A new study suggests that Mars’ impact basins, previously thought to be demagnetized due to a dormant planetary dynamo, may now reflect the effects of a reversing magnetic field. Led by Dr. Silapaja Chandrasekhar, PhD, it indicates that Mars’ fluctuating dynamo may have been active for longer than thought, which may have implications for understanding planetary evolution.
Impact basin and cooling effect
In a paper published in the journal Nature Communications, researchers explored how the magnetic fields of large Martian impact basins, which appear weak, lead to a prolonged cooling and reversal of dynamo activity, rather than a quick shutdown of the dynamo. May be affected. They modeled the cooling patterns in these basins and found that repeated polarity reversals – changing the direction of the magnetic field – significantly reduce the intensity of magnetism within these regions, creating a “demagnetized” appearance.
Martian Dynamo History
Historically, studies on the Martian dynamo – the mechanism that generates planetary magnetism – have focused on determining its operational timeline and role in planetary climate and composition. Evidence from young volcanic formations and meteorites such as Allen Hills 84001 suggests that the Mars dynamo may have persisted as long as 3.7 billion years ago, challenging notions of its early shutdown.
Researchers theorized that during the cooling period, magnetic field reversals caused contrasting magnetic layers to form within Mars’ basins, producing weak magnetic signals. The study quantified this by evaluating factors such as reversal rate, Curie depth, and thermal cooling timescale.
Reversal rate and magnetic field evolution
Using finite element analysis and thermal simulations, the team analyzed cooling behavior in different Martian basins, assessing how different reversal frequencies affected the field strength. For high reversal rates (more than 1.5 reversals per million years), a significant decrease in magnetic field strength was observed, especially at altitudes above 200 kilometers.
The size of the basin influenced the magnetic patterns discovered: smaller basins displayed dipole fields, while larger basins displayed complex magnetic structures, with field strengths peaking at their edges. The gradual decline in peak field strength is in agreement with theoretical predictions for materials undergoing slow magnetization changes in response to sustained reversals.
Implications for the magnetic evolution of Mars
This study proposes that repeated dynamo reversals, rather than initial dynamo shutdown, explain the weak magnetic field in the Martian basin. Basins larger than 800 km exhibit weak magnetism, with high reversal rates. However, small basins may appear demagnetized even at moderate reversal frequencies, adding complexity to Mars magnetic analysis.
The findings provide new insights into Mars’ original convection and atmospheric dynamics, strengthening the possibility of a reversing Martian dynamo that persisted until 3.7 billion years ago, shaping the planet’s early magnetic landscape.
