Mars' Missing Magnetic Field
Mars may just be the best magician yet. We know that Mars doesn’t possess a magnetic field comparable to Earth’s, but scientists have been researching for years to determine what caused the magnetic field’s’ disappearance. A recent study may have given us insight on how Mars’ magnetic field vanished over four billion years ago. But there’s a plot twist: this theory includes self-sabotage.
Mars’ Missing Magnetic Field
A magnetic field is an important planetary component. It protects a planet’s surface from charged particle damage. Earth, for example, has an inner dynamo that produces its magnetic field. This is the process of a planet’s rotation producing rotating currents in the molten core, acting as an electromagnet. In turn, this generated magnetic field keeps Earth safe from harmful radiation emitted from the sun in the form of solar wind. Mars, however, doesn’t have an internal dynamo capable of producing a magnetic field and is therefore much more susceptible to harmful cosmic radiation.
Researchers suggest Mars’ magnetic field disappeared over a span of 100 million years. In terms of astrophysics, that’s pretty quick. Without its magnetic field, Mars is vulnerable to solar winds stripping away Martian atmosphere and surface water. But how did the magnetic field go missing in the first place?
The Answer Might Be Convection
At the Lunar and Planetary Science Conference on March 21, 2018, planetary scientist Joseph O’Rourke proposed that shutting down convection of the planet’s molten iron core caused Mars’ magnetic field to disappear.
Convection—the transference of heat through the movement of bulk molecules like molten rock—relies on denser materials sinking into the core, which shifts lighter material to the surface. This movement of materials, specifically iron in the planet’s core, generates a magnetic field that protects the atmosphere from solar wind.
O’Rourke suggests that an excess of hydrogen possibly shut down convection in Mars’ core, switching off the magnetic field. The study proposes that as water got close to the molten iron core, it split into hydrogen and oxygen. While the oxygen formed compounds with other molecules and remained high in the mantle, the hydrogen molecules settled close to the core and suffocated the dynamo. As it settled, it blocked denser material from sinking deep enough to keep convection going.
Mars’ Mineral Composition
Mars’ crust includes the mineral olivine, which doesn’t bond well with water. This leaves the planet’s crust dry. Beneath the crust, interior pressure forces olivine to transform into wadsleyite and ringwoodite -- these minerals bond better with water. Closer to the core, the mineral turns into bridgmanite and dries again. O’Rourke’s study suggests the bridgmanite layer potentially behaved as a water buffer, allowing convection in the core to continue, and therefore producing a magnetic field. As the mantle cooled, however, the layer shrank and eventually disappeared, leaving the planet without a protective barrier.
Another theory, proposed by Johns Hopkins Applied Physics Lab’s James Roberts, suggests a large impact, perhaps from an asteroid, may have shut down convection by heating the outermost core. Doing so would have kept the core’s material from sinking, a similar idea to O’Rourke’s.
For more up-to-the-minute magnetic stories and news on magnetism in space, including the speculation of Mars' atmosphere supporting life, the planet's magnetic surface, and the research into the benefits of magnetic levitation for astronauts striving to reach Mars, visit our blog.