Mars’ global magnetic field may have hung around for 200 million years longer than scientists had thought, possibly giving life a longer window to take hold on the Red Planet.
It is possible that Mars’ magnetic field has endured for 200 million years longer than previously believed. This is significant because it allows the magnetic field to overlap with the existence of liquid water on the Red Planet’s surface.
That’s the conclusion of new research headed by Harvard University planetary scientists who suggest that at the time enormous impact craters, known as basins, were developing on Mars, magnetic-pole reversals produced the false appearance that the planet’s magnetic dynamo had stopped.
Knowing what occurred to Mars’ magnetic field is essential to understanding the ancient history of the Red Planet.
Sarah Steele of Harvard, who led the study, said in a statement, “We are attempting to address fundamental, significant questions about how everything came to be as it is, even why the entire solar system is that way.” We can only learn about the deep innards and early histories of planets through planetary magnetic fields, which are also our best probes to address many of those issues.
Deep within a planet, a geodynamo effect creates a global magnetic field. The iron-nickel core of a planet like Earth is composed of two components: a molten outer core and a solid inner core. Any terrestrial planet’s core is completely molten when it is born, and with time, the solid inner core expands. Convection currents rise through the blazingly hot rotating molten outer core as heat seeps out of the hardening inner core. By rising through an existing magnetic field, these convection currents cause electric currents to create their own magnetic field, which feeds back into and intensifies the pre-existing one. The geodynamo is this.
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However, as heat escaped and convection stopped, the geodynamo rapidly cooled inside Mars, which is about half the diameter of Earth. The geodynamo inside the Red Planet stumbled and stopped as it did so. This has important implications for Mars’s later evolution. Without its worldwide magnetic field, Mars was unable to protect the surface from dangerous cosmic rays or repel the solar wind that started removing its atmosphere, including the water on the Red Planet.
The global magnetic field of Mars was believed to have died more than 4.1 billion years ago by planetary scientists. This is because there is no evidence of high magnetism in the rocks of massive impact basins that were created during a bombardment period between 4.1 and 3.7 billion years ago. During a violent impact, ferromagnetic minerals in molten rock can align with the surrounding magnetic field. As the impact-heated rocks gradually cool, the alignment of these ferromagnetic minerals is locked in, enabling researchers to study the ancient magnetic field billions of years later. However, the data from the biggest impacts on Mars points to the absence of a magnetic field at the time of the impacts.
However according to Steele and her coworkers, including her Harvard supervisor Roger Fu, planetary scientists have misread the indications. Sections of the well-known Martian meteorite Allan Hills 84001, which has been the focus of much debate since researchers claimed it contained microfossils in the 1990s, were analyzed in 2023 and showed evidence of magnetic field reversals recorded by the meteorite’s ferromagnetic minerals.
This assertion has now been reinforced by computer modeling, which indicates that the absence of a magnetic field observed throughout the impact basin formation process was due to a pole reversal of the magnetic field rather than the dynamo shutting off. When the north and south magnetic poles alternate on Earth every few hundred thousand years, the ferromagnetic materials are unsure of where to point, giving the impression that the magnetic field is weak or nonexistent. The global magnetic field on Mars remained until at least 3.9 billion years ago, if Steele’s research is right, rather than vanishing 4.1 billion years ago.
According to Steele, “We are essentially demonstrating that there might not have ever been a valid reason to assume Mars’ dynamo shut down early.”
Even though all of these periods were quite long ago, the additional 200 million years might have had a significant impact on the possibility of life on ancient Mars. The reason for this is that it crosses over into the period when the Red Planet’s surface was submerged underwater, as NASA Mars rovers have found evidence of. Life might have had an opportunity to begin in a watery environment without being wiped out by radiation from space if the magnetic field shielding the surface had remained intact.
The rate of air loss, which is still occurring and being monitored by NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter, is also affected by the potential survival of the magnetic field on Mars for a longer period of time than previously believed. In order to determine how thin Mars’ atmosphere may have formerly been and how much water it may have once possessed, scientists can study the rate of air and water loss and extrapolate backward. Scientists may need to slightly revise their timing of the changing conditions on Mars if air loss starts later and the magnetic field doesn’t vanish until later.