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Water and Other Volatiles on Mars: Resource Base and Implications for Terraforming

Abstract

Water ice and other volatiles are vital in sustaining human settlement in space. Hydrogen and oxygen extracted from water by hydrogen-oxide reactions can be used as propellants on short-range interplanetary missions in the inner Solar System prior to developing more advanced propulsion systems for subsequent long-range interplanetary missions. The resource base for Martian water-ice and other volatiles far exceeds the resource base on the Moon and Mercury. Water ice occurs in abundance on Mars in polar ice caps, shallow permafrost, and in layered terrain adjacent to the poles. Martian permafrost, which holds more water ice than the poles, occurs as tropical mountain glaciers and in polygonal terrain with morphologies similar to those of terrestrial periglacial features. Subsurface ice on Mars has an areal distribution exceeding 20 million square kilometers, whereas the polar caps, although 2.7 and 3.1 km thick at the North and South Poles, respectively, each encompass an area <1 million square kilometers. Mars possesses sufficient water and volatile resources amenable to terraforming, although other volatiles from ammonia-rich comets can also be introduced artificially from human-induced impacts to accumulate greenhouse gases in the tenuous Martian atmosphere. At least four comets, each with a mass of 10 Gt (10 billion metric tons), would be required to trigger a Martian greenhouse effect. Moreover, in situ methods of constructing an artificial Martial atmosphere could involve greenhouse gas factories expelling halocarbon gases (CFC's), with 39 Mt (million metric tons) necessary to sublimate the southern carbon-dioxide ice cap. Other methods can involve deploying orbital reflection arrays with a collective mass of up to 200,000 tonnes to produce sufficient insolation for volatilizing the Martian polar caps. However, the lack of a robust magnetosphere is a major obstacle to successful terraforming of Mars, as solar flares could periodically strip away up to 30% of the newly created, sparse atmosphere. Best-case terraforming scenarios may require centuries, and the technology to construct a protective Martian electromagnetic field protection could involve a similar timescale.