[Space] Terraformed Venus as a setting

[Captain Joy]

Originally Posted by Nereidalbel

Without a magnetic field, solar winds literally blow your upper atmosphere away. If Mars hadn't lost its magnetic field, it would still have enough atmosphere to support liquid water and (possibly) life.

Mars's lower gravity was also a factor. If anybody can point me to a(n online) paper or NASA site or some such that discusses the relative importance of each effect, I would greatly appreciate it.

My impression is that low gravity is a primary reason Mars lost its atmosphere. If I'm wrong about this, please enlighten me.

[Flyndaran]

I imagine that low gravity alone would have drastically reduced the thickness of the atmosphere, but wasn't quite enough for it to effectively disappear.

Also, I doubt the physics of billions of years of planetary effects is as pinned down as threads imply.
There are still many mysteries of ancient earth's environment.

[dataweaver]

Slight tangent: to the Hill figures say anything about what the minimum month-to-year ratio is?

[Nereidalbel]

Originally Posted by Captain Joy

Mars's lower gravity was also a factor. If anybody can point me to a(n online) paper or NASA site or some such that discusses the relative importance of each effect, I would greatly appreciate it.

My impression is that low gravity is a primary reason Mars lost its atmosphere. If I'm wrong about this, please enlighten me.

The air column above the remnants of Mars' magnetic field is substantially taller than above areas without remnants. The lower gravity became a factor after the magnetic field died.

[Captain Joy]

Originally Posted by Nereidalbel

The air column above the remnants of Mars' magnetic field is substantially taller than above areas without remnants. The lower gravity became a factor after the magnetic field died.

I'm not just asking for my own personal edification. I teach an Astronomy course. In order to incorporate this information into my class, I really need a source.

All I've seen that mention both low gravity and no magnetic field admit they're not sure which is more important. Also, an impact event could have been responsible—significantly, or in part.

My personal take is that if the lack of a magnetic field was the primary cause, then Venus should have a thin atmosphere as well. Obviously, there is more to the story; how much more I don't think we know for sure yet.

[Flyndaran]

I don't think anyone knows how thick any of the inner planets' initial atmospheres were. Are there any ideas exactly how much CO2 photosynthesisers removed from ours?

[Captain Joy]

Originally Posted by Flyndaran

I don't think anyone knows how thick any of the inner planets' initial atmospheres were.

I was just wondering exactly this.

Originally Posted by Flyndaran

Are there any ideas exactly how much CO2 photosynthesisers removed from ours?

Nothing close to "exactly". Much of the CO2 simply dissolved into Earth's liquid H2O oceans and was removed from the atmosphere that way.

[Nereidalbel]

Originally Posted by Captain Joy

I'm not just asking for my own personal edification. I teach an Astronomy course. In order to incorporate this information into my class, I really need a source.

All I've seen that mention both low gravity and no magnetic field admit they're not sure which is more important. Also, an impact event could have been responsible—significantly, or in part.

My personal take is that if the lack of a magnetic field was the primary cause, then Venus should have a thin atmosphere as well. Obviously, there is more to the story; how much more I don't think we know for sure yet.

Venus also has significantly stronger gravity than Mars. As for a source, I'll dig that up when I'm at home.

Do we know how long ago Mars lost its magnetic field, compared to Venus?

[Captain Joy]

Originally Posted by Nereidalbel

Venus also has significantly stronger gravity than Mars.

Agreed, which I maintain is the more significant factor (but will not be too surprised when I find out I'm wrong).

Originally Posted by Nereidalbel

As for a source, I'll dig that up when I'm at home.

Cool, thanks. I did a bit of googling around and found several mentions of it myself. By nothing compared the relative importance of the different causes.

Originally Posted by Nereidalbel

Do we know how long ago Mars lost its magnetic field, compared to Venus?

On Earth, we know stuff like this based on the magnetic record contained in tectonic plate formation. We do not know when Venus or Mars lost their magnetic field (and will be extremely and pleasantly surprised when I find out I'm wrong (crazy surprised for Venus, less so for Mars)).

[Nereidalbel]

Originally Posted by Captain Joy

We do not know when Venus or Mars lost their magnetic field (and will be extremely and pleasantly surprised when I find out I'm wrong (crazy surprised for Venus, less so for Mars)).

Studies of craters on Mars have shown evidence that the magnetic field died out roughly 3.5-4 billion years ago. Venus, however, just doesn't rotate fast enough to generate a magnetic field via internal dynamo. There does appear to be a very, very weak magnetic field induced by interactions between the upper atmosphere and solar winds, though.