Terraforming Mars: His moon Phobos can help us!
Ours is a special planet. Probably not unique, but certainly rare. An extraordinary combination of
events has created conditions favorable to life, which has evolved into a wide variety of species,
transforming it into the world we know.
Seen from space, the Earth always leaves us amazed: its "pale blue" color, as Carl Sagan
had defined it, mainly due to the dispersion of sunlight in the atmosphere and the abundant
mass of water in the oceans, has not yet found equals in the search for extrasolar planets.
Many factors contribute to making the Earth habitable: some are constantly (and literally)
under our noses (like the air we breathe), others are less tangible but just as basic.
One of these is the magnetic field that from the center of the planet propagates into space
creating a giant invisible bubble, which protects us from the most harmful external radiation. This
natural physical phenomenon is far from obvious and is very dynamic: it can change intensity,
shape, and orientation, globally and locally. Without the magnetosphere, we would not exist,
and the Earth - despite its ideal temperature and its perfect location in the habitable
zone - would probably resemble a desolate and lifeless desert. Just like the Martian one.
And this suggests that it would be unfortunately completely useless to try to terraform Mars
without first solving its biggest problem: the absence of magnetic protection able to
divert the malevolent flow of solar particles. What to do, then? Is there really no solution?
Terraforming Mars is one of the dreams of mankind. Mars would have a lot to offer.
Its day is about as long as Earth's, it has plenty of water ice just below its surface,
and in the distant future we might even be able to create a reasonably breathable atmosphere.
But that wouldn't be enough... To make these changes last would require the
presence of a magnetic field, which doesn't exist, or hasn't existed for some time.
The reason magnetic fields are so important is that they protect a planet
from the harmful effects of solar wind. Earth's magnetic field, for example,
prevents most high-energy particles from the sun from reaching and sterilizing our planet's surface
and prevents the solar wind from tearing and scattering the atmosphere into space.
Mars also probably once had a dense, water-rich atmosphere, which was then gradually dispersed
precisely because of the lack of a magnetic shield.
There are a few mechanisms that control the loss of a planet’s atmosphere.
The first is thermal escape. Gas molecules move around at a distribution of speeds determined
by the temperature of the gas and mass of the molecule. If a molecule in the upper
atmosphere is moving fast enough (faster than the escape velocity), it will escape the gravity
of Earth and be lost to space. Hot and light atmospheres on small planets escape easily.
This is why the atmospheres of the inner solar system (less massive and warmer) planets are
made up of heavy molecules such as carbon dioxide and nitrogen while gas giants (massive planets) in
the outer solar system (where it is cold) can hold on to light elements such as hydrogen and helium.
Another important mechanism for atmospheric loss is solar-wind stripping. Without a magnetic field,
the solar wind can erode away an atmosphere just like a river erodes its shores. Just because a
planet does not have a magnetic field does not mean that solar wind will strip its atmosphere.
Venus does not have a magnetic field (and even experiences a stronger solar wind as it is closer
to the sun) yet has a very thick atmosphere. Venus can hold on to its atmosphere because it is dense
and tightly bound to the planet. Mars’s gravity is too weak to compress its atmosphere like this,
causing its atmosphere to be too thin to prevent this erosion from happening. Going
back to our river analogy, this is similar to how a rock erodes much slower than a mound of sand.
OK, we have clarified that a magnetic field is absolutely necessary.
But why Earth has one, very efficient, while other rocky planets are without it?
To answer this question it is necessary to understand the mechanism that put it in function
The magnetic field of a planet is generated by the process that scientists call
geodynamo (because its operation resembles that of the electric machine of the same name):
a continuous flow of molten metal within the planetary core that produces an electric current.
For the formation of a planetary dynamo, three basic elements are essential:
1 - A conductive fluid within the body; 2 - A mechanism that allows convective
motions to form within this fluid; 3 - A vigorous planetary rotation;
And this explains the absence of a magnetic field for some planets. Mars is very small,
which means that it has been able to cool much faster than Earth since the formation
of the Solar System. It follows that convective motions within it are probably not there or are
too weak. Venus rotates very slowly, and this implies that the convection bubbles can return
to their equilibrium during the motion, which is therefore not intense enough to produce a dynamo.
If we take the terrestrial case, we see that all three requirements are met.
The internal structure of the Earth provides in fact a solid inner core around which there is the
outer core, a thick layer of liquid conductor composed mostly of iron and its compounds.
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The Earth, since the time of its formation, is slowly cooling down as all planets. However,
this cooling occurs through the surface, which means that the outer part of the Earth is
cooling much faster than the inner part. The difference in temperature between the core and the
surface causes convective motions to be generated within the outer core, just as it happens in a pot
of water when the bottom is in direct contact with the stove and the surface with colder air.
The Earth's rotation is then sufficiently vigorous that every bubble of fluid that moves from the
inside to the outside is curved during its motion, following the Earth's rotation due
to the Coriolis force (the force that occurs when the motion occurs on a rotating reference system).
The result is that the bubbles, rotating, generate as spirals within the fluid
aligned with the axis of Earth's rotation. But because of the high temperatures, the fluid
bubbles are also electrically charged. And what happens if we put electrical charges in motion?
A magnetic field is generated, as the theory of electromagnetism teaches us.
Mars' dynamo, on the other hand, died out billions of years ago. Currently, the Red
Planet has only residual local magnetic fields concentrated in the southern hemisphere; however,
data collected by the Mars Global Surveyor orbiter, active between 1999 and 2006, have shown
the presence of rocks magnetized by a magnetic field still active about 3.5 billion years ago.
And with that, we return to the initial question: What to do,
then, in case we want to try in the next 50 years to reactivate the Martian magnetosphere?
The answer may come from a paper that a staff of the Rutherford Appleton Laboratory (UK)
published recently with the title "How to create an artificial magnetosphere for Mars".
Among the options considered in their article, the researchers discuss the possibility of
restarting Mars' iron core using nuclear power. But after calculating that the amount of energy
required to melt Mars' iron core is the equivalent of 100 billion 1-megaton H-bombs,
the researchers obviously conclude that this is unlikely to be a viable option,
not to mention the insurmountable difficulty of digging down to the core to place them.
This solution turned out to be unrealistic and beyond any possible engineering solution...
and was therefore discarded. Another option could involve using a
vast ground-based solenoid loop system. Solenoid loops are long, thin loops of wire, often wrapped
around a metallic core, that produce a magnetic field when current is passed through them.
But this approach would require the construction of huge physical structures that, depending on
the material used, could be very heavy and involve large quantities of rare substances.
The magnetic field generating structures could be made of superconducting materials or
permeant magnets both of which minimize operating power
but have the disadvantage of being heavy and made from rare minerals. Alternatively,
carbon nanotubes offer a potentially lighter conducting structure but are fragile and have
a finite resistivity requiring continuous power and therefore power losses to overcome.
Again, the required power would be enormous, but not unimaginable, especially if controlled nuclear
fusion was successfully developed in the future. The solution would also require the laying of
superconducting cables to surround Mars from north to south and probably along the equator.
Certainly not easy, but somehow within the reach of our technology.
In the end, the scientists propose what they say is a "completely novel" solution, which
they deem to be the best approach for creating an artificial magnetic field around the red planet.
This solution would involve the creation of an artificial ring of charged particles
around the planet, possibly by ionizing matter on the surface of Mars' moons.
Ionization refers to the process of converting an atom or molecule into an ion - a positive
or negative electric charge as a result of having lost or gained one or more electrons.
The moons of Mars are so small (Phobos' diameter is 22 km and Deimos is 13 km) that
they have virtually zero escape velocity, so if there was a “plasma generator” such
as an ablation or gas release system (powered by the already referenced nuclear reactors),
the plasma would easily escape from the surface. Phobos is the larger of the two moons, but it is
also that of the two moons of Mars that orbit as close as possible to the Red Planet.
On a relatively circular trajectory, just 6,000 kilometers above the Martian ground.
After the matter from Phobos' surface has been ionized, these charged particles would then be
accelerated to create a ring-shaped cloud of plasma - one of the four fundamental states
of matter consisting of ionized gas - around Mars. Even though Mars’ moons are not large,
there would be no risk of running out of raw material for the ring itself.
Using Phobos, it would take Earth years to completely exhaust the available material.
A similar, naturally occurring effect has been observed at Jupiter's moon Io.
The volcanic material ejected from Io's surface in fact creates a toroidal (donut-shaped) cloud
of charged particles that follows Io's orbit and wraps part of its path around Jupiter. The ejected
material contains mainly ionized oxygen, sodium, and sulfur atoms with smaller amounts of hydrogen
and potassium. As the satellite travels in its orbit, passing through Jupiter's magnetic field,
it produces an electric current of about five million amperes along a spiral electron flux
tube connecting Io with the giant planet. The researchers argue that a similar approach
would create a persistent magnetic field, strong enough to protect a terraformed Mars.
If this plan to prepare Mars for human arrival on its soil seems ambitious and
achievable in theory, it is no less complicated in practical application.
The scientists and engineers of the future responsible for its realization
will face incredibly complex technical challenges. For example, the amount of
energy required to ionize and accelerate soil particles in Phobos is enormous. The researchers
calculated that this would represent the amount of energy consumed on Earth in one year!
"Paradigm-changing" shifts, such as the development of successful and efficient
nuclear fusion reactors, would likely be necessary to enable the colonization and terraforming of
the red planet on such a scale - or would at least make the technology much more feasible.
Nuclear fusion is by far the most efficient technology.
Because of the massive energy requirements, it is the only technology that would come
anywhere close to providing a viable - if incredibly challenging - engineering solution.
But as of this time, a viable, commercial fusion reactor has yet to be developed.
But, as the authors point out, it is important to start thinking about certain problems in time,
so that we are ready to test them when humanity begins to inhabit Mars.
With the new era of space exploration underway, now is the right time to start thinking about
these bold new concepts of the future and start filling in the gaps in strategic knowledge.