Ancient Mars, water or ice?

[Moontanman]

It has been long touted that ancient Mars was a water world much like Earth is today but was it? Is it even possible? 

I suggest that ancient Mars was more of an ice world far more similar to Europa than Earth. The Sun was significantly dimmer then so Mars should need a more extensive atmosphere than Earth to maintain liquid water but an ice world similar to Europa could not only have maintained liquid water under the ice but as the ice retreated into space along with the atmosphere, due to being closer to the sun, geological patterns like rivers and lakes could have formed beneath the retreating glaciers much like happens on Earth. Unlike Earth rivers and streams their Mars analogs would have evaporated away into the thin atmosphere to be swept away by the solar winds eventually result in the barren sometimes salt covered surface we see today...

[Moontanman]

So no one has a take on this? 

[Danijel Gorupec]

While I tend to agree with you, I just want to notice that volcanic activity could supply greenhouse gases.

[Moontanman]

2 minutes ago, Danijel Gorupec said:

While I tend to agree with you, I just want to notice that volcanic activity could supply greenhouse gases.

Yes, this is true but the atmosphere of Mars would have had to be denser than Earth's and Earth, while lots closer to the sun, still managed to freeze over a couple times in the deep past. 

[Danijel Gorupec]

That is why I agree with you that if there was liquid water on Mars, for most of the time it had to be covered by ice. However for brief times of increased volcanic activity, some of that ice could melt down exposing liquid water... but I am just talking staff, I have no real knowledge here.

[Janus]

3 hours ago, Moontanman said:

Yes, this is true but the atmosphere of Mars would have had to be denser than Earth's and Earth, while lots closer to the sun, still managed to freeze over a couple times in the deep past. 

Not denser overall, just a greater partial pressure of CO₂.

The average  CO₂  content of the Earth's atmosphere is ~405 parts per million. Mars' atmosphere is 96% CO₂.   That means that Earth's atmosphere only has ~ 1.3 times the CO₂ per volume as Mars atmosphere even given that Mars' atmosphere is only 0.0003 times as dense as the Earth's.   So I don't think you would need to raise the atmospheric pressure on Mars as much as you think to  create enough of a greenhouse effect for liquid water to exist.

[Moontanman]

3 hours ago, Danijel Gorupec said:

That is why I agree with you that if there was liquid water on Mars, for most of the time it had to be covered by ice. However for brief times of increased volcanic activity, some of that ice could melt down exposing liquid water... but I am just talking staff, I have no real knowledge here.

Ok, my mistake, the idea of liquid water under the ice while the ice above slowly sublimes would allow you to start out with miles of ice and the water flowing streams left behind could have been under the ice as happens on Earth. 

21 minutes ago, Janus said:

Not denser overall, just a greater partial pressure of CO₂.

The average  CO₂  content of the Earth's atmosphere is ~405 parts per million. Mars' atmosphere is 96% CO₂.   That means that Earth's atmosphere only has ~ 1.3 times the CO₂ per volume as Mars atmosphere even given that Mars' atmosphere is only 0.0003 times as dense as the Earth's.   So I don't think you would need to raise the atmospheric pressure on Mars as much as you think to  create enough of a greenhouse effect for liquid water to exist.

How much would be enough? How long did Mars hold onto a relatively dense atmosphere? Sunlight at Mars is about 1/2 the sunlight at Earth and while CO2 is important it makes little difference in Mars today without other gasses. 

My "idea" is that most of the surface features on Mars that point to liquid water could have occurred beneath a deep ice sheet that was lost to space along with the other gases when Mars lost it's magnetic field.. 

[Janus]

2 hours ago, Moontanman said:

How much would be enough? How long did Mars hold onto a relatively dense atmosphere? Sunlight at Mars is about 1/2 the sunlight at Earth and while CO2 is important it makes little difference in Mars today without other gasses. 

I'd say a minimum of 0.006 atm.  This is the lowest pressure where water can exist as a liquid.  This is twenty times the present pressure, but still pretty thin compared to Earth's while having a partial pressure of CO₂ 19.2 times that of the Earth's.

As to how long it could have lasted.  It would be hard to say given that we really don't know how it lost so much of its atmosphere. (there are a few possible reasons)

Mars doesn't seem to be doing too badly on the greenhouse effect front.  As you said, it only gets half the radiation from the Sun, yet its average temp is 218° K compared to 287.6° K for the Earth, this is 76% as warm.

[Moontanman]

2 hours ago, Janus said:

I'd say a minimum of 0.006 atm.  This is the lowest pressure where water can exist as a liquid.  This is twenty times the present pressure, but still pretty thin compared to Earth's while having a partial pressure of CO₂ 19.2 times that of the Earth's.

As to how long it could have lasted.  It would be hard to say given that we really don't know how it lost so much of its atmosphere. (there are a few possible reasons)

Mars doesn't seem to be doing too badly on the greenhouse effect front.  As you said, it only gets half the radiation from the Sun, yet its average temp is 218° K compared to 287.6° K for the Earth, this is 76% as warm.

There is also the faint young sun problem to deal with as well, in the deep past the Earth had no oxygen, lots of methane, CO and CO2, ammonia and the ever present water vapor and sun was much dimmer than it is today. 

 

https://en.wikipedia.org/wiki/Faint_young_Sun_paradox