Far back in its “childhood” as a planet, Mars really was Earth’s twin with its watery climate and substantial amounts of carbon dioxide in the atmosphere. Common processes led to almost all of its carbon dioxide being trapped in carbonate rocks.
However, there was a big difference between Earth and Mars. Mars lacked the mechanism of plate tectonics which enables the carbon to be recycled i.e. ground down, heated up and spewed out as gas. The fact that Mars was unable to recycle any of its carbon dioxide back into its atmosphere meant that it was unable to sustain a significant greenhouse effect. This in turn has meant that the surface of Mars is much colder than an equivalent more Earth-like planet would be at that distance from the Sun.
Mars orbits the Sun once every 687 Earth days. This is what defines the Mars year – it’s nearly twice as long as the Earth year. That might of course take a little bit of mental adjustment on the part of our would-be colonists. However, like Earth, Mars rotates on its axis from west to east – no challenge to our habits of mind there. The solar day on Mars (now generally known as a “Sol”) is 24 hours 39 minutes 35 seconds long – comfortably close to the time the home planet takes to rotate in relation to the Sun. At least the first colonists on Mars won’t find the day length too taxing in terms of mental adjustment. Our physiology should be able to adapt to the extra half hour or so. Think of it as an extra half hour in bed in the morning!
Mars also has seasons much like out own (though of longer duration). This is thanks to another point of comparability in that Mars's axis, like that of Earth's, is tilted in relation to its orbital plane. The angle of tilt is 25.19 degrees on Mars, compared with 23.45 degrees for Earth - so again no great difference. As on Earth, this tilt means that the quantity of solar radiation (i.e. sunlight) received on certain parts of the planet varies greatly during the year, which is another way of saying it has seasons - which if nothing else will be a boon for future generations of Martian poets. The Mars seasonal year thgough is actually slightly longer than the Mars solar year - a consequence of the fact that Mars's axis wobbles slightly as the planet turns.
Our not so smaller cousin
So how big is Mars exactly? It’s our cousin, all right, but something of a poor relation in terms of size. Its radius at 2,107 miles (3,390 kilometres) is actually about half the radius of Earth.
Still, it tips the scales at a respectable 642,000,000,000 billion tonnes in terms of mass – albeit Earth is about ten times as massive as Mars (partly because it is significantly denser than Mars). But, there is no doubt we are talking about a big planet, the sort of thing we are used to culturally – when we talk about the four corners of Mars, they also are thousands of kilometres apart. The circumference of Mars at the equator is about 21,343km (13,300 miles), which is about half that of Earth’s.
Of course nearly 71% of Earth’s surface is covered in water – not a great medium for living in - or on. The total land area on Earth is 148.94 million sq km. That is only slightly more than Mars’s surface area of 144.80 million square kilometres. In terms of land area then the two planets are virtually the same in extent.
Is it surprising, then, that men and women have dreamed of living on Mars one day. After all, it is not so very different to our own planet – and now we know for sure (as we shall explain further) that it has plenty of water, that essential ingredient for life. If only we could give it an atmosphere and make it a lot warmer…Is it really such an absurd idea? And isn’t that what gives Mars that ultimate allure, the idea that it can and will - given time - become our perfect match?
Making another Earth.
Mars is as we say humanity’s potential second home. Of course, as already noted it does not come as a green and pleasant land wrapped in a breathable atmosphere.
However, of all the other planets in our solar system it is the one most like our own. In fact much of it resembles a landscape with which we (or at least a few of us) are familiar: the cold, dry deserts of
Antarctica, certainly in terms of appearance, ground conditions and temperature.
If we are to make Mars green and pleasant, then it will take a great deal of work and vast investment. On Earth such effort with respect to
Antarctica seems pointless. We have plenty of perfectly good and productive land on which to make our homes. In any case, if we were to warm Antarctica (leaving aside the environmental menace that would represent) we would probably have to boil the rest of the planet – not an attractive prospect. But in the case of Mars, if ultimately we want to create a comfortable home, we can do that only through our own efforts, through what is known as terraformation.
In fact it was Venus that first excited Sagan’s interest, with him proposing in 1961 that our overheated twin be engineered to make it a suitable home for humans. After all, in many ways Venus does seem a better prospect. In terms of size it offer virtually the same gravitational force as on Earth and being so much closer to the Sun, there would be no difficulty in keeping it at the reasonably warm temperature humans like. Carl Sagan proposed using algae to remove carbon dioxide from Venus’s atmosphere, thus reducing the greenhouse effect which made the planet unbearably hot and thus also – at the same time - helping to create a more breathable, oxygen rich atmosphere.
However, as we learnt more about the planet it became apparent that this rosy prospectus was not capable of being fulfilled: any sequestered carbon would (given the very hot conditions at the Venusian surface) simply return to the atmosphere rather than be fixed in the regolith (the technical term for the surface rock and soil). Venus’s extremely long day – equivalent to 243 Earth days – was also something that no terraformer could really get by.
Gradually then, interest in terraformation has settled on Mars – where the problems are the opposite to those on Venus: how to thicken the atmosphere, and how to make it warmer. There appears to be a growing consensus that these goals are not unachievable but that to attain them will however certainly be difficult in the extreme.
Terraformation of Mars would be a very long term project, probably to be measured in the thousands of years. How it is to be achieved is, as yet, not clear. The simplest way might be to reverse our environmental approach on earth – where we endeavour to prevent pollution entering the atmosphere - and, instead, to do our level best to pump out as much greenhouse gas (e.g. carbon dioxides, fluorocarbons) into the atmosphere as quickly as possible. It is a rather wicked thought: that earnest environmental scientists on Mars might be urging us to do the exact opposite to what they urge us to do on Earth! But this approach will help thicken the atmosphere and retain heat, so fostering the warm and wet conditions we need as human beings to prosper. Once there is sufficient carbon dioxide in the atmosphere then we can use bacteria and plants to begin the process of creating oxygen and turn the atmosphere into one that we can breathe (although the likelihood is that science and technology would make it possible for us to breathe atmospheres which are less like our own with lightweight equivalents of gas masks or aqualungs).
Eventually, if the recipe followed in the terraformer’s cookbook translates into a tasty dish, we should end up with a verdant Mars, with its own oceans lapping shorelines in the northern hemisphere. Then the only thing really distinguishing Mars from its more senior cousin would be the lower gravity, about which little could be done (although you could simulate higher gravity with a heavy body suit to help weigh you down – an idea we will return to later). We don’t actually know yet whether the lower gravitational force on Mars will be a problem in the longer term. On the plus side it should mean far less wear and tear on joints. Humans on Mars are likely to be far less troubled by arthritis than on Earth.
So then, should our goal be the terraformation of Mars? Is that why we want to go there?
Well, yes and no.
To make it clear, terraformation is desirable but if it is ever to be embarked upon it will be a long, long process. If you are interested in seeing how it goes, too bad: you will be dead before it even gets started.
In any case, we can’t wait for the planet to be terraformed from a safe distance. We have to be there before we can get the process going. So, from that point of view, the “terraformation versus life-supported missions” debate is in reality a false dichotomy. Whether your main interest is terraformation or simply colonisation, you have to get to the planet.