# Venus vs Mars for colonization

Why is Mars getting so much attention vs Venus, which to me seems like a much more attractive option, in regards to habitability.

I've read that the upper atmosphere of Venus has the most Earth-like conditions in the solar system, also terraforming seems pretty straightfoward.

1. Mine CO2, Water (from sulfuric acid), and necessary "fertilizers" from the atmosphere
2. Mine acidic salts from the surface to make more water
3. Continue until temperature lowers.

The ease of high(er) pressure environments vs low pressure environments in regards to habitat size, redundancy, and safety in general.

Also the propellant needed to land on the surface of Mars vs the near zero amount of propellant needed to deploy vehicles in the atmoshpere of Venus.

Not sure if this is allowed but Convince Me

• PBS Space Time did a video about this. Worth a look. Jun 11 '18 at 20:55
• Venus landers go dark quickly: "The spacecraft was designed to last about half an hour on Venus' harsh surface, but sent back data for more than two hours after its landing March 1, 1982. Since no lander has ventured on to Venus since the 1980s, the Venera program's images of the surface stand as the best close-up record of the planet today." Curiosity has existed for much longer. Terra-forming, isn't really considered as a valid mission plan yet (for either of the planets). We're doing basic reconnaissance. Recon is easier on Mars, therefore, Mars. Not really sourced enough for an answer tho. Jun 12 '18 at 19:41
• Your ability to sustain a colony without any mineral resources from the surface will be limited, not to mention the complication of deploying giant balloons during descent for every incoming transport. Also, Venus is much more difficult to launch from than Earth, since not only do you need a similar sized multi-stage rocket, but you need to launch it from an floating platform. Jun 13 '18 at 22:35
• Number of permanently airborne installations on Earth: 0. "easy" is a big overstatement. Aug 30 '18 at 19:56
• Which are those fertilizers in the atmosphere ? Will there be water in those salts at 462 $^0$C ? Dec 22 '18 at 12:54

The reason Mars gets more attention than Venus is because we could walk on Mars. Our current technology can handle Mars. Venus on the other hand everything dissolves in a few hours from the heat and acid which makes it a terrifying planet to visit.

But on the subject of terraforming. Terraforming is still very much sci-fi and far off from any fact. We are talking about resource allocations on a planetary scale. But I have been looking at both and I too agree that Venus is more terraformable than Mars. Unlike Mars which has a litany of problems to overcome, Venus has just one, it is too hot.

But geologically and chemically Venus has more favorable conditions than Mars.

But for a species that is currently having a heat crisis of its own homeworld, I think we are far off from being able to fix that.

• If terraforming were so extremely simple as to only increase the CO2 ratio from 0.03% to 0.04% and all of the doomsday horrors that theologian Al Gore preached will have come true already today (did they?), then we could easily turn Mars into a second paradise. Mars is popular because Hollywood directors find it to be a better scene for their sci fi movies. And because Elon Musk is dead set on becoming its first settler. Not because its fun or practical or profitable. But because that would for ever make him the most famous human being that ever lived. Even aliens would take notice. Dec 22 '18 at 19:19
• Terraforming Mars and terraforming Venus are, I'd say, both roughly similarly hard. The chief problem in each is atmospheric mass, secondly composition: too little in the first case, and too much in the last case. Although the amounts by which each are so are, of course, different. But the answer is on the order of magnitude of at least $10^8\ \mathrm{Tg}$ in the easiest case for mass change amount (Mars). That's equal to hundreds of thousands of comets. Jun 23 '19 at 5:02
• @LocalFluff : The action of a small $\mathrm{CO_2}$ increase on Mars versus on Earth cannot be compared - at all. The two planets are dramatically different. The very first thing you need to note, out of many , is the vastly differing thermal inertia. Then comes that Earth has a very significant reservoir of water at the surface and Mars doesn't. Then ... Jun 23 '19 at 5:04
• Comments are not for extended discussion; this conversation has been moved to chat. Jul 2 at 3:37

Leaving aside the terraforming question, having a floating habitat is non trivial since pretty much the only thing that is earthlike at the proposed altitude is the temperature. The pressure is very close to the death zone, the winds are cyclonic and up to 100m/s and the atmosphere contains sulfuric acid.

This can work for a scientific mission where you arrive, deploy a limited lifetime balloon and abort to orbit when resources run out, you get blown into a cyclonic region or anything else goes wrong but a permanent habitat has to persist hopefully forever in that environment and becomes a lot more complicated, where the need to remain afloat at an altitude approximating 18000 feet on earth while surviving turbulence means that your weight will be critical (think living in an RV/caravan, not Bespin mining station).

There are some things that will kill you on the moon/mars but not Venus (lose of power to heating/cooling, and leaks will be slightly less urgent) but you also do not have handy access to a surface to keep spare parts on, mine from, bury your reactor in or just to keep your two domes in the same position with respect to each other.

• A floating habitat could be easily pressurized with the needed oxygen. Towards the poles zonal winds diminish in speed to almost zero. mps.mpg.de/phd/theses/… page 16,17 Dec 22 '18 at 12:45
• "easily" is not a word often used when referring to building floating habitats on another planet. Dec 22 '18 at 15:11
• wouldn't designing larger habitats with more buoyancy allow for more control and stability? instead of building like a compact submarine, you could build like a large cruise liner. Dec 23 '18 at 16:24
• Correct me if I'm wrong, but I thought the "death zone" was specific to Earth. The lower pressure means it is harder to get oxygen, but with supplemental oxygen this is avoided. Obviously on Venus one would be using supplemental oxygen.
– ben
Mar 3 '19 at 1:23
• @GremlinWranger oh yeah totally agree that the issues are usually understated and you did a good job outlining that. Was just curious about that one specific point. I don't know of any reason humans can't exist at ~500mbar other than the whole "needing to breathe" thing.
– ben
Mar 3 '19 at 3:04

I agree with some of the comments, terraforming should not be considered a serious target at this early stage of solar system colonization.

Both Venus and Mars have their problems, but what make the real difference is our lack of experience in missions that are not surface-based, since on Venus we should colonize the upper atmosphere layers. With Mars we can reuse what we learned from the Moon.

Terraforming:

Terraforming is not necessary for colonization, but: Venus requires importing about 40 quadrillion tons of hydrogen to lock up enough of the excess carbon and oxygen in its atmosphere in the form of water and biomass before its atmosphere can be thinned down enough to make the surface easily survivable.

Mars may have enough trapped volatiles to allow walking around on the surface in an oxygen mask, just by warming the planet up. A low-pressure breathable oxygen atmosphere could be built using oxygen sourced from rocks, with a byproduct being enormous quantities of metals and silicon.

Transport:

Colonizing anywhere is going to involve moving large amounts of material, and ideally you'll want to get multiple trips out of the spacecraft used for the job.

Landing large amounts of mass on Venus requires heat shields and parachutes, and enormous air-deployed balloons if you want to avoid the surface.

Venus has nearly as deep a gravity well as Earth, and a much denser atmosphere. Launching spacecraft from Venus requires a multi-staged launch vehicle just like you'd need on Earth, except it needs to launch from a balloon floating in the atmosphere. A fully reusable Venus transport is basically impossible with any available technology.

Landing large amounts of mass on Mars requires heat shields and rocket propulsion. Small payloads can get some use from parachutes.

Launching from Mars is far easier than launching from Earth or Venus. A spacecraft that can launch from LEO and land on Mars can easily have the propulsion capabilities needed to launch back to Earth for another mission, if it can refuel on the surface. And Mars has the raw materials needed to produce propellants.

Habitation:

Venus would require buoyant habitats drifting through skies filled with concentrated sulfuric acid mist. Surface robotics would have to be built to tolerate conditions where common solders melt, aluminum alloys soften, and most plastics evaporate.

Mars requires little more than a pressure vessel and the life support you'll need anywhere. There'll probably be active temperature control, but it would be feasible to keep things survivable passively. In terms of temperature and radiation, it's a better environment than LEO. Mining equipment can use much the same materials and designs as it does on Earth...the big difference is that you'll probably run a coolant loop through a radiator for a lot of things that would use air cooling on Earth.

Resources:

The only things easily acquired on Venus are components of its atmosphere: CO2, N2, SO2, H2SO4. The surface appears to be entirely volcanic, basalt as far as the eye can see (about 3 km under surface conditions).

Mars has a lot of basalt too, but it has had enough tectonic activity to give it a more Earthlike variety of igneous and metamorphic rocks, and a long enough history of liquid water to form all sorts of interesting concentrated minerals. There's clays, useful salts...one of our rovers got stuck in a patch of powder that appeared to be iron sulfate, and there's going to be similar deposits of copper minerals and other stuff you're going to need to actually build anything.

• Would any of that hydrogen be locked in the crust? Nov 10 at 23:16
• @FamousJameis are you asking if Venus has hydrogen locked in its crust? Not useful amounts. Terraforming it is going to require undoing billions of years of loss of hydrogen from its upper atmosphere to the solar wind while water was being baked out of the surface rock by high temperatures. Its thought that the periodic volcanic resurfacing events and the lack of plate tectonics may be due to a lack of water in its crust making it too rigid to subduct. Nov 10 at 23:30

with regards for surface mining, it wouldn't be impossible to design mining drones that work on the surface.

No. Currently, any continued operation would require continuous use of large amounts of consumables - say, evaporating water - to sustain cooling of such a drone. Sustained operation is outright impossible.

Venus surface temperature: 475 degrees Celsius src.

State-of-the-art vapor-compression refrigeration systems (most energy-efficient method we know) have coefficient of performance equal about 4.5 src - that means for 4.5 kilowatt of heat energy transferred, they produce 1 kilowatt of waste heat. The typical temperature gradient achievable at this energy-optimal operation is around 65 °C (same source).

To drop the temperature from Venus' 475 °C to something operational, we need to pass the heat through 7 stages of cooling (65*7 = 455, 475 - 455=20; we might get away with 6 if we design the systems to run in toasty 85 °C, but let's assume 7 stages):

Unlike all cryo-coolers that operate on Earth, in ambient temperature just fine, this thing needs to account for all the heat produced by its own operation.

That means, our nice COP of 4.5 kW transferred for 1 kW of waste heat produced means in fact that 1 kW eats into our heat budget - we need to transfer it out, and subtract it from what we have at our disposal, to cool the control systems. We're left with 3.5 kW for actual operation needs - and that's just from one motor, one stage.

After four stages, we've produced 4 kW of waste heat, we have 0.5 kW left to cool the system, and we've dropped the temperature from 480 to 220 °C. That's still too hot to operate.

If we add the remaining three stages, out cooling system produces 7 kW of waste heat while still removing 4.5 kW - it's no longer cooling the drone, it heats it.

If we managed to get a cooling stage of COP=7, then we'd (barely) break even, 7 kW produced, 7 kW emitted, no room left for systems - so in fact the efficiency must be higher than that. The maximum theoretical COP for cooling is 7.8 , and we're nowhere near technologically to reach it. And even if we did, that would leave 10% of the drone's energy usage to everything else than cooling - e.g. mining!

• Although Venus's atmosphere is not very suitable for it, couldn't the cooling system be combined with radiative cooling ? en.wikipedia.org/wiki/Radiative_cooling It's proposed as one of the methods for terraforming en.wikipedia.org/wiki/… Sep 8 at 9:08
• @Cornelis Radiative heat transfer in dense medium is completely overwhelmed by convective/conductive heat transfer. The suggestion on Wikipedia is how to cool Venus, not equipment on Venus. Your radiator wouldn't be running any cooler than the surrounding atmosphere, it would just absorb heat from it and re-radiate it into space.
– SF.
Sep 8 at 9:17
• Right above the radiative cooling layer you could place an isolated gas layer to greatly reduce the convective/conductive heat transfer.. Sep 8 at 9:26
• @Cornelis This to work would need to be a vacuum layer, otherwise the gas layer will happily conduct heat from whatever "screen" is shielding your radiator. And that means a transparent shield that can withstand 92 bars pressure differential. Such mass of glass or similar material will be radiating a lot of heat it acquires through conduction, right into our radiator. The idea has some merit, but it won't be sufficient alone - it might allow skipping a stage of a vapor-compression cryocooler, but there's no way you're getting >400 degrees gradient between the "shield" and the radiator.
– SF.
Sep 8 at 9:34
• @Cornelis Yes, and I believe Venus will be colonized and terraformed... maybe in 500 years. Maybe more. Humanity slowly chipping away at the obstacles. Regardless, it's a task vastly more difficult than colonizing Mars.
– SF.
Sep 8 at 10:04

Venus would be easier for multiple reasons. It takes less fuel and time to get there. Hydrogen is much more buoyant there than on Mars and can be used to float a craft 90 miles above the surface where atmosphere pressure is equal to Earth and it's only 120-140 degrees F. Building materials that are not corroded by sulfuric acid are available. You will be able to bring larger payloads with you and Earth can send more unmanned payloads per dollar and park them in orbit until they are needed. 3d printing will make available all the spare parts you need. The reason we are more likely to to Mars first is because the long term habitation of it is more feasible, we won't be mining Venus for raw materials so any habitation of it would be for purely scientific research purposes. Terraforming is out of the question untill we can automate to process completely. The tech required to build a payload that could use machines that mine asteroids and build more machines to do the work, eventually building giant Solar shades for Venus or Mirrors for Mars, ect., All without a space based human workforce and nothing more than an initial cost, is not unfeasible.

• "Hydrogen is much more buoyant" ? Are you sure? The density of carbon dioxide (96.5 % of the venusian atmosphere) is 1.98 kg/m^3, the density of air is 1.293 kg/m^3, that is only 53 % more density. You may compare only densities measured under the same pressure and temperature.
– Uwe
Jun 22 '19 at 17:17

Even living on the surface of Venus could be much better than living on Mars if there is much less radiation higher gravity less problems with dust storms maybe there is even something like unobtainium or naquadah on Venus to mine,if there was better technology to build stuff on the surface that does not melt or get crushed and better lighting during the long nights and better ways to keep the air fresh in the buildings on the surface of Venus.

• Welcome to Space! We try to support answers with sources. Could you please provide some? Jun 22 '20 at 1:09
• It's very hot at the night side too, due to the thick atmosphere. It is probably impossible to develop a Venus suit in the near-future. If any, then one astronauts could walk with in the Maxwell Montes (highest mountains on Venus). There, the temperature and air pressure are about halved, perhaps managable. Jun 22 '20 at 7:58

With terraforming the planets Mars is ... impossible, the gravity of Mars isn’t strong enough to keep enough air and water in it from solar winds and currently there is no way to prevent that decay, so a permanent self sufficient terraformed Mars colony is impossible.

Venus however has the atmosphere can can support the changes for the end of time, however it requires much more complicated work to terraform the atmosphere than Mars would.

Venus would be able to support a second earth and Mars can’t granted that the knowledge, technology and will to do so comes

• The atmospheric escape time for Mars is measured in millions of years. That may not be "permanent" on an absolute scale, but on merely human timescales, it certainly is.
– Mark
Sep 9 at 20:20

The biggest problem is Mars has no magnetosphere because its core has gotten too cold. It’s basically pointless since you’ll die of cancer within a few years as has just been recently pointed out that Mars missions should be less than 4 years in length. There is no feasible way to solve the magnetosphere problem. Given what others have already pointed out about Venus, I would say it’s a much better target for colonization. Still the timescale would be hundreds of years into the future so establishing equilibrium on Earth in terms of population and renewable resources should be the top priority…

• It is a lot easier to shield from the radiation on the surface of Mars (which is about 30% as bad as the radiation in open space), than it is to shield from the ultra solvent saturated CO2 furnace that is Venus's surface. The first requires a meter of water or two meters of dirt. The second requires..... No idea. We haven't figured out how to even keep electronics working for a day down on Venus, much less keep anything organic alive at all Sep 7 at 5:43