# 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

• Manned landing on Venus is impossible using available technology due to the very high temperature and pressure on the surface. If we are able to build landers that survive not only hours or some days but many years, you may think about this question again. – Uwe Jun 11 '18 at 20:41
• PBS Space Time did a video about this. Worth a look. – jpaugh 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. – Magic Octopus Urn Jun 12 '18 at 19:41
• Number of permanently airborne installations on Earth: 0. "easy" is a big overstatement. – Hobbes Aug 30 '18 at 19:56
• Which are those fertilizers in the atmosphere ? Will there be water in those salts at 462 $^0$C ? – Cornelisinspace 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.

• The Earth has no heat crisis, temperatures were higher in the early Middle Ages, man-made global warming is a communist deception. The question is about Venus' upper atmosphere (about 32 miles high), not about landing on its surface. If you create cloud cities in Venus' upper atmosphere (like planned with HAVOC) you of course can walk on them. – user27822 Oct 28 '18 at 15:53
• en.wikipedia.org/wiki/High_Altitude_Venus_Operational_Concept – user27822 Oct 28 '18 at 15:53
• @user27822 that is nonsense. AGW is real. – Hobbes Dec 21 '18 at 11:37
• @user27822 Typical flat-earther? That's what I'd thought. – Boosted Nub Dec 22 '18 at 10:35
• 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. – LocalFluff Dec 22 '18 at 19:19

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 – Cornelisinspace Dec 22 '18 at 12:45
• "easily" is not a word often used when referring to building floating habitats on another planet. – Organic Marble 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. – Famous Jameis Dec 23 '18 at 16:24
• As the volume of the gas bag gets bigger you start to have stability problems as gas withing the bag moves around and forms layers of different density, so there are limits to the total cell size. Having multiple cells works but then needs more structure mass to keep them from harm, especially under turbulent conditions as hog/sag becomes a problem. Yes they are solvable, but you will crash several learning how to do it, and the only abort option is returning to orbit. – GremlinWranger Dec 23 '18 at 23:26
• 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 at 1:23

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.

Venus would be easier for multiple reasons. It takes less fuel and time to get there. Hydrogen is much more buoyant 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 at 17:17