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The planet Mars, rocky and located in a so-called “habitable” zone, could be almost perfect to accommodate the human species. The immense disadvantage of this planet, however, is that it does not have a magnetosphere, which directly exposes it to solar winds and their energetic particles. In the past, however, it had an active magnetic field, which mysteriously “went out”. A group of researchers, including scientists from NASA, believe that reestablishing this magnetic field is the only way to envision a lasting human presence on Mars and are reviewing the various ways to achieve it.
Due to the fact that it has been dispossessed of its magnetic field (unlike the Earth), Mars has a very fine atmosphere; the average atmospheric pressure there is 600 Pa, or about 170 times lower than that of the Earth. However, at this pressure (which is below Armstrong’s limit), without a pressurized suit, body fluids exposed to the air (saliva, tears, water in the lungs) would spontaneously boil. It’s hard to imagine colonization under these conditions.
« For a long-term human presence on Mars to be established, serious consideration would have to be given to the terraforming of the planet. A major requirement for such terraforming is to have the protection of a planetary magnetic field that Mars does not currently have. », Write the researchers. Therefore, in a new article to be published in the journal Astronautics Act in January 2022, they explain the different approaches that would restore a magnetic field on Mars.
A project that would require massive energy resources
Mars contains a lot of frozen water below its surface and has a lot of similarities with our planet; however, creating an artificial magnetic field is the only way to really make it a second Earth. The Earth’s magnetic field not only prevents high-energy particles from reaching our planet’s surface, but it also prevents solar winds from slowly sweeping away our atmosphere – and this is precisely what Mars was lacking. The InSight mission revealed the presence of a residual magnetic field, coming from magnetized rocks buried beneath the surface. Would it be possible to reactivate this magnetic field today?
The creation of a magnetic field would obviously require massive resources: the absolute minimum of power required would be around 1018 joules, which is almost all of the energy consumption of all humans on Earth in 2020! The only way to get that power would be to use nuclear fission reactors, which the team said would be necessary for permanent colonization anyway.
Surprisingly, the authors point out that the force required to deflect the solar wind from Mars is about the same as that of an ordinary fridge magnet. But it would have to be generated on the whole planet, which represents a major challenge: a field of about 100 nT over 37 million km2. To achieve this, scientists suggest, for example, taking inspiration from our own planet, namely “restarting” the circulation of iron in the Martian core, which by a dynamo effect could generate a magnetic field. This option, however, is the least feasible: the core of Mars is too small (its radius is about half that of the Earth’s core according to data from the Insight mission) and not hot enough.
Other approaches would make it possible to generate a Martian magnetic field; they generally involve solenoids, which would be arranged on the Martian surface and / or in orbit, or even a plasma torus of charged particles with an artificial current – like the tori of Io and Europe, two moons of Jupiter. This last approach appears to be the most interesting.
A toroidal cloud of plasma thanks to Phobos?
As the study points out, creating a planetary magnetic field requires an intense flow of charged particles, either inside the planet or around the planet. Since the first option is much less feasible in practice, the team focused on the second. It turns out that Mars has two small natural satellites, Phobos and Deimos; Phobos is the largest and closest to its planet, and researchers believe it might be possible to create a ring of charged particles around Mars with it.
Phobos goes around Mars in eight hours. The team proposes to ionize the particles on its surface, then accelerate them to create a torus of plasma along its orbit. According to them, this would create a magnetic field strong enough to protect the planet and allow possible human settlers to settle there.
This is a very ambitious plan – but just sending humans to Mars is ambitious. And many technical “details” remain to be resolved. However, experts believe it is necessary to think about this kind of problem now if we plan to terraform the red planet. ” The intention here is to explore in a quantifiable way the practical means of achieving this if humanity chooses to do so, and to estimate the resources that this would involve. », They summarize.
Note that the subject had already been mentioned in 2017 by part of the team that wrote this new study: at the time it was a question of positioning a magnetic shield at the Lagrange L1 point of Mars to protect it from solar bombardments. Computer simulations showed that in a few years, such a shield would restore Martian atmospheric pressure to reach half of Earth’s pressure.