Nuclear war. Collapse of the biosphere. Catastrophic global warming. Space elevators. Whatever the reason, Earth is no longer green and friendly. Many want to live on other planets, and have the resources necessary to go. So how will life on other planets look like?
|Mercury as seen by MESSENGER|
The first on our list. Known for being our Solar System's equivalent of a moth flying too close to the light, it is a planet of extremes. Sunlight varies between five and ten times the intensity on Earth, leading to surface temperatures of up to 700K.
That is 427 degrees Celsius. Aluminium loses 90% of its strength. Astronauts will boil in regular spacesuits.
The cold side is not any better. Without any atmosphere, it drops to 100K, or -173 degrees Celsius. That is cold enough to freeze oxygen. It rotates three times (three Mercury days) in two orbits (two Mercury years). Originally much larger, it was struck by an object thousands of kilometres wide: a massive impact that stripped off most of the crust and mantle. Today, it is the cold, naked core of that planet.
|Polar craters with unusually reflective basins highlighted in yellow .|
One of Mercury's distinctive features is the existence of craters and crevasses at high latitudes (near the poles), deep enough to keep their lowest point in permanent shadow. In these dark pits accumulate volatiles such as water. Scientists believe that a layer of dust and sediments on top of the volatiles prevents their sublimation into space.
So, on the smouldering inferno of Mercury, there are frozen lakes. They contain water and probably ammonia and carbon too. These are all the ingredients needed for an autonomous colony!
Mercury is only 40% wider than our Moon, but its density means it produces a gravity of 0.38G. This is believed to be sufficient for preventing the effects of microgravity, such as bone loss, eyesight problems and muscle atrophy.
|Notice the 'flux transfer events'|
The planet's iron core is still active. It produces a magnetic field, giving Mercury a magnetosphere about 1.1% as strong as Earth's. It is insufficient to reduce the radiation at the surface in any significant way. Worse, it can reconnect with the interplanetary magnetic field in gigantic magnetic storms, producing funnels that concentrate the solar wind onto a spot on the surface.
The lack of atmosphere, like most places in the Solar System, means that anything exposed to sunlight receives the full dose of UVs and X-rays.
Mercury is nothing special in terms of the minerals available at its surface. Rocky or metallic asteroids offer the same without any digging or any gravity to slow things down. However, it has two advantages over the asteroids:
Unlike on a barren rock in space, water is freely available. The dark pits mentioned above contain hundreds of trillions of water in total. They can be connected with overland travel routes (rail, roads, tunnels) or simply pumped from extraction site to mining site.
|Water marked on Mercury's North Pole.|
An asteroid miner would have to get his water from a comet, which is separated by millions of kilometres, thousands of meter of deltaV and several months, if not years, of travel.
Solar energy is the other advantage. With 5-10x the intensity of sunlight on Earth, solar panels can be expected to produce up to 5kW/m^2, more as efficiency rises. With thin film technology, this translated into energy densities rivalling nuclear reactors, and vastly exceeding them when power generation equipment is taken into account (the solar panels produce electricity directly).
Energy on Mercury does not need fissile materials, and can be produced with a much lower mass investment compared to elsewhere in the solar system. It makes perfect sense to sell this energy as laser beams shooting off into interplanetary space. Without an atmosphere to absorb the beam, low-wavelength lasers can be used to beat diffraction at long distances.
The major downside to an industry on Mercury is the deltaV requirements to get anything from Mercury Low Orbit to the rest of the Solar System. It takes 12.5km/s of deltaV to get from Mercury to Earth. This is very expensive to do by chemical rockets (4500m/s exhaust velocity means you need 16 kg of propellant for every kg of rocket) and difficult even with nuclear propulsion (4.9kg of propellant per kg of rocket).
Cheap solar energy around Mercury allows the effective use of electric drives with 0.4kg of propellant per kg of rocket. They can perform the braking or departure burn near Mercury, which would otherwise cost 7km/s. This reduces the deltaV requirement of a Mercury mission to something comparable to a Mars mission.
In conclusion, despite all of its metals, minerals and volatiles, Mercury is best used as a workshop for energy-intensive items. These high value products are the actual items being sent to the rest of the Solar System, off-setting the cost in propellant. Examples include energy-intensive microelectronics and electro-formed precision components.
An upside to Mercury's position is that it can send out cargo four times a year to anywhere in the Solar system, thanks to its synodic period. Mars, in comparison, requires a two-year wait between minimum deltaV trajectories becoming available. It allows a Mercury colony to be built up quicker, and produce returns twice as fast. This might become of lesser concern for time-insensitive trade, such as bulk metals or volatiles, that can use low thrust electric propulsion.
The Mercury Colony
As described above, the best place to position a Mercury colony is in the shadow of a large, polar crater. Average temperature in the shadow is 108K, or about -165 degrees Celsius. Large amounts of water can be found, covered in dark dust rich in hydrocarbons and unknown amounts of nitrogen.
Solar reflectors are mounted over the edge of the crater. They bounce down calculated amounts of sunlight to where it is needed. It is concentrated on certain parts of the frozen lake, to melt it, and diffused over working areas to create warmer conditions.
The colony will have three main sections.
The first is the habitation section. It consists of inflated living areas and farms sunk into the lake. It will have transparent roofs to take in reflected sunlight. The walls will be insulated, but heat will escape and partially melt the surrounding lake. It will create a muddy ring around the colony.
The habitation section has two levels. The upper level is warm and well-lit, but is not well protected from radiation. It is where colonists enter and exit from, and where most machinery is located. Solariums and greenhouses can be installed near the transparent roofs. Entering and leaving the colony is done through hatches in the roof. The lower level is completely buried under frozen water. Is is well protected from radiation, but might end up feeling claustrophobic to some inhabitants. Flexible walls hold in the breathable atmosphere, but escaping heat will make the other side a cold water slush. The walls might move, flex and bulge with temperature variations.
Walkways extend out of the habitation area and over the lake. It connects to the powerplant and the factory.
|PS10 and PS20 solar thermal powerplants in Seville, Spain.|
The powerplant uses focused sunlight and boiling water to generate electricity from turbines. It is cheaper and lighter than producing the equivalent energy from solar panels. Some of the energy goes into melting water and splitting it into hydrogen and oxygen. This is used to refuel rockets landing nearby. The rest goes into powering the factory. The most visible features are the large black panels extending up into the sunlight, and the pipes snaking into the lake to extract water.
The factory is the most important component of the colony's survival in the long term. It provides the main economic benefit, and gives work to the colonists. Automated mining machines depart from the factory and onto Mercury's surface. They are covered in gold foil to protect them from sunlight, and drag large tractor-scarpers and buckets behind them. Seen in action, they resemble white flares slowly leaving a dark trail of disturbed earth behind them.
The mining machines return to the factory and dump their load. It is sorted and separated into useful minerals and metals. Some are packaged into large blocks of pure elemental material, others are processed into chemicals. The most valuable items require precision machinery and lots of energy. If it is microprocessors, they might follow a 'rad chain', similar to the cold chain existing for frozen food products. A rad chain ensures that electronics are never exposed to naked solar radiation, and kept inside radiation shielding from production through transport and until delivery.
The factory will sent its products to the launch site. This can be an orbital tether, a laser battery powering rockets or a mass driver.
Mercury presents some unique dangers.
As Mercury is an airless world, decompression is a significant risk. This is especially important for space-suited colonists. Inside a habitat, the ice that the buildings are sunk into slow down decompression enough for the walls to be patched up.
Freezing or getting trapped might be counter-intuitive, but it is the risk of living on a lake at -165 degrees Celsius. While water melts at 0 degrees Celsius, the lake can contain frozen oxygen or nitrogen. They evaporate and much lower temperatures, low enough that the heat from a human body can cause them to burst out of their bubbles and create a sinkhole. This is made worse by the fact that most of the lake will be covered by gray-brown dust and look like solid ground. Getting stuck in the ice can cause hypothermia and death...
Overheating will happen. A man in a space-suit might be asked to hike out to a damaged mining robot and fix it. He will take the reflective cover, the water cooler, the insulated sheath... but these will only provide a few extra minutes in case of an accident. The combination of intense sunlight and insulating vacuum will mean that direct exposure to sunlight is a messy, if at least rapid, way to go.
|The reflective, insulating sheets used for the James Webb telescope.|
Blinding might be a more commonplace danger. With everything covered in reflective surfaces, the risk of catching some of the sun's rays at an unexpected angle is great. This might enforce the use of dark sunglasses even in shadowy or dim areas on Mercury.
Orbital debris is very dangerous on an airless world. Without anything to slow them down, even the tiniest speck of dusk makes it to the surface without slowing down. These can penetrate habitats, kill people on the surface or wreck equipment. Armored plates might become habitual features of anything designed to work on the surface. Thankfully, 0.38G gravity might not make them much of a burden.
Spaceships in orbit face dangers related to the intense sunlight. Radiators are less efficient and have to angled edge-on to the sun. Large tanks of liquid hydrogen become dangerous explosives, as they catch a lot of sunlight, and the transition of the contents from a liquid to a gas can rupture the tank.
A Mercury colony will start out in craters, and scrape the surface for minerals.
As colonists increase in number and decide to spend a large part of their lives on the planet, more permanent habitats will be dug into the rock around the crater. This will greatly improve radiation protection, enough for infants to develop with no risk of cancer.
|In grreen, the habitable ring.|
Eventually, the craters will not be enough. There exists a vast ring of habitable underground area around Mercury's poles. Only 70cm deep and covering 200 thousand square kilometers, they offer comfortable living conditions at a constant 22 degree Celsius (room) temperature.
Mercury's industries will start focusing on planetary megaprojects. A 2km wide reflector can focus an infrared (1000nm) laser beam on a 1km wide target at the distance of Jupiter! Even with transmission and conversion losses, it will provide plenty of cheap energy... and a potent weapon.