Terraforming Mars using a combination of aerogel and GM microbes?

Question

Silica aerogel is a technology that's been proposed for colonisation of Mars. Basically, it's a very good insulator that's also transparent to visible light, and could be used to warm up parts of Mars to Earth-like temperatures through the greenhouse effect simply by placing it on the soil. Moreover, it would also block the more damaging wavelengths of UV. However, it wouldn't be a practical way of terraforming the entire planet.

Genetically modified microbes have been proposed for the terraforming of Mars. However, the current Martian environment is very harsh for life, being a cold near-vacuum with no liquid water and intense radiation (among other hazards). While microbes might be able to survive this environment, their growth and reproduction would probably be very slow.

I had the idea of combining these two approaches: using aerogel on the icecaps of Mars to create pockets of liquid water, then adding to the water microbes that are genetically modified to produce perfluorocarbons (PFCs). The PFCs would warm up Mars due to being very strong greenhouse gases. The benefit of using the aerogel is that the microbes wouldn't need to withstand the harsh conditions of Mars directly, and this is achieved with a relatively simple technology that has no moving parts.

Once the entire planet is warmed to Earth-like temperatures, the atmospheric pressure would also increase somewhat (due to sublimation from the icecaps and release of gases adsorbed in soil), the thicker atmosphere would reduce the radiation levels reaching the surface, and a water cycle would now be possible. Even if the atmosphere were to remain thinner than Earth's, Mars would still be much more hospitable than before, assisting colonisation and further terraforming efforts (which could very well involve more GM microbes).

What are the challenges with this approach? The ones I can think of are:

• Whether or not microbes could be genetically modified to produce PFCs. For the purposes of this question, assume that it is possible.
• The PFC-producing microbes undergoing unexpected mutations that cause them to either die off or produce unwanted chemicals. To minimise the chances of this happening, extensive testing would need to be done first (culturing the microbes in samples of melted Martian ice, for example).
• The PFC-producing microbes producing too much PFCs, warming up Mars to an uninhabitable extent. This could be dealt with by careful monitoring and (when the time is right) introducing other microbes to the water, where they would outcompete the PFC-producers.

Answer 1

The underlying aerogel scheme seems to have some serious fundamental flaws:

• Aerogel is extremely expensive, and you need enough to cover a significant portion of a planet.
• Aerogel is extremely brittle and easy to pulverize.
• The poles are dark much of the year. Photosynthetic organisms won't function during the winter, and it'll get cold enough to form heavy CO2 deposits that would crush any aerogel structures and potentially kill any living organisms.
• Even in the summer, the low sun angle will limit productivity, and a thin layer of dust will block even that sunlight.
• Raising the temperature of the ground to water's melting point will raise water's vapor pressure above the surface pressure of the atmosphere. The atmosphere under the aerogel would be pure water vapor, escaping from the edges (or by blowing holes in the aerogel) and preventing the ambient atmosphere from intruding. Plants won't grow in that.

As for the PFC-generating microbes, fluorine isn't widely available in a form easily biologically processed. You'd have to mine and process it and distribute it in fertilizer.

An actual PFC-generating chemical plant, extracting fluorine from mined minerals, seems likely to be far more effective and vastly cheaper than the equivalent in polar aerogel greenhouses.

Answer 2

"Microbes that are genetically modified to produce perfluorocarbons" do not exist, for good reason.

Carbon is a useful building block for life not only because each atom can form 4 bonds, but also because the building blocks can be taken apart and re-used to form a different compound. That's the whole idea behind the carbon cycle.

Hydrogen and fluorine atoms each make one bond. Either can be used to "cap" an otherwise unfilled bond on a carbon atom, preventing the molecule from extending further in that direction. Because hydrogen is much smaller than carbon, there is plenty of space for enzymes and other chemicals to attack the C-H and C-C bonds, allowing the recycling of carbon atoms mentioned above.

_{Hydrogen atoms on a carbon backbone. See the black carbon atoms underneath?}

Perfluorocarbons have a bond between a carbon atom and a fluorine atom. The atomic radius of fluorine is slightly larger than carbon, and the C-F bond is particularly short and strong. When an organic compound contains large amounts of fluorine atoms, the fluorine atoms almost perfectly cover the carbon atoms, and it is difficult for any chemical to get in and attack either the C-F or the C-C bonds. Here is the chemical structure of polytetrafluoroethylene, also known as PTFE, Teflon, and Gore-Tex:

_{We've replaced the hydrogen with fluorine. You can barely see the black carbon atoms in (C).}

This explains the chemical, physical, and biological properties of fluorinated polymers. They are practically chemically inert, which is why Teflon is used to make chemical containers. Another object sliding along their surface does not form many intermolecular bonds, which is why Teflon has such low friction. No enzyme or other biologically-produced substance has been shown to degrade fluorinated polymers, which is why Teflon and Gore-Tex are used as implanted materials. Fluorine is added to drinking water and toothpaste because bacteria lack the enzymes to destroy fluorinated tooth enamel.

Because fluorinated polymers are so stable, no biological organism has evolved an enzyme to decompose them. These compounds are thus a biological dead-end; they can't be recycled. Furthermore, there is no point for an organism to evolve enyzmes to synthesize them, either.

You're not going to be able to genetically modify a microorganism to produce perfluorocarbons. There isn't anything even close to an existing enzyme which does that.

Answer 3

Leaving aside the question of whether this is desirable, I think the biggest issue is the availability of fluorine.

While Mars is estimated to have more fluorine than Earth, tracing that back to its source confirms that it is quite a weak estimate - it's based on inferring a correlation of fluorine to lithium, and estimating based on lithium abundance in meteorites.

Even if there is a reasonable amount of it around, as the WP article notes, fluorine tends to be found concentrated in particular minerals, rather than more evenly distributed like some other elements.

The most fluoride-rich natural water found on Earth has 50mg/L of fluoride. Let's assume we've lucked out and all of the Martian ice is this rich. A ton of water would contain 50g of fluorine. Assuming we can make 75g of fluorine-rich CFCs from each 50g of fluorine, this suggests that in the best case, each kilo of CFCs would need about thirteen tonnes of ice. A tonne of CFCs would need 13,000 tonnes of ice. And we're looking at needing millions of tonnes of CFCs...

At this point it starts seeming a bit more reasonable to mine for fluoride and synthesise the CFCs.