Image of the day looks at Mars again

A few days ago, I posted a Martian landscape. Today, we have another look at Mars, from a distance.

Here we have a nice view of Mars with the snow cap on the North Pole.

Another one showing the South Pole.

And in crescent view.

Except… this isn’t really Mars at all, but a sphere with a map of Mars wrapped around it. It’s really cool. You can turn it, and change the lighting, and move closer and further away (well–not THAT close because the resolution isn’t that great).

Farming on Mars

Let’s presume the collective world has gotten out of its space-exploration budget-funk, and has decided it’s worth sending people to Mars. The first have gone and have returned, and now it’s time to set up a colony.

Of course that colony will have to be self-sufficient. Thankfully, there are a number of very useful things on Mars, so the colonists won’t need to bring everything, but the more they can find locally, the better. Ideally they should not need anything from elsewhere to survive after an initial supply of resources.

Most importantly, the colonists will have to grow their own food.

At its distance from the Sun, sunlight on Mars is about 40% up to half that on Earth, but still sufficient as power source.

Unless the colonists choose to grow plants in hydroponic systems, they will have to use Martian soil. Preliminary analysis shows that the basic composition of Martian soil is fairly similar to certain soil types on Earth. To be sure, no one has ever taken a sample from Mars and returned it to Earth, but we have two methods for determining composition of Martian soil and/or rocks. In the first place, there are meteorites that have reached Earth from Mars, of which 34 are known. Without going into a lot more detail, they are all igneous rock, in other words, hardened lava. These rocks tell us about the composition of the Martian crust, but very little about sediments, water and free elements in the soil. Secondly, in 2008, the Phoenix lander carried equipment that allowed it to perform an in-situ analysis of the soil near Mars’ north pole. The soil turned out to be alkaline, and contain elements necessary for plant growth, such as sodium, magnesium, potassium and chloride.

However, things are unlikely to be as simple as that. For one, it’s not correct to refer to the substrate as ‘soil’ (but failing a different, similarly evocative word, I will use it anyway), since the definition of soil includes the presence of organic material. The Martian regolith (which is a word I should use instead) contains none. Plants need soil for two basic purposes: for anchoring, and for their nutrition. Plants can anchor themselves in virtually anything (which is why you get plants growing in concrete and on roofs), as long as they have enough water and food. Water is available on Mars in the form of ice. The colonists will be deposited somewhere close to a source of this ice.

But what do you think would happen if you wet a soil that has been dry for billions of years? A soil that has been subject to direct radiation and dust storms. For one, there will be a lot of fine material. On Earth, growing crops in heavy, gluggy soils with lots of fine particles (clays) is hard. Plants need adequate aeration to grow properly. If the soil becomes too compacted (either because it is too fine or because people walk over it) plants don’t grow properly. This is why there is frequently no grass in a soccer goal. So you’ll have to get rid of excess dust before you wet the Martian soil else the stuff will turn into something akin to cement and be of no use for cropping. Also, there will be something like four billions years’ worth of accumulated salts that are freed if you wet this soil. When the Phoenix lander wetted the Martian soil, it released perchlorates, which are poisonous to plants. The soil pH was alkaline (8.3), which indicates accumulated salts of one type or another.

There are plants, notably those that are native to deserts, that tolerate a high salt concentration in the soil, but in order to grow highly-strung and finicky crop species, it’s necessary to get rid of excess salt. This probably requires a lot of (recycled) water, but at the very least, it will require lots of detailed testing, and time.

Next: the air. Mars has lots of carbon dioxide. Plants grow better with a higher concentration of carbon dioxide than present on Earth. It makes sense to run the glasshouses with a high carbon dioxide level. But at high carbon dioxide concentrations, the plants are likely to take up an increased percentage of poisonous elements from the soil, such as arsenic, cadmium and lead. Some areas of Mars are known to have fairly high concentrations of arsenic.

The big trouble is going to be nitrogen, because there is very, very little of that on Mars. Nitrogen is an element that does not easily form bonds with other elements. Whereas oxygen facilitates chemical reactions by reacting with other elements (for example by burning or rusting), atomic nitrogen just does… nothing. Since we have seen in an earlier post that Mars is too small to hold onto its atmospheric nitrogen, there may not be all that much of nitrogen to be found on Mars in any of its forms. So unless early explorers locate a deposit of nitrogen-rich substrates, the colonists will have to import nitrogen from elsewhere. And nitrogen is the most essential of the essential elements for plant growth.

All of which is not suggesting that using Martian soil for cropping is impossible, but that it likely isn’t easy or straightforward, and that early colonists are probably better off starting with hydroponic installations while all this other testing takes place.

Terraforming: Mars or Venus?

In an earlier post, I described the difficulty a small planet, like Mars, faces when people are trying to terraform it: the planet simply doesn’t have enough gravity to hang onto the gases we need to survive.

Some people suggested that maybe instead of Mars, we might look at Venus, since it has the right size.

In this post, I look at the most important deciding factors for the success of a terraforming operation.

Distance from the sun:
Venus is at 0.7 AU from the Sun, which is beyond the inner margin of the habitable zone at roughly 0.9 AU – yeah, we’re very close to that. I hope it doesn’t give you nightmares.
Mars is at 1.5 AU from the Sun, on the very outer edge of the habitable zone. However, the width of the habitable zone depends not just on the sun and its strength, but also on the composition of the planet’s atmosphere and on the presence f clouds. With the addition of clouds, the inner boundary of the habitable zone could be made to stretch inwards. However, water vapour and carbon dioxide (the most likely gases to form clouds) are both greenhouse gases, so the effect likely cuts both ways. There is a lot more leeway on the outer side of the habitable zone. With the addition of carbon dioxide clouds, it can be made to stretch outwards, to as much as 2 AU or even more.
Winner: Mars.

Atmosphere composition and density
The atmosphere of Venus is so dense that we can’t see its surface. It consists of mainly carbon dioxide (96%), some nitrogen and sulphur dioxide. Nasty, nasty stuff
The atmosphere of Mars also consists of mainly carbon dioxide, but it is extremely thin. Both atmospheres lack oxygen and nitrogen, but because of its high temperature, Venus also lacks water, of which Mars has quite a bit, even though it’s frozen. Mars also has frozen carbon dioxide. When thawed, both carbon dioxide and water vapour are greenhouse gases, and both would further increase the rate of warming (this is called positive feedback). At Venus, you’d need to get rid of massive quantities of carbon dioxide. Again, this is possible in theory (see Terraforming by Martin Beech), but even if you got it to work, it would be a process taking millennia, while a warming of Mars could be achieved in a few hundred years.
Winner: Mars

Planet mass
Mars, at only 15% of the Earth’s mass, with 32% of Earth’s gravity, is below the mass required to hold onto a breathable atmosphere.
Venus, at 81% of Earth’s mass, and 90% Earth gravity, is not.
Basically, providing you can create an atmosphere resembling Earth’s, Venus would retain it without the need to replenish it, whereas Mars would not.
Winner: Venus

Daylength
Mars has a nice 24-and-a-bit hour day. At Venus, however, the planet’s day (243 Earth days) is longer than its year (225 Earth days). This, in combination with stronger sunlight, would make plant growth extremely hard, unless you could somehow speed up the planet’s rotation. I need not say that this would be hard to achieve, although theoretically possible.
Winner: Mars

Required change in temperature
In order to harbour life, the plant’s average temperature must be high enough for liquid water to exist on its surface. Every degree of change a planet requires to bring its temperature within this range is going to cost effort and time, and a lot of resources.
The freezing point of water is 273K; the average surface temperature of the Earth is 288K.
The temperature of Mars is 210K
The average temperature of Venus is 735K, and is the hottest object in the solar system apart from the sun, hotter even than Mercury.
Add to this that an increase in temperature is probably easier to achieve than a decrease, the clear winner is Mars, by many, many miles.

So yes, while people may have concluded from a previous post that Mars is too hard to terraform, and maybe we should look at Venus, maybe these people need to think again. It seems that its size is just about the only thing it has going for it.

The conclusion from this should probably be that terraforming is never going to be easy, and nor should it be in your fiction. Lots of things to go wrong, lots of things taking longer than expected, lots of unexpected stuff happening.

How the size of a planet determines its atmosphere

People have asked me to write something about terraforming Mars, a subject that is of great interest to SF buffs. I think Kim Stanley Robinson in his Mars series does a pretty good summary of all the currently-held scientific opinions on techniques of how we could achieve this. Yes, it would involve some form of artificial warming, it would involve melting the polar ice and finding underground water. It would involve long-term (think hundreds of years) and large-scale engineering, but most importantly, two things: it would involve the introduction of large quantities of nitrogen, and it would be a constant and ongoing process, since there is nothing we can do about the main reason why Mars lost nitrogen and oxygen from its atmosphere in the first place: the planet is simply too small.

The mass of a planet defines its gravity. To understand this, we need to go back to physics. According to Newton’s law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses, and inversely proportional to the square of the distance between them:
If one of the masses were really small, say a human body compared to a planet, the force described by this law would be what we experience every day as gravity. The law says: more mass, more gravity. Hence, gravity on the Moon is smaller than that on Earth, which in turn is smaller than that on Jupiter (presuming there was a surface on Jupiter you could stand on).

Another term: escape velocity, which is the speed needed to break free from a gravitational field. Speed itself is attained as function of an object’s mass and the forces holding it in place versus the forces applied to it in the other direction (OK, I’m confuddling speed with acceleration here, but you get the gist). Since the force that holds all objects on a planet is gravity, which is the same for objects of all sizes, it becomes easy to see that if you are planning to propel something off a planet, the best tool available to you to make it easier is to reduce the object’s mass.

In simple terms: your highest jumps on Earth would be mega-leaps on the Moon, while on an asteroid, your best effort at jumping might well hurtle you into space. Try jumping on Jupiter, however, and you might not even get off the ground. Say you wanted to get off the ground on Jupiter, you might train your muscles, but assuming you are reasonably fit, it’s probably more effective to go on a strict diet.

Now imagine you were a particle in the atmosphere. Our atmosphere is made up of gas. The gas state indicates atoms or molecules moving about freely without any attachment to each other. In a gas, particles are constantly bouncing off against each other. In doing so, they acquire speed, helped along by the heat of the Sun’s rays. For a proportion of these particles, that will mean gaining a speed greater than the escape velocity of the planet.

Following the above, the heavier a particle is, the less easy it will gain that speed. Earth’s gravity, for example, is too weak to hold onto its hydrogen or helium. Jupiter’s gravity is not. This is why the large planets are all gas giants. A planet starts retaining helium at about 6 Earth masses, and when it is bigger, about 10 Earth masses, it will retain hydrogen.

Move down the periodic table and see that of the next of the most common elements in the universe that exist in gas form at relatively low temperatures, Earth’s gravity is strong enough to retain atomic nitrogen. Nitrogen (atomic weight 14 grams per mol) is an element that doesn’t tend to form bonds easily. Simply said, it likes being a gas. The next element down, oxygen (atomic weight 16 grams per mol), loves attaching itself to other things, and bonds readily with carbon, another element common in the universe, but not a gas at any temperatures below 4000C. Carbon dioxide, nitrogen dioxide water and methane are all simple combinations of these common elements that we find in Earth’s atmosphere. Add up their atomic weights (44, 46, 18 and 16 grams per mol respectively) and you will see that as planet size becomes smaller, the atmosphere will lose its methane at approximately the same size as it loses its oxygen, then water, then carbon dioxide and then nitrogen dioxide.

Where is Mars on this scale? Well, it’s just big enough to retain carbon dioxide and nitrogen dioxide. There is plenty of the former, but since nitrogen in atomic state is lost from Mars, and since nitrogen doesn’t easily react with anything much, there is not much nitrogen dioxide to be had. Thus the atmosphere of Mars contains mainly carbon dioxide. If we were to artificially establish an atmosphere on Mars, any oxygen wouldn’t immediately evaporate into space, but the atmosphere would require constant and probably expensive maintenance.

This a very simplistic summary of an interesting subject. Yes, things are not quite as straightforward as this (you may stop yelling ‘Titan’ in the background, you over there), but these are the simple, physical processes involved. If you want to read more, I recommend the book Terraforming by Martin Beech.

The next step: should we go to Mars?

From a Worldcon panel Race to the Red planet with science fiction writers Kim Stanley Robinson and David Levine and physicist Jim Benford, identical twin brother of science fiction writer Greg Benford (who was also at the con, which made for plenty of confusion).

It’s a fact that humanity already has the technology to go to Mars, and to put people on the surface of the planet that’s the most hospitable to human life outside Earth. So hospitable that it would kill us in minutes. But we can do it. There are books written on the subject. Kim Stanley Robinson says that his books are often quoted as a blueprint for going to Mars, but they, in turn, are based on real research (a good reference book is Looking for life – searching the solar system, edited by Paul Clancy, Andre Brack and Gerda Horneck. PS – if you want to buy this book, do so at ABE (http://www.abebooks.com/), where it is factors cheaper than at regular online venues).

The main issue about going to Mars is getting into orbit. We have chemical propulsion rockets that would take us there in about nine months. New propulsion technology is continuously being invented. Ion rockets are an option but are slow to build speed. Nuclear power is an option, and various forms of slingshots, formerly thought outrageous, are being looked into.

We can shield astronauts against radiation. Normal cosmic background radiation exposure for a duration of a 9-month trip would increase the risk of radiation-related problems by 1%. It’s the solar flares that will kill you, and they are as unpredictable as they are vicious (for a realistic description of what a solar flare will do to astronauts, read Titan by Stephen Baxter). Fortunately the very thing we will be carrying on the trip, water, is a very good shield against radiation. Even towards the end of the trip, you will have plenty of water, because it never leaves the closed system of the ship (go figure). Unfortunately, water is heavy, which brings us back to the problem of getting into orbit.

But all these problems can be solved, even with current technology.

The main question is: why would we want to go?

Yes, why? This has been the major source of apathy that has plagued the space program. The public perception is that it’s a waste of money that could be better spent elsewhere, that nothing ever came out of the Moon landings except a few rocks in museums. In reality, the race to get people on the Moon delivered many technologies we are still using today but whose origins people have long since forgotten. It is true that the Moon landings themselves were too short to deliver much scientifically useful data. They were not a scientific undertaking, but a matter of prestige. They were, perhaps, an opportunity missed. We have had people on the Moon, but we are still unsure as to whether there is water.

Going to Mars is expensive. That said, estimates are (according to David Levine) that it would take four years’ worth of NASA’s annual budget, money that’s currently being frittered away here and there.
Space travel has lost its sexy image. People can’t see the point, and therefore the collective will to do it has evaporated. When going to the Moon was a matter of beating the Soviets there, there was a reason; people need a reason. We now know we’re alone in the solar system, and that knowledge is rather depressing. If we really must continue to look at these dead pieces of rock, why not keep sending our little robots there instead of risking people’s lives?

Indeed, we have learned a lot from the rovers, even if they are now all out of action. The new Curiosity vehicle will have more capability to ‘defend’ itself against adverse geology. It will run on nuclear power and will have a laser to blast things out of its way. Successful though the rovers are, fact remains that they have covered a grand total of 14 kilometres, their success rate has been 50%, and they are liable to run into serious problems when faced with obstacles a human would find trivial. They can’t make quick decisions. Time lag in transmission is about 18 minutes, so communicating with them is a slow and arduous process. Do we wait that long? In short, a human observer could collect much more data much more efficiently.

But why would we need this data?

We could be doing it as an insurance policy. Kim Stanley Robinson said that this notion is both simplistic and naïve. Mars is not easy. Mars is cold and inhospitable. It is dusty. Dust gets into everything. It has less energy than Earth. While 15% less sunlight might not be detectable with the human eye, generating energy through solar power will require more effort. Terraforming is largely in the realm of Science Fiction, and the question is if we should attempt it in the first place. Is it ethical to modify an environment that may harbour information vital to understanding our origins?

Because Mars is now thought to be possibly the originator of life on Earth. Jim Benford said that lately there have been patterns observed in methane production in the Martian atmosphere. Methane can be the result of volcanic activity, of which we have no proof that it exists on Mars. In fact people agree that Mars is volcanically dead.

Methane could rise from past volcanic activity, but the patterns are seasonal.

That leaves the possibility of bacterial activity.

It is now widely believed that we will probably find microbial life on Mars, either as fossils or extant. The question is whether this life has the same roots as life on Earth or is completely alien. That, according to David Levine, is one of the great questions we can solve by going to Mars. We need to re-capture public interest. Some of that has already happened. With all the amazing pictures available, the place is becoming real; it is coming to life, both figuratively and perhaps literally.

Not one nation should be asked to bear the burden of mounting an expedition. It will need to be a collective human effort in the name of public domain science. More nations need to become involved.
Overall, having worked in science, I am sadly not convinced that humanity collectively values pure science as much as it should. There will probably no major step towards going to Mars until a group of people finds it necessary to do so, and that will probably be for emotional and all the wrong reasons.

Picture: Images like this one, the Echus Chasma on Mars, snaffled from the Mars Express site, do a lot to make Mars feel like a real place. You can almost see yourself clamber up the dunes and slide – wheeeeeee!! – down the hill again.