Estimate of the magnetic field of Mars based on the magnetic characteristics of the Yamato 000593 nakhlite

Abstract

Abstract-Yamato 000593, a nakhlite, was analyzed in terms of its magnetic record and magnetomineralogy. The natural remanent magnetization (NRM: 3.55-6.07 × 10 −5 Am 2 /kg) was thermally demagnetized at ~320 °C, and it was unstable against alternating field demagnetization. Based on analyses of thermomagnetic curves, the temperature dependence of hysteresis parameters, and microscopic observations, the magnetic minerals mainly consist of magnetite (0.68 wt% of the sample, including ~5% Fe 2 TiO 4 ) of less than 100 µm in size, associated with minor amounts of monoclinic pyrrhotite (<0.069 wt% of the sample) and goethite. Thermal demagnetization of NRM at ~330 °C is explained due to an offset of magnetization of antipodal NRM components of magnetite, whereas it is not due to a pyrrhotite Curie point. Large magnetite grains show exsolution texture with ilmenite laths, and are cut by silicate (including goethite) veins that formed along cracks. Numerous single-domain (SD) and pseudo-single-domain (PSD) magnetite grains are scattered in the mesostasis and adjacent olivine grains. Moderate coercive forces of H C = 6.8 mT and H RC = 31.1 mT suggest that Yamato 000593 is fundamentally able to carry a stable NRM; however, NRM was found to be unstable. Accordingly, the meteorite was possibly crystallized at 1.3 Ga under an extremely weak or absent magnetic field, or was demagnetized by impact shock at 12 Ma (ejection age) on Mars. This finding differs from the results of previous paleomagnetic studies of SNC (shergottites, nakhlites, chassignites, and orthopyroxenite) Martian meteorites. The significant dipole magnetic field resulting from the molten metallic core was probably absent during the Amazonian Epoch (after 1.8 Ga) on Mars.

Pre-mission InSights on the Interior of Mars

“…These suggest that the Martian dynamo could have persisted up to 3.7 Gy or so. The magnetic records of 1.3 Ga nakhlites are compatible with the absence of a dynamo field at that time (Gattacceca and Rochette 2004;Funaki et al 2009). An important, related issue is whether all crustal magnetization was acquired in a core field or partly in the presence of existing crustal fields (Gattacceca and Rochette 2004).…”

Paleointensity and Rock Magnetism of Martian Nakhlite Meteorite Miller Range 03346: Evidence for Intense Small‐Scale Crustal Magnetization on Mars

“…If MIL 03346 indeed recorded crustal fields, the recovered nakhlite paleointensities (Collinson, 1997; Funaki et al., 2009; Gattacceca & Rochette, 2004) suggest surface field intensities that are much stronger than those inferred from MGS and MAVEN observations. This is consistent with recent surface observations from InSight's magnetometer.…”

The Mars 2020 Candidate Landing Sites: A Magnetic Field Perspective

“…There are a number of magnetically interesting Martian meteorites whose magnetic properties have been described and are dominated by magnetite: SD‐sized magnetite has been discovered in the Amazonian‐aged nakhlites and shergottites (e.g., Cisowski, , Funaki et al, , Jambon et al, , Herd et al, ). However, the magnetic properties of these younger rocks may differ from those of older, more strongly magnetized crust.…”

“…A further source of magnetic field information is the ancient and strongly magnetized Martian meteorite, ALH 84001, which suggests that a dynamo with an Earth‐strength field was active at, or before, 4 Ga (Weiss et al, ). Other Martian meteorites, that is, the shergottite, nakhlite, and chassignite meteorites, provide insight into the formation and intrinsic magnetic properties of Martian rocks (Rochette et al, ) and indicate that the dynamo had declined to no more than ∼1 μT at 1.3 Ga (e.g., Collinson, ; Funaki et al, ). Because these Martian meteorites could have been magnetized by a crustal remanent field rather than an active dynamo, the results only require that a dynamo existed at, or prior to, the timing of magnetization acquisition.…”