(2019 Archived) Is Venus a Better Home than Mars? [Outdated]

 

Venus’s Close Proximity to the Earth

 There comes a time where two planets of a solar system are closer to each other. This happens when such planets are in their ‘opposition’. An opposition mostly occurs when the middle-planet is directly between its star and the other planet. For example, in a scenario where the Earth is directly in-between the Sun and Mars: Mars is said to be in “its opposition with the Earth”. Mars is approximately 54,600,000km away from us, when in opposition ^[2]. Venus, on the other hand, is approximately 38,000,000km in opposition with the Earth ^[3]. This makes Venus about 16,600,000km closer. But for a more realistic estimate, we have to use Hohmann transfer:

Hohmann transfer is an orbital mechanism often used in interplanetary voyages. It involves a ‘Hohmann transfer orbit’, which is “an elliptical orbit used to transfer between circular orbits of different radii in the same plane” ^[4]. But, in this case, the ‘circular orbits’ are the slightly eccentric and angled orbits of the planets, while the ‘radii’ are the distances between the sun and the respective planet. The key characteristic of this orbit is that it “uses the lowest possible amount of energy in travelling between the two objects” ^[4]. Or more succinctly, the Hohmann transfer orbit is the most economic path between two planets. There’s also this factor names ‘∆v’ (delta-v), needed to change the trajectory of the spacecraft from the orbit of the first planet, to the Hohmann transfer orbit (∆v is change in velocity). Hence, the lower the magnitude of ∆v, the more economically sound the trip is. Being 2.5kmh^-1, Venus has the lowest ∆v of any Hohmann transfer from the Earth. This, by far, makes the journey to Venus the most economically sound one. (Although, the difference may seem minute, it translates to a huge sum of money).

Figures 6: The above diagrams depict Hohmann transfer to Mars and Venus respectively. Venus has a shorter Hohmann transfer orbit,, meaning a more economically sound trip.

Body	Distance from sun (AU*)	∆v needed for Hohmann transfer
Sun	0	29.8 kmh-1
Mercury	0.39	7.5 kmh-1
Venus	0.79	2.5 kmh-1
Mars	1.52	2.9 kmh-1
Jupiter	5.2	8.8 kmh-1
Saturn	9.4	10.3 kmh-1
Uranus	19.19	11.3 kmh-1
Neptune	30.07	11.7 kmh-1
Pluto	39.48	11.8 kmh-1
∞ (Infinity)	∞	12.3 kmh-1

Figure 7: Table depicting bodies of our solar system and the respective ∆v required to change trajectory from planetary orbit to Hohmann transfer orbit ^[4]. *1AU=Distance from sun to Earth.

More Frequent Launch Windows

Hohmann transfer cannot be done at any time we please, in order to be the ‘most economically-friendly path’. The different eccentricities, angular placements and orbital velocities of the planets and their orbits, constantly change the distances between them. The distances occasionally become so vast, that interplanetary voyages become impractical. This makes us wait for a certain period known as the ‘launch window’, where the planets are practically ‘close’: The launch window mostly opens at times near ‘perihelic opposition’, which happens when the planet, which is closer to its star, is at its aphelion (farthest away from its star), and the further planet is at its perihelion (most closest to its star).

For example, if Mars were at its perihelion and the Earth was at its aphelion; Mars is said to be ‘in its perihelic opposition with the Earth’. Therefore, the launch window opens to the shortest Hohmann transfer orbit; the most economically-friendly path between the two worlds. The launch windows of the different planets open at different frequencies owing to the different eccentricities, angular placements and orbital velocities of the different planets of our solar system, constantly change interplanetary distances. The Martian launch window opens every 779.94 days- which is almost once every 2.2 years ^[5]. Venus opens her launch windows more often, being 584 days or 1.6 years ^[3]. We can conclude from this that Venus opens her launch window 25% more frequently than Mars does. Hence, we can visit there more often and readily, and at a more cost-effective budget.   

 

Less Travel Time

It's possible to deduce from the below table that, it takes an average of 7 months to reach Mars, with present means of propulsion. NASA’s Mariner 2, which flew-by Venus on 14^th December 1962, took 4 months to do so ^[3]. Hence, the trip to Venus takes 3 months less than Mars. It could minimize the risks of interplanetary travel along with more efficient usage of every launch window.

Figure 8: Table depicting time taken for missions from launch to landing ^[6].

Lander	Time taken (days)
Viking 1	335
Viking 2	360
Phoenix Lander	295
Curiosity Lander	253

        Minimized Risks of Interplanetary Travel

Interplanetary space isn’t a safe place to be in. It is then reasonable, to argue that interplanetary travel comes with its repertoire of complications; it has negative effects on human physiology and psychology ^[7]. I’ll begin with the effects of absence of gravity. Having evolved to the pull of the Earth’s gravity, we are unable to ‘keep ourselves together’ in its absence, in the longer run. Below is a summary of the alleged effects;

·         Loss of minerals: In zero-gravity, the mineral density of bones decreases by 1% monthly ^[7].  Old people, on the other hand experience this at a rate of 1-1.5% annually. Logically speaking, space voyagers will undergo mineral loss 1200% more harshly than old people! Creepy!

·         Increased risk of osteoporosis, which might lead to related fractures in life.

·         Loss of muscle tone, strength and endurance, due to lack of exercise.

·         Pressure build-up in eye due to fluids shifting up to head.

·         Vision problems due to pressure build-up in eye.

·         Formation of kidney stones due to dehydration.

·         Bone decalcification: Increased excretion of calcium from bones.

·         Dizziness and reduced blood flow due to blood pooling in head and chest.

The 3-month longer journey to Mars results in the Martian colonists being more prone to the above effects. They would have lost 75% more minerals from their bones and experienced more physiological damage than a Venusian colonist. The very thought of landing on a cold desert in ill health is indeed torturous. Exposure to cosmic radiation is another grave threat in interplanetary voyages. Radiation sickness, Tissue degeneration, increased risk of cancer and damage to central nervous system are some of the undesirable effects of exposure ^[7]. Psychological effects arise mostly due to isolation and severely lagged communication with Earth. This will be discussed at a later point

Conclusion from the Aforementioned Points:

Longer travel, and maximized risks of interplanetary voyage, inarguably deems the trip to Mars as a cumbersome one. Meanwhile, the perfect combo of increased frequency, practicality, safety and economically-friendly nature of the trip to Venus, makes it the perfect place to visit. I reiterate that this is assuming Venus and Mars are equally hospitable.

Brief Introduction to the Concept of Venusian Cloud-Cities

The reader might recall the earlier mention of the need to build floating cities in Venus’s hospitable upper atmosphere given the uninhabitable nature of its surface. The question now remains as to how exactly we could make a city float? Before discussing this point, it is necessary to introduce some basic physics: It is universally known that, a helium balloon will float in air. This is because helium is less dense than air and that helium is a lifting gas in air. The balloon will continue to rise until it finds a place in Earth’s upper-atmosphere where the pressure in the balloon is equal to the pressure outside it. Let’s improvise a similar scenario for Venus; Carbon dioxide (CO₂) is the dominant gas in the Venusian atmosphere. Air, being less dense than CO₂, will therefore be a lifting gas on Venus. Hence, if we were to fill a vessel or ‘city’ with air, it will float in a region of the Venusian upper-atmosphere with sea-level pressure. To put is simply, if the cloud-city were a geodesic structure like Buckminster Fuller’s Cloud Nine, the city will be lighter than the air it displaces and the city will float. The remaining argument is based on the context that, the Venusian colonists live in these cloud-cities (Refer page 76 for further explanation).

 

Earth-Like Atmospheric Pressure

Mars has a thin atmosphere which exerts merely 0.0618 bars or 1.9 inches of mercury of an atmospheric pressure ^[14]. This low pressure makes it mandatory for the Martian-immigrants to wear pressurized spacesuits. About that, “spacesuits are amazingly clumsy... because of internal pressure. It’s been described as working with your fingers in a pressurized hose” and  “spacesuits take ages to put on and take off, is a long process (on the ISS* the process of donning a spacesuit starts the previous day with lowering the pressure of the ISS)”^[1]. [International Space Station].

The cloud-city will float in an altitude where, the pressure in the city is equal to the pressure outside. Hence, the outside pressure is already one bar. There’s no need for those clumsy pressurized suits when going out of the cities or habitats. The underlined values of the below table correspond to the pressure-altitude range and temperature range of the exterior of the cloud-cities.

Altitude (km)	Temperature (oC)	Atmospheric Pressure (bar*)
0	462	92.1
5	424	66.65
10	385	47.39
15	348	33.04
20	306	22.52
25	264	14.93
30	222	9.851
35	180	5.917
40	143	3.501
45	110	1.979
50	75	1.066
55	27	0.5314
60	-10	0.2357
65	-30	0.09765
70	-43	0.0369
80	-76	0.00476
90	-104	0.0003736
100	-112	0.0000266

Figure 9: Table depicting repertoire of altitudes of Venus with their respective temperature and atmospheric pressure ^[8].* Sea-level atmospheric pressure on Earth= 1bar.

 

Stability of temperature  

Metals expand and contract in accordance to temperature change. Through repetitive expansion and contraction, metal structures deteriorate. “The upper cloud level stays at much the same temperature day round, year round” ^[1].Martian temperatures don’t fluctuate much either. But, the temperature range does fluctuate wildly, from summer to winter and vice versa. This could cause expansion-contraction related damages over a course of extended periods of time.

Figure 10: Atmospheric temperature of Venus, as a function of its altitude

Earth-like Temperature

Figures 3 and 5 make it absolutely clear that the outside temperature is 75^oC, if we were floating at 1bar. It’s manageable, but we can do better! The city will float 55km above Venusian terra at a temperature of 27^oC when pressurized at 0.5 bars. It’s manageable too, but the pressure is slightly harsh. I believe that we will resort to somewhere between these two altitudes. It’ll be ideal for human colonization, unlike the bitter and perhaps deadly sub-zero coldness of Mars. I like to call it the ‘Venusian goldilocks zone’; the habitable area of the Venusian atmosphere.

More Solar Energy                                                                          

The intensity of light decreases, the further away you get from its source. This, being true with the sun, makes it easier to calculate light received by different planets using inverse proportion. We’ll assume the Earth receives 1 unit of solar energy. Then Mars, lying 1.52AU from the sun, receives 0.65 units while Venus, lying 79AU from the sun receives 1.42 units. Hence, Venus receives 42% more solar energy than the Earth, while Mars receives 35% less; Thereby, Venus receives 218% more solar energy then Mars.

Protection from Cosmic Radiation

Everything in space is bombarded with cosmic radiation. We, lying under the haven of the Earth’s magnetosphere and thick atmosphere, are shielded from them. Mars, which barely has an atmosphere, offers no such protection. The Radiation Assessment Detector (RAD) on the Mars Science Laboratory’s Curiosity rover measured cosmic ray and energetic particle radiation environment on the Martian surface. These measurements provide insights into the “radiation hazards associated with human mission to the surface of Mars”, and estimated a “total mission dose equivalent of Sv for a round trip Mars surface mission...for this current solar cycle” ^[10].This exposure will give the unprotected Martian-immigrants radiation sickness; which causes nausea, vomiting, anorexia and fatigue, and tissue degeneration; which causes cataracts and cardio-circulatory degeneration. More acute effects include; increased risk of cancer and damage of central nervous system, which might manifest themselves as altered cognitive function, decreased motor function and behavioural change ^[7]. Unless the Martian-immigrants live majority of their lives metres underground, they would have to face the consequences...

The cloud-cities of Venus, on the other hand, have an ‘Earth-equivalent’ atmosphere above it, which would protect the Venusian-immigrants from cosmic radiation. “Even though the flux of ionizing radiation can be sterilizing, high in the atmosphere, the total dose delivered at the top of the habitable zone… is not likely to present a significant survival challenge” ^[11].

Planet	Gravity
	Gravitational Acceleration (ms-2)	Relative to Earth (G)
Earth	9.806	1.0000
Mercury	3.700	0.3800
Venus	8.870	0.9040
Moon	1.620	0.1654
Mars	3.711	0.3800
Jupiter*	24.79	2.5280
Saturn*	10.44	1.0650
Uranus*	8.69	0.8000
Neptune*	11.15	1.1400

 

Figure 11: Table depicting planets with their respective gravities. (*from cloud-tops).

Earth-Like Gravity

Gravity is a fundamental force of nature – one we often take for granted. Over a course of millions of years, we’ve adapted and evolved to the steady pull of the Earth’s gravity (1G) ^[12]. The ‘gravity’ of an object is determined by its mass, density and force exerted. This results in gravity varying from planet-to-planet. Having evolved to the incessant pull of the Earth’s gravity, over the course of millions of years, the human body doesn’t fare well in higher or lower gravitational fields. They could give rise to undesirable effects: For example, lower gravity could cause bone decalcification, loss of muscle tone and similar effects to that in zero-gravity.  Saturn has the most Earth-like gravity followed by Venus and Neptune. On the contrary, the Martian gravity is approximately one-third of that of the Earth ^[12]. Thus, between Mars and Venus; Venus is gravitationally ideal for inhabitation.

Protection from Meteorites

“The Earth is hit by meteorites with energy [of] about 3n kilotons every 1.3 years, but this is no problem” ^[1]. This is because; they burn-up completely in the Earth’s upper atmosphere, long before they reach the Earth’s surface. The Venusian cloud-colonies will have a similar equivalent-of-an atmosphere above them, which will give a similar protection from meteorites. On the other hand, Mars barely has one! The meteorites will literally ‘burn a hole’ in its atmosphere on its way to impact its surface. This is the reason for craters being present on Mars. In fine, The Venusian atmosphere is a safer haven from meteorites, and the Venusian cloud-colonists would not need to worry about being hit. Furthermore, any possible meteor showers on Venus ought to be a wonderful and special as a hitherto unseen spectacle.

Constituents	Composition
Carbon Dioxide	96.5%
Nitrogen	3.5%
Sulphur Dioxide	0.015%
Argon	0.007%
Water Vapour	0.002%
Carbon Monoxide	0.0017%
Hydrogen	0.0012%
Neon	0.0007%

Figure 12: Composition of the Venusian Atmosphere ^[13]

Constituents	Composition
Carbon Dioxide	95.35%
Nitrogen	2.7%
Argon	1.6%
Oxygen	0.13%
Carbon Monoxide	0.007%
Water	0.03%
Neon	0.00025%
Krypton	0.0003%

Figure 13: Composition of the Martian atmosphere ^[14].

Presence of Carbon Dioxide in the Venusian Atmosphere 

The composition of Carbon Dioxide in both Mars and Venus are remarkably similar; Carbon Dioxide is inarguably the most abundant gas in both worlds ^[13][14]. Carbon Dioxide is not breathable, but it could be useful as a means of extracting the oxygen and water we need. Below are some methodologies, by which we may do so ^[15]:

Electrolysis of Atmospheric Carbon Dioxide.

Carbon Dioxide could be reduced into Carbon Monoxide and Oxygen through electrolysis.  It only requires electricity and a catalyst like zirconia ^[15], which could be reused, as catalysts are not used-up in reactions.                                                    

 Carbon Dioxide + Energy → Carbon Monoxide + Oxygen                              

  2CO₂ + energy → 2CO +O₂

Electrolysis of Carbon Monoxide 

Carbon Monoxide could be reduced to elemental Carbon and oxygen through electrolysis, similar to Carbon Dioxide ^[15].

Carbon Monoxide + Energy → Carbon + Oxygen                                                           

2CO + Energy → 2C + O₂                                                                                                     

Carbon Monoxide could be retrieved from the outside, but it might be a bit too sparsely dispersed, as it accounts for only 0.0017% of the Venusian atmosphere. Therefore, the Carbon Monoxide produced during the electrolysis of Carbon Dioxide is technically our only consistent source of it. Not only could we obtain more breathable oxygen, but we could obtain carbon too; which could be used for organic processes and compensating for lost carbon to the external environment, and keep the carbon cycle up-and-running. The only problem is the requirement for “more input energy to break carbon-oxygen trivalent bond” ^[15].

Photosynthesis:                                                                                         

 This process is a plant’s mean of synthesizing the ‘food’ it requires, while utilizing water and carbon dioxide in the environment, and light and the chlorophyll in its cells.

 6CO₂ + 6H₂O + Photons→ C₆H₁₂O₆ + 6O₂                                                           

 Carbon Dioxide + Water + Photons → Glucose + Oxygen 

Glucose is the main product formed by natural photosynthesis, and it is used to give energy to the plant during respiration and metabolism. Oxygen, on the other hand, is released as a by-product. Crops and photosynthetic micro-organisms could be used for oxygen production, by means of natural photosynthesis. After all, natural photosynthesis accounts for almost all of the Earth’s oxygen production. Furthermore, photosynthesis is more effective on Venus, due to the availability of 42% more sunlight, which is required to run it. But the down-side is that plants respire in the darkness, as in the Venusian night, which would generate CO₂.

Artificial Photosynthesis 

Artificial photosynthetic technology, though still under development, would be able to generate oxygen as a by-product, by using the receivable Carbon Dioxide, Water and photons ^[15].

CO₂ + 2H₂O + Photons → CH₂O + O₂                                                 

Carbon Dioxide +Water + Photons → Formaldehyde +Oxygen                  

Notice how in natural photosynthesis, that twelve molecules of raw material will produce six molecules of oxygen (in a 2:1 ratio), while three molecules of raw material are needed to produce a molecule of oxygen (in a 3:1 ratio). Thus, natural photosynthesis is more resource efficient relative to artificial photosynthesis. But, we would not have to worry of Carbon Dioxide production at night, with artificial photosynthesis, as machines don’t respire. Furthermore, we get Formaldehyde, which could be used as an antiseptic, a fungicide when humidified ^[16], and for mummification of organic matter.      

Bosch Reaction

 A Bosch reaction is another methodology of generating not only oxygen, but elemental Carbon too. It would need a steady supply of Hydrogen, a catalyst like iron, and temperatures of ~450-600^oC.

CO₂ + 2H₂ + (∆Heat) → C + 2H₂O                                                      

Carbon Dioxide + Hydrogen + (∆Heat) → Carbon + Water

Carbon produced during this reaction could again be used for the requirements of the city and basically maintain the Carbon cycle, and compensate for Carbon lost to the external environment. Carbon Dioxide is somewhat quintessential in Oxygen generation in other worlds (if present). Mars, which has a near vacuum for an atmosphere, will not have much Carbon Dioxide quantity-wise, though it makes up the majority of its atmosphere. The sheer amount of Carbon Dioxide in the Venusian atmosphere, which is ~92 times larger than the Earth’s, will be much more than required for the generation Oxygen and Water.

Presence of ‘Hydrogen’ in the Venusian Atmosphere            

It is safe to say that Hydrogen is absent in the Martian atmosphere, in any form. If Hydrogen were to be present in the Martian atmosphere, its concentration would be so low that it will technically be negligible. Venus, on the other hand, has 0.0012% of Hydrogen in its atmosphere, and a lot of Hydrochloric Acid (H₂SO₄) and Hydrogen Sulphide (H₂S), which are much more substantial sources of Hydrogen. Hydrogen could also be formed by the electrolysis of water:

2H₂O + Energy → O₂ + H₂                                                                                       

Water + Energy → Oxygen + Hydrogen

Hydrogen and Oxygen, that’s Rocket Fuel! Furthermore, the water produce by the Bosch reaction could be electrolyzed to form Hydrogen, which could be re-used in the Bosch reaction ^[15]. It would be a perpetual system of generating Carbon! The rocket fuel, that could be produced this way, is useful as a means of propulsion, and its efficiency in doing so.

Abundance of Nitrogen in the Venusian Atmosphere               

As much as 2.7% of the Martian atmosphere is molecular gaseous Nitrogen. However, quantity-wise, it is low in abundance, again due to the thin nature of the Martian atmosphere. On the other hand, “Venus has 3 bars of nitrogen compared with 0.78 bars of nitrogen for Earth” ^[1]. Simply, Nitrogen is found in abundance in Venus. But why is Nitrogen so important? Because, it acts as a ‘buffer gas’ that prevents ‘oxygen toxicity’:

‘Oxygen toxicity’ is a condition that arises with exposure to higher levels of oxygen, at normal or higher pressures. The body gets affected differently based on type of exposure. In outer space and alien worlds, it is mostly long-duration exposure to higher oxygen levels in normal pressure, which could result in pulmonary or ocular toxicity. Furthermore, “symptoms may include disorientation, breathing problems, and vision changes such as myopia” ^[17].

Oxygen toxicity could be prevented with the presence of a buffer gas, which should be inert, not-poisonous and affordable. Nitrogen is the most suitable as a buffer gas, unlike the noble gases (Helium, Neon, Argon, Krypton and Xenon), which are more rare and expensive. After all, Nitrogen acts as the buffer gas, here on the Earth.  The presence of 3 bars of Nitrogen on Venus implies that “even if the entire atmosphere was filled with cloud cities, with populations greater than the Earth, they would never run out of nitrogen for plants and for a buffer gas for breathing” ^[1].

The derived ions of Nitrogen; the Nitrites, Nitrates and Ammoniums, are used in the artificial fertilization of soil, required for agricultural and Horticultural activities. It would also be helpful in maintaining the Nitrogen cycle on the cloud cities, as atmospheric Nitrogen, goes into the soil, which will eventually be recycled back into the atmosphere, and the cycle repeats.

For further information, bacteria including Rhizobium, Nitrobacter, and Nitrosomonas could help in nitrification in cloud-city soil, along with de-nitrifying bacteria like Thiobacillus and Pseudomonas, which convert the Nitrates back to atmospheric Nitrogen. Thus, they could together contribute in maintaining soil fertility and keeping the Nitrogen cycle up-and-running.

 

Easy to send materials to the Venusian Cloud-tops

Materials will most likely be sent to the cloud-cities by means of aeroshells, in a similar fashion to atmospheric re-entry in the Earth. Parachutes will deploy from the aeroshell during atmospheric entry, along with the inflation of supportive balloons filled with a lifting gas. Similar to the cloud-cities, the aeroshells and the supplies in it will float in the right altitude, to be retrieved by the Venusian colonists.

Similarly, an enclosed Titanium sphere filled with gas to the right buoyancy could be used. During atmospheric entry, the kinetic energy of the object gets dissipated as heat, due to air-resistance. It sometimes gets hot enough to melt the body. Entry energy is calculated using the following equation, where “m is the entry mass, V_e is the escape velocity of Venus, 10.46km/sec, and V_∞ the hyperbolic excess velocity” ^[18].

E=¹/₂m(V_e²+V_∞)

Detailed calculations reveal that “large-diameter hollow spheres of titanium have no difficulty surviving atmospheric entry. It is in fact experimentally demonstrated that a titanium sphere can enter the atmosphere burning through” ^[18]. This would be harder on Mars, with more risk of the supplies meeting the Martian surface with a bang. The usage of much larger parachutes, along with some other precautions, are needed to send material to the Martian surface.

Figure 14: This Titanium tank, used for storing helium of Salyut 7, was still intact after re-entry in 1991. The usage of Titanium spheres for sending supplies is quite plausible as it doesn’t burn-up during entry.

Manageable Day-Night Cycle

We humans have a biological clock, which tells us when to sleep and when to wake-up, called the Circadian rhythm. It was built explicitly to work with the Earth’s day of ~24 hours, by million years of evolution. The Martian colonists will have problems with their sleep, because a sol (a Martian day) lasts 24 hours, 39 minutes and 35.244 seconds, which is ~39 minutes longer than our day. Developing a new Circadian takes a very long time, and until then, those 39 extra-minutes in a sol, will accumulate. This accumulation and messed-up Circadian rhythm, could lead to sleep disorders ^[7]. The Venusian cloud-cities, on the other hand, will circumnavigate Venus every four days, due to the super-rotation of the Venusian atmosphere ^[1]. This day-night cycle will be challenging, but it is subtly systematic. That roughly translates to two sleep-cycles each, in the Venusian day-side and night-side. But, the colonists who live nearer to the Venusian poles might have to deal with a five-month day-night cycle.

The Venusian habitats and Cloud-cities would not explosively decompress when seriously compromised

In retrospect, the pressure inside the Venusian cloud-cities and habitats would be equal to that of the outside. For this reason, “all that would happen after a large hole is that the outside atmosphere would slowly diffuse into the habitat. This would give plenty of time to repair any damage” ^[1]. This is unlike any other space-habitat that would dangerously implode, when seriously compromised, with little-to-no time for repairing.

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Achinthya Nanayakkara (31.03.2025)

Original - 2019