The Earth's magnetic field, created by molten iron in its crust, refracts radiation that would otherwise damage its atmosphere. Scientists have long tried to figure out why there is no such field on Mars, until data from an orbiting spacecraft brought an answer to this question. Intense magnetic anomalies have been identified that have damaged rocks throughout the southern hemisphere of Mars. It looks like these are the remnants of a field that previously surrounded the entire planet
The giant asteroid could punch a hole in the crust of Mars, which damaged its magnetic field and deprived it of the chance to become the same "blue planet" as the Earth, scientists say.
Such anomalies are absent in the northern hemisphere, which suggests that something happened in the distant past that changed the planet's magnetic field. This is complemented by another oddity of Mars: the rocks in the northern hemisphere are much thinner than in the southern. This phenomenon is known as the “bark dichotomy”.
"The evidence suggests that a powerful impact early in the planet's history could have wreaked havoc on the liquid core by altering motion and affecting the magnetic field," said Sabin Stanley, assistant professor of physics at the University of Toronto, whose research has just been published.
Presumably, Mars, along with the Earth and the entire solar system, appeared about 4.6 billion years ago as a result of the combination of rocks and other debris formed when the sun emerged.
The nascent planets began to grow, rocks melted, allowing the heaviest elements, such as iron, to be in the center. Iron, which was kept liquid by radioactive elements, began to move, creating magnetic fields on both planets.
Previously, it was assumed that the core of Mars has cooled down simply because the Red Planet is half the size of Earth, but this theory has been undermined by the recent discovery that Mercury, which is even smaller, has a liquid core and a magnetic field.
“We know that Mars had a magnetic field that disappeared 4 billion years ago, and that this happened simultaneously with the beginning of the crustal dichotomy, which may be due to the influence of an asteroid,” Stanley notes.
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Perhaps the main question is what would happen if Mars retained its magnetic field, and life could arise on it.
Monica Grady, professor of planetary and space sciences at the Open University, notes: "Mars once had a denser atmosphere, stagnant water and a magnetic field, so it was not like the dry, barren planet we see today."