Terraforming Venus

[Moontanman]

[Moderator note: this thread was split off from the thread 14413, because the two subjects are literally worlds apart]

[CraigD]

Why assume Earth would loose its atmosphere? I don't think it would - at least not quickly. Venus has no magnetic field, more solar wind, and less mass. All that, and more atmosphere then it knows what to do with.

Venus’s atmosphere has been stripped of nearly all of its light molecules, so that it’s now about 96.5% [ce]CO2[/ce] (mass 44 AMU) and 3.5% [ce]N2[/ce] (28 AMU), vs. Earth’s 78% [ce]N2[/ce], 21% [ce]O2[/ce] (32 AMU), and 1% argon (40 AMU). Being about Earth’s mass (82%) and distance from Sol (72%), Venus should have had an initial composition about like Earth. Counterintuitively, stripping its of more light molecules has resulted in Venus’s atmosphere not only having a higher average molecular mass, but a higher total mass (about 93 times) than Earth’s.

All the light molecules like oxygen and nitrogen are gone.

In absolute terms, this isn’t an accurate statement.

 

Though small as a percentage, note that Venus’s 3.5% nitrogen times its total atmosphere mass of 93 times Earth’s means it has about 4.5 times as much nitrogen as Earth’s 78%. The oxygen in Venus’s 96.5% [ce]CO2[/ce] atmosphere is over 420 times that of Earth’s 21% [ce]O2[/ce]!

This makes me think, could we more easily terraform Venus by stripping away its atmosphere than terraforming mars?

I don’t think you could just strip Venus’s atmosphere away into space, but rather would have to get as much of the carbon out of it as possible (a carbon sequestration project dwarfing any terrestrial one), and dispose of the freed oxygen. The ideal use of the freed oxygen is to bond with hydrogen into that human-friendliest of molecules, [ce]H2O[/ce].

 

A big problem is that Venus doesn’t appear to have much hydrogen left. Its surface temperature is so high there’s nearly no liquid [ce]H2O[/ce]. All its [ce]H2O[/ce] is a gas, which appears to be getting unbonded and swept into space – one of the Venus Express probe major instruments, its ASPERA-4, found that Venus is venting about 1.9 H+ ions for every 1 O+ ion, and small traces of He+, suggesting that nearly all of it is coming from lost [ce]H2O[/ce].

 

So, as with Mars’s, terraforming Venus’s atmosphere would likely require adding a lot of hydrogen – which, with what there is to work with in the solar system, comes mostly in the form of [ce]H2O[/ce] ice. Unlike Mars, there’d be a lot of left-over oxygen, which would have to be bound into solids on the surface.

[modest]

Venus’s atmosphere has been stripped of nearly all of its light molecules, so that it’s now about 96.5% [ce]CO2[/ce] (mass 44 AMU) and 3.5% [ce]N2[/ce] (28 AMU), vs. Earth’s 78% [ce]N2[/ce], 21% [ce]O2[/ce] (32 AMU), and 1% argon (40 AMU).

 

While I could intuitively see how this would be true of Hydrogen, I'm unconvinced of the other elements. Venus has [imath]1.68 \times 10^{19} kg[/imath] of nitrogen while earth has [imath]4 \times 10^{18} kg[/imath]. Twenty four percent considering Venus is lighter seems comparable to me. Like a lifeless earth, I wouldn't expect Venus to have Oxygen though I don't know why we'd attribute this to the solar wind. Oxygen's molecular weight is 32 g/mol while carbon dioxide's is 44 g/mol. I would be very supprised if that difference in mass makes the difference between getting stripped or not.

 

Being about Earth’s mass (82%) and distance from Sol (72%), Venus should have had an initial composition about like Earth. Counterintuitively, stripping its of more light molecules has resulted in Venus’s atmosphere not only having a higher average molecular mass, but a higher total mass (about 93 times) than Earth’s.

 

Can you explain how stripping 75% of the nitrogen would result in such a big carbon dioxide build-up. Are we sure one has something to do with the other?

 

//edit

 

Sorry, I had Earth and Venus inverted in my percent calculation up there, I believe the mass of Nitrogen on Venus is 4.2 that of Earth and it is lighter than oxygen. I don't think we can say the oxygen was stripped off or infer that Earth's would be if we lost our magnetic field.

[Moontanman]

Venus’s atmosphere has been stripped of nearly all of its light molecules, so that it’s now about 96.5% [ce]CO2[/ce] (mass 44 AMU) and 3.5% [ce]N2[/ce] (28 AMU), vs. Earth’s 78% [ce]N2[/ce], 21% [ce]O2[/ce] (32 AMU), and 1% argon (40 AMU). Being about Earth’s mass (82%) and distance from Sol (72%), Venus should have had an initial composition about like Earth. Counterintuitively, stripping its of more light molecules has resulted in Venus’s atmosphere not only having a higher average molecular mass, but a higher total mass (about 93 times) than Earth’s.In absolute terms, this isn’t an accurate statement.

 

Though small as a percentage, note that Venus’s 3.5% nitrogen times its total atmosphere mass of 93 times Earth’s means it has about 4.5 times as much nitrogen as Earth’s 78%. The oxygen in Venus’s 96.5% [ce]CO2[/ce] atmosphere is over 420 times that of Earth’s 21% [ce]O2[/ce]!I don’t think you could just strip Venus’s atmosphere away into space, but rather would have to get as much of the carbon out of it as possible (a carbon sequestration project dwarfing any terrestrial one), and dispose of the freed oxygen. The ideal use of the freed oxygen is to bond with hydrogen into that human-friendliest of molecules, [ce]H2O[/ce].

 

A big problem is that Venus doesn’t appear to have much hydrogen left. Its surface temperature is so high there’s nearly no liquid [ce]H2O[/ce]. All its [ce]H2O[/ce] is a gas, which appears to be getting unbonded and swept into space – one of the Venus Express probe major instruments, its ASPERA-4, found that Venus is venting about 1.9 H+ ions for every 1 O+ ion, and small traces of He+, suggesting that nearly all of it is coming from lost [ce]H2O[/ce].

 

So, as with Mars’s, terraforming Venus’s atmosphere would likely require adding a lot of hydrogen – which, with what there is to work with in the solar system, comes mostly in the form of [ce]H2O[/ce] ice. Unlike Mars, there’d be a lot of left-over oxygen, which would have to be bound into solids on the surface.

 

Actually in real terms the earth probably has the same or similar amount of both nitrogen and CO2 it's just that water allows these chemicals to sequestered in the rocks of the surface. The first to go would be the water, after the water is gone the carbonate rocks would release all their carbon dioxide and then the temps really start to climb and most all volatile compounds are released into the atmosphere to be swept away by the suns radiation or solar wind. As for left over oxygen that would depend on how much oxygen was bound up in the surface and how much CO2 would be disolved into any ocean that would form after the ice was deposted on the surface. formation of carbonate rocks would take care of the surplus of free oxygen. Of course you would have to sped up the planets revolutions for any changes to have real effects. that might even start up a magnetic field. Be a hot place but it might be livable after all the cO2 was sequestered. I'm betting it would take much longer to terra form Venus than it would Mars!

[CraigD]

Can you explain how stripping 75% of the nitrogen would result in such a big carbon dioxide build-up. Are we sure one has something to do with the other?

As I understand it, the current composition of Venus’s atmosphere (which is known with pretty high precision, having been directly and remotely measured by several lander and orbiter spacecraft) isn’t due to the loss of fairly massive nitrogen molecules, but to a massive transfer of [ce]CO2[/ce] from carbon and oxygen formerly in surface carbon and oxygen-bearing solids and liquid [ce]H2O[/ce] – what’s commonly described as a “runaway greenhouse effect”, believe to have occurred anywhere from 2 to 4 billion years ago. Prior to that, Venus is believed to have been fairly Earth-like.

 

This wikipedia section has a brief description and references of the subject.

[Moontanman]

As I understand it, the current composition of Venus’s atmosphere (which is known with pretty high precision, having been directly and remotely measured by several lander and orbiter spacecraft) isn’t due to the loss of fairly massive nitrogen molecules, but to a massive transfer of [ce]CO2[/ce] from carbon and oxygen formerly in surface carbon and oxygen-bearing solids and liquid [ce]H2O[/ce] – what’s commonly described as a “runaway greenhouse effect”, believe to have occurred anywhere from 2 to 4 billion years ago. Prior to that, Venus is believed to have been fairly Earth-like.

 

This wikipedia section has a brief description and references of the subject.

 

One fairly new theory stipulates that a massive impact like the one that is believed to have formed earth's Moon stopped the rotation of Venus and started it turning slowly the opposite direction from the Earths rotation. This impact either didn't form a moon or since it was from the opposite direction than the Earths giant impactor any moon that was formed spiraled down into Venus instead of spiraling out as Earths Moon has. This second impact event and or the slow rotation could have been the trigger that started the runaway greenhouse we see today. Of course all this is highly speculative.

[modest]

Why would Venus have it's Oxygen stripped off and not it's Nitrogen? Oxygen is heavier. This theory seems to have more leaky holes than our sister planet out there.

 

-modest

[Moontanman]

Why would Venus have it's Oxygen stripped off and not it's Nitrogen? Oxygen is heavier. This theory seems to have more leaky holes than our sister planet out there.

 

-modest

 

That is a good question and my only answer is maybe the oxygen didn't get stripped from the atmosphere but it reacted with the surface and other chemicals to form the sulfer dioxide and sufuric acid seen in the atmosphere. I'm not sure but I think it would also form nitric acid as well. But I'm not completly sure about that. One thing is sure oxygen would not be stable in the atmosphere of Venus with out a contuinous source of resupply. On the earth plants do that. I don't think Venus has much in the way of plant life.

[modest]

That is a good question and my only answer is maybe the oxygen didn't get stripped from the atmosphere but it reacted with the surface and other chemicals to form the sulfer dioxide and sufuric acid seen in the atmosphere. I'm not sure but I think it would also form nitric acid as well. But I'm not completly sure about that. One thing is sure oxygen would not be stable in the atmosphere of Venus with out a contuinous source of resupply. On the earth plants do that. I don't think Venus has much in the way of plant life.

 

I could see that. I suppose we also say that of nitrogen and nitrogen compounds - but there's nothing sure about that.

 

However, like I said, I don't find it too strange that there's no atmospheric, elemental oxygen. I just thought there might be more evidence linking the loss of Venus' magnetic field and the run-away greenhouse. Perhaps there is and I just need to find it.

 

-modest

[Moontanman]

I could see that. I suppose we also say that of nitrogen and nitrogen compounds - but there's nothing sure about that.

 

However, like I said, I don't find it too strange that there's no atmospheric, elemental oxygen. I just thought there might be more evidence linking the loss of Venus' magnetic field and the run-away greenhouse. Perhaps there is and I just need to find it.

 

-modest

 

Actually the loss of water can be atributed to the lack of a magnetic feild. Loss of water means that all the planets CO2 is in the atmosphere. this accounts for the greenhouse effect, pretty straight forward to me. oh yeah slow rotaion probably accounts for the lack of a magentic feild which could have been caused by a giant impactor that hit in the dead wrong orieintation to it's original rotation.

[modest]

Actually the loss of water can be atributed to the lack of a magnetic feild. Loss of water means that all the planets CO2 is in the atmosphere. this accounts for the greenhouse effect, pretty straight forward to me. oh yeah slow rotaion probably accounts for the lack of a magentic feild which could have been caused by a giant impactor that hit in the dead wrong orieintation to it's original rotation.

 

So what you're saying is that a planet with no water but with a magnetic field may well look like Venus. :eek_big:

[CraigD]

Why would Venus have it's Oxygen stripped off and not it's Nitrogen? Oxygen is heavier.

This is a good question, and not for which my understanding of the physics involved is adequate.

 

Via the recent (2006) Venus Express probe, we have for the first time precise, reliable observations that, at present, Venus is venting hydrogen, oxygen, and helium at a ratio (by count of atoms) of about 1.9:1:0.07, and essentially no nitrogen. (source: The loss of ions from Venus through the plasma wake). Note that, since the density of escaping atmosphere is small compared to that of the solar wind, there is an assumption that nearly all escaped atmosphere is ionized into plasma state, and that neutral molecules and atoms are little effected by the solar wind compared to ionized ones.

 

For so much of oxygen to be escaping, and for the H:O ratio to be so close to water’s 2:1, something other than simple Jean’s escape (in which the lightest elements, having the highest average velocity and thus the greatest number of molecules exceeding escape velocity) is responsible. The observed ratios suggest it’s related to water.

 

My best guess is that the dominant factor is how the Venusian atmosphere is segregated by altitude, resulting in a lot of O+ ions and hardly and nitrogen high up in the ionosphere where it can be stripped by collision with the solar wind. Speculating way over my head, I think a major mechanism for this may be the photochemical reaction of UV light with Venus’s atmosphere’s ubiquitous [ce]CO2[/ce] to produce [ce]CO[/ce] and singlet [ce]O[/ce], driven by oxygen’s slightly lower ionization energy than nitrogen and the Venusian atmosphere’s complicated convection patterns.

 

Somehow, something is putting a lot of O+ into Venus’s ionosphere, where it’s knocked into space by the solar wind. Why the H+:O+ ratio is so close to 2:1 mystifies me.:confused:

… maybe the oxygen didn't get stripped from the atmosphere but it reacted with the surface and other chemicals to form the sulfer dioxide and sufuric acid seen in the atmosphere. I'm not sure but I think it would also form nitric acid as well.

Although there’s a lot of chemistry going on in the Venusian atmosphere, in terms of significant quantities of elements, it’s pretty much just 96.5% [ce]CO2[/ce] and 3.5% [ce]N2[/ce]. Even it’s [ce]SO2[/ce], the next most abundant compound and main constituent of its thick clouds, comprise only about 0.015% of the atmosphere. So, compared to its quantity of atmospheric [ce]N2[/ce], I don’t think atmospheric nitrogen compounds are very significant.

One thing is sure oxygen would not be stable in the atmosphere of Venus with out a contuinous source of resupply. On the earth plants do that. I don't think Venus has much in the way of plant life.

I agree. Another important terrestrial carbon-cycle mechanism is the uptake of [ce]CO2[/ce] by seawater into carbonic acid ([ce]CO2 + H2O \to H_2CO_3[/ce]), which, having no oceans, Venus also lacks.

 

Artificial carbon-fixing schemes for Venus are popular hard science fiction subjects. For example, In the fictional universe of Steven Baxter’s 2004 novel “Exultant”, humans seed the Venusian atmosphere with artificially engineered “bugs” in tiny water droplets, which make more of themselves and form carbon-oxygen-polymer shells that fall out of the atmosphere to form a hundred-meter thick layer of chalk, not to terraform Venus, but because of the engineering value of such a large amount of carbon, resulting in Venus coming to be commonly known only as “the carbon mine”.

 

Not every planet-scale engineering project need have as an end making human-friendly worlds.

[CraigD]

Actually the loss of water can be atributed to the lack of a magnetic feild.

Because atmosphere loss, whether for Venus, with a magnetopause averaging only 0.3 planetary radii above its surface, or for Earth, with a magnetopause averaging 15 radii, is due to losses from the outermost layers of their atmospheres, Venus’s smaller magnetosphere (note that despite its lack of an internally-generated magnetic field, Venus still has a magnetosphere) can’t be the direct cause of loss of water, because water is not found in either planet’s upper atmosphere.

 

Venus clearly appears to lack much water. Although its thick atmosphere (93 time the mass of Earth’s, and 92 times its surface pressure) has more of most compounds and elements than Earth’s, at a mere 0.002% water vapor, vs. Earth’s average of about 1%, it has less than 1/5th Earth’s water vapor, and apparently no liquid water. Venus is very hot, and very dry.

 

The scientific consensus, as I read it, is that Venus’s lack of water is due simply to its temperature, which despite its immense atmospheric pressure, remains well above the boiling point of water. A strong greenhouse gas, the vaporization of effectively all of Venus’s ancient water set in motion an evolution that resulted in the atmosphere we presently observe.

 

In short, I think the physics and evidence indicate that temperature, not magnetic field, is the dominant cause of the transformation of a once liquid-water rich, Earth-size planet like Venus into its present condition. Even if Venus had a magnetic field as strong or stronger than Earth’s, it wouldn’t have evolved much differently. If Earth were heated as strongly as Venus, despite its magnetosphere, it would evolve similarly to Venus. For this to happen as it did with Venus, the Sun would have to be roughly [math]\frac{R_{\mbox{Earth}}^2}{R_{\mbox{Venus}}^2} \cdot \frac{P_{\mbox{Sun 4 billion years ago}}}{P_{\mbox{Sun now}}} = \frac1{0.72^2} \cdot \frac1{1 \,\mbox{to}\, 1.25} \dot= 1.93 \,\mbox{to}\, 1.55[/math] times its current brightness.

[Moontanman]

So what you're saying is that a planet with no water but with a magnetic field may well look like Venus. :eek_big:

 

Yes if it is close enough to the sun, too far away the CO2 will freeze out in high clouds that will reflect even more sunlight and the CO2 will snow out on the surface as Frozen CO2 much like Mars! CO2 stays because it isn't easy to break down by solar radiation as water is. actually to be precise loosing hydrogen is what messed up venus.

[Moontanman]

Because atmosphere loss, whether for Venus, with a magnetopause averaging only 0.3 planetary radii above its surface, or for Earth, with a magnetopause averaging 15 radii, is due to losses from the outermost layers of their atmospheres, Venus’s smaller magnetosphere (note that despite its lack of an internally-generated magnetic field, Venus still has a magnetosphere) can’t be the direct cause of loss of water, because water is not found in either planet’s upper atmosphere.

 

Venus clearly appears to lack much water. Although its thick atmosphere (93 time the mass of Earth’s, and 92 times its surface pressure) has more of most compounds and elements than Earth’s, at a mere 0.002% water vapor, vs. Earth’s average of about 1%, it has less than 1/5th Earth’s water vapor, and apparently no liquid water. Venus is very hot, and very dry.

 

The scientific consensus, as I read it, is that Venus’s lack of water is due simply to its temperature, which despite its immense atmospheric pressure, remains well above the boiling point of water. A strong greenhouse gas, the vaporization of effectively all of Venus’s ancient water set in motion an evolution that resulted in the atmosphere we presently observe.

 

In short, I think the physics and evidence indicate that temperature, not magnetic field, is the dominant cause of the transformation of a once liquid-water rich, Earth-size planet like Venus into its present condition. Even if Venus had a magnetic field as strong or stronger than Earth’s, it wouldn’t have evolved much differently. If Earth were heated as strongly as Venus, despite its magnetosphere, it would evolve similarly to Venus. For this to happen as it did with Venus, the Sun would have to be roughly [math]frac{R_{mbox{Earth}}^2}{R_{mbox{Venus}}^2} cdot frac{P_{mbox{Sun 4 billion years ago}}}{P_{mbox{Sun now}}} = frac1{0.72^2} cdot frac1{1 ,mbox{to}, 1.25} dot= 1.93 ,mbox{to}, 1.55[/math] times its current brightness.

 

Actually newer research seems to indicate the biosphere of the earth could maintain a much more equitable temperature on the earth even with the extra radiation. Probably too hot for much in the way of complex life but not the hot house Venus is today. As long as the oceans do not boil away CO2 is sequestered in the rocks. Higher temps do cause the atmosphere to puff out from the surface higher where solar radiation can strip hydrogen from water. Without a magnetic field this happens much faster than it does on the Earth. There is no doubt that lack of a magnetic field will accelerate the loss of volatile compounds from a planets atmosphere. There is no reason to assume Venus didn't have as much water the earth does. It simply lost it to space by loosing hydrogen to the solar wind. When I say radiation I am not talking about electromagnetic radiation alone. I am also talking about the solar wind. The solar wind will blow away the lighter elements of a planets atmosphere, Hydrogen especially. There is also no doubt that higher temps would allow more water vapor into the planets atmosphere which would put more water in harms way so to speak. Venus is not so close to the sun it's surface temperature would automatically be higher than the boiling point of water. The Earth average temperature isn't very high, we forget that sometimes because most of us live where the temps stay well above freezing most of the time. Venus wouldn't have ice caps but it could maintain oceans if not for its lack of hydrogen. A magnetic field of suitable strength will slow this process down by orders of magnitude. For hydrogen to be stripped from water it doesn't have to be at the edge of the atmosphere but extra heating will cause the atmosphere to be larger than it is in a lower temperature environment. The earth is loosing hydrogen as well just at a much slower rate than Venus. At some point the Earth will loose enough of it's hydrogen i.e. water for CO2 to start coming out of the rocks at a much higher rate than it is being put back. When this happens the CO2 level will begin to rise accelerating this effect by raising temps and puffing out the Earth atmosphere, run away greenhouse is what results. But as long as the Earth has a significant magnetic field this will still be a slower process than it was on Venus without a magnetic field. Of course as the Earth cools and it looses it's molten core it will also loose it's magnetic filed as well. The Moon will also slow the Earth's spin accelerating this process somewhat. So many feed back mechanisms I loose track!

[Moontanman]

This is a good question, and not for which my understanding of the physics involved is adequate.

 

Via the recent (2006) Venus Express probe, we have for the first time precise, reliable observations that, at present, Venus is venting hydrogen, oxygen, and helium at a ratio (by count of atoms) of about 1.9:1:0.07, and essentially no nitrogen. (source: The loss of ions from Venus through the plasma wake). Note that, since the density of escaping atmosphere is small compared to that of the solar wind, there is an assumption that nearly all escaped atmosphere is ionized into plasma state, and that neutral molecules and atoms are little effected by the solar wind compared to ionized ones.

 

For so much of oxygen to be escaping, and for the H:O ratio to be so close to water’s 2:1, something other than simple Jean’s escape (in which the lightest elements, having the highest average velocity and thus the greatest number of molecules exceeding escape velocity) is responsible. The observed ratios suggest it’s related to water.

 

My best guess is that the dominant factor is how the Venusian atmosphere is segregated by altitude, resulting in a lot of O+ ions and hardly and nitrogen high up in the ionosphere where it can be stripped by collision with the solar wind. Speculating way over my head, I think a major mechanism for this may be the photochemical reaction of UV light with Venus’s atmosphere’s ubiquitous [ce]CO2[/ce] to produce [ce]CO[/ce] and singlet [ce]O[/ce], driven by oxygen’s slightly lower ionization energy than nitrogen and the Venusian atmosphere’s complicated convection patterns.

 

Somehow, something is putting a lot of O+ into Venus’s ionosphere, where it’s knocked into space by the solar wind. Why the H+:O+ ratio is so close to 2:1 mystifies me.:confused:Although there’s a lot of chemistry going on in the Venusian atmosphere, in terms of significant quantities of elements, it’s pretty much just 96.5% [ce]CO2[/ce] and 3.5% [ce]N2[/ce]. Even it’s [ce]SO2[/ce], the next most abundant compound and main constituent of its thick clouds, comprise only about 0.015% of the atmosphere. So, compared to its quantity of atmospheric [ce]N2[/ce], I don’t think atmospheric nitrogen compounds are very significant.I agree. Another important terrestrial carbon-cycle mechanism is the uptake of [ce]CO2[/ce] by seawater into carbonic acid ([ce]CO2 + H2O to H_2CO_3[/ce]), which, having no oceans, Venus also lacks.

 

Artificial carbon-fixing schemes for Venus are popular hard science fiction subjects. For example, In the fictional universe of Steven Baxter’s 2004 novel “Exultant”, humans seed the Venusian atmosphere with artificially engineered “bugs” in tiny water droplets, which make more of themselves and form carbon-oxygen-polymer shells that fall out of the atmosphere to form a hundred-meter thick layer of chalk, not to terraform Venus, but because of the engineering value of such a large amount of carbon, resulting in Venus coming to be commonly known only as “the carbon mine”.

 

Not every planet-scale engineering project need have as an end making human-friendly worlds.

 

I agree but wouldn't Titan make a better carbon mine than Venus? Lower gravity, higher in the suns gravity well? Bring carbon in from Titan would be easier than bringing it out from Venus wouldn't it?

[Moontanman]

So much speculation, so little time!