Magnetic field of Mars

Whereas the Martian northern lowlands are largely unmagnetized, the southern hemisphere possesses strong remanent magnetization, showing alternating stripes.

[3] The large basins formed during the Late Heavy Bombardment (LHB) (~ 4.1–3.9 Ga) (e.g., Argyre, Hellas, and Isidis) and volcanic provinces (e.g., Elysium, Olympus Mons, Tharsis Montes, and Alba Patera) lack magnetic signatures, but the younger Noachian and Hesperian volcanoes (e.g., Tyrrhenus Mons and Syrtis Major) have crustal remanence.

[2] This detailed ground-level data is an order of magnitude higher than satellite-based estimates of ~200 nT at the InSight landing site.

Younger (~1.4 Ga) Martian Nakhlite meteorite Miller Range (MIL) 03346 recorded a paleofield of only ~5 μT.

[14] It has been proposed that these bands are formed by plate tectonic activity similar to the alternating magnetic polarity caused by seafloor crust spreading on Earth[14] or the results of repeated dike intrusions.

[17][18] As the mantle and core cooled over time, inner-core crystallization (which would provide latent heat) and chemical convection may have played a major role in driving the dynamo.

[17] One theory is giant impacts during the early and mid-Noachian periods stopped the dynamo by decreasing global heat flow at the core-mantle boundary.

[20] The seismic measurements from the InSight lander revealed that the Martian outer core is in a liquid state and larger than expected.

[19] In one model, a partially crystallized Martian core explains the current state of Mars (i.e., lack of magnetic field despite liquid outer core), and this model predicts that the magnetic field has the potential to be reactivated in the future.

Martian Dynamo. The schematic illustration of the ancient dipolar magnetic field of Mars generated by a core dynamo process.
Map of Martian crustal magnetism. Cylindrical projection map of crustal magnetism on Mars observed by MGS satellite at 400 km altitude. Colors represent intensities of the median value of the radial magnetic field components contoured over two orders of magnitude variation.
Timing of the Martian dynamo. Grey shading represents possible age constraints (in Ga years) for the early and late dynamo. Stars indicate new age constraints from MAVEN data. [a] Early dynamo before the formation of Hellas, Isidis, and Argyre. [b] The cessation of the early dynamo based on large basin population. [c] The age of ALH84001. [d] Late dynamo after the formation of the major basins.