The lost magnetic field of Mars could "drown" in the core of the planet. The excess hydrogen, which appeared as a result of the splitting of water molecules and accumulated in the Martian mantle, could stop convection (heat exchange), thus turning off the planet's magnetosphere forever. This assumption was made by the planetary scientist of the University of Arizona (USA) Joseph O'Rourke at the Conference on lunar and planetary sciences.
At the moment, the generally accepted model explaining the nature of the internal magnetism of planets is the theory of the magnetohydrodynamic dynamo: a magnetic field is generated due to convection flows in a conductive liquid core. In the process of convection, the lower layers of matter heat up, become lighter and float, while the upper layers, on the contrary, cool down, become heavier and sink down, after which the process is repeated over and over again. The movement of streams of iron in the core of the planet, which can carry an electric charge, forms a magnetic field that protects the atmosphere from the effects of solar wind.
However, according to O'Rourke, if layers of a lighter substance, for example, the same hydrogen, settle closer to the iron core, then they can block layers of a denser substance from sinking down, thereby stopping the convection process.
“Too much hydrogen - and convection processes can stop completely. Hydrogen is a ruthless killer,”said O'Rourke during his presentation.
The scientist, along with his colleague Dan Shim from the same university, put forward the assumption that a large supply of hydrogen in the bowels of the planet could appear from the water contained in Martian minerals. Closer to the hot core, the water would split into hydrogen and oxygen. Chemical reactions of oxygen and other elements could hold it in the upper layers of the planet's mantle, while hydrogen could settle practically on the core and thus effectively slow down the magnetohydrodynamic dynamo.
The main question here is whether the minerals on Mars had what it takes to get the hydrogen to the right place. Recent studies on the Red Planet show that the crust of Mars is rich in the mineral olivine, which binds poorly to water and is therefore relatively dry.
In the deeper bowels of the planet, the pressure causes olivine to convert into wadsley and ringwoodite minerals, which can hold more water. Deeper still, these minerals turn into bridgmanite, which becomes dry again. For some time, this bridgmanite could act as a buffer against water, allowing the core to continue convection. However, as the mantle cooled, the bridgmanite layer would shrink and eventually disappear entirely, O'Rourke's study suggests.
Whether or not this salvage layer of bridgmanite ever was inside Mars depends on how large the planet's core is. This information can be obtained using the Mars InSight spacecraft, which is scheduled to launch in early May, O'Rourke said.
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Scientists believe that Mars did have a magnetic field about 4 billion years ago. Researchers have struggled to explain how it disappeared, leaving the planet vulnerable to a devastating solar wind, which likely blew away its atmosphere and deprived its surface water.
But if hydrogen really blocked the convection of the planet's core, then by geological standards, everything should have happened in a very short time. Previous research suggests that Mars' magnetic field disappeared relatively quickly, in about 100 million years.
Nikolay Khizhnyak