Kurzgesagt – In a Nutshell
Sources – Terraform Venus
– Leaving earth to find new homes in space is an old dream of humanity and will sooner or later be necessary for our survival. The planet that gets the most attention is Mars, a small, toxic and energy poor planet that just seems good enough for a colony of depressed humans huddled in underground cities.
Mars has about half the diameter of Earth, with a surface covered in toxic dust and illuminated by only 43% of the sunlight that we receive.
#Mars Fact Sheet, NASA, 2020
https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html
Quote: “ Mars Earth Ratio (Mars/Earth)
Equatorial radius (km) 3396.2 6378.1 0.532
Solar irradiance (W/m2) 586.2 1361.0 0.431”
We’ve done a whole video on how horrible it is on Mars:
#Building a Marsbase is a Horrible Idea: Let’s do it!, Kurzgesagt, 2019
https://www.youtube.com/watch?v=uqKGREZs6-w
– Venus is by far the hottest planet in the solar system with a surface temperature of 460°C. Hot enough to melt lead. This heat is due to the most extreme greenhouse effect in the solar system.
The temperature on the surface of Venus isn’t precisely defined, but we know that it ranges from 450°C to 470°C.
#Venus, NASA, retrieved 2021
https://solarsystem.nasa.gov/planets/venus/in-depth/
Quote: “Venus' atmosphere consists mainly of carbon dioxide, with clouds of sulfuric acid droplets. The thick atmosphere traps the Sun's heat, resulting in surface temperatures higher than 880 degrees Fahrenheit (470 degrees Celsius).”
#Venus Lithograph, NASA, retrieved 2021
– CO2 is great at trapping heat – even a rise from 0.03% to 0.04% in Earth's atmosphere is significantly heating up our planet right now. Venus's atmosphere is 97% CO2.
Before the industrial revolution, CO2 levels in Earth’s atmosphere were under 300 ppm, or ‘parts per million’, which is 0.03%. They’ve increased to over 400 ppm today.
#Climate Change Synthesis Report, Intergovernmental Panel on Climate Change, 2014
https://www.ipcc.ch/site/assets/uploads/2018/02/SYR_AR5_FINAL_full.pdf
#The Greenhouse Effect, NASA, 2019
http://www.ces.fau.edu/nasa/module-2/how-greenhouse-effect-works.php
Quote: “The sun's visible wavelengths of radiation pass easily through the atmosphere and reach Earth. Approximately 51% of this sunlight is absorbed at Earth's surface by the land, water, and vegetation. Some of this energy is emitted back from the Earth's surface in the form of infrared radiation.
Water vapor, carbon dioxide, methane, and other trace gases in Earth's atmosphere absorb the longer wavelengths of outgoing infrared radiation from Earth's surface. [...]This process creates a second source of radiation to warm to the surface – visible radiation from the sun and infrared radiation from the atmosphere – which causes Earth to be warmer than it otherwise would be.”
#Venus Fact Sheet, NASA, 2020
https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html
Quote: “Atmospheric composition (near surface, by volume):
Major: 96.5% Carbon Dioxide (CO2), 3.5% Nitrogen (N2)”
– Also, Venus's atmosphere is 93 times denser than earth’s. Standing on Venus’ surface would feel like taking a dive about 900 meter deep into the ocean. The pressure would kill you instantly.
#The surface of Venus, Alexander T. Basilevsky and James W. Head, 2003
http://planetary.brown.edu/planetary/documents/2875.pdf
Quote: “The average surface temperature on this planet is much higher (about 740 K) than on Earth. Venus’s atmosphere is composed predominantly of CO2 and its average surface atmospheric pressure is much higher (about 93 bar)”
You can calculate the pressure at a certain depth below the ocean’s surface by using:
Pressure (Pascals) = 9.81 * Depth (metres) * Density (kg/m^3)
Seawater has a density of 1027 kg/m^3, so at a depth of exactly 923 metres, we would have a pressure of 9,300,000 Pascals, which is equivalent to 93 bars.
– First and foremost, Venus is almost as big as Earth and has 90% of its surface gravity.
In the full comparison between Venus and Earth’s main characteristics, we find that it has 81% of the mass, 95% of the radius and 90% of the gravity of our own planet. Pretty close!
#Venus Fact Sheet, NASA, 2020
https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html
– Surface gravity is a big problem with colonizing the solar system because it is very likely that long stays in low gravity places have negative health effects.
We know what happens to the human body when placed in microgravity for long periods. It is less clear what the effects of partial gravity are, as testing is much more limited. We won’t have thousands of people willing to go to Mars if partial gravity causes substantial harm.
#The Human Body in Space, NASA, 2021
https://www.nasa.gov/hrp/bodyinspace
Quote: “NASA has learned that without Earth’s gravity affecting the human body, weight-bearing bones lose on average 1% to 1.5% of mineral density per month during spaceflight. After returning to Earth, bone loss might not be completely corrected by rehabilitation; however, their risk for fracture is not higher. Without the proper diet and exercise routine, astronauts also lose muscle mass in microgravity faster than they would on Earth. Moreover, the fluids in the body shift upward to the head in microgravity, which may put pressure on the eyes and cause vision problems”
#Human Biomechanical and Cardiopulmonary Responses to Partial Gravity – A Systematic Review, Charlotte Richter et al., 2017
https://www.nasa.gov/hrp/bodyinspace
Quote: “Biomechanical studies reveal that ground reaction forces, mechanical work, stance phase duration, stride frequency, duty factor and preferred walk-to-run transition speed are reduced compared to 1 g. Partial gravity exposure below 0.4 g seems to be insufficient to maintain musculoskeletal and cardiopulmonary properties in the long-term.”
– Before anything else, we need to cool Venus down and remove the gas that makes up the extremely heavy atmosphere. As mentioned, there is a lot of it. Around 465 million billion tons.
We draw inspiration from the work of Paul Birch and his paper on terraforming Venus quickly. His plan was supposed to start in 2030 and involve spinning up the entire planet to give it a 24h day, so we’ve taken the liberty of adapting it into something slightly more reasonable.
#Terraforming Venus Quickly, Paul Birch, 1991
https://www.orionsarm.com/fm_store/TerraformingVenusQuickly.pdf
We have also learnt more about planetary geology and chemistry, and have more advanced technologies today, so we aren’t obligated to follow each of the steps he proposed precisely. Still, it is mostly accurate and a useful guide.
#Venus Fact Sheet, NASA, 2020
https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html
Quote: “Venus Atmosphere
Total mass of atmosphere: ~4.8 x 10^20 kg”
97% of this mass is CO2, which means 4.65 x 10^20 kg. For comparison, Earth’s atmosphere masses 5.2 x 10^18 kg.
– How do we do that? There are a few options. We could create giant solar collectors powering a huge array of laser beams, that heat up the atmosphere so much that it is blasted into space. Although we would need thousands of times the entire power generating capacity of humanity and it would still take thousands of years to remove the atmosphere.
Gases at the edge of an atmosphere naturally absorb the sun’s radiation and heat up. The particles in hotter gases travel faster, according to the kinetic theory of gases. At high enough temperatures, those gases reach escape velocity and break free of the planet’s gravity entirely. This is the mechanism for Jean’s escape and the most relevant equation for it is that of the the most probable velocity of particles inside a gas, which is related to its temperature and molar mass.
The equation is given as:
V0 is the velocity in metres per second. k is the Boltzmann constant, T the temperature in Kelvin and m the molar mass in kilograms per mole.
Venus’ atmosphere is mostly carbon dioxide. If we want to rapidly remove that atmosphere through Jean’s escape, we need to heat up carbon dioxide particles until their average velocity exceeds Venus’ escape velocity of 10,360 m/s.
We solve the equation for V0 = 10,360, k = 8.314 and m = 0.044 kg/mol.
We find that T must equal 284,000 Kelvin. That’s nearly fifty times hotter than the surface of the Sun, a temperature achievable only by intense lasers.
We can also estimate the minimum energy required for this task, using the kinetic energy equation.
K is the kinetic energy in Joules, m is the mass of the atmosphere in kg and v is the velocity we want to achieve. Using m = 4.8*10^20 kg and v = 10,360 m/s, we find a total energy of 2.5*10^28 Joules.
Even if we collected every bit of sunlight that reaches Venus (about 300 PetaWatts) and converted it all into laser beams that perfectly heat up the atmosphere, it would take over 2600 years to deliver the required energy. That’s over 16 thousand times more than the total electrical output of humanity today.
A realistic setup with inefficiencies and limitations would probably take a hundred times longer, adding up to hundreds of thousands of years.
Here is a detailed look at the Jean’s escape mechanism.
#Atmospheric escape, A.J.Coates, retrieved 2021
https://sci.esa.int/documents/33745/35957/1567258799920-Weihai-093-Coates-escape.pdf
The velocity v = 10,360 m/s we used came from the escape velocity for Venus.
#Venus Fact Sheet, NASA, 2020
https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html
Quote: “Escape velocity (km/s) 10.36”
– Another way is to sequester the atmosphere. Binding the CO2 in different compounds through chemical reactions. We could mine elements like Calcium or Magnesium on Mercury and shoot them at Venus via mass driver systems – Electrical rails that make rockets unnecessary on smaller planets. The metals would combine to bind the CO2 into different carbonates basically forever. But the scale makes the whole thing impractical. We need about hundreds of million, billion tons of material to sequester the CO2 this way. Seems like a waste of material and might take too long.
Carbon dioxide from the atmosphere can be made to react with a number of common elements on planetary crusts to form carbonates, such as calcium, potassium, magnesium or even iron. It is studied today as a method of removing this greenhouse gas from Earth’s atmosphere, and it has naturally occurred over millions of years to form all the limestone we find on our planet’s surface.
#Chemical Equations Online, retrieved 2021
https://chemequations.com/en/?s=MgO+%2B+CO2+%3D+MgCO3
Quote: “CO2 + MgO → MgCO3”
#Chemical Interaction of Calcium Oxide and Calcium Hydroxide with CO2 during Mechanical Activation, Alexander M. Kalinkin et al., 2005
Quote: “CaO + CO2 = CaCO3 (Calcite)”
#Capturing carbon using calcium oxide, Materials Today, 2020
https://www.materialstoday.com/biomaterials/news/capturing-carbon-using-calcium-oxide/ Quote: “Calcium carbonate, some forms of which we know as chalk and marble, could be a good product to keep CO2 reliably locked away in a very stable form.”
Geoffrey A. Landis suggests using the mineral resources in Venus’ crust to perform these reactions and capture the CO2 in its atmosphere. It would require digging up the entire planet’s surface down to a kilometer depth and processing that entire mass to extract the necessary elements. A monumental task!
#Terraforming Venus: A Challenging Project for Future Colonization, Geoffrey A. Landis, 2011
Quote: “Chemically sequestering the atmosphere could be done if the carbon dioxide is combined with surface rock to form carbonate rock such as dolomite (CaMg(CO3)2), by reactions such as CaMgO2 + 2CO2 --> CaMg(CO3)2 rm carbonate rock such as dolomite (CaMg(CO3)2), by reactions such as CaMgO2 + 2CO2 --> CaMg(CO3)2
The reaction shown requires slightly over one kilogram of CaMgO2 to sequester one kilogram of carbon dioxide, and not all of the surface rocks of Venus will comprise minerals suitable for forming carbonates. It would require pulverizing the surface to a depth of at least 1 km, and possibly more, to produce enough rock surface area to convert enough of the atmosphere.”
Note: We are using a simplified representation in the video here.
Hinweis : Wir verwenden hier eine vereinfachte Darstellung im Video.
– An equally ridiculous idea that could actually work is to put Venus in the shade. Literally. By constructing a huge mirror to blot out the sun to just freeze the atmosphere. The mirror does not need to be complex or massive, just a very thin foil with a little structural support.
If we cut off Venus from its supply of sunlight, it will cool down relatively rapidly. This is because hot objects radiate away their heat into space, and Venus starts off very hot.
The objective is to turn Venus’ large gaseous atmosphere into a more manageable layer of CO2 ice. Paul Birch’s Venus Terraforming paper instructs us to start with this step first. The mirror he suggests would be made of ultra-lightweight aluminium film that masses just 0.3 grams per square metre, so even a disk that covers all of Venus would only add up to 76 million tons.
However, studies of thin materials have progressed since then. Aluminium achieves its maximum reflectivity from a thickness of just 30 nanometres, which gives it a mass of 0.081 grams per square metre. We could reduce that mass by a significant amount if we manage to manufacture these thinner mirrors.
#Terraforming Venus Quickly, Paul Birch, 1991
https://www.orionsarm.com/fm_store/TerraformingVenusQuickly.pdf
Quote: “If one positions a large mirror between Venus and the Sun, the planet will radiate into deep stace and cold down. Such a mirror, although very large, can be very light and flimsy; [...] Solar sail material, and aluminised film of ~3x10^-4 kg/m^2, would be suitable. It would cover an area of ~2.2πR^2 ~2.5x10^14 m^2 and would have a total mass of ~7.6x10^10 kg.”
#Terraforming Venus: A Challenging Project for Future Colonization, Geoffrey A. Landis, 2011
Quote: “A final possible proposal would be to use a large shadow-shield, placed between Venus and the sun, to reduce the solar input and so cool the planet sufficiently that the carbon dioxide would condense into liquid, and then (as the pressure reduces further) freeze out in the form of carbon dioxide ice. The shield would have to be extremely light weight; presumably a technology similar to a solar sail, although much larger.”
As we can see in the chart below, a thin film of aluminium, just 30 nanometres thick, achieves practically maximal reflectance for that material.
#Reflectance calculator, Filmetrics, retrieved 2021
#Features, Evaluation, and Treatment of Coronavirus (COVID-19), Marco Cascella et al., 2021
https://www.ncbi.nlm.nih.gov/books/NBK554776/
Quote: “Thus, SARS-CoV-2 belongs to the betaCoVs category. It has round or elliptic and often pleomorphic form, and a diameter of approximately 60–140 nm.”
– Building such a massive flat surface so close to the sun will turn it effectively into a solar sail and push it out of position, so instead of one giant circular object, our mirror will consist of many different pieces. Annular slats of angled mirrors can reflect sunlight from one set of mirrors to the next. Mirrors would be angled, reflecting light from one to another until the light is redirected to the back - balancing the force on the front and holding them in position.
Solar radiation pressure is a constant force that acts on all surfaces exposed to sunlight. Most of the time, it is negligible as it is very weak. However, a thin mirror is so lightweight that it will get pushed around and drift out of position.
#Radiation pressure, Encyclopaedia Britannica, retrieved 2021
https://www.britannica.com/science/radiation-pressure
Quote: “Radiation pressure, the pressure on a surface resulting from electromagnetic radiation that impinges on it, which results from the momentum carried by that radiation; radiation pressure is doubled if the radiation is reflected rather than absorbed.”
Paul Birch devised a solution to this problem, by arranging the mirrors into angled rings and a central cone that deflect sunlight onto a second mirror that cancels out the radiation pressure:
– For the first few decades, the atmosphere slowly cools down but stays dense and deadly. Until, after some 60 years it reaches the critical temperature of 31° Celsius. Suddenly, the Great Flood begins on Venus, as CO2 turns to liquid at this pressure and begins to rain down- a constant global rainstorm of unbelievable proportions lasting 30 years. The pressure and temperature suddenly begin to drop in unison. For almost a century, puddles turn into lakes and oceans. The surface temperature is now -56° Celsius and the pressure has dropped to only seven times the pressure on earth. Finally, at a really unpleasant -81°, the CO2 oceans begin to freeze and the rain turns into snow. This leaves us with a frozen Venus covered in oceans as hard as rock and gigantic CO2 glaciers.
This sequence of events is calculated by Paul Birch. Here is the table of stages of cooling and how long they take:
The emissivity ε is an important factor here. We can deduce from the table that ε =0.1 for the first stage, ε =0.33 for the second stage and ε =0.5 for the third stage. Heat is radiated into space fastest when a surface is black and ε = 1.
Venus would naturally take 200 years for its surface to freeze. If we modify the atmosphere and surface to become darker, perhaps by dusting them with dark carbon flakes, we can reduce that time to a minimum of 87.2 years.
If you are confused as to how CO2 is turning liquid at a warm temperature of 31°C, it is because CO2 acts differently at high pressures. The phase transitions occur at different temperatures depending on the pressure - this is described by a phase diagram.
#Phase changes of CO2, Wikimedia Commons, 2015
https://commons.wikimedia.org/wiki/File:Phase_changes_of_CO2.png
– What remains of the atmosphere is mostly nitrogen with a pressure of three bars, triple what’s on Earth. If you don’t mind freezing and suffocating, you can now take a stroll over Venus' surface.
Nitrogen condenses at a much lower temperature than carbon dioxide. This means that once all of the carbon dioxide has been frozen out of the Venusian atmosphere, the nitrogen will remain as a gas.
In nitrogen’s phase diagram, you will notice that it at low pressures (at the bottom of the chart), temperatures have to drop below -200°C for it to stop being a gas:
#Nitrogen - Thermophysical Properties, The Engineering Toolbox, retrieved 2021
https://www.engineeringtoolbox.com/nitrogen-d_1421.html
Nitrogen makes up about 3% of Venus’ 93 bar atmosphere, so after all the CO2 is removed, it will still add up to 2.79 bars of pressure. Humans can survive these pressures and breathe in them after a few minutes of adaptation time… you just have to bring your own oxygen!
– One is to simply cover it all with cheap plastic insulation and cover it up with ground up venus rock or water oceans. Although some planetary scientists will be very stressed out about us building a new planet on a potential timebomb like that. A few unfortunately timed volcanoes could melt a lot of CO2 at once and ruin everything.
This is the solution that Paul Birch believes to be most practical and expedient. It is quite easy to just cover up all the new CO2 ice with plastic insulation. This is how it would look like:
The problems with this solution are numerous. We would be left with a planet covered by plastic sheets, which complicates mining, farming and all the other activities that makes terraforming interesting. A bubble-wrapped planet is also featureless and boring. It is also an unstable solution. No insulation is perfect, and heat will leak into the CO2 ice, causing it to boil off. Machinery will have to be used constantly to recover that CO2 and freeze it again. If the machinery fails, CO2 will bubble out from underneath, undoing all the hard terraforming work.
There’s also the risk of a volcanic eruption blowing through the insulation and releasing huge amounts of CO2 all at once. It would turn the new atmosphere toxic, while also bringing back the massive greenhouse effect that turned Venus into a hell-scape in the first place.
To these, we also add the possibility of a meteorite strike, an industrial accident, a spaceship crash, human warfare and more.
#Present-day volcanism on Venus as evidenced from weathering rates of olivine, Justin Filiberto et al., 2020
https://advances.sciencemag.org/content/6/1/eaax7445
Quote: “If so, then Venus is volcanically active today because our experimental results show that the emissivity/reflectance signature of olivine should be obscured by oxide coatings within months to years. This active volcanism is consistent with episodic spikes of sulfur dioxide in the atmosphere measured by both the Pioneer Venus Orbiter and the Venus Express”
– Another obvious solution is to shoot it all out into space and collect it into a small moon for storage and future use. We can make this more efficient by using mass drivers instead of rockets, but moving all that mass will still be a pretty intense challenge that will take some time to solve.
A definitive method for dealing with CO2 on Venus is to remove it from Venus entirely. Lifting it into orbit will be difficult and expensive, but we can do it if we massively scale up existing technology.
A mass driver, also known as a coilgun, is an electrically powered accelerator. It is composed of a series of electromagnets that can switch on and off very quickly. When on, they produce a magnetic field that pulls on a conductive armature or ‘bucket’. A payload like frozen CO2 can be placed inside that bucket. The field pulls on the sabot and accelerates it along a short section. As the bucket reaches the electromagnet, it is switched off, so that it continues into the next section without resistance. Multiple sections and powerful magnets allow for very high velocities to be achieved. At the end of its run, the bucket releases its payload and is recovered for reuse.
Here is a design for a mass driver that is nearly 100% efficient, through the use of magnetic levitation and superconducting magnets (‘quenching’ rapidly deactivates the magnets):
#A Superconducting Quenchgun for Delivering Lunar Derived Oxygen to Lunar Orbit, Nathan Nottke and Curt Bilby, 1990
https://ntrs.nasa.gov/api/citations/19900012490/downloads/19900012490.pdf
Quote: “This design, termed a quenchgun, is the most efficient launcher theoretically possible.”
Quote: “One approach to enhance the utility of LLOX is to employ a non-chemical method to achieve orbital or escape velocities from the lunar surface. One such method was the "mass driver" proposed by O'Neill (ref. 4) which would launch projectiles containing lunar regolith to a predetermined point in space. The payload canisters are accelerated on recirculating buckets and collected by an on-orbit “catcher”.”
Quote: “The quenchgun design is not too far removed from the standard coaxial electromagnetic accelerator, or coilgun. Thrust is generated from the Lorentz force by passing a smaller charged projectile coil inside and through a larger current carrying barrel coil. [...] In the standard coilgun application, the charge required for launch is stored in large capacitors, or similar devices, that have the storage time tuned to coincide with projectile
passage. [...] By using presently available superconductors to store the launch energy rather than capacitors, the entire amount can be stored in the barrel and transferred to the projectile almost completely without loss.”
These masses of CO2 only need a small nudge once they’re in space to enter a closed orbit around Venus. It would be efficient to gather them into one big sphere, and then cover the sphere with aluminium foil to reflect away sunlight. This prevents the CO2 from sublimating back into gas and perhaps falling back down onto Venus. If we put together all of the CO2 from Venus into a ball in orbit, it would form an artificial moon with a diameter of 822 km. That’s about 4 times smaller than our own Moon, but it might be placed much closer to Venus, so it would appear quite large in the sky (and also very bright from the shiny surface).
We might also choose to keep some CO2 ice in reserve on Venus, perhaps in small insulated zones near the polar caps (where there is less heat leaking in, and less chance of tectonic activity), while shooting off the majority into space.
#Terraforming Venus: A Challenging Project for Future Colonization, Geoffrey A. Landis, 2011
Quote: “An alternative concept would be to blast away the atmosphere. At the escape velocity of Venus, the minimum energy needed to remove atmosphere is about 50 MJ/kg. The energy required would be on the order of 2.5E28 Joules: equal to a terawatt of power applied continuously for 850 million years. This number is very large.”
– Whatever we end up doing with the atmosphere, to move forward we need water, which we might get from Ice-Moons. Europa, a moon of Jupiter, holds twice as much water than Earth’s oceans. Now catching a moon and transporting it through the solar
system is not exactly easy.
The moons of Jupiter, Saturn and the planets beyond formed outside the Solar System’s frost line. This is a distance from the Sun where sunlight is not strong enough to melt water or turn ‘volatile’ substances like carbon dioxide and ammonia into gases. This means they could accumulate as thick layers of ices around rocky cores, creating the icy moons we see today.
Europa is one of the smaller icy moons. It orbits Jupiter and is 3,120 km wide. If we take its icy shell to be 20 km thick, it would amount to 6.17*10^15 m^3. Ice has a density of 917 kg/m^3, so the total mass is 5.6*10^18 kg. Below it is a salty ocean roughly 100 km deep. It would have a volume of 3.06*10^18 m^3 and mass 3.14*10^21 kg.
If we add these figures up, we have 3.15*10^21 kg, which is 2.3 times more water than in all the oceans on Earth. Plenty enough for terraforming Venus!
#Europa in depth, NASA, 2019
https://solarsystem.nasa.gov/moons/jupiter-moons/europa/in-depth/
Quote: “Like our planet, Europa is thought to have an iron core, a rocky mantle and an ocean of salty water. Unlike Earth, however, Europa’s ocean lies below a shell of ice probably 10 to 15 miles (15 to 25 kilometers) thick and has an estimated depth of 40 to 100 miles (60 to 150 kilometers).”
We can derive the mass of water from its volume. 1 km^3 of water is 10^9 kilograms.
#How Much Water is There on Earth?, USGS, retrieved 2021
https://www.usgs.gov/special-topic/water-science-school/science/how-much-water-there-earth
Quote: “The volume of all water would be about 332.5 million cubic miles (mi^3), or 1,386 million cubic kilometers (km^3). A cubic mile of water equals more than 1.1 trillion gallons. A cubic kilometer of water equals about 264 billion gallons (1 trillion liters).”
However, moving that entire moon is pretty much an impossible task. At least, if we want the terraforming project done quickly and with the technologies we’ll have available in the near future.
– So instead it might be easier to cut chunks of ice off Europa with an army of construction drones and shoot them at Venus using more of those mass drivers. Space tethers could save us a lot of effort and energy here – we made a whole video explaining how they work, but in a nutshell, they are slings that can take a payload on both ends.
On Europa, they do most of the work needed to catapult our ice to Venus. The ice hits the Venus tethers, which gently drop it into the atmosphere, where it falls down as snow. In exchange, the Venus tethers get to catch CO2 ice shot up from below and accelerate it into orbit.
We can remove excess nitrogen using this same method to further lower our atmospheric pressure.
Paul Birch suggests smashing a small icy moon into Venus so that its water can be added to the surface. It would be enormously difficult and would set back the cooling process by many years. Instead, we could just take the exact amount of water ice we need and deliver it gracefully to the surface. And to kill two birds with one stone, we also use the water delivery to help with our CO2 removal.
A mass driver on the surface of Europa can accelerate a payload and put it on a trajectory that intercepts Venus.
Let’s calculate how fast the water ice has to be boosted to make this interplanetary trip.
We use the Escape Velocity equation to work out how fast you need to go to escape Europa’s gravity.
We use G = 6.67*10^-11 m^3/kg/s, M = 4.8*10^22 kg, and r = 1,560,000 m, to get Ve = 2026 m/s.
#Europa by the numbers, NASA, 2019
https://solarsystem.nasa.gov/moons/jupiter-moons/europa/by-the-numbers/
The minimum energy trajectory to transfer between Jupiter and Venus is possible when these planets are at opposite sides of the Sun, as far away from each other as possible. It requires an additional 6500 m/s. Let’s add this velocity to the velocity required to leave Europa, for a total of 8500 m/s.
#Cosmic Train Schedule, Hop David, retrieved 2021
These trips across interplanetary space would be long, from a year to nearly two and a half years, so having a little drone that keeps the ice on the right path would be important. The drone could extend solar sails that reflect sunlight and get a little push to nudge the ice back on track. With even bigger sails, they can accelerate or slow down their payloads by several hundreds or thousands of metres per second, and allow for ice to be delivered to Venus even when Jupiter is far outside the ideal position for a minimum energy trajectory. With huge sails (on the order of 25m^2 for each 1 kg of payload), the whole interplanetary trip can be completed at any time, just by riding on sunlight and with the mass drivers on Europa providing only enough velocity to escape Europa. Once they get close to Venus, the drones would split off to make their way back to Jupiter for reuse.
Below is a paper with examples of the trajectories that can be taken. Note that the trajectory of a solar sail spiralling slowly outwards to the gas giants is the same as the one of a solar sail coming back down to the inner planets.
#Optimal Solar Sail Trajectories for Missions to the Outer Solar System, Bernd Dachwald, 2004
https://core.ac.uk/download/pdf/206589652.pdf
Quote: “Utilizing solely the freely available solar radiation pressure for propulsion, solar sails enable a wide range of high-∆V missions, many of which are difficult or even impossible to accomplish with any other type of conventional propulsion system. Solar sails enable even missions to the outer solar system and beyond, despite the fact that the solar radiation pressure decreases with the square of the sun–sail distance.”
When the ice reaches Venus, it will be travelling at a range of velocities, from a maximum of 40 km/s to a minimum of 17 km/s. The more ‘out of position’ the planets are, the faster the ice will strike. If we let the ice hit Venus, it will add between 144.5 MJ and 800 MJ of energy per kilogram. We don’t want all that energy heating up the planet we just cooled down. Instead, we can use that energy constructively.
Imagine a space station orbiting Venus. It’s velocity over the surface is 7000 m/s. In the back, it has several large loops of wire generating a powerful magnetic field between them. It’s a magnetic nozzle, a large version of the magnetic nozzles found on electric thrusters today.
#Magnetic Nozzles, Electric Propulsion and Plasma Dynamics Laboratory, retrieved 2021
https://alfven.princeton.edu/research/past/MagneticNozzle
Quote: “Simply stated, a magnetic nozzle converts thermal energy of a plasma into directed kinetic energy. This conversion is achieved using a magnetic field contoured similarly to the solid walls of a conventional nozzle (see, for example, Fig. 1). The applied magnetic field in most cases possesses cylindrical symmetry and is formed using permanent magnets or electromagnetic coils, which confines the plasma and acts as an effective "magnetic wall" through which the thermal plasma expands into vacuum.”
A package of ice, let’s say 1 kg, is positioned to hit the center of this magnetic nozzle. It will be travelling away from the ice as it arrives, so the relative velocity between the station and the ice will be between 10 and 33 km/s. We can average this out to 21.5 km/s.
Instants before the high velocity ice reaches the magnetic nozzle, a 0.1 kg disk of frozen CO2 is moved into the ice’s path. This only slows down the ice by 9.1%, but the energy of the impact is enough to make the water ice explode. 0.1 kg at 21.5 km/s means a kinetic energy of 23.1 MJ is transformed into heat within the ice; this is enough energy to strip electrons from atoms and transform it into an 1.1 kg ball of expanding plasma.
Plasma is useful because it responds to magnetic fields. The magnetic nozzle receives this plasma, still travelling at 19.6 km/s, and absorbs its momentum. In effect, the water ice has become thrust that accelerates the space station. With each 1 kg of ice it receives, and each 0.1 kg of CO2 it spends, it gains 21,560 kg.m/s of momentum.
The best way to use that momentum is with a momentum exchange tether. We have described these devices in a previous video.
#1,000km Cable to the Stars - The Skyhook, Kurzgesagt, 2019.
For this terraforming project, those payloads can be loads of frozen CO2 that we want to send into space. A long tether can reach down into the upper Venusian atmosphere, catch a payload and bring it up to orbit. The benefit is that the mass drivers on the surface don’t have to accelerate CO2 all the way into orbit (which means a boost of nearly 8000 m/s). Instead they only have to push CO2 into a much more modest arc that rises up to the edge of the atmosphere, requiring a much more modest velocity of perhaps 2000 m/s (1000 m/s to go up and 1000 m/s sideways to catch the tether). 1000 m/s sideways plus 6000 m/s from the tether equals orbital velocity of 7000 m/s.
Frozen CO2 has no g-force limitations, so a short and thick tether can be used to bring it up to orbital velocity quickly. Of course, this action does not come from free. A tether sacrifices momentum to accelerate its payloads. If a tether is attached to a space station, that space station would lose about 6000 kg.m/s for each kilogram it pulls up to orbit.
You might have guessed by now how exactly delivering water to Venus can help pull CO2 up into space. The momentum that is lost to the tether as it catches CO2 and accelerates it into orbit is regained when water ice strikes the magnetic nozzle and provides thrust.
In this scenario, 1 kg of water ice received can help bring up 3.17 kg of CO2 from Venus, on average. Getting all of Venus’ 465 million billion tons of CO2 into space would require 147 million billion tons of water. The mass drivers on the surface have to do 16 times less work (2000 m/s vs 8000 m/s), so perhaps the most difficult part of terraforming Venus could be completed that much faster.
– After a few decades or centuries, Venus would be covered by a nice, shallow frozen ocean a few hundred meters deep. It would look extremely different from today. A few continents and countless islands have formed. This is beginning to look a bit like our planet!
Whether we deliver water ice to Venus directly, or catch it with magnetic nozzles first, we will have large oceans forming on the surface when it reaches the surface.
From our previous example, 147 million billion tons of water ice would be needed to lift 465 million billion tons of CO2 into space. That amount of water averages out to a depth of 320 metres over all of Venus’ surface. For comparison, if we do the same calculation for Earth, we find an average depth of 2647 metres.
However, Venus is a pretty flat planet. Based on topographical data, we expect 30 to 50% of its surface to be covered by thin oceans.
#Surface elevations for Earth, Venus and Mars, Kenneth R. Lang, 2010.
– A Venus day is 2802 hours long. More than 116 Earth days. So if we just remove our giant mirror, we would grill half of our planet. Even without the massive atmosphere, temperatures would reach unbearable levels. The simplest way to create a day/night cycle and let some energy in again, is with another set of mirrors to illuminate our continents and melt our water oceans. Which would let us completely control how much energy we get and where it goes.
A day on Venus can mean different things.
A sidereal day is the time it takes for a planet to make one complete rotation around its axis. Venus rotates very slowly, so this takes about 5832 hours or 243 Earth days. In fact, one rotation of Venus takes longer than one of its orbits around the Sun, which are 224.7 Earth days long.
A solar day is the time it takes for the Sun to return to the same point in the sky. The combination of Venus’ retrograde rotation (it’s clockwise, while Earth rotates counterclockwise) and orbital motion makes its solar day much shorter: 2802 hours of 116 Earth days. The Sun will appear to move backwards, West to East, in the sky.
#Planet Venus, Natural History Museum, retrieved 2021
https://www.nhm.ac.uk/discover/planet-venus.html
Quote: “Venus rotates very slowly. It has the longest days of any planet in the solar system. A full rotation on its axis (a sidereal day) takes 243 Earth days. On Venus, a day is longer than a year, taking 225 Earth days to make one full circuit around the Sun.
But a full solar day (the time taken for the Sun to return to the same place in the sky) on Venus lasts for around 117 Earth days. This is shorter than a full rotation because the planet rotates very slowly in retrograde.”
These day and night cycles are not practical for species that evolved on Earth, nor do they create comfortable climates. Controlling how much sunlight Venus receives, and creating an artificial shadow that covers half the planet in 24 hour cycles, is a straightforward solution. Paul Birch calls the orbital mirror that provides this shadow a ‘soletta’.
#Terraforming Venus Quickly, Paul Birch, 1991
https://www.orionsarm.com/fm_store/TerraformingVenusQuickly.pdf
Quote: “A more elegant approach is to use a soletta, orbiting in a 24 hour polar orbit, to provide a day exactly 24 hours long.
The sunshade is retained and the soletta given a filling factor of 50%, cutting the sunlight down from a full 2650 W/m^2 to about half as much, equivalent to the sunlight on Earth.”
– The atmosphere is now mostly made up of nitrogen and basically devoid of oxygen. So the first inhabitants will likely be trillions and trillions of Cyanobacteria. We know that they can quickly turn around the atmosphere of a planet because billions of years ago, they were probably responsible for turning the toxic atmosphere of our young Earth into an atmosphere with enough oxygen for more complex animal life.
Cyanobacteria are considered responsible for the ‘Great Oxygen Event’ that occurred between 2.45 and 2.22 billion years ago. They transformed the atmosphere from an anoxic environment to one filled with oxygen.
We would bring in cyanobacteria from Earth and perhaps use little drone aircraft to spread them all over Venus’ new oceans.
#Timing the Evolutionary Advent of Cyanobacteria and the Later Great Oxidation Event Using Gene Phylogenies of a Sunscreen, Ferran Garcia-Pichel, 2019
https://mbio.asm.org/content/10/3/e00561-19
Quote: “Most paleoenvironmental models argue that the composition of the Earth’s atmosphere was mildly reducing and anoxic before the emergence of oxygenic photosynthesis in the cyanobacteria. For possibly hundreds of millions of years, the newly produced oxygen reacted in the environment with reduced compounds, so that molecular oxygen was only temporarily and locally available in “oxygen oases” where cyanobacteria were present with sufficient biomass. Once the pool of reduced minerals had been oxidized, though, molecular oxygen started to accumulate in the atmosphere in what is known as the Great Oxidation Event (GOE)—an accumulation that eventually would result in the oxygen-rich atmosphere that we know today”
#Great Oxygenation Event, Heinrich D. Holland, 2011
https://commons.wikimedia.org/wiki/File:Oxygenation-atm-2.svg
To terraform Venus, we want to recreate this event by placing cyanobacteria in the oceans of water we delivered to its surface.
– But not only that – Cyanobacteria can fix Nitrogen from the atmosphere and turn it into nutrients that can be used by living beings. This way they will essentially fertilize our dead ocean water and prepare it for more complex organisms.
In low oxygen conditions, cyanobacteria can convert nitrogen in the atmosphere into ammonia or other nitrogen-bearing compounds. This ‘fixes’ nitrogen into a form that other bacteria and plants can absorb.
However, as oxygen levels rise, cyanobacteria stop fixing nitrogen, so it is up to other species to take on that role. Azobacter and Rhizobia, for example, are well known for their nitrogen-fixing activity, but they consumes oxygen instead of producing it.
#Nitrogen Fixation in Cyanobacteria, Lucas J Stal, 2015
https://onlinelibrary.wiley.com/doi/10.1002/9780470015902.a0021159.pub2
Quote: “Cyanobacteria are oxygenic photosynthetic bacteria that are widespread in marine, freshwater and terrestrial environments, and many of them are capable of fixing atmospheric nitrogen. However, ironically, nitrogenase, the enzyme that is responsible for the reduction of N2, is extremely sensitive to O2. Therefore, oxygenic photosynthesis and N2 fixation are not compatible. Hence, cyanobacteria had to evolve a variety of strategies circumventing this paradox, allowing them to grow at the expense of N2, a ubiquitous source of nitrogen.”
– On land, our colonists need to ground down some of the former venusian surface to make soil for nitrogen fixing plants to grow on.
We can get a lot more oxygen and fixed nitrogen if we turn the land surfaces of Venus green. However, this is trickier than just introducing bacteria to water.
The Venusian surface is almost entirely hard rocks of volcanic origin. They need treatment before plants can attempt to dig their roots through them. The rocks need to be crushed into fine grains, mixed with water and ‘vivified’ using bacteria, mosses and lichen. Only then is it possible for plants to grow. This process happens naturally on Earth, such as on Hawaiian islands a few years after volcanic eruptions, but we need to kick-start it artificially on Venus.
#Ask a Question, UCSB Scienceline, 2017
https://onlinelibrary.wiley.com/doi/10.1002/9780470015902.a0021159.pub2
Quote: “Soil is a mixture of minerals and organic matter derived from the decayed remains of plants and other organisms. The minerals that make up soil come from rocks. So to make soil, we have to start with rock. As you know, the rock on Hawaii is hardened lava which we call basalt. But in rainy climates, the basalt that is in contact with the atmosphere does not stay fresh and hard for long. When basalt is exposed to a lot of rain, it will start to physically erode and break down into small mineral particles. Some of these minerals will chemically react to form new minerals which we more commonly find in soil. [...]
Soil is not just made from rock though, it also contains organic matter from decayed organisms. The first organisms to grow on a basalt rock are mosses and lichens, because they can live without soil. Moss and lichen will start to grow on freshly cooled lava flows before soil has started to form. When these plants die, their decayed remains become part of the soil, along with the broken down minerals from the basalt rock. Once there is a small amount of soil on the lava flow, more plants can grow, contributing more material to the soil. Eventually enough soil will build up to support forests and grasslands.”
– To speed things up, CO2 would be strategically released to supply the plants and cyanobacteria. Areas already covered with plants could get extra daylight from our orbital mirrors, so the plants would be active for most of each day.
We know that plants respond positively to increased light and CO2.
#Does Enhanced Photosynthesis Enhance Growth?, Miko U.F. Kirschbaum, 201
https://onlinelibrary.wiley.com/doi/10.1002/9780470015902.a0021159.pub2
Quote: “For plants grown under optimal growth conditions and elevated CO2, photosynthetic rates can be more than 50% higher than for plants grown under normal CO2 concentrations.”
Some plants grow better when more hours of sunlight are provided, but other develop disorders. The right plant species has to be selected to take advantage of Venus’ access to endless sunlight.
#Does Enhanced Photosynthesis Enhance Growth?, Miko U.F. Kirschbaum, 2011
https://www.researchgate.net/publication/225040540_Plants_under_continuous_light_review
Quote: “The continuous lighting was found to give benefits to some tolerant crops, which do not develop leaf injuries and can take advantage of the extra light energy provided by continuous lighting.”
Quote: “Growing of plants under continuous light may increase yield, but it also increases light energy input per unit biomass produced. Therefore for each particular case the compromise is to be found, especially when planning is to be made for bioregenerative life support systems for space.”
– Maybe, we won’t have to do this with the same plants and animals we know today. As genetic engineering matures and our understanding of genetics and the machinery of life expands, we might just engineer life as we need it.
Genetic engineering is regularly used today to enhance crop yields, reduce fertilizer use and grow plants in harsher conditions. If we develop this technology further, we could engineer species that are best suited to growing on Venus and producing a maximum amount of oxygen.
For example, here is a recent achievement in significantly increasing rice yields with a single genetic modification:
#Plasma membrane H+-ATPase overexpression increases rice yield via simultaneous enhancement of nutrient uptake and photosynthesis, Maoxing Zhang et al., 201
https://www.nature.com/articles/s41467-021-20964-4
Quote: “Nitrogen (N) and carbon (C) are essential elements for plant growth and crop yield. Thus, improved N and C utilisation contributes to agricultural productivity and reduces the need for fertilisation. In the present study, we find that overexpression of a single rice gene, Oryza sativa plasma membrane (PM) H+-ATPase 1 (OSA1), facilitates ammonium absorption and assimilation in roots and enhanced light-induced stomatal opening with higher photosynthesis rate in leaves. As a result, OSA1 overexpression in rice plants causes a 33% increase in grain yield and a 46% increase in N use efficiency overall.”
In other research, the photosynthesis efficiency was increased by 20%, resulting in 19-37% better growth.
#Synthetic glycolate metabolism pathways stimulate crop growth and productivity in the field, Paul F. South et al., 2019
https://science.sciencemag.org/content/363/6422/eaat9077
Quote: “Depending on growing temperatures, photorespiration can reduce yields by 20 to 50% in C3 crops. Inspired by earlier work, we installed into tobacco chloroplasts synthetic glycolate metabolic pathways that are thought to be more efficient than the native pathway. Flux through the synthetic pathways was maximized by inhibiting glycolate export from the chloroplast. The synthetic pathways tested improved photosynthetic quantum yield by 20%. Numerous homozygous transgenic lines increased biomass productivity between 19 and 37% in replicated field trials. These results show that engineering alternative glycolate metabolic pathways into crop chloroplasts while inhibiting glycolate export into the native pathway can drive increases in C3 crop yield under agricultural field conditions.”
– All in all, it would take several thousand years to make the atmosphere breathable by humans. In the meantime, you could stroll around with nothing more than regular clothes and an oxygen mask.
The temperature would be comfortable, so regular clothes would be sufficient. The air is at the right pressure and not toxic, but it lacks oxygen. An oxygen mask like the one you would use in a hospital can keep you breathing normally. Oxygen would be supplied from bottles, like those used by a Scuba diver, and refilled using electrolysis units in homes.
This is only possible after a lot of work because the atmosphere immediately after cooling isn’t very nice.
#Terraforming Venus Quickly, Paul Birch, 1991
https://www.orionsarm.com/fm_store/TerraformingVenusQuickly.pdf
Quote: “After cooling the atmosphere will consist of about 2 bar of N2, about 0.8 bar of CO2, about 0.5 mbar of CO (~250ppm), and traces of carbon and other inert gases. The CO2 will in due course be converted into oxygen, and the carbon monoxide must be removed, in order to produce a breathable atmosphere.”