Terraforming of Mars

The terraforming of Mars or the terraformation of Mars is a hypothetical procedure that would consist of a planetary engineering project or concurrent projects, with the goal of transforming Mars from a planet hostile to terrestrial life to one that can sustainably host humans and other lifeforms free of protection or mediation. The process would presumably involve the rehabilitation of the planet's extant climate, atmosphere, and surface through a variety of resource-intensive initiatives, and the installation of a novel ecological system or systems.

Justifications for choosing Mars over other potential terraforming targets include the presence of water and a geological history that suggests it once harbored a dense atmosphere similar to Earth's. Hazards and difficulties include low gravity, low light levels relative to Earth's, and the lack of a magnetic field.

Disagreement exists about whether current technology could render the planet habitable. Reasons for objecting to terraforming include ethical concerns about terraforming and the considerable cost that such an undertaking would involve. Reasons for terraforming the planet include allaying concerns about resource use and depletion on Earth and arguments that the altering and subsequent or concurrent settlement of other planets decreases the odds of humanity's extinction.

Motivation and side effects

Future population growth, demand for resources, and an alternate solution to the Doomsday argument may require human colonization of bodies other than Earth, such as Mars, the Moon, and other objects. Space colonization would facilitate harvesting the Solar System's energy and material resources.

In many aspects, Mars is the most Earth-like of all the other planets in the Solar System. It is thought that Mars had a more Earth-like environment early in its geological history, with a thicker atmosphere and abundant water that was lost over the course of hundreds of millions of years through atmospheric escape. Given the foundations of similarity and proximity, Mars would make one of the most plausible terraforming targets in the Solar System.

Side effects of terraforming include the potential displacement or destruction of indigenous life, even if microbial, if such life exists.

Challenges and limitations

The Martian environment presents several terraforming challenges to overcome and the extent of terraforming may be limited by certain key environmental factors. Here is a list of some of the ways in which Mars differs from Earth, which terraforming seeks to address:
* Reduced light levels (about 60% of Earth)
* Low surface gravity (38% of Earth's)
* Unbreatheable atmosphere
* Atmospheric pressure (about 1% of Earth's; well below the Armstrong limit)
* Ionizing solar and cosmic radiation at the surface
* Average temperature compared to Earth average of )
* Molecular instability - bonds between atoms break down in critical molecules such as organic compounds
* Global dust storms
* No natural food source
* Toxic soil
* No global magnetic field to shield against the solar wind

Countering the effects of space weather

Mars doesn't have an intrinsic global magnetic field, but the solar wind directly interacts with the atmosphere of Mars, leading to the formation of a magnetosphere from magnetic field tubes.The Structure of Martian Magnetosphere at the Dayside Terminator Region as Observed on MAVEN Spacecraft.
Vaisberg, O.L et al. ''Journal Of Geophysical Research'', Vol. 123, pp. 2679-2695. 2018. This poses challenges for mitigating solar radiation and retaining an atmosphere.

The lack of a magnetic field, its relatively small mass, and its atmospheric photochemistry, all would have contributed to the evaporation and loss of its surface liquid water over time. Solar wind–induced ejection of Martian atmospheric atoms has been detected by Mars-orbiting probes, indicating that the solar wind has stripped the Martian atmosphere over time. For comparison, while Venus has a dense atmosphere, it has only traces of water vapor (20 ppm) as it lacks a large, dipole induced, magnetic field.
Earth's ozone layer provides additional protection. Ultraviolet light is blocked before it can dissociate water into hydrogen and oxygen.

Low gravity and pressure

The surface gravity on Mars is 38% of that on Earth. It is not known if this is enough to prevent the health problems associated with weightlessness.

Mars's atmosphere has about 1% the pressure of the Earth's at sea level. It is estimated that there is sufficient ice in the regolith and the south polar cap to form a atmosphere if it is released by planetary warming. The reappearance of liquid water on the Martian surface would add to the warming effects and atmospheric density, but the lower gravity of Mars requires 2.6 times Earth's column airmass to obtain the optimum pressure at the surface. Additional volatiles to increase the atmosphere's density must be supplied from an external source, such as redirecting several massive asteroids (40-400 billion tonnes total) containing ammonia () as a source of nitrogen.

Breathing on Mars

Current conditions in the Martian atmosphere, at less than of atmospheric pressure, are significantly below the Armstrong limit of where very low pressure causes exposed bodily liquids such as saliva, tears, and the liquids wetting the alveoli within the lungs to boil away. Without a pressure suit, no amount of breathable oxygen delivered by any means will sustain oxygen-breathing life for more than a few minutes. In the NASA technical report ''Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects'', after exposure to pressure below the Armstrong limit, a survivor reported that his "last conscious memory was of the water on his tongue beginning to boil". In these conditions humans die within minutes unless a pressure suit provides life support.

If Mars' atmospheric pressure could rise above , then a pressure suit would not be required. Visitors would only need to wear a mask that supplied 100% oxygen under positive pressure. A further increase to of atmospheric pressure would allow a simple mask supplying pure oxygen. This might look similar to mountain climbers who venture into pressures below , also called the death zone, where an insufficient amount of bottled oxygen has often resulted in hypoxia with fatalities. However, if the increase in atmospheric pressure was achieved by increasing CO₂ (or other toxic gas) the mask would have to ensure the external atmosphere did not enter the breathing apparatus. CO₂ concentrations as low as 1% cause drowsiness in humans. Concentrations of 7% to 10% may cause suffocation, even in the presence of sufficient oxygen. (See Carbon dioxide toxicity.)

In 2021, the NASA Mars rover Perseverance was able to make oxygen on Mars. However, the process is complex and takes a lot of time to produce a small amount of oxygen.

Advantages

According to scientists, Mars exists on the outer edge of the habitable zone, a region of the Solar System where liquid water on the surface may be supported if concentrated greenhouse gases could increase the atmospheric pressure. The lack of both a magnetic field and geologic activity on Mars may be a result of its relatively small size, which allowed the interior to cool more quickly than Earth's, although the details of such a process are still not well understood.

There are strong indications that Mars once had an atmosphere as thick as Earth's during an earlier stage in its development, and that its pressure supported abundant liquid water at the surface. Although water appears to have once been present on the Martian surface, ground ice currently exists from mid-latitudes to the poles.