Terraforming Mars for the Long Term

Terraforming Mars for the Long Term, from the writer of The Terraformers’ Toolkit. (The Terraformers’ Toolkit: Everything you have ever wanted to know about terraforming and our future in space. The where, why, when, how and what of terraforming.) www.amazon.co.uk/dp/B09X6739P...
One of the major risks with Mars is that we might terraform the red planet, only for it to revert to its previous lifeless state over the course of tens of thousands of years. It would seem sensible that if terraforming is going to be done and all that money invested, the job should be done properly.
Moons
Earth’s moon helps to stabilise our planet’s obliquity (tilt) and gives us our seasons. Mars’ obliquity is currently 25.2°, which is very similar to earth’s 23.4°. However it has varied from 0° to 60° in the past and if this happened again, it would seriously damage a terraformed Mars’ ability to host life from earth.
Additionally, our moon gives us our tides and helps to ensure that ocean circulation distributes nutrients between the continents. On a planet with no large moon, the lack of tides would stop this process working adequately and might lead to the development of dead zones in the ocean where all the nutrients had been used up.
Additionally, most animals and plants use the moon and the seasons it induces to time their lives. In its absence, they may not be able to time their breeding, migration, feeding or hibernation, and so may not survive.
Therefore, if we want to terraform for the long term, we should consider giving Mars a large moon. Perhaps an asteroid or one of the outer solar system moons might be right. However, the amount of propellant needed to get it from its current location to Mars, slow it down and put it into a circular orbit will be very large indeed.
Plate Tectonics
Earth’s plate tectonic geological system means that nutrients and elements such as carbon are constantly recycled between ocean and the land. The way this happens is that nutrients are washed by rivers from the land onto the ocean floor, then that is subducted beneath continents where it is melted in the mantle. The melted rock and seafloor sediments are then erupted as lava and vapour by volcanoes on the edge of the continents.
This has worked to keep our planet habitable for nearly four billion years. Mars may have a tectonic system called degree 1 convection, in which one hemisphere is dominated by up-welling, while the other by down-welling. This is evidenced on Mars by the great Northern depression and the Tharsis Rise mega volcanic region. However, if volcanism is currently absent on Mars, the northern basin would accumulate nutrients washed from the uplands and would gradually fill. The southern uplands would become nutrient deficient, and the ocean might become too salty for life.
On earth plate tectonics has meant that the salt concentration in the sea has remained stable at 6% over billions of years. if this rose on Mars due to the lack of salt recycling, it could cause a mass die off, leaving only microorganisms in a hyper-saline ocean.
Unfortunately, Mars crust is considerably thicker than earth’s, which means that there is no chance that we could initiate an earth like plate tectonic system. Instead, we would have to develop some kind of recycling system that took nutrients from the northern ocean and distributed them over the southern Uplands.
Atmosphere
In the absence of a magnetic field, Mars would need a thick atmosphere with an ozone layer to protect the surface against cosmic and solar radiation. Small planets like Mars do have some difficulty in hanging on to atmospheres, simply because their gravity is much lower. Mars, with only one third of the earth’s gravity will always have this problem. But having a thick atmosphere which extends further into space than earth’s with greater Atmospheric pressure at the surface would reduce the chance that portions would be blown away by the solar wind.
Additionally, on earth volcanoes pump carbon dioxide into the atmosphere, which stays there until it is removed by plants during photosynthesis. If no volcanoes were erupting carbon dioxide on Mars, the atmosphere’s content of carbon dioxide would decline to nothing, and because plants need this for photosynthesis, they would all eventually die. Therefore, some artificial system would be needed to replenish the carbon dioxide in the atmosphere on a permanent basis.
Summary
Earth is a mass of cycles and systems that have kept our planet habitable for billions of years. If we want to terraform any planet for the long-term we have to understand our own planet a great deal better. Then we have to try and recreate our planet’s structures, cycles, systems and feedbacks on another world.

[@salemsmith2878]

Couldn't you just group together thousands of smaller asteroids together to build a moon vs say moving a really big rock?

[@charlesjoynson7758]

Some of them are metal rich, so we'll need them for our technology. Together all the asteroids in the belt make up just 4% of our moon's mass, so they may not be enough. But it depends on the technology our descendants have at their disposal and how powerful their rocket engines are.

[@salemsmith2878]

@@charlesjoynson7758 Wow, I had no idea the volume of asteroids was actually that small. Honestly, I thought there was another planet worth of asteroids out there, lol.