New research reveals how dynamo reversals affect Mars’ magnetic fields
Impact basins on Mars, previously thought to be demagnetized due to an inactive planetary dynamo, may instead reflect the impact of a reversing magnetic field, a new study suggests. Under the leadership of Dr. Silpaja Chandrasekar, PhD, indicates that Mars’ fluctuating dynamo may have been active for longer than expected, with implications for understanding planetary evolution.
Impact cymbals and cooling effects
In a paper published in the journal Nature Communications, researchers explored how the magnetic fields of large Martian impact basins, which appear weak, might be affected by prolonged cooling and reversing dynamo activity rather than an early shutdown of the dynamo. They modeled cooling patterns in these basins and found that frequent polarity reversals – changing the direction of the magnetic field – significantly reduced the intensity of magnetism in these areas, creating a “demagnetized” appearance.
Dynamo history of Mars
Historically, studies of the Martian dynamo – a mechanism that generates planetary magnetism – have focused on determining its operational timeline and role in the planet’s climate and structure. Evidence from young volcanic formations and meteorites, such as Allan Hills 84001, implies that Mars’ dynamo may have persisted until 3.7 billion years ago, questioning assumptions about its premature shutdown.
Researchers theorized that during cooling periods, oppositely magnetized layers formed in Mars’ basins due to magnetic field reversals, leading to weak magnetic signals. The study quantified this by evaluating factors such as the reversal rate, the Curie depth and the thermal cooling time scale.
Reversal rates and magnetic field evolution
Using finite element analysis and thermal simulations, the team analyzed the cooling behavior in different Martian basins, assessing how different reversal frequencies affected the field strength. At higher reversal rates (greater than 1.5 reversals per million years), significant reductions in magnetic field strength were observed, especially at higher altitudes above 200 kilometers.
The size of the basin affected the magnetic patterns detected: smaller basins showed dipolar fields, while larger ones showed complex magnetic structures, with field strength peaks along their edges. A gradual decrease in peak field strength in line with theoretical predictions for materials undergoing slow magnetization changes in response to continuous reversals.
Implications for the magnetic evolution of Mars
This study suggests that frequent dynamo reversals, rather than an early dynamo shutdown, explain weak magnetic fields in Mars’ basins. With higher reversal rates, larger basins over 500 miles in length showed weakened magnetism. However, smaller basins can appear demagnetized even at moderate reversal frequencies, complicating the magnetic analysis of Mars.
The findings provide new insights into Mars’ nuclear convection and atmospheric dynamics, strengthening the possibility that a reversing Martian dynamo persisted until 3.7 billion years ago and shaped the planet’s early magnetic landscape.
