You are not logged in.
Pages: 1
We really don't need to worry about a magnetic field for Mars. If we give Mars an atmosphere it will last for hundreds of millions of years (the Earth won't even be habitable in much longer than that).
Still, if you must, then you can wrap super-conducting cables around the planet and create a magnetic field that way, there's really no need to spend the effort on raising it up above the surface (that's the magic of magnetism after all).
Because Mars is 1.5AU from the sun, it doesn't suffer from atmospheric thermal loss (Jeans escape), but it still suffers from solar winds stripping the atmosphere. This form of atmospheric loss increases the closer the planet is to the star, and how active that star is. The habitable zone is extremely close to Red Dwarf stars, and red dwarf stars are extremely active early on. The closer a planet is to it's star, the more likely it is to be tidally locked, which also means that it is less likely to have the rotation necessary to maintain a significant dynamo in it's core to keep a magnetic field.
M stars are the most common, and live for a ridiculous amount of time, unfortunately, it seems that they're not very friendly to planets in their habitable zones. G stars are reasonably friendly, but have a limited lifespan. For example, Earth has been around for ~4.5Gya years, it took the first 0.5-1Gya until the planet was habitable, then 3-3.5Gya until complex life formed, then 0.5Gya from complex life (worms) forming to intelligence forming (us), and we now have less than 1Gya until the Earth is no longer habitable. It's a relatively small window for intelligent life to form under a G type star.
However, between M type and G type stars we have K type stars, more friendly than M type, and more common and longer lived (longer than the current age of the universe) than G type stars. This would be my target star for exoplanet atmosphere biomarkers.
Edit: Venus is massive enough to retain it's atmosphere even at Mercury distance from the sun, as is Earth. A magnetic field can only help less massive worlds (Mars has only 10% of Earth mass) retain their atmosphere when they are cold enough. Don't forget that Mars still has an atmosphere, yes much has been stripped after billions of years, but it still retains enough of an atmosphere for liquid water to be possible at it's lowest elevations on summer days.
So, those are two things that I don't think rule out habitability.
1) Moonless Terrestrial.
Agree
2) A claim that the outer bound of habitability is 1.5 AU in our solar system.
Kind of agree, but it would need a greenhouse gas atmosphere, and be massive enough to retain it. It would probably also require the planet migrating outwards rather than inwards.
I claim that Planetary Volatile Displacement likely can extend the outer bound to 2.0 AU and even more.
And then there is the total mass of atmosphere. Anything from 10 mb to 10,000 mb could be habitable.
And then there is Tidal Geothermal as in Io, Europa, Ganymede.
Right, subsurface life doesn't really have an outer limit when tidal forces are considered, but for detectable surface life the world needs to be massive enough to at least retain it's atmosphere.
https://en.wikipedia.org/wiki/TRAPPIST-1
Quote:Tidal locking[edit]
All seven planets are likely to be tidally locked (one side of each planet permanently facing the star),[34] making the development of life there "much more challenging".[11] A less likely possibility is that some may be trapped in a higher-order spin–orbit resonance.[34] Tidally locked planets would typically have very large temperature differences between their permanently lit day sides and their permanently dark night sides, which could produce very strong winds circling the planets. The best places for life may be close to the mild twilight regions between the two sides, called the terminator line.
Tidal heating[edit]
Tidal heating is predicted to be significant: all planets except f and h are expected to have a tidal heat flux greater than Earth's total heat flux.[5] With the exception of TRAPPIST-1c, all of the planets have densities low enough to indicate the presence of significant H2O in some form. Planets b and c experience enough heating from planetary tides to maintain magma oceans in their rock mantles; planet c may have eruptions of silicate magma on its surface. Tidal heat fluxes on planets d, e, and f are lower, but are still twenty times higher than Earth's mean heat flow. Planets d and e are the most likely to be habitable. Planet d avoids the runaway greenhouse state if its albedo is ≳ 0.3. [47]Some planets could have too much or just right amounts of tidal heating in the Trappist-1 system.
If they are tidal locked, this could very much help in redistributing water from the dark side to the sun side.https://www.centauri-dreams.org/?p=39185
https://www.centauri-dreams.org/wp-cont … RATION.jpg
Quote:Given that their orbits are slightly eccentric, there is the possibility of tidal heating, which in the Galilean moons has intrigued us for its possibilities at providing an energy source for life beneath an icy crust, and indeed, the paper notes that “…on planets b, e, f, g and h, life might appear in the tidally heated (subsurface) ocean close to hydrothermal vents.“
And then their is the chance of inductive heating of some planets:
http://www.newsweek.com/trappist-1-alie … ace-690638My understanding is that likely it is 1000 times larger than for our solar system.
The article says that the four closest planets could experience inductive heating. Personally, I expect that the others also do, but of a much lesser magnitude.
https://www.centauri-dreams.org/wp-cont … RATION.jpgPlanetary Volatile Displacement on tidal locked worlds would be very significant as to it's habitability I believe.
Planets 'd' and 'e' were said to be the most likely to be habitable in one of the above quotes.
For 'f', 'g', and 'h' I also give chances due to Volatile displacement, and also potential tidal heating.
These worlds should have a very tricky way they conserve heat, if they maintain an atmosphere and have significant water/ice. For this I will presume 1 bar just to keep it simpler.
It is mentioned that their is a real possibility of tidal heating, so if the dark sides are occupied by a giant slab of ice, it will likely be melting from the bottom. And there will likely be flows of water from there to the sunward sides.
There has to be a limit to how high ice can pile up on the dark sides. 5000 feet? Maybe more?
But if the dark side surface is 5000 feet higher on average than the presumed relatively ice free day side, then strange things happen with heat.
Winds coming off that ice sheet must drop 5000 feet and that will compress that air and heat it up. So it becomes difficult for the night side cold to impose itself with the full force that otherwise might be imagined.
And also there is atmospheric displacement from the dark side to the day side. The day side has a very significantly thicker atmosphere, so, presumably a better greenhouse effect, and very likely improved protection from harmful radiation.
But another form of displacement would be that of CO2. I would expect that it would pretty much try to freeze out on the dark side. Methods for it to return to the day side would be:
1) Glacial flows into the sunlight.
2) Melt water flows from under the ice cap (Tidal Heating).
3) Katabatic air flows carrying snow (Dust) to the day side.So, I feel that these worlds may have better chances for habitability on their day sides than what is typically presumed. Also, I presume that the further from a star a planet is, up to the point of collapse of the atmosphere by condensation, the better chances that planet will retain an atmosphere.
I went very far with Red Dwarf planets, but I feel that many of these principles will work for terrestrial planets around orange and yellow stars as well.
The issue with M dwarfs is that they are extremely variable, especially when young, and the habitable zone is so close to these stars that the effects of these violent events might strip any terrestrial planets of their atmospheres before they have enough time to become habitable. Of course this is all just theoretical, we don't actually know that yet.
Still, as you mention, the further from a star, then the more likely it is to retain an atmosphere. Of course, the further from the star, then the less likely it is to be tidally locked, so K and G type stars are the most promising.
If a tidally locked planet does have an atmosphere which freezes out on the dark side, what would stop this becoming a runaway effect? As the atmosphere freezes out it becomes less dense, reducing the affectiveness of the atmosphere to transfer heat around the planet, resulting in more atmosphere freezing out ... etc ... etc. If this distributes more mass to the dark side of the planet, then gravity will eventually pull it back to hydrostatic equilibrium. NASA can actually detect the change in mass at the Martian poles when CO2 freezes out there.
Venus may be a paradise at those distances, but note that CO2 would freeze at distances past 2 AU, not modelling for any greenhouse effect at least.
The sun's luminosity is increasing by 1% every 100 million years, in a billion years time the Earth will no longer be in the habitable zone, the oceans will evaporate, with photodissociation resulting in the hydrogen being lost to atmospheric escape. We need to move the Earth far before the red giant phase!
Fortunately this can be done slowly as the habitable zone gradually moves outwards. As long as the Earth is moved at the same speed as the habitable zone moves, then we don't need to be concerned about climatic change.
Mining and manufacturing greenhouse gases will take up quite a lot of energy resources, which would be better spent on other projects if no longer needed.
http://onlinelibrary.wiley.com/doi/10.1 … 02306/full
If artificial greenhouse gases are used to warm Mars, then compounds containing chlorine or bromine would not be desirable because both elements catalytically destroy ozone. Fluorine-based compounds (e.g., SF6 and perfluorocarbons) are therefore of particular interest for the warming of Mars. In addition, it would be desirable to have gases with a strong greenhouse effect and a long lifetime. For practical reasons, the gases must be composed of elements readily available on the Martian surface. In this study we have focused our modeling efforts on four gases that satisfy these criteria: CF4, C2F6, C3F8, and SF6. The relative global warming potential (GWP, with respect to CO2) of these compounds in Earth's present atmosphere are estimated to be 5700, 11900, 8600, and 22200, respectively [Houghton et al., 2001], and they have extremely long lifetimes in Earth's atmosphere: 50000, 10000, 2600, and 3200 years, respectively [Houghton et al., 2001]. On Mars, these lifetimes may be longer due to the reduced solar flux reaching Mars, but might be shorter due to the less effective UV shielding of the CO2 atmosphere compared to the O2 and O3 in Earth's atmosphere. Accurately estimating the lifetime of these gases on Mars is difficult (as it is on Earth). For example SF6 is discussed by Ko et al. [1993]; it may not be destroyed by UV that penetrates the Martian CO2 (>200 nm), but may be destroyed by electron capture and ion reactions. Ramanathan et al. [1985] state that for CF4, C2F6, and SF6 (and presumably for C3F8), the loss rate is due to extreme UV and electron capture removal in the ionosphere. In this case the lifetimes on Mars could be much longer than on Earth due both to the reduced solar flux and the absence of a magnetosphere. A detailed analysis of the lifetimes of these gases on Mars remains to be done.
Once the desired level of greenhouse gases is achieved only a small amount is required to "top up" as they have extremely long lifetimes on the order of thousands or tens of thousands of years.
Note that Mars only has 28% of the surface area of Earth, with 38% of the gravity. If Mars had Earth's atmosphere, the pressure would be higher on Mars.
Very interesting proposal. But I think I would look at this from another way round - how much nitrogen do we need on Mars in the atmosphere? Do we really need to replicate the Earth proportions? Are there other inert gases we can use? Nitrogen in the air is not absolutely essential for plant growth if we can deliver it through the soil and there are bacteria that can do that (taking it from the air).
I prefer a low resource solution - using solar sails to reflect solar radiation on to Mars and thus heat up the planet as quickly as possible.
The issue then is what sort of atmosphere you would end up with? We might be able to influence that by directing the reflected solar radiation on to particular parts of the planet, beginning with the north polar region.
If you don't want to import then you're stuck with C02, 02, and N2 for substantially thickening the atmosphere (if we ignore toxic gases like S02). Oxygen is available in virtually unlimited supply from regolith and water ice. "Impact processing of nitrogen on early Mars" estimates ∼30 mbars of N2 fixed as nitrates in the regolith, which fits with the findings of "Evidence for indigenous nitrogen in sedimentary and aeolian deposits from the Curiosity rover investigations at Gale crater, Mars". If you could bake that all out of the regolith and convert to N2 and 02 it would be quite useful. There's currently about 6 mbars of CO2 in the atmosphere, with perhaps the same again frozen. Carbon is also locked up in carbonates, some of which should produce CO2 once liquid water is present. It's not clear how extensive or how accessible the carbonate deposits are, so it's difficult to estimate an upper figure for this, but 30 mbar of CO2 might well be possible.
If you had a 120 mbar atmosphere of
O2: 60 mbar
N2: 30 mbar
CO2: 30 mbar
Then bottom of Hellas would be ∼240 mbar
O2: 120 mbar
N2: 60 mbar
CO2: 60 mbar
Oxygen equivalent of 4,800m on Earth (La Rinconada, Peru has a pop. of 50k @ 5,100m). CO2 is a bit high, but should be tolerable with acclimatisation. O2 could be continuously increased to bring higher elevations to breathable levels.
Mars atmosphere is currently about 25 trillion tons, or 25 Teratonnes (Tt). This equates to about 6.0 mbar at the datum, although at the depths of Hellas Basin, the pressure is roughly double that.
According to the paper "Radiative-convective model of warming Mars with artificial
greenhouse gases", "Only" 0.002 mbar of super greenhouse gases is required to set off a runaway greenhouse effect. The actual gases would have little effect on pressure themselves, but by releasing the frozen polar CO2 we might expect pressure to double, and with additional CO2 outgassing from regolith, and acidic water reacting with shallow carbonate deposits me might expect more, although it's difficult to say how much. Let's say it doubles the atmosphere again, to 100Tt.
Mars is estimated to have over 5,000Tt of water in polar ice and relatively shallow glaciers, with more even deeper. Enough to cover the planet (if it was flat) in 35m of water. Venus has only 20ppmv of water vapour in it's atmosphere, but as the atmosphere is so dense, then this could still be 5Tt worth, enough to cover the surface (flat) in 1cm of water. Clearly Venus needs more water (or at least hydrogen, which makes up about 11% of water by weight).
So if Martians are electrolysing water to pump oxygen into the atmosphere (I'll assume they have fusion), they might want to export the excess hydrogen to the floating cities of Venus.
Mars/Venus close approach is every 11 months, a 6/7 month trip gives enough time to return at the next window, and leave for Venus again at the window following that, for a round trip every 22 months.
A 500m diameter spherical tanker would have a volume of 65,449,800m³, liquid hydrogen has a density of 70.8 kg/m³, so 4,633,845t/tanker. After unloading the hydrogen at Venus, you could load up with liquid nitrogen at Venus, which has a density of 804 kg/m³, for 52,621,639t/tanker. However, Venus has argon at 70ppmv, which could be about 46Tt worth, and argon is denser still at 1,394 kg/m³ for 91,237,021t/tanker.
If the Martian atmosphere is still so thin that nowhere is even above the Armstrong limit (62mbar), then it might make more sense to import argon first, in order to thicken up the atmosphere quicker.
So let's say that there's a tanker manufacturing plant on Phobos producing 100 tankers/year with a lifetime of 100 years each. Each tanker can make 54 round trips in 99 years before being retired. After 100 years the number of tankers will have risen to 10,000, and from then on remain steady as newly produced tankers replace retired ones.
These 10,000 tankers can make 540,000 round trips every hundred years, we can halve that for the first hundred years as the fleet was building up.
Applying that to the following;
Liquid hydrogen = 2.50Tt
Liquid nitrogen = 28.42Tt
Liquid argon = 49.27Tt
Oxygen produced from water at Mars = 19.86Tt
Water produced from hydrogen at Venus = 22.36Tt
So after the first hundred years we've transported enough hydrogen to Venus to make 11.18Tt of water, tripling the current inventory of 5Tt.
Produced 9.93Tt of oxygen on Mars, and imported 24.635Tt of Argon, adding a total of 34.565Tt to the atmosphere. If we already had 100Tt mainly CO2 atmosphere, then that's enough extra to bring the very lowest altitudes above the Armstrong limit ... no pressure suit needed.
For the second hundred years we exhaust the supply of argon after 43 years;
Liquid argon = 21.365Tt
Oxygen produced from water at Mars = 8.61Tt
Adding another 30Tt of atmosphere the area of land above the armstrong limit continuously expands.
For the remaining 57 years;
Liquid Nitrogen = 16.10Tt
Oxygen produced from water at Mars = 11.25Tt
Atmosphere ;
After 200 years = 192Tt (46mbar at datum / ~92 mbar bottom Hellas)
After 300 years = 240Tt (58mbar at datum / ~116 mbar bottom Hellas)
After 400 years = 288Tt (69mbar at datum / ~138 mbar bottom Hellas)
After 500 years = 337Tt (81mbar at datum / ~162 mbar bottom Hellas)
After 600 years = 385Tt (92mbar at datum / ~184 mbar bottom Hellas)
After 700 years = 433Tt (104mbar at datum / ~208 mbar bottom Hellas)
After 800 years = 482Tt (116mbar at datum / ~232 mbar bottom Hellas)
After 900 years = 530Tt (127mbar at datum / ~254 mbar bottom Hellas)
After 1,000 years = 578Tt (139mbar at datum / ~278 mbar bottom Hellas)
After 1,000 years the atmosphere at the bottom of Hellas would be;
N2: 134 mbar (48.25%)
O2: 91 mbar (32.7%)
CO2: 35 mbar (12.6%)
AR: 18 mbar (6.45%)
This would be a breathable atmosphere (equivalent to 7,000m on Earth ... the death zone is said to start at 8,000m / 75 mbar O2), although you probably wouldn't want to spend more than a few days without supplementary oxygen.
Venus now has ~217Tt of water, up from ~5Tt originally, if they've cooled it down and sequestered much of the carbon atmosphere they now have enough water to cover the planet in 40cm+ of water. Mars has lost over 200Tt of water, but still has nearly 5,000Tt left, and has increased it's atmosphere by nearly 500Tt.
So first 100 years was spent warming Mars, next 1,000 years spent gradually pressurising higher elevations on Mars to above the Armstrong limit, and the next 2,000 years can be spent gradually oxygenating higher elevations to breathable atmospheres.
After 2,000 years = 1,061Tt (255mbar at datum / ~509 mbar bottom Hellas)
N2: 140 / 279 mbar (54.81%)
O2: 90 / 179 mbar (35.20%)
CO2: 17 / 34 mbar (6.61%)
AR: 9 / 17 mbar (3.38%)
Datum is now breathable (but not really "livable" yet), bottom of Hellas has partial pressure of Oxygen close to Earth (18% Vs 21%).
After 3,000 years = 1,544Tt (371mbar at datum / ~741 mbar bottom Hellas)
N2: 212 / 423 mbar (57.14%)
O2: 134 / 267 mbar (36.09%)
CO2: 17 / 33 mbar (4.48%)
AR: 8 / 17 mbar (2.29%)
You'd probably want to stop pumping oxygen into the atmosphere now. 26.7% O2 partial pressure at lowest elevations and 3.3% of CO2, much of which will eventually be photosynthesised into O2. <30% should be fine. At the datum O2 levels are equivalent to 3,800m on Earth. Highest peaks still require pressure suits, but probably not worth spending another 2,000 years importing nitrogen just to make mountains climbable without pressure suits.
There's a lot of technical issues that I haven't addressed here, but on a logistical level at least, I think that importation of nitrogen is plausible over 100 year+ timescales, and the good thing is that you don't have to wait a long time to see the benefits, every delivery slightly increases the land area of viable liquid water /survivable pressure / breathable atmosphere, so that people are motivated to continue the process over the centuries and millennia required.
Pages: 1
