Life on Mars: terraforming the Red Planet
Submitted by rau on 28 April 2008
Early astronomers gazed at Mars and thought they saw a planet criss-crossed by irrigation canals and vegetation. One hundred years later, in 1964, the Mariner 4 spacecraft reached Mars. The disappointment for scientists must have been bitter, as they saw a barren world with no signs of vegetation, water or life. To those scientists, the idea of a wet Mars covered by plants suddenly seemed like science fiction.
In the 40 years since Mariner 4, we have learned a lot about Mars from the many spacecraft that have been sent to the Red Planet. We now know that Mars’ surface temperature varies between -143 °C at the poles and +27 °C at the equator. Mars has a very thin atmosphere (about 1% of Earth’s pressure), no liquid water, and the incident UV radiation combined with the highly oxidising regolith make Mars’ surface a deadly place for life. However, from images showing large river channels and networks, and the Mars Exploration Rovers showing layered sediments and alteration of the layers by water, we have learned that in the first half billion years of its history, Mars was a warm, wet place with a thick atmosphere. So could Mars be made habitable again?
This is the premise of terraforming – changing a planet to make it habitable to Earth-like life (terra = Earth). The idea of terraforming was first suggested in the 1930s – purely in the science fiction domain. However, in the 1960s, scientists started thinking about the idea more seriously. Is this really feasible? Can it be done with current technology?
To answer the question of whether terraforming Mars is possible, we must first look at what is required for life and if Mars has these basics. Mars currently cannot support liquid water on its surface due to its low temperatures and thin atmosphere (the atmospheric pressure is below the triple point of water, the pressure below which a material can only exist as a solid or vapour, regardless of the temperature). In addition to liquid water, the most basic life on Earth needs only an atmosphere with which to exchange gases. More complex organisms have more stringent and numerous requirements – plants need small amounts of oxygen, animals need a higher atmospheric pressure – but micro-organisms are low-maintenance.
How could we warm Mars or force the frozen carbon dioxide to be released into the atmosphere? Many ideas have been proposed, such as: putting mirrors in orbit around Mars to reflect extra light onto the Martian surface, thus warming it up; sprinkling dark dust on the poles to decrease their albedo (i.e. brightness) so that more of the Sun’s energy is absorbed; and releasing super-greenhouse gases into the atmosphere to warm up the planet. There are groups working on making the first two of these ideas technologically feasible. But we have already implemented the greenhouse gas idea on Earth – making it, at least for now, the most promising terraforming method.
Super-greenhouse gases are molecules which are very effective at absorbing energy released by the surface of the planet, and then re-radiating this energy both upwards into space – to be lost forever – but also downwards towards the surface of the planet, thus further heating it. They work in a similar way to a blanket. But we don’t want just any blanket! For example, carbon dioxide would be like a thin sheet whereas a super-greenhouse gas, like perfluoropropane (C3F8), would be like a thick wool blanket. So we would want to use super-greenhouse gases – with high warming potentials, and also long atmospheric lifetimes (1000s to 10 000s of years) – to reduce the required replenishment rate. A final key aspect is to choose super-greenhouse gases that do not destroy Mars’ natural current – and future – ozone layer (unlike chlorofluorocarbons, or CFCs).
Greenhouse gases are currently drastically – and undesirably – changing the Earth, so using them on Mars may seem irresponsible or just wrong. However, changing the climate on Earth is undesirable because there is already a highly evolved ecosystem that is intimately tied to the climate. But on Mars there is no such ecosystem: chemical and photographic investigations have shown that life is not proliferated and does not control its environment. There may still be dormant organisms, or organisms living underground. As good explorers and scientists, and in compliance with the planetary protection treaty, we should thoroughly explore Mars for extant life before contaminating our science investigations with Earth organisms or causing a competition between Earth and Mars life.
Fortuitously, the first stages of terraforming are expected to revert Mars to the way it was in its early history – when life would have started – thus giving any dormant or struggling survivors a chance to come out of hibernation and recreate a biosphere.
The terraforming of Mars would also allow us to more easily colonise and explore the planet, requiring us only to wear oxygen masks but no space suits in the higher pressure atmosphere.
One hundred years ago, astronomers thought they saw water and vegetation on Mars. They were wrong at the time, but maybe they were just seeing the future.
A key feature of good science-fiction writing is that no matter how fanciful the idea, it must be theoretically feasible, such that at some future date the onward march of technology turns futuristic fiction to everyday fact. Margarita Marinova of Caltech details the feasibility of the sci-fi-sounding prospect of terraforming Mars – making conditions on the Red Planet more similar to our blue one, in the hope of sustaining (human) life.
Most students have an inherent interest in astronomical matters as well as in environmental issues, and the article neatly straddles both domains, incorporating aspects of the three traditional strands of science, together with geology. There is also scope for the ethics of terraforming to be covered in personal, social and health education (PSHE) lessons. Alternatively, artists could create illustrations of what a recently greened Red Planet could look like, and perhaps see how these compare with illustrations produced in the middle of the last century.
The article lends itself to use as a comprehension exercise or as a stimulus for class debate, where a variety of questions can be devised which cut right across the traditional science subdivisions. Comprehension questions could include:
You could also wander into the realm of moral rights and wrongs of carrying out this planetary makeover. The big question of ‘should we?’ should generate a lot of discussion, and students could be asked to consider if their response to the question could depend on circumstances. For example, would it still be morally wrong to terraform Mars if life on our home planet was in terminal decline, and there was nowhere else for the human species to go? As mentioned above, this could form part of an ethics debate in PSHE lessons, and a larger scale example than the standard ‘right to life’ debate that tends to be used when science and ethics domains meet.
As well as a good introduction to the topic, this article is a useful starting point for further research should the idea stimulate students’ interest. They may want to watch clips of An Inconvenient Truth, in which Al Gore discusses greenhouse gases, and suggest how there could be a silver lining after all, in the global climate change cloud. Or they could investigate Mars further: how do we know what we know about Mars, given that no human has ever visited it? What plans currently exist to send people to Mars? What are the challenges of such a mission, and how do they compare with the challenge faced in the 1960s and 1970s to send men to the Moon? Finally, students could be asked to find examples of historical science fictions that have already become science fact.