GROWING PAINS ON MARS

If you're a person in need of a change of appearance, call a plastic surgeon. If you're a planet, call a terraformer.

Terraforming is planetary engineering on a global scale, and its changes are far more than skin-deep, involving grabbing an inhospitable planet by the scruff of its neck and modifying its temperature, surface and atmosphere to make it capable of supporting life.

Sound like another slice of sci-fi fantasy? Far from it, though the concept has most often reached the popular conscious through science-fiction books and films. The unfortunate human colonists of the planet in Alien were indulging in a spot of terraforming themselves - until they became monster fodder.

It was a science-fiction writer who coined the term, when Jack Williamson introduced it in his 1942 story Collision Orbit, and writers such as Robert Heinlein and Arthur C Clarke have all published stories based on the idea, with candidates for terraforming ranging from Jupiter's moon Ganymede to the hothouse hell of Venus.

Venus provided the subject of the first seriously scientific consideration of terraforming when Carl Sagan published a paper in 1961 on how to make the planet a cooler place for people to be, though his ideas have not stood the test of time. But books like The Greening Of Mars, published in 1984 by biologist James Lovelock, who formulated the Gaia hypothesis about the inter-relatedness of the systems of planet Earth, have confirmed the subject's arrival in respectable scientific circles, and sparked growing interest as our understanding of planetary behaviour, both on Earth and our neighbours', increases.

It is Mars, however, that has focused the attention of terraforming experts. The reasons are not hard to understand, given the tantalising visions of the planet offered by the Mariner, Viking and Pathfinder missions. Cameras capture a place where the sky is a ravishing Mediterranean pink, where water-ice clouds occasionally drift by, and hoar frost forms on rocks during the icy Martian night. On good days the early afternoon equatorial temperatures can reach 20C, though the nights can get down to -90C. Dramatic pictures from space show evidence of channels carved out by running water, and the current Pathfinder mission has landed in the middle of what appears to be an ancient flood plain. Not only did water once apparently run on Mars, scientists now believe that all the chemical requisites of life - water, nitrogen, carbon dioxide and other carbon compounds - are present on the red planet. So where are they, and why isn't Mars a planet of abundant life?

The answer is that the elements of life are now thought to be trapped in the very fabric of the planet, having become bound in polar ice, permafrost and carbonate rocks as the thick carbon dioxide atmosphere that once cloaked Mars (not dissimilar to how Earth was during its pre-Cambrian period) was absorbed by the early waterways of Mars and deposited as carbonate rocks. On Earth, constant volcanic action kept the atmosphere recycling but on the less active Mars it became trapped, and the planet's atmosphere grew thinner and thinner until falling temperatures froze the water itself into the planet's fabric. Mars had sunk into its cold and sterile state, where a gossamer-thin atmosphere combines with an average global temperature of around 60C and, in the absence of any atmospheric shield, a barrage of deadly UV radiation bathes the surface.

Yet the knowledge of its very different past gives real hope to the would- be terraformers of Mars. As on Earth, global climate is the result of the interaction of a range of things. Mars is freezing and UV-scarred because of the loss of its atmosphere but if the atmosphere is still there, albeit embedded in the planet, then it can be restored - a restoration that would, in theory, trigger a chain of positive feedback mechanisms. Get the atmosphere back into play and up goes the temperature as more of the Sun's heat is retained. Get back the atmosphere and down goes the surface bombardment of UV. Get back the atmosphere, and the composition of the air on Mars begins to be transformed. Get back the atmosphere and Mars can begin to come alive.

The Martian terraformer will play a five card hand, with the cards in this game of planetary transformation marked increased surface temperature, increased atmospheric mass, liquid water, reduced surface UV, and increased oxygen and nitrogen in the atmosphere. The first four of these changes would be enough to turn Mars into a place hospitable for basic forms of life such as bacteria and simple plants. But for more complex plants, animals and humans, the increased nitrogen and oxygen is vital. This first step to full terraforming is called ecopoiesis, and various mechanisms have been considered to achieve it.

Terraformers believe that only a reasonably small change in temperature may be needed to trigger the release of trapped carbon dioxide from the surface layer of Mars, triggering a runaway greenhouse effect that would initiate the desired cascade of positive changes. Possible methods differ widely, but all are theoretically feasible, though some seem exotic. The least startling involves darkening the Martian polar ice caps to reduce the significant amount of the Sun's heat which is at present reflected back into space. This reduction in the albedo (reflectivity) of the poles could be achieved by covering them with a thin layer of dark dust, which could be mined on Mars. A reduction of the albedo by 4 per cent has been calculated to raise the temperature the few degrees needed to melt the caps and initiate a runaway greenhouse effect.

Another suggestion is to let some CFCs loose on Mars. These gases, in the Earth dog-house for their global warming properties (10,000 times greater than that of carbon dioxide), initially seem ideal for warming up Mars. However, Christopher McKay of Nasa's Ames Research Center has pointed out that CFCs would be unstable in the present Martian atmosphere where the massive UV presence would tend to break their basic bonds, reducing their lifetime from years in Earth's ozone-protected atmosphere to just hours. One way round this, according to British expert Martyn Fogg, would be to use compounds called perfluorocarbons, whose basic bond (carbon- fluoride) would be much more robust under Mars' UV bombardment than the carbon-chlorine bond of CFCs. The most optimistic projections suggest that using such greenhouse gases may be capable of warming Mars by up to 30 degrees.

Rather than cutting the amount of heat reflected from the poles another method of gently simmering Mars would be to increase the input of solar energy (Mars' distance from the Sun means it gets about 40 per cent of the heat energy Earth receives) using gigantic mirrors behind the planet to reflect sunlight back on to it. Nasa's Christopher McKay and aerospace engineer Robert Zubrin have published plans for a 125km diameter solar mirror to be erected behind Mars in a stationary position, from where it would beam back enough sunlight to raise the temperature of Mars' south pole by five degrees which many believe is all that's needed. The Russians have already successfully tested the first space mirrors in Earth orbit with the Znamia project, and there is nothing in practice to forbid such a huge mirror in the weightlessness of space. Two hundred thousand tons of aluminium (five days' worth of Earth's current production) would be enough.

Two final methods of releasing the trapped carbon dioxide atmosphere of Mars are more explosive. Bolder terraformers have suggested a dramatic assault on Mars by diverting asteroids to smash into the planet, generating heat from the impact at the same time as releasing trapped gas from the point at which it crashes. Princeton physicist Freeman Dyson has even suggested breaking up one of the icy moons of Saturn, Enceladus, and sending its fragments crashing into Mars in an orderly procession, a controlled Armageddon which he manages to make sound poetic, speaking of "the incessant sparkle of small meteors ... Day and night the sky is warm ... A little later, it rains on Mars for the first time in a billion years." However fantastic Dyson's conception, it is not ruled out by any impossible factors. But his imagination outstrips what is likely to be feasible within the near future.

Martyn Fogg has a similarly explosive suggestion to help turn up the Martian thermostat - setting off thermonuclear devices deep beneath the surface. While there is growing evidence for the existence of carbonate rock on Mars in significant quantities, to release carbon dioxide from such a source (devolatilisation) requires high temperatures and/or sudden shock pressures. And that's just what an underground nuke will give you. There have already been tests of such nuclear mining on Earth, as part of America's Plowshare Program to assess the civilian use of nuclear weapons. Data from part of the programme, Project Gasbuggy, suggests that massive H-bombs (which work by releasing energy from the fusion of light non-radioactive atoms, as opposed to fission weapons which work by breaking apart heavy radioactive ones) could release useful amounts of carbon dioxide if exploded deep within carbonate rocks (such as limestone). Ideal sites of fairly pure carbonate deposits are believed to exist in many places on Mars, most notably in the Mariner Valley.

Nuclear devices for terraforming Mars would be very different to those held by the armed forces. For one thing, they would be many times more powerful than current thermonuclear explosives - there is no theoretical upper limit to the power of a fusion nuke (the Sun, for example, is basically an enormous fusion device). Fewer giant explosions would be cheaper than having lots of smaller ones. One obvious worry about nuclear mining is radioactive fallout, though the placement of the devices deep within rock layers would minimise the amount which would be released to the surface or atmosphere - the point of the bang after all is to generate pressure and heat deep inside the rock, not blow up an enemy on the surface. Current fusion devices use a smaller fission bomb inside them to generate the enormous temperatures needed to trigger the fusion reaction, which makes the very big bang, and it is the explosion of the fission trigger that creates the nasty fallout. There is no theoretical reason why it would not be possible to design a fusion bomb which does not require a fission trigger. It could perhaps be one that utilised a powerful laser to trigger the fusion reaction, creating "clean" nuclear blasts and producing none of the long-living, deadly radioactive rubbish. Deuterium compounds exist on Mars that would provide a supply of suitable fuel for Martian nuclear mining devices, and an added bonus would be that massive heat injection deep underground would also melt vast amounts of ice to create liquid water - the fusion of 1kg of deuterium would melt up to a million tons of ice, greatly speeding up a thawing process that could otherwise take millennia. As with CFCs, it seems, what is bad for Earth may in another form be ideal for terraforming Mars.

Using some or all of these methods, many experts believe that sufficient degassing of the Martian surface, to create the first stage of a terraformed planet, could be achieved in little more than a century. Picture yourself then visiting Mars early in the 22nd century. The surface temperature is a bracing -8C (pack those woollies), the atmospheric pressure is much higher than before the terraformers moved in, and the atmosphere consists of carbon dioxide, nitrogen and some oxygen, albeit not in breathable amounts - though even the small amount of oxygen released by the first stage of terraforming Mars might be enough to block out unwanted UV at certain wavelengths.

There is now water on the surface. The amount released by the rise in temperature alone would probably amount to only small pools gathering in basins, but Martyn Fogg has pointed out that nuclear blasts could also be used to blow open the aquifers (underground water sources) that surveys suggest exist within the planet's crust, especially beneath the northern Martian plains. In fact, this is where he sees his megaton nuclear miners working at their best. "Much less explosive may be required to release large quantities of water from aquifers than the amount required to melt the equivalent amount of ice," he says. Fogg's book on terraforming, the only textbook yet written, is very much a practical "how to" manual. Its publisher is America's Society of Automotive Engineers, not noted for their crazy speculation - and perhaps the most soul-stirring aspect of his vision of New Mars is of oceans. Fogg pictures 10 per cent of the surface covered by water, including the creation of a sea 1km deep in the planet's Boreal region. This Boreal Ocean would drive a new hydrological cycle on the reborn Mars, with rain on the southern uplands and water once again flowing through ancient run-off channels.

But what of introducing life to complete the transformation of Mars? Although a vast improvement on what it was, Mars is still no picnic. Thankfully, the range of conditions tolerable by micro- organisms known on Earth is remarkable, and candidates for a transplant to Mars have been identified already in the coldest place on Earth - Antarctica. The toughest critters in cold environments are a form of algae called psychrophiles found in the Ross Ice Desert, where temperatures can fall to -48C. Anything above -10C will get their metabolic functions ticking along, so the new Mars should seem positively cosy, at least in terms of temperature, though the low concentrations of nitrogen in the atmosphere of New Mars won't make things easy. Another Martian pioneer could be a primitive cyanobacterium called Chroococcidiopsis, which is one of the most extraordinary survival experts on Earth, handling extremes of dryness, salinity and temperature with equanimity. American microbial exologist Imre Friedmann has also nominated a recently discovered cyanobacteria called Matteia which was discovered in Israel's Negev desert, and which is unique among cyanobacteria in being able to dissolve carbonate rocks, freeing carbon dioxide gas from rock as part of its biochemical processing. Lichens are other hardy candidates for Mars, due to their dual ability to tolerate extremely dry conditions and UV light, both of which would be factors on New Mars.

Having achieved so much and developed dramatic new planetary engineering skills, the terraformers of Mars would have still only achieved partial success. Sure, humans could walk on the surface of Mars without pressure suits and without instantly freezing to death but they would still need breathing apparatus. To change the Martian atmosphere into an oxygen-rich one would require the hardest skills of patience.

On present estimates, even managing the primitive lifeforms of the new Martian biosphere for maximum oxygen production by photosynthesis, the most optimistic estimate of the time needed for the atmospheric conversion is currently around 10,000 years. Giving Mars large amounts of nitrogen to speed up the creation of oxygen by plants and bacteria has been suggested, using dramatic methods such as crashing asteroids or comets rich in nitrogen compounds on to the planet. This is one of the few suggestions of terraforming theory that stretches beyond the limits, as such asteroids have never been found, while studies of comets suggest they contain at most 10 per cent nitrogen compounds.

This is not defeat, of course, just a long pause. Humans could live on Mars after a century but there would have to be two ecosystems. Outdoors, the imported biomass would be doing its slow work on New Mars but the planet's human pioneers would require their own structures. However, there is no reason why Martian pioneers could not build these on a grand scale - greenhouses several miles wide with their own Earth-style atmosphere, venturing out as and when they wished with an oxygen backpack.

For some, patience is not a virtue. Vanessa Bentley, of the University of Kentucky, says, "there are more important things to do as far as exploring space and even working on Earth. If we are so hell- bent to terraform a planet, why can't we start with our own?" What we learn by considering how to terraform Mars may help tackle problems nearer home such as global warming. But does a desire to sort out problems on Earth mean we shouldn't take a leap towards creating new environments where humans can thrive? If people just want to stay at home, let them. But terraformers will be the key pioneers of space. For they will be making new homes. !

OTHER CANDIDATES FOR TERRAFORMING

VENUS: Earth's twin in terms of size but currently a hothouse pressure cooker of a planet. Making Venus habitable would involve getting rid of much of its atmosphere (it is too dense, the opposite problem to that on Mars). Possible ways include chemical precipitation, reaction with the planet's crust, or physically ejecting it. The planet's proximity to the Sun means terraformers would need to halve the amount of solar energy the planet receives by insulation. If these could be achieved, says Martyn Fogg, "Venus might be made into a paradise ..."

THE MOON: The only other place in the solar system to feel the weight of human feet is, despite its proximity, not a good candidate for terraforming. The main problem is that the Moon is so small that it would have great difficulty holding on to an atmosphere - and, as there is nothing on the Moon that could be used to create it, any atmosphere would have to be imported. In theory this could be done but the atmosphere would leak gradually into space and need topping up every 1,000 years or so. However, to get an atmosphere to cling to such a small body it would have to be built very high - so high that it would generate a greenhouse effect making the Moon too hot.

THE MOONS OF JUPITER: Of the planet's 16 moons, Ganymede was one of the earliest sci-fi sites for terraforming in a 1950 Robert Heinlein story. The problem that far out is lack of sunlight and to boost solar energy to Earth-like levels would be extremely difficult. Even if this was achieved, it would melt the surfaces of Europa, Ganymede and Callisto, turning them into mini ocean worlds (inhospitable oceans at that).

Europa has excited many people with evidence that it may already possess an environment that would support life. It may have a core that provides an internal heat source, which means it could possess a 100km deep ocean (beneath a 10km thick ice crust) which may have hot hydrothermal events on its floor. On Earth, such vents are a rich oasis of life in the ocean depths. A Nasa probe will soon be on its way to Europa to find out more.

Partial melting of the equatorial regions of Callisto and Ganymede has also been suggested, notably by Gregory Benford, who came up with the feasible idea of using the large amounts of deuterium on these moons to power mobile fusion reactors. These would create equatorial oceans with adjacent "temperate" regions where, though chilly (around 0C), life could exist.

Io could be transformed easily thanks to an active volcanic cycle that provides internal heat - in fact, parts of Io are a cosy 30C, though the average temperature is -140C. Added water is all that is needed to bring life to Io (it would dissolve some of its sulphur and produce compounds) followed by sulphur-loving bacteria from Earth. Truly terraforming Io would be very difficult but making it habitable for some kind of life would not. For one expert, James Oberg, Io is actually "top of the heap" for planetary engineering, even more than Mars.

TITAN: Saturn's largest moon has excited some terraformers, because of its size (larger than Mercury) and the fact that it has an atmosphere (twice the mass of Earth's). There is also evidence that it has an ocean and a continental land mass. However, it is very cold (-180C) and its chemical composition means that if you did manage to raise the surface temperature you'd end up with a smell like "a cross between a refinery and a sewage plant", according to one expert. On the plus side, a heated- up Titan could be used as a massive refinery, synthesising a host of useful oils and other chemicals - it could even support certain forms of Earth bacteria which can use these products to live, even without oxygen.

THE REST: Of the other planets or moons none is a candidate for terraforming, within our present imagination, either because of their size, composition or distance from the Sun.