Terraforming of Mars

The terraforming of Mars is a hypothetical procedure that would consist of a planetary engineering project or concurrent projects aspiring to transform Mars from a planet hostile to life to one that could sustainably host humans and other lifeforms free of protection or mediation. The process would involve the modification of the planet's extant climate, atmosphere, and surface through a variety of resource-intensive initiatives, as well as 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, toxic soil, low light levels relative to Earth's, and the lack of a magnetic field. Although new techniques have emerged that could raise Mars's average global temperature by tens of degrees within a few decades, the terraforming of Mars is considered to be infeasible using present-day technology. Disagreement exists about whether future technology should render the planet habitable. Reasons for supporting terraforming the planet include allaying concerns about resource consumption and depletion on Earth and arguments that the alteration and settlement of other planets decreases the odds of humanity's extinction. Reasons for objecting to terraforming the planet include ethical concerns about terraforming, and the considerable energy and resource costs that such an undertaking would involve.

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. Research on terraforming Mars continues to advance. Mars, once terraformed, could become humanity's last hope in the event of various catastrophes, such as an unlimited nuclear war that could result in high radioactive contamination of the Earth, uncontrolled global warming, or an epidemic of particularly virulent bacteria or viruses. Side effects of some methods of terraforming include the potential displacement or destruction of any indigenous life 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. The process of terraforming aims to mitigate the following distinctions between Mars and Earth, among others:

Reduced light levels (about 60% of Earth) Low surface gravity (38% of Earth's) Unbreathable atmosphere Low atmospheric pressure (about 1% of Earth's; well below the Armstrong limit) Ionizing solar and cosmic radiation at the surface Average temperature −63 °C (210 K; −81 °F) compared to Earth average of 14 °C (287 K; 57 °F) 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 has no 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. 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. The current loss rate of CO2 from Mars's atmosphere to space is equivalent to approximately 1 millibar per billion years. 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 CO2 atmosphere has about 1% the pressure of the Earth's at sea level. It is estimated that there is sufficient CO2 ice in the regolith and the south polar cap to form a 30 to 60 kilopascals [kPa] (4.4 to 8.7 psi) 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 100 kPa (15 psi) 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 (NH3) as a source of nitrogen.

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