Magnetic mineralogy of the Mercurian lithosphere

Abstract

Mercury and Earth are the only inner solar system planets with active, internally generated dynamo magnetic fields. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission recently detected magnetic fields on Mercury that are consistent with lithospheric magnetization. We investigate the physical and chemical environment of Mercury's lithosphere, past and present, to establish the conditions under which magnetization may have been acquired and modified. Three factors are particularly crucial to the determination of crustal composition and iron mineralogy: redox conditions in the planet's crust and mantle, the iron content of the lithosphere, and, for any remanent magnetization, the temperature profile of the lithosphere and its evolution over time. We explore potential mechanisms for remanence acquisition and alteration on Mercury, whose surface environment is both hot and highly reducing. The long‐term thermal history of Mercury's crust plays an important role in the longevity of any remanent crustal magnetization, which may be subject to remagnetization through thermal, viscous, and shock mechanisms. This thermal and compositional framework is used both to constrain plausible candidate minerals that could carry magnetic remanence on Mercury and to evaluate their capacity to acquire and retain sufficient magnetization to be detectable from satellite orbit. We propose that iron metal and its alloys are likely to be the dominant contributors to induced and remanent magnetization in Mercury's lithosphere, with additional contributions from iron silicides, sulfides, and carbides.

A New Tool for Separating the Magnetic Mineralogy of Complex Mineral Assemblages from Low Temperature Magnetic Behavior

“…As mineral magnetism aims to broaden its reach, contributing for example to the study of the formation of the solar system (e.g., Strauss et al, 2016;Wang et al, 2017), of deep-time terrestrial environments (e.g., Carlut et al, 2015;Slotznick and Fischer, 2016) or of extreme environments of hydrothermal vents (e.g., Toner et al, 2016), it is necessary to accompany these new frontiers with experimental tools adapted to the greater diversity of mineral compositions and greater complexity of mineral assemblages resulting from the superposition of geological and biogeochemical processes through time. Magnetic characterization presents the advantages of a low detection limit (order of 1 ppm) and in situ bulk sample analyses avoiding time consuming physical and chemical separation techniques shown to be biased (e.g., Lagroix et al, 2004;Wang et al, 2013).…”

Studying the Composition and Mineralogy of the Hermean Surface with the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) for the BepiColombo Mission: An Update

“…Although the hermean surface is generally much poorer in iron than the lunar surface, it has been argued that even for the extreme endmember case where the surface of Mercury has no native FeO, the iron brought in by meteorites should be sufficient to produce significant amounts of npFe 0 through vapor fractionation (Noble and Pieters 2003). The formation of npFe 0 might also be responsible for the observed remnant crustal magnetization (e.g., Johnson et al 2015;Strauss et al 2016). Thus, understanding the effects of space weathering on MERTIS spectra is critical for their accurate interpretation and justifies a comprehensive laboratory program that simulates SW by short-pulsed lasers, ion bombardment, and shock recovery experiments on various minerals and their mixtures (Weber et al 2019.…”

Constraining the Early History of Mercury and Its Core Dynamo by Studying the Crustal Magnetic Field

“…Such a distinction on the basis of paleopole estimates could only be possible if the paleopoles, accounting for their location uncertainties, are estimated to lie northward of 70°S. On the other hand, metal iron is the probable magnetic carrier present in Mercury's surface (Strauss et al, ). In addition, the abundance of metal iron present in the crater melt sheet is constrained by the crater's size.…”