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Thread: Living on Mars?

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    I imagine the most interesting aspect of colonization is how quickly colonists would become their own species. The gravity on the moon is so low that very large, low muscle humans would quickly become the norm. Less pressure on joints and heart could easily lead to 10+ foot tall humanoids who can't breed with Earthlings at all.
    Now if everyone could please "Sig" something along the lines of "Gosh 2D8HP, you are so very correct (and also good looking)", I think that would be good progress.

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    Quote Originally Posted by Leewei View Post
    Another one is colliding asteroids in orbit around Mars to produce a substantially larger moon, which would then jump-start convection in the planet's interior by way of tidal forces.
    Oh, there's an interesting idea. It'd take a hellishly large amount of asteroids, though, and I'm not sure how well they'd coalesce into a moon. Wouldn't you need to smack 'em hard enough to melt them together?

    Quote Originally Posted by Leewei View Post
    Until we can put structures on Venus that don't immediately melt into slag, we'd be stuck in orbit at microgravity.
    No, the plan would be to have balloons floating in 1-atm, rather than in orbit. I believe that at that altitude, gravity would still be pretty Earth-like, and the amount of sulfuric acid rain would be manageable. What the people in said balloon cities would do to pass the time, though, that's where "having robots that can go down to the surface to mine" would come in.

    ETA:
    Quote Originally Posted by Tvtyrant View Post
    I imagine the most interesting aspect of colonization is how quickly colonists would become their own species. The gravity on the moon is so low that very large, low muscle humans would quickly become the norm. Less pressure on joints and heart could easily lead to 10+ foot tall humanoids who can't breed with Earthlings at all.
    I don't know about that. IVF would allow for a significant period of interbreeding even after the point where it becomes physically unfeasible.

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    Last edited by Grey_Wolf_c; 2017-12-13 at 01:52 PM.
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    Quote Originally Posted by Leewei View Post
    The atmospheric issue is brought on not by gravity, but by solar wind and very weak magnetosphere. Mars' gravity, as low as it is, can sustain an atmosphere with enough pressure to support life.
    Citation needed. The cause of atmosphere loss AIUI is the speed of gas molecules exceeding escape velocity, which is why all that's left is CO2 (which is heavy, and thus has a low enough velocity at current Martian temperatures that it doesn't exceed escape velocity). The kinetic energy of gas molecules depends on temperature, only, that's what temperature is, and thus the speed at a given temperature depends on the mass of the molecule. Hydrogen and helium escape from Earth because their velocity is above escape velocity, luckily hydrogen usually bonds with something else before that happens, but helium is rare and getting rarer.

    This is supported by the planet's own geological record.
    As guesstimated from Earth. It's possible that at some time a big comet, or a lot of littler ones dumped enough water there to make things flow, but how long that would last is debateable. There can be erosion from sandstorms, and we know there are quite a few of those.

    We'd still need to somehow produce enough of a magnetic field to deflect the erosive charged particles being kicked out by the sun. Fission plants powering a planet-wide electrical grid would be one possibility. Another one is colliding asteroids in orbit around Mars to produce a substantially larger moon, which would then jump-start convection in the planet's interior by way of tidal forces.
    The gravity is still too low.

    If Mars can sustain an atmosphere, warming is possible using carbon dioxide, methane, or other greenhouse gasses. Between the challenges of heating up or cooling down bodies in a vacuum, heating up is far, far easier to accomplish. (Note that the interior of Mars is toasty. The planet's core is still magma.)
    That's a very big "if".

    By comparison, Venus has an enormous amount of heat. Even with the sun's radiation blocked, the planet would need ages to cool down. This isn't a thousand year problem, but a million year one. Losing heat into a vacuum is just that slow.
    As I said, Earth loses 30 degrees celcius in six months, we have less cloud cover, but we aren't half that hot, we need a reasonable simulation of Venus' atmosphere to begin to guess what would happen. If the winds dropped, the back might freeze out too fast.

    Until we can put structures on Venus that don't immediately melt into slag, we'd be stuck in orbit at microgravity.
    Yeah, we need to get that temperature down, electronics without solder is difficult, iron would hold up, but the electronics would be a problem.

    I agree with the lunar outpost idea. The moon is certainly the next step in a logical progression from Antarctic stations and ISS. The challenges look similar to those presented by creating an outpost on another planet.
    It's the obvious first place to go after LEO.
    Last edited by halfeye; 2017-12-13 at 02:15 PM.
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    Quote Originally Posted by Grey_Wolf_c View Post
    I don't know about that. IVF would allow for a significant period of interbreeding even after the point where it becomes physically unfeasible.

    GW
    That is fair I suppose. I imagine the communities would seperate pretty quick though, as Mooninites couldn't survive on Earth and Earthlings would be tiny compared to natural Mooninites.

    Even 1 generation in would be a big difference, as the cartilidge in a Mooninite would fill with liquid and not compress during the day and would grow more during childhood.

    You might get a lot of old folk colonization as it would keep their mobilility more into old age though. The moon as a retirement center is the moat hilarious ending.
    Now if everyone could please "Sig" something along the lines of "Gosh 2D8HP, you are so very correct (and also good looking)", I think that would be good progress.

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    Quote Originally Posted by Tvtyrant View Post
    That is fair I suppose. I imagine the communities would seperate pretty quick though, as Mooninites couldn't survive on Earth and Earthlings would be tiny compared to natural Mooninites.

    Even 1 generation in would be a big difference, as the cartilidge in a Mooninite would fill with liquid and not compress during the day and would grow more during childhood.

    You might get a lot of old folk colonization as it would keep their mobilility more into old age though. The moon as a retirement center is the moat hilarious ending.
    I don't think it will happen that quickly, but once people begin to adapt to space, we've achieved it, the colonisation of space is begun, from then on, it's humans in space.
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    Quote Originally Posted by halfeye View Post
    As I said, Earth loses 30 degrees celcius in six months,
    Wait, what? You mean every winter? The heat wasn't lost, it just migrated South.

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    @halfeye:

    Fair enough to ask for citations:

    https://en.wikipedia.org/wiki/Atmosp...ape_mechanisms

    You're thinking Jeans Escape.

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

    NASA data shows that solar storms (i.e. lack of magnetosphere) are the culprit.

    Note that the gravity on Mars is significant (~3/8 G) and could hold a lot more of an atmosphere than Mars currently has. Intuitively, one would think Mars would hold a bit under half of Earth's atmospheric pressure based on gravitational difference. Maybe a bit less than half of that -- half the atmosphere pulled by half the gravity. Instead, it's a hair over half a percent of Earth's.

    Mars' geological record is hardly a "guesstimate".

    http://geology.com/stories/13/rocks-on-mars/

    Note the mudstone in the 2nd image. Mars certainly has had liquid water; the atmosphere must have been above water's triple point for a fair amount of the planet's history to produce this kind of rock.

    Earth's annual temperature cycle you reference is atmospheric. Venus's entire planetary mass is enormously hot. This makes it somewhat more efficient at radiating heat, but adds orders of magnitude to what must be radiated off to make the surface livable.

    TL/DR Magnetosphere, not gravity for Martian atmosphere. Venus takes far longer to cool than you indicate. Gravity's effect on human population is an important unknown.
    Last edited by Leewei; 2017-12-14 at 02:01 PM.

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    Quote Originally Posted by Bohandas View Post
    ...
    Didn't he also once say that he was legitimately worried about the world being overrun by evil robots like in The Matrix or Terminator?
    Then I don't think you understand what he's talking about. He's not talking about a Roomba or a RPV/Drone. Go do a little reading on Deep Learning machines. Sure, Deep Q only learned to play Pong and it took it a few hundred games to learn. But how quickly could a similar computer play a thousand games of Pong if allowed to run at clock speed? And then if it learned that self-survival might be important? What else might it learn?

    Quote Originally Posted by Rakaydos View Post
    You clearly havn't been paying attention to modern politics. 'Bots are already being used as a weapon to shape the way people think at a national level. Just because they arnt carrying a gun, doesnt mean they cant be used to change our way of life- just look at the Net Neutrality controversy.
    Our children will have to face the issue of computers that can learn faster than they can. And if those computers are connected to our existing computer controlled production facilities...

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    Quote Originally Posted by Grey_Wolf_c View Post
    Wait, what? You mean every winter? The heat wasn't lost, it just migrated South.

    GW
    I know it went. I suppose I don't care that much where it went, on the personal level. How did it migrate south (presumably north in the southern hemisphere)? The tropics don't get hotter in winter that I'm aware of.

    @ Leewei

    That Jeans escape thing does seem to be what I was talking about, I don't like that graph, Venus is way too cool, it's nearly Earth mass which is right, but it's temperature is 600+ degrees celcius, which ought to be about 900 degrees Kelvin, I'm not so sure Jupiter is that cool either.
    Last edited by halfeye; 2017-12-13 at 02:52 PM.
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    Quote Originally Posted by Grey_Wolf_c View Post
    Oh, there's an interesting idea. It'd take a hellishly large amount of asteroids, though, and I'm not sure how well they'd coalesce into a moon. Wouldn't you need to smack 'em hard enough to melt them together?
    Deimos + Phobos + various bodies from the asteroid belt. Some of them, such as Ceres, could instead be smacked into Mars to increase surface heat and water presence. Velocities involved would be enormous due to the planet's gravitational pull. Care would be needed to decelerate these bodies. Even a relatively small delta V between bodies translates into an enormous amount of energy (i.e. heat and ejected mass). Collisions would vaporize a fair amount of mass, which would then precipitate into a dust cloud. Over time, the dust would either settle onto Mars, or onto the new moon.

    Collisions with smaller bodies seem pretty ideal. The mass hitting the nascent moon would have its force dispersed into heat more than blowing bits off. With a regular enough stream of mass, the heat generated would melt the entire mass into a ball of slag.

    It's a neat idea which could work out well in the long run, but it's also enormously costly compared to the artificial magnetosphere idea (which also comes with a planetary energy grid).

    No, the plan would be to have balloons floating in 1-atm, rather than in orbit. I believe that at that altitude, gravity would still be pretty Earth-like, and the amount of sulfuric acid rain would be manageable. What the people in said balloon cities would do to pass the time, though, that's where "having robots that can go down to the surface to mine" would come in.
    Russia landed an explorer on Venus's surface. It died quickly after broadcasting a brief amount of image and technical data. The 870 degree Fahrenheit surface temperature simply does not allow for any modern mechanism to work.

    Those balloons would need a lot of redundancy. Buoyancy seems a lot less reliable than inertia for holding up an outpost.

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

    50kph winds and sulfuric acid clouds don't seem insurmountable. 1atm pressure, Earth-similar temperature, and Earth-similar gravity all look fairly favorable.

    I'm not convinced that Venus could be terraformed over the long run, but it absolutely has potential for the site of a manned research station. We'd need a heck of a good reason for humans to be there, though.
    Last edited by Leewei; 2017-12-13 at 03:15 PM.

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    Quote Originally Posted by Grey_Wolf_c View Post
    Oh, there's an interesting idea. It'd take a hellishly large amount of asteroids, though, and I'm not sure how well they'd coalesce into a moon. Wouldn't you need to smack 'em hard enough to melt them together?
    If you can get enough asteroids together that their gravitational effects would be significant enough to jump-start Mars' internal magma conveyor, I suspect they'll take care of smushing themselves.

    I have some significant reservations about restarting Mars' tectonic processes, though- the place had volcanoes ten times higher than everest, once upon a time, and I don't wanna poke that bear. I think inducing an artificial electromagnetic field would be much easier to control.

    However, if you're prepared to engineer megastructures on that scale... then it's probably easier to just erect greenhouse canopies across the surface as when you need to expand. That way you don't have to worry about losing atmo to space, or little things like dust storms, winter and unscheduled rain.

    No, the plan would be to have balloons floating in 1-atm, rather than in orbit. I believe that at that altitude, gravity would still be pretty Earth-like, and the amount of sulfuric acid rain would be manageable. What the people in said balloon cities would do to pass the time, though, that's where "having robots that can go down to the surface to mine" would come in.
    IIRC, the conditions on the venusian surface are so hellish that even robots don't even have an easy time operating- the lifetime of our probes so far has been on the order of hours, versus months or years for martian rovers. There are designs for refrigerating the electronics and so forth, but it still seems like a non-trivial technical problem to me.

    I don't know about that. IVF would allow for a significant period of interbreeding even after the point where it becomes physically unfeasible.
    I suspect that DNA tailoring and related technologies are going to render the question rather quaint long before you see much in the way of natural genetic drift.

    Hmm. I really have Alita on the brain these days.
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    Quote Originally Posted by halfeye View Post
    I don't like that graph, Venus is way too cool, it's nearly Earth mass which is right, but it's temperature is 600+ degrees celcius, which ought to be about 900 degrees Kelvin, I'm not so sure Jupiter is that cool either.
    I see what you mean. It appears the graph subtracts 273 degrees from Venus's surface temperature rather than adding to it.

    In any case, the second article, especially the NASA link showing the impact of solar storms on Mars, is what's critical. The first article merely provides definitions of the methods of atmospheric loss.
    Last edited by Leewei; 2017-12-13 at 03:14 PM.

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    Quote Originally Posted by halfeye View Post
    I know it went. I suppose I don't care that much where it went, on the personal level. How did it migrate south (presumably north in the southern hemisphere)? The tropics don't get hotter in winter that I'm aware of.
    I don't care how it got there - just that your claim that Earth lost 30K in 6 months is not true. The total heat reservoir of Earth did not go down by 30K, it just moved around where those 30K are at any given time.

    Quote Originally Posted by Leewei View Post
    Those balloons would need a lot of redundancy. Buoyancy seems a lot less reliable than inertia for holding up a city.
    Not having crunched the numbers, I think they'd come to be about the same level of overall reliability. The biggest issue for any orbiting craft around Venus is that it must spend half of its time Sun side, and that's gonna be a nightmare for reliability, I suspect. But I know little of this other than the "NASA actually proposed a floating city for Venus, and some argue it is simpler than landing on Mars". If you are interested in going deeper than that, I can't really rebut your arguments one way or the other; I simply don't know enough about it, and I am not in a position to learn it - sorry.

    Quote Originally Posted by Lacuna Caster View Post
    If you can get enough asteroids together that their gravitational effects would be significant enough to jump-start Mars' internal magma conveyor, I suspect they'll take care of smushing themselves.
    Yeah, but before we get there we'd have a 3-Body-problem from hell.

    Quote Originally Posted by Lacuna Caster View Post
    IIRC, the conditions on the venusian surface are so hellish that even robots don't even have an easy time operating- the lifetime of our probes so far has been on the order of hours, versus months or years for martian rovers. There are designs for refrigerating the electronics and so forth, but it still seems like a non-trivial technical problem to me.
    Well, yeah, it goes without saying that when discussing the viability of extraterrestrial construction, we always sooner or later hit a non-trivial technical problem. But the nice thing about those is that they might be difficult, but they are not unsurmountable (unlike, say, the tether material, which is so close to the edge of inviability that it might just be on the other side of it). It's not like I am suggesting we could set up a city-sized balloon in Venus next week.

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    Quote Originally Posted by halfeye View Post
    That's what I'm saying, we can make lightsails ten km wide with current tech, and self driving cars look as if they will be here very soon, so that's do-able, and we know that temperate regions drop in temperature 30 degrees centigrade on Earth in half a year, so getting the temperature of Venus down isn't a thousand year problem, though it's not a five week one either.

    Once the temperature is somewhere reasonable, plant life would love all the CO2, and bacteria would love the sulphur, then it's a matter of getting some water there, and then it'll be a nice place.
    Yeah, unfortunately, as Leewei touched on, the reason why Venus is so hot in the first place is because it's atmosphere is stuffed with very effective greenhouse gases, and it has a lot of volcanism, which suggests that even without sunlight it would take quite a while for surface temperatures to drop. It's an intriguing scenario, but I think you'd need to chemically modify the atmosphere first. I dimly recall someone proposing that you could seed the Venusian atmosphere with some kind of airborne algae that could sequester the carbon, but I think there's a critical shortage of water thanks to the sulphuric acid acting as a dessicant?

    As for Mars- I don't know what effects reduced gravity are likely to have on foetal development, but on that score I'd be more concerned about perchlorates in the soil, which we know have an impact on thyroid function. Parts of Mars can actually reach 25 degrees C in the summer, so I'm not too worried about average temperatures if you stay underground or build greenhouse structures. And Mars appears to have all the elements necessary for life, along with substantial mineral deposits for building projects. Sure, it'd be tough, but once people are there I think they'll figure it out. Necessity and invention, yo.
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    Quote Originally Posted by Grey_Wolf_c View Post
    The biggest issue for any orbiting craft around Venus is that it must spend half of its time Sun side, and that's gonna be a nightmare for reliability, I suspect.
    Venus isn't *that* much closer to the Sun than we are--in fact, the temperature at the cloud tops is around -70C, because the albedo of the clouds are so high they reflect away most of the incoming heat. It's the small remnant which gets trapped *under* the clouds that gives rise to the hellish temperatures at the surface. It's also worth noting that the Magellan spacecraft which was sent to map Venus' surface via radar was orbiting the planet for more than four years without any major reliability issues--the main reason they had to terminate the mission was because the solar arrays had degraded to the point they couldn't reliably power the spacecraft, so if our hypothetical Venus orbiter used something other than solar cells to power it, it could presumably last much longer.

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    Quote Originally Posted by Grey_Wolf_c View Post
    Well, yeah, it goes without saying that when discussing the viability of extraterrestrial construction, we always sooner or later hit a non-trivial technical problem. But the nice thing about those is that they might be difficult, but they are not unsurmountable (unlike, say, the tether material, which is so close to the edge of inviability that it might just be on the other side of it)
    Yeah, I suppose that's true- even a 50-day robot working life might be long enough to be useful if you have a service/repair station in orbit and a lot of initial capital investment, and one imagines that material sciences will advance a bit in the next few centuries.

    Aside from the gravity, though, I'm just not seeing a major cost/benefit advantage? I guess if it turns out that < 1g is really seriously bad for long-term human health, you could make an argument for it, but I'd almost incline to genetically modify humans to suit Mars before tackling the challenges of terraforming Venus.
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    Quote Originally Posted by factotum View Post
    Venus isn't *that* much closer to the Sun than we are--in fact, the temperature at the cloud tops is around -70C, because the albedo of the clouds are so high they reflect away most of the incoming heat. It's the small remnant which gets trapped *under* the clouds that gives rise to the hellish temperatures at the surface. It's also worth noting that the Magellan spacecraft which was sent to map Venus' surface via radar was orbiting the planet for more than four years without any major reliability issues--the main reason they had to terminate the mission was because the solar arrays had degraded to the point they couldn't reliably power the spacecraft, so if our hypothetical Venus orbiter used something other than solar cells to power it, it could presumably last much longer.
    Yeah, that wasn't the issues I had in mind. More radiation exposure for any humans on board the hypothetical Venus orbital base. As someone posted, there is a weird pseudo-magnetic field on the far side of Venus (plus, you know, having a planet in the way is probably good protection too).

    Quote Originally Posted by Lacuna Caster View Post
    Aside from the gravity, though, I'm just not seeing a major cost/benefit advantage?
    But that's the issue that started this all: is there really a major cost/benefit to any extraterrestrial base right now? It really always comes down to "putting our eggs in more than one basket", in which case the benefit is infinite and cost is therefore irrelevant to some (including, let me be clear, me), but the benefit is 0 and costs therefore excessive for others.

    I don't have an answer to this. I have not seen anything that suggests that having a colony in mars or Venus would be economically beneficial. There might be some economic benefits to a Moon base, but that'd never be really self-sufficient, and it's not much of a second basket when anything that destroys Earth would probably take the moon with it as well. So, yeah, I admit that my idea of a floating Venus colony with quasi-magical mining robots its probably more sci-fi than anything else.

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    Quote Originally Posted by Lacuna Caster View Post
    And Mars appears to have all the elements necessary for life, along with substantial mineral deposits for building projects. Sure, it'd be tough, but once people are there I think they'll figure it out. Necessity and invention, yo.
    If you dig around in the right areas, Mars has uranium. (Some evidence even suggests a naturally triggered runaway fission reaction on the red planet in the distant past.)

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    Quote Originally Posted by Grey_Wolf_c View Post
    Oh, there's an interesting idea. It'd take a hellishly large amount of asteroids, though, and I'm not sure how well they'd coalesce into a moon. Wouldn't you need to smack 'em hard enough to melt them together?
    Probably about all of them, if it's possible at all. Ceres contains a quarter of the mass of the main belt, and it's quite small compared to our moon.

    And as you said, getting them to stick together is going to be a bit of a trick. The escape velocity on Ceres is about 500m/s. That's quite fast even compared to say the speed of sound (+-350m/s), but I'd still worry that landing nine asteroids gently and screwing the tenth attempt up would turn it into a bowling party. Getting the combined body to orbit Mars (after you've managed to weld them together or wait long enough for that to happen by itself) is also going to take a bit of energy.

    But hey, if it saves more energy in the long run... I'm just not sure if giant engineering projects like this will ever be preferable to just building large space ships for people to live in. Maybe if you specifically want something from Mars, you can't automate the process far enough and you want the circumstances to be nice for the employees and closed Mars habitats are not an option for some reason (like you're mining using massive earthquakes or something.)
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    Quote Originally Posted by Grey_Wolf_c View Post
    I don't care how it got there - just that your claim that Earth lost 30K in 6 months is not true. The total heat reservoir of Earth did not go down by 30K, it just moved around where those 30K are at any given time.
    Yes, the overall exposure of the Earth to sunlight is pretty static due to our orbit being nearly circular. The south pole gets warmer when the north pole gets cooler. This is due to the axial tilt, and the relative amount of solar heating arriving being lower in winter than in summer. It gets down to freezing in winter here. It gets up to 30 degrees Centigrade in summer. That's a 30 degree swing, it's local to parts of each hemisphere in each respective winter-summer cycle, but it's a significant effect produced as far as I know solely by varying solar illumination. There is still some sunlight here in winter, days last 8 hours instead of 16, and the angle of the sun is much lower, but it still shines, and it's still too bright to look at. Cut it out completely and you would get a much more significant effect. For Earth, I don't think I would recommend a sunshade, winters are cold enough here anyway, but a limited sunshade is definitely one possible solution to global warming. Thinking further, an eqatorial sunshade that cooled the tropics but allowed the temperate zone to rise in temperature might be nice, but it probably wouldn't work out.
    Last edited by halfeye; 2017-12-13 at 05:04 PM.
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    That 30 degrees Celcius is fair to use -- in fact, it's probably understating the heat our planet radiates into space by a fair amount. Consider the temperature drop each night following sunset.

    That said, ground temperature is far more constant, and solid matter holds far more heat than a gas at a similar temperature. According to Google, Venus is 10,000 times the mass of its atmosphere. Venus's atmosphere is about 100 times as massive as Earth's, for that matter. Surface area is similar to Earth, but the total amount of heat stored on this pizza oven of a planet is staggeringly high.

    If you only need to radiate off 1% of Venus's total heat (very dubious), you'd need 10,000 years to drop 30 K. (1% cancels out the x100 atmospheric size, leaving 10,000 times the mass.) Assuming you can make the planet somehow livable at 600 K, it would need to radiate for 100,000 years. 200,000 years gets you to a comfortable 300 K.

    This is just spitballing, of course. Hotter bodies radiate heat faster, it likely will take more than 1% of the mass cooling to make Venus's surface livable, and the heat radiated annually from Earth is probably more than 30 K. Still, this illustrates an optimistic time frame of many multiple thousands of years for Venus to become habitable.
    Last edited by Leewei; 2017-12-13 at 06:01 PM.

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    Quote Originally Posted by Leewei View Post
    That 30 degrees Celcius is fair to use -- in fact, it's probably understating the heat our planet radiates into space by a fair amount. Consider the temperature drop each night following sunset.

    That said, ground temperature is far more constant, and solid matter holds far more heat than a gas at a similar temperature. According to Google, Venus is 10,000 times the mass of its atmosphere. Venus's atmosphere is about 100 times as massive as Earth's, for that matter. Surface area is similar to Earth, but the total amount of heat stored on this pizza oven of a planet is staggeringly high.

    If you only need to radiate off 1% of Venus's total heat (very dubious), you'd need 10,000 years to drop 30 K. (1% cancels out the x100 atmospheric size, leaving 10,000 times the mass.) Assuming you can make the planet somehow livable at 600 K, it would need to radiate for 100,000 years. 200,000 years gets you to a comfortable 300 K.

    This is just spitballing, of course. Hotter bodies radiate heat faster, it likely will take more than 1% of the mass cooling to make Venus's surface livable, and the heat radiated annually from Earth is probably more than 30 K. Still, this illustrates an optimistic time frame of many multiple thousands of years for Venus to become habitable.
    Looking at wikipedia, there is an up to 25 K variation in some parts of the US over the course of a single day. Now, the Venusian atmosphere is currently very well mixed such that there doesn't seem to be any difference between day-side and night-side temperature wise, so completely blocking sunlight from Venus would probably only result in twice as much energy leaving as currently (using a really bad simplifying assumption about how planetary temperatures work).
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    Quote Originally Posted by Leewei View Post
    That said, ground temperature is far more constant, and solid matter holds far more heat than a gas at a similar temperature. According to Google, Venus is 10,000 times the mass of its atmosphere. Venus's atmosphere is about 100 times as massive as Earth's, for that matter. Surface area is similar to Earth, but the total amount of heat stored on this pizza oven of a planet is staggeringly high.
    The Earth is flipping hot too. Lava comes out at about 1k Celcius. The temperature that needs to go at Venus is in the atmosphere, and maybe in the crust.
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    Quote Originally Posted by Leewei View Post
    That 30 degrees Celcius is fair to use -- in fact, it's probably understating the heat our planet radiates into space by a fair amount. Consider the temperature drop each night following sunset.
    Much the same way that the summer winter cycle represents a local change in thermal energy storage from the northern to southern or southern to northern hemispheres the day-night cycle represents a local change of thermal energy that is constantly moving in the opposite direction of the apparent direction of the sun.

    There's also the matter of how temperature isn't heat, and if we were concerned about heat we'd be using a power unit. That also makes our lives easier, as earth is very close to an equilibrium between heat out and heat in (it's every so slightly off, hence warming), and you can basically neglect everything but direct sunlight for heat in and call it a day.

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    You're not going to dump *any* heat from Venus until you strip off its atmosphere. At the moment, as I said above, the actual amount of solar radiation reaching the ground is less than on Earth because of the amount that gets reflected away by the clouds; it's purely the greenhouse effect which keeps temperature so high. Therefore, you've got to remove the clouds before you can start radiating heat into space, and that's not going to be easy!

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    Quote Originally Posted by factotum View Post
    You're not going to dump *any* heat from Venus until you strip off its atmosphere. At the moment, as I said above, the actual amount of solar radiation reaching the ground is less than on Earth because of the amount that gets reflected away by the clouds; it's purely the greenhouse effect which keeps temperature so high. Therefore, you've got to remove the clouds before you can start radiating heat into space, and that's not going to be easy!
    The temperatures on Venus are fairly stable, therefore heat in equals heat out. Based on some sketchy numbers I found on the internet, Venus has an albedo of .8, so only 20% of the solar energy hitting it is absorbed. Thus it is absorbing 59,794,200,993,800,000 J per second and emitting 59,794,200,993,800,000 J per second. If we removed solar input, how long would it take the atmosphere to drop 10 K?
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    Quote Originally Posted by halfeye View Post
    The Earth is flipping hot too. Lava comes out at about 1k Celcius. The temperature that needs to go at Venus is in the atmosphere, and maybe in the crust.
    The calculations I put up included the assumption that we'd only need to cool 1% of Venus's mass - the atmosphere and the crust.

    Good points from Knaight and Rockphed regarding both planets being essentially at thermal equilibrium.
    Last edited by Leewei; 2017-12-14 at 10:29 AM.

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    Quote Originally Posted by Leewei View Post
    The calculations I put up included the assumption that we'd only need to cool 1% of Venus's mass - the atmosphere and the crust.
    I did like the idea of that calculation, but I'm pretty sure that the crust is a lot less than 1% of Venus's mass. Earth's crust is on average something like 20 miles thick, call that 40km to be generous. Earth is 6,300 km in radius, so (approximating wildly) the crust is something like 0.3% of the volume, we don't need Venus's crust to initially be quite that thick, though it would be nice if it dropped to the right sort of temperature reasonably quickly.
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    Venus doesn't have plate tectonics, though, so the crust will tend to stay in one place rather than moving around as it does on Earth--that gives the heat more chance to seep down into the depths.

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    @halfeye:
    You're right that the interior of our planet is enormously hot -- moreso than the surface of Venus, if you go down far enough.

    Our lithosphere is about 2% of planetary mass and has an average temperature of around 400 C. This still is in the same order of magnitude as my earlier very rough estimate (1% at 300 C). That is, around a hundred thousand years to cool down.

    If you want to bring this value down, I'd suggest going after the heat radiation and heat storage (as opposed to temperature, which we've been covering so far).

    I'd be surprised if we end up at 100,000 years on the dot; still, you need to somehow decrease this by four orders of magnitude to make the endeavor worthwhile.

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