1. Join Date
Mar 2019
Posts
4

## Planet with a thin atmosphere and radical water cycle

Ok so I have a question.
let us say a planet exists that is 50 percent Earths radius and 13 percent Earths mass.
This planet is around 3 billion years old and has a magnetic field.
The planet is in the habitable zone of its G8V type star and receives around 0.95 percent the sunlight Earth does.
The atmosphere is 0.15 bar.
The rotation rate is 36 hours.
The tilt is 25 degrees
The eccentricity is 0.05
Could the planet in this state have liquid water or would the planet essentially have a steam atmosphere in the summer and be ice in the winter?
I am thinking it would be an interesting scenario to think about.

I put in details because I think every detail helps

2. Originally Posted by ktevolved365123
Ok so I have a question.
let us say a planet exists that is 50 percent Earths radius and 13 percent Earths mass.
This planet is around 3 billion years old and has a magnetic field.
The planet is in the habitable zone of its G8V type star and receives around 0.95 percent the sunlight Earth does.
The atmosphere is 0.15 bar.
The rotation rate is 36 hours.
The tilt is 25 degrees
The eccentricity is 0.05
Could the planet in this state have liquid water or would the planet essentially have a steam atmosphere in the summer and be ice in the winter?
I am thinking it would be an interesting scenario to think about.

I put in details because I think every detail helps
The water phase diagram a little under halfway down in this Wiki article is your friend.
https://en.wikipedia.org/wiki/Triple_point
At your hypothetical pressure of 0.15 bar, liquid water can exist between 0oC and about 50oC. You are describing something about the size of Mars with much higher atmospheric pressure. In such a thought exercise we can vary the atmospheric composition, and thus the amount of greenhouse effect, to set the temperature to this range. Planetary scientists have inferred that Mars once had such conditions, including surface water. Perhaps the magnetic field on your planet will protect it from atmospheric depletion from the solar wind.

3. Established Member
Join Date
Feb 2009
Posts
2,201
Originally Posted by Hornblower
The water phase diagram a little under halfway down in this Wiki article is your friend.
https://en.wikipedia.org/wiki/Triple_point
At your hypothetical pressure of 0.15 bar, liquid water can exist between 0oC and about 50oC. You are describing something about the size of Mars with much higher atmospheric pressure. In such a thought exercise we can vary the atmospheric composition, and thus the amount of greenhouse effect, to set the temperature to this range. Planetary scientists have inferred that Mars once had such conditions, including surface water. Perhaps the magnetic field on your planet will protect it from atmospheric depletion from the solar wind.
Or you are observing a young planet whose atmosphere has not yet been depleted - how long did rivers flow on Mars?
Or the star, stated as G8, has less wind than G2 Sun.
Or the planet is just slightly denser than Mars:
Mars - 53 % Earth radius, 10,7 % Earth mass, 45 % Earth escape speed
the planet - 50 % Earth radius, 13 % Earth mass, 51 % Earth escape speed
and that makes the difference between rivers lasting 2 Gyr or 6 Gyr?

What was young Mars like? The rivers were mapped, and found to be quite wide. But how much permanent gases was in Martian atmosphere when rivers flowed? How much ice?

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