There are three Martian geological epochs.
The ocean formed in the Northern hemisphere. This is the ESA's artist's impression of the second, most recent ocean
ESA's Mars Express radar gives strong evidence for former Mars ocean
The evidence for this is in the form of ancient coastlines, with signs of deltas - which run all the way around the Northern hemisphere of Mars - and they are all on the same level - after you adjust for changes in the shape of Mars over the billions of years. Then the ESA observations are based on radar measurements of subsurface sediments covering the area of the former oceans.
The Mars oceans, they think, started off very hot, well over 100C with a dense atmosphere like Venus, same for Earth also, kept from boiling away because of the high pressure maybe 90 atmospheres or so, like a pressure cooker.
But they soon cooled down. Eventually they may have been frozen over at least some of the time. Mars has much more variable orbit than Earth - sometimes it is almost circular and sometimes it is highly elliptical. When it is very elliptical then there are big differences between summer and winter in one of the hemispheres, the hemisphere closest to the sun during its summer.
So its Northern ocean may well have completely frozen over in the Northern winters at times, and then melted at least partly in the summer.
It could still have occasional large bodies of water on the surface to this day. No evidence of any right now. But if you had a big meteorite or comet impact into the polar regions - this would melt a large area of the ice cap. It would soon freeze over. But ice is a good thermal insulator, and it floats on the surface of the water - and when it is a thin sheet it also acts as a sold state greenhouse helping to trap warmth.
So - someone worked out (I can't find the reference right now) that after an impact on the polar regions you could get a temporary lake, frozen over but still liquid underneath, for about a millenium or so depending on the size of the impactor.
It also probably has water very deep underground. This is the hydrosphere. Mars is unusual compared to Earth.
As you go down from the surface - the very top few cms actually go above melting point for water frequently in the summer everywhere except in the polar regions. But just for a few hours. Below that you have the permafrost layer. That continues down for many kilometers. But just as on the Earth - the rocks get warmer the deeper you go - and eventually it gets warm enough for ice to melt. Also any ice down there when it turns to water is trapped by the rock above it.
So they think there is at least - perhaps a few 100 meters of "hydrosphere" down there - liquid water. On Earth you get life in rocks deep below the surface so long as you have a source of water. So if life did evolve on Mars or got transferred there from Earth, it may still be there in the hydrosphere.
Higher up you get geological warming. The volcanoes are still geologically active occasionally - with what is now clear evidence that they have erupted in the recent geological past and will do so again, though none are erupting right now.
So that can lead to melted ice also. And even without erupting, underground you have potential for liquid water through geothermal heating.
Finally - you also have potential for occasional droplets and thin films of water on the surface of Mars. Various ways these could form. One way is on the salt / ice interface where liquid forms in experiments in Mars simulation chambers.
Nilton Remmo - a project scientist for Curiosity in charge of the REMS weather station on Mars - he thinks there is a reasonable chance that there are droplets of water on Mars on the salt / ice interface and that there may be life in those droplets.
Another way they can form is due to the solid state greenhouse effect of a thin overlying layer of ice - which both traps the water so it doesn't evaporate - and also heats it up. This is a process that leads to liquid water in Antarctica a short distance below the surface of the ice, while the surface ice remains frozen, due to greenhouse warming of the subsurface layer by the solid state greenhouse effect.
This is one of the features on Mars that has liquid water as its best explanation - in this case due to the solid state greenhouse effect, and it is
Then, you have 100% night time humidity despite the thin almost vacuum, it's possible that this may be taken up by deliquescing salts. They also observe occasional mists e.g. deep in Hellas basin, which may be a source of water. And then you have the Warm Seasonal Flows - which because they form only on sun facing slopes and when temperatures go above 0C, are hard to explain as anything else except somehow formed as a result of melting ice.
See also my articles
Where Should we Send our Rovers to Mars to Unravel Mystery of Origin of First Living Cells?
and
Where To Search On Mars For Droplets, & Shallow Flows Of Liquid Water - Where Microbial Life May Flourish
Where you can also find many more details and links to the original articles on the subject.
Mars geological epochs
- The oldest Martian epoch is the Noachian period, period of oceans, first few hundred million years
- The next period is the Hesperian period, period of floods, with a second ocean forming briefly a billion years after the first.
- The final geological period is the Amazonian period which we are in now, with the atmosphere a near vacuum and the surface almost entirely dry though still with some traces of surface liquid water able to interact with the atmosphere either now or in the recent geological past (isotope measurements by Phoenix show this).
The ocean formed in the Northern hemisphere. This is the ESA's artist's impression of the second, most recent ocean
ESA's Mars Express radar gives strong evidence for former Mars ocean
From that article:
"Two oceans have been proposed: 4 billion years ago, when warmer conditions prevailed, and also 3 billion years ago when subsurface ice melted, possibly as a result of enhanced geothermal activity, creating outflow channels that drained the water into areas of low elevation."
The evidence for this is in the form of ancient coastlines, with signs of deltas - which run all the way around the Northern hemisphere of Mars - and they are all on the same level - after you adjust for changes in the shape of Mars over the billions of years. Then the ESA observations are based on radar measurements of subsurface sediments covering the area of the former oceans.
The Mars oceans, they think, started off very hot, well over 100C with a dense atmosphere like Venus, same for Earth also, kept from boiling away because of the high pressure maybe 90 atmospheres or so, like a pressure cooker.
But they soon cooled down. Eventually they may have been frozen over at least some of the time. Mars has much more variable orbit than Earth - sometimes it is almost circular and sometimes it is highly elliptical. When it is very elliptical then there are big differences between summer and winter in one of the hemispheres, the hemisphere closest to the sun during its summer.
So its Northern ocean may well have completely frozen over in the Northern winters at times, and then melted at least partly in the summer.
It could still have occasional large bodies of water on the surface to this day. No evidence of any right now. But if you had a big meteorite or comet impact into the polar regions - this would melt a large area of the ice cap. It would soon freeze over. But ice is a good thermal insulator, and it floats on the surface of the water - and when it is a thin sheet it also acts as a sold state greenhouse helping to trap warmth.
So - someone worked out (I can't find the reference right now) that after an impact on the polar regions you could get a temporary lake, frozen over but still liquid underneath, for about a millenium or so depending on the size of the impactor.
It also probably has water very deep underground. This is the hydrosphere. Mars is unusual compared to Earth.
As you go down from the surface - the very top few cms actually go above melting point for water frequently in the summer everywhere except in the polar regions. But just for a few hours. Below that you have the permafrost layer. That continues down for many kilometers. But just as on the Earth - the rocks get warmer the deeper you go - and eventually it gets warm enough for ice to melt. Also any ice down there when it turns to water is trapped by the rock above it.
So they think there is at least - perhaps a few 100 meters of "hydrosphere" down there - liquid water. On Earth you get life in rocks deep below the surface so long as you have a source of water. So if life did evolve on Mars or got transferred there from Earth, it may still be there in the hydrosphere.
Higher up you get geological warming. The volcanoes are still geologically active occasionally - with what is now clear evidence that they have erupted in the recent geological past and will do so again, though none are erupting right now.
So that can lead to melted ice also. And even without erupting, underground you have potential for liquid water through geothermal heating.
Finally - you also have potential for occasional droplets and thin films of water on the surface of Mars. Various ways these could form. One way is on the salt / ice interface where liquid forms in experiments in Mars simulation chambers.
Nilton Remmo - a project scientist for Curiosity in charge of the REMS weather station on Mars - he thinks there is a reasonable chance that there are droplets of water on Mars on the salt / ice interface and that there may be life in those droplets.
Another way they can form is due to the solid state greenhouse effect of a thin overlying layer of ice - which both traps the water so it doesn't evaporate - and also heats it up. This is a process that leads to liquid water in Antarctica a short distance below the surface of the ice, while the surface ice remains frozen, due to greenhouse warming of the subsurface layer by the solid state greenhouse effect.
This is one of the features on Mars that has liquid water as its best explanation - in this case due to the solid state greenhouse effect, and it is
One of the Flow Like Features which form briefly in spring in the south polar region around dark dune spots inside Richardson crater. These may be caused by liquid fresh water trapped under ice and melted by the solid state greenhouse effect, details below. Just a thin layer of water - it's not like a flood of water, just a few mms perhaps.
Animation Credits: Collegium Budapest, Mars Astrobiology Group
Then, you have 100% night time humidity despite the thin almost vacuum, it's possible that this may be taken up by deliquescing salts. They also observe occasional mists e.g. deep in Hellas basin, which may be a source of water. And then you have the Warm Seasonal Flows - which because they form only on sun facing slopes and when temperatures go above 0C, are hard to explain as anything else except somehow formed as a result of melting ice.
See also my articles
Where Should we Send our Rovers to Mars to Unravel Mystery of Origin of First Living Cells?
and
Where To Search On Mars For Droplets, & Shallow Flows Of Liquid Water - Where Microbial Life May Flourish
Where you can also find many more details and links to the original articles on the subject.
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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