digging a hole. With that caveat, here's a rough ...
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  • 121
2 votes

What atmospheric pressure and temperature are reasonable to maintain water on a low gravity planet?

As low as 0.5 atmospheres, the boiling point of water is still above 80 degrees C. So yes, equatorial temperatures in the 70s Fahrenheit (20s Celsius) are fine, as far as keeping the oceans from ...
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2 votes
Accepted

Could a planet be cut in half and still sustain life?

I see three possible scenarios here, with some gray area between them. Cut cleanly in half, the parts sent flying in opposite directions In this case, not by any stretch of the imagination could they ...
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