I wonder if Venus could be terraformed via a sun shield placed in orbit around it. How big would it have to be to reverse the runaway greenhouse effect?
Part of the problem is having too much atmosphere. In the original Cosmos Carl Sagan talked about a hypothetical solution where we capture asteroids, and throw them at Venus in such a way that they just nick the atmosphere and knock large quantities of atmosphere out into space. One you reduce atmospheric pressure to a certain level, things could become habitable.
Then throw in iron form the atseroid belt to react with it to form carbonates. Venus is dry so brining in hydrogen form the outer planets would be necessary anyway to form wate r and thta will account for a good bit. Garden the surface so subsurface rocks which might react with the atmosphere cna absorb some. (Assumign the subsurface rocks are thta reactive.) Scoop it off with smaller versions of the same scoops used to harvets hydrogen from the gas giants.
Couldn't we just build a MegaMaid and suck the atmosphere out? If we're going to go sci-fi, it seem easier to hoover it out than capture an asteroid and nick the atmosphere just right.
I’ve read that a large asteroid could be positioned at a particular Mars L point and it would protect the planets atmosphere from being stripped by the sun.
That would require a lot of energy to ensure the gasses escape Venus' gravitational pull, which would in turn effectively be a rocket. So then we'd be adjusting to ensure we don't mess with Venus' orbit too much.
Venus outweighs its atmosphere by about 10,000 times. This is actually less than I thought -- for comparison Earth outweighs its atmosphere by over 1,000,000 times, which is still far less than I would have guessed.
Venus's escape velocity is less than 1/3rd of its orbital velocity. According to google, Venus's orbit, despite being very circular, causes its velocity to vary by a KM/s from aphelion to perihelion.
So I believe you could send all of Venus's atmosphere off permanently into space at the cost of about 1/30,000th of Venus's orbital velocity, meaning you could very slightly circularize its orbit further.
I thought the Venus theory was runaway greenhouse driven initially by water vapor. Going off memory, H2O is roughly 10 times as effective a greenhouse gas as CO2, with Venus being closer to the sun A larger percentage of water ended up in vapor form, leading to a feed back loop where the increased heat pushes more water to vapor leading to more heat, eventually liberating the co2 from the rock, making everything worse, ending up with the current situation where venus has way too much atmosphere.
Which is the long way to say, I think there is a lot of water on venus.
Moreover, I think Venus has lost most of its hydrogen to space, so you can't even make water anymore. Hydrogen escapes the atmosphere relatively easily for Earth- and Venus-sized planets[1], and the vaporization of all the water and subsequent disassociation[2] of H2O allowed the hydrogen to escape into space.
Earth's oxygen rich atmosphere is really important here-- any free hydrogen can readily combine with the free hydrogen, decreasing the chance of any being loss.
According to that wiki article, the hydrogen was mostly lost in the form of water vapor. The hydrogen and oxygen in the magnetotail are in almost a perfect 2:1 ratio. At least,
> Currently the main ion types being lost are O+, H+ and He+. The ratio of hydrogen to oxygen losses is around 2 (i.e. almost stoichiometric for water) indicating the ongoing loss of water.
Also Earth didn't have an oxygenated atmosphere until relatively late, a couple billion years in, so I didn't know if that could be the thing that saved it.
I don't have primary sources, unfortunately -- I'm recalling something I read in _Oxygen_, which I found reassuring. It said that, one of the benefits of our oxygen-rich atmosphere was that we would lose an insignificant amount of hydrogen/water over the next billion years. It's one of those things that doesn't actually matter to me in my daily life, but I still find comforting, so it's stuck with me.
I recall one of the plans being to use the sun shield to entirely freeze out the atmosphere, then use a mass driver to chuck most of the CO2 into space. I don't recall exactly where that was supposed to be on the feasible to scifi spectrum.
I'd rather try to keep the carbon around for organic molecules. Are we sure we can't get in enough H2O and N to balance it out and build a nice thick biosphere?
I guess I'll count that as another reason to prefer managing it in situ. But it might be fine, actually? Slow re-accretion can probably be managed by whatever terraforming process we've kickstarted while most of it was gone.
Oh wait, I remember the plan, ship it to Mars so they can have some decent atmospheric pressure.
Mars could use only a small fraction of it. If the entire atmosphere of Venus were moved to Mars, the surface pressure there would be 120 bars (more at the lowest point).
1. "Humidify" the atmosphere by crashing comets into Venus. This will also allow us to create a temporary "cloud" around Venus that can shield it from the Sun and lower down the temperature.
2. Once the temperature is low enough, Venus will get oceans on its surface.
3. At this point, CO2 can be split into carbon and oxygen. Oxygen will be immediately bound by the huge amount of under-oxidized iron on the surface, and carbon can be buried under the new ocean. Essentially, carboniferous age for Venus.
4. Once this is done, the atmosphere will be mostly nitrogen (at ~3 bar) and people could live there with just respirators. Eventually, once the surface iron is oxidized, the atmosphere can even be made breathable.
Apparently, this can be done within 2000-5000 years without any exotic-level engineering.
My understanding is that it was water that started the whole thing. water vapor is about ten times as effective a greenhouse gas as co2. and the runaway heat started with too much water vapor(closer to to the sun I think), leading to more heat, leading to more water vapor. eventually it got hot enough to start liberating co2 out of the rocks. leading to the current situation today where venus has way too much atmosphere.
Which is to say, putting a ring around venus to block the sun may have merit, but adding more water sounds like pouring petrol on a fire.
Depending on a size, probably on the order of tens of thousand.
Comets in the Oort cloud take very little energy to put on a collision orbit, the Sun barely holds them gravitationally, orbital speeds in the Oort cloud are measured in _meters_ per second. So they require (relatively) little energy to put them into a required orbit. It might be doable with just regular thermonuclear charges.
It will then take these comets more than a thousand years to "fall" from the Oort cloud.
If you're interested in human habitation of Venus overall, you may find it interesting to learn Venus is probably preferable kept at about its current temperature or only made a little colder.
See, the atmosphere at ~50 altitude... happens to be about 1 bar (which happens to be Earth's atmospheric pressure ASL)... and happens to have temperatures that can support human and plant life!
And better still, the atmosphere being mostly co2 with a little nitrogen actually means normal Earth air is a lifting gas! Starting to see where this is going?
It's not too hard to imagine the skies of Venus full of floating habitats that move to stay in the sunlight, or occasionally dock with tethers or balloons carrying cargo from extremely reinforced mining facilities deep underground (where they could be much more protected most of the time from the pressure/temperature/corrosion) -- a future where people (or machines!) might scoff at the idea of cooling off Venus and losing out on such an excellent habitation zone, one which could also fairly easily support elevated runways or launch platforms to more cheaply reach space from.
With Venus also having 91% of Earth's gravity, and those atmospheric conditions at high altitudes that add some radiation shielding and would probably let a human worker only need a very limited suit more akin to a hazmat or firefighting suit with SCBA to work outside habitats... Venus is actually easily the single best planet for humans to live on after Earth!
(Can you tell I'm writing a story set there? Hehehe)
Haha, i totally feel that. Maybe people will have little personal balloons for emergencies like that :p
At the same time, do consider how you already count on conventionally supported structures like bridges, buildings, tunnels, etc. not to have any defects or design flaws. Or once-in-100-years storms or earthquakes.
This magnifies further if you've ever flown on a plane or sailed on a ship. It only takes the right series of failures to be plummeting to the bottom. Now imagine people who spend months or years counting on technology and redundancy to keep them alive in space, and might expect to do so indefinitely.
You need to give us more. I feel that just the heat is a tricky problem, even at 50km altitude. Anything todo with Venus is very much scifi at the moment. It might be easier than a moon base but we can not know.
Oh it wouldn't be easier than a moon base or simple orbital habitats. And as for Venus being scifi, anything to do with space colonization period is scifi right now; humans haven't even stepped foot on another celestial body of any kind in over half a century.
Rather my meaning was that it's (a little shockingly) the best suited planet for humans in terms of most closely and reliably resembling conditions humans could survive in, which relates to the terraforming notions I was replying to.
It'd be overwhelmingly harder to make all of Venus Earthlike than to just use the existing relatively Earthlike regions of the upper atmosphere to our advantage along with their unique properties. Cool off Venus and you just get a big ocean of liquid or frozen co2 to have to deal with after a loooong time and a lot of construction. Keep it like it is and a fraction of the resources/effort will yield far more utility while we can still enjoy a segment of the atmosphere.
Isaac Arthur on YouTube makes videos on sci-fi ideas that we might be able to do within the laws of physics, albeit not with today's technology. He did a video on Colonizing Venus some years ago, and an updated one a few months ago, and some others around colonisation and teraforming of the planets in the Solar System:
If the commenters are discussing diverting enough meteors to terraform Venus, there's enough fantasy to consider using nukes to apply the necessary torque to speed the orbit up
With that much atmosphere that’s a lot of tidal forces too, if you just get some I to orbit.
But the question. Is do you spin it backward or slow it down to spin it the right way, creating a situation where one side of the planet always faces the sun for a while. Might be an opportunity to freeze and cart off the other side of the atmosphere…
