When you buy through links on our articles, Future and its syndication partners may earn a commission.Credit: NASA/JPL-Caltech/USGSMars’ magnetic field may have survived 200 million years longer than scientists had thought — crucially, long enough for it to overlap with the presence of liquid water on the surface of the Red Planet.That’s the conclusion of new research led by planetary scientists at Harvard University, who propose that magnetic-pole reversals gave the mistaken impression that Mars’ magnetic dynamo had stopped by the time large impact craters, called basins, were forming on the planet.Understanding what happened to Mars’ magnetic field is vital if we are to learn the Red Planet’s ancient history.”We are trying to answer primary, important questions about how everything got to be like it is, even why the entire solar system is that way,” said Harvard’s Sarah Steele, who led the research, in a statement. “Planetary magnetic fields are our best probe to answer a lot of those questions, and one of the only ways we have to learn about the deep interiors and early histories of planets.”A planetary magnetic field is produced by a geodynamo effect deep inside a planet. A planet like Earth has an iron-nickel core that comes in two parts, a solid inner core and a molten outer core. When any terrestrial planet is born, its core is entirely molten, and the solid inner core grows with time. As heat leaks from the solidifying inner core, it produces convection currents that rise up through the searingly hot rotating molten outer core. These convection currents rise through a pre-existing magnetic field, sparking electric currents that induce their own magnetic field, feeding back into the pre-existing one and amplifying it. This is the geodynamo.Related: Life on Mars: Exploration & evidenceHowever, inside Mars, which is roughly half the diameter of Earth, the geodynamo cooled quickly as heat leaked away and convection ceased. As it did so, the geodynamo within the Red Planet stuttered and halted. This had significant repercussions for the subsequent evolution of Mars. Without its global magnetic field, Mars could not ward off the solar wind that began stripping away its atmosphere, including the Red Planet’s water, nor shield the surface from harmful cosmic rays.Planetary scientists had thought that Mars’ global magnetic field died over 4.1 billion years ago. This is because huge impact basins that were formed during a period of bombardment between 4.1 and 3.7 billion years ago do not retain any record of strong magnetism in their rocks. In the violence of an impact, ferromagnetic minerals in molten rocks can align themselves with the surrounding magnetic field and, as the rocks rendered hot by the impact slowly cool, the alignment of these ferromagnetic minerals becomes locked in, allowing scientists billions of years later to study the ancient magnetic field. Yet the evidence from Mars’ largest impacts suggests that there was no magnetic field when the impacts happened.However, Steele and her colleagues, including her supervisor Roger Fu of Harvard, think planetary scientists have misinterpreted the signs. In 2023, their a …
