Mars Future

Although our solar system currently has only one world with a global ecology, this may not always be the case. There has been serious discussion of planetary ecosynthesis on Mars. The fact that Mars once supported widespread liquid water, and possibly life, motivates the question of restoring such conditions on Mars by artificial means.

The fundamental challenge of restoring habitable conditions on Mars is to warm up the planet from its current -60 °C to over 0 °C, and perhaps as warm as Earth, +15 °C. Humans have demonstrated, and implemented, the technology to warm planets with Earth as our first target. The level of human-induced warming on Earth is debated but is probably of order a few degrees. On Mars the warming needed would be tens of degrees - many times larger than on Earth - but the extrapolation from Earth to Mars is conceptually straightforward. Energy balance calculations suggest that warming Mars might be achieved in 100 years or less. However, producing an oxygen-rich atmosphere would take more than 100 000 years. Thus, warming Mars is within current technology and this fact frames the discussion about Mars in a fundamentally different way than planetary-scale environmental alteration on any other world of the solar system.

We tend to think of the present oxygen-rich Earth as the only model for a global ecology. However, there are two alternative possibilities for life supporting states for Mars: one with oxygen and one without. These two alternative states are listed in Table 1.

If there was life on Mars and it is now extinct beyond recovery, then planetary ecosynthesis can be viewed as a type of 'restoration ecology'. If there is life on Mars, or recoverable life, but it shares a common ancestor with life on Earth then it seems plausible that planetary ecosynth-esis can proceed using Earth life forms as needed.

Perhaps the most interesting and challenging case is that in which Mars has, or had, life and this life represents a distinct and second genesis. I would argue that if

Table 1 Habitability

Parameter

Limits

Note

Global temperature

0-30°C

Earth = 15 °C

Composition for plants, algae, microorganisms

Total pressure

>1 kPa

Water vapor pressure plus O2, N2, CO2

CO2

>0.015 kPa

Lower limit set by photosynthesis

No clear upper limit

n2

>0.1-1 kPa

Nitrogen fixation

o2

>0.1 kPa

Plant respiration

Composition for breathable air

Total pressure

Pure O2

>25kPa

Lung water vapor plus CO2, O2

Air mixture

>50kPa

Based upon high elevation

<500 kPa

Buffer gas narcosis

CO2

<1 kPa

Set by toxicity

n2

>30kPa

Buffer gas

o2

>13kPa

Lower limit set by hypoxia

<30kPa

Upper limit set by flammability

Adapted from McKay CP, Toon OB, and Kasting JF (1991) Making Mars habitable. Nature 352: 489-496.

Adapted from McKay CP, Toon OB, and Kasting JF (1991) Making Mars habitable. Nature 352: 489-496.

there is a second genesis of life on Mars, its enormous potential for practical benefit to humans in terms of knowledge should motivate us to preserve it and to enhance conditions for its growth - a second genesis in a second global ecology.

See also-. Biosphere: Vernadsky's Concept; Climate Change 2: Long-Term Dynamics; Coevolution of the Biosphere and Climate; Gaia Hypothesis; Phenomenon of Life: General Aspects.

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