No FeS layer in Mercury? Evidence from Ti/Al measured by MESSENGER

Cartier, Camille; Namur, Olivier; Nittler, L. R.; Weider, S. Z.; Crapster-Pregont, E. J.; Vorburger, Audrey; Frank, Elizabeth A.; Charlier, Bernard

doi:10.1016/j.epsl.2020.116108

Cited by 28 publications

(41 citation statements)

References 66 publications

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“…Analyses of Mercury's surface composition indicates, that the planet formed under highly reduced formation conditions (Nittler et al 2011;McCubbin et al 2012), such that Si could have entered the liquid iron in a sufficient amount and prevented the dissolution of S in the iron alloy. A small amount of sulfur (around 1.5 wt% (Namur and Charlier 2017;Cartier et al 2020)) means that a large silicon content of at least 10 wt% must be present to keep the core liquid (Hauck et al 2013). Considering this kind of distribution of light elements in the interior, the resulting models agree with the estimated polar moment of inertia (Mann et al 2009;Malavergne et al 2014;Chabot et al 2014;Namur et al 2016;Margot et al 2018).…”

Section: Mercury's Core Statementioning

confidence: 53%

The BepiColombo Planetary Magnetometer MPO-MAG: What Can We Learn from the Hermean Magnetic Field?

et al. 2021

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The magnetometer instrument MPO-MAG on-board the Mercury Planetary Orbiter (MPO) of the BepiColombo mission en-route to Mercury is introduced, with its instrument design, its calibration and scientific targets. The instrument is comprised of two tri-axial fluxgate magnetometers mounted on a 2.9 m boom and are 0.8 m apart. They monitor the magnetic field with up to 128 Hz in a $\pm 2048$ ± 2048 nT range. The MPO will be injected into an initial $480 \times 1500$ 480 × 1500 km polar orbit (2.3 h orbital period). At Mercury, we will map the planetary magnetic field and determine the dynamo generated field and constrain the secular variation. In this paper, we also discuss the effect of the instrument calibration on the ability to improve the knowledge on the internal field. Furthermore, the study of induced magnetic fields and field-aligned currents will help to constrain the interior structure in concert with other geophysical instruments. The orbit is also well-suited to study dynamical phenomena at the Hermean magnetopause and magnetospheric cusps. Together with its sister instrument Mio-MGF on-board the second satellite of the BepiColombo mission, the magnetometers at Mercury will study the reaction of the highly dynamic magnetosphere to changes in the solar wind. In the extreme case, the solar wind might even collapse the entire dayside magnetosphere. During cruise, MPO-MAG will contribute to studies of solar wind turbulence and transient phenomena.

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Section: Mercury's Core Statementioning

confidence: 53%

The BepiColombo Planetary Magnetometer MPO-MAG: What Can We Learn from the Hermean Magnetic Field?

et al. 2021

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“…Parameterization of partitioning data for Ti between silicate, sulfide and metallic melts enables calculation of the relative depletion of Ti in the bulk silicate fraction of Mercury as a function of putative FeS layer thickness. Comparing the model results and current best surface elemental data, suggests that Mercury most likely lacks the putative iron sulfide layer at the core-mantle boundary (Cartier et al 2020). However, MESSENGER detection of Ti was close to the XRS detection limit, yielding only a global average of Ti/Si of 0.0098±0.0030 (Nittler and Weider 2019), whereas BepiColombo's MIXS is expected to achieve an improved sensitivity for Ti due to the higher energy resolution of the detector, providing spatially-resolved measurements during active Sun conditions.…”

Section: How Did Redox Conditions During Planetary Formation and Diffmentioning

confidence: 87%

“…Under these reducing conditions, elements behave differently to within the Earth: familiar lithophile (i.e., tending to form silicates or oxides) elements can become chalcophile (i.e., having an affinity for sulfur), whereas siderophile (i.e., having an affinity for metallic iron) elements can become lithophile. Titanium becomes chalcophile below IW -4 and can be used as a tracer for the likelihood of the presence of an iron sulfide layer at Mercury's core-mantle boundary (Cartier et al 2020).…”

Section: How Did Redox Conditions During Planetary Formation and Diffmentioning

confidence: 99%

Rationale for BepiColombo Studies of Mercury’s Surface and Composition

et al. 2020

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BepiColombo has a larger and in many ways more capable suite of instruments relevant for determination of the topographic, physical, chemical and mineralogical properties of Mercury’s surface than the suite carried by NASA’s MESSENGER spacecraft. Moreover, BepiColombo’s data rate is substantially higher. This equips it to confirm, elaborate upon, and go beyond many of MESSENGER’s remarkable achievements. Furthermore, the geometry of BepiColombo’s orbital science campaign, beginning in 2026, will enable it to make uniformly resolved observations of both northern and southern hemispheres. This will offer more detailed and complete imaging and topographic mapping, element mapping with better sensitivity and improved spatial resolution, and totally new mineralogical mapping. We discuss MESSENGER data in the context of preparing for BepiColombo, and describe the contributions that we expect BepiColombo to make towards increased knowledge and understanding of Mercury’s surface and its composition. Much current work, including analysis of analogue materials, is directed towards better preparing ourselves to understand what BepiColombo might reveal. Some of MESSENGER’s more remarkable observations were obtained under unique or extreme conditions. BepiColombo should be able to confirm the validity of these observations and reveal the extent to which they are representative of the planet as a whole. It will also make new observations to clarify geological processes governing and reflecting crustal origin and evolution. We anticipate that the insights gained into Mercury’s geological history and its current space weathering environment will enable us to better understand the relationships of surface chemistry, morphologies and structures with the composition of crustal types, including the nature and mobility of volatile species. This will enable estimation of the composition of the mantle from which the crust was derived, and lead to tighter constraints on models for Mercury’s origin including the nature and original heliocentric distance of the material from which it formed.

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“…The bulk amount S of Mercury inferred from chondritic compositions that are considered feasible for Mercury does not accommodate a solid FeS layer more than 90 km thick (Namur et al., 2016). Additionally, the concentration of titanium of Mercury's surface measured by MESSENGER is indicative of a solid FeS layer of at most 13 km thick, if present at all (Cartier et al., 2020).…”

Section: Interior Structure Models Of Mercurymentioning

confidence: 99%

Mercury's Interior Structure Constrained by Density and P‐Wave Velocity Measurements of Liquid Fe‐Si‐C Alloys

Knibbe

Rivoldini

Luginbuhl³

et al. 2021

JGR Planets

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Experimental measurements of density by X‐ray absorption and of P‐wave velocity by ultrasonic techniques of liquid Fe‐(<17 wt%) Si‐(<4.5 wt%) C alloys at pressures up to 5.8 GPa are presented. These data are used to construct an Fe‐Si‐C liquid mixing model and to characterize interior structure models of Mercury with liquid outer core composed of Fe‐Si‐C. The interior structure models are constrained by geodetic measurements of the planet, such as the obliquity and libration of Mercury. The results indicate that S and/or C with concentrations at the wt% level are likely required in Mercury's core to ensure the existence of an inner core with a radius (below ∼1,200 km) that is consistent with reported dynamo simulations for Mercury's magnetic field. Interior structure models with more than 14 wt% Si in the core, estimated for Mercury by assuming an EH chondrite‐like bulk composition, are only feasible if the obliquity of Mercury is near the upper limit of observational uncertainties (2.12 arcmin) and the mantle is dense (3.43–3.68 g·cm−3). Interior structure models with the central obliquity value (2.04 arcmin) and less than 7.5 wt% Si in the core, consistent with estimates of Mercury's core composition from an assumed CB chondrite‐like bulk composition, are compatible with 3.15–3.35 g·cm−3 mantle densities and an inner core radius below 1,200 km. Interior structure models with the obliquity of Mercury near the lower observational uncertainty limit (1.96 arcmin) have a low‐density mantle (2.88–3.03 g·cm−3), less than 4 wt% Si in the core, and an inner core radius larger than 1,600 km.

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No FeS layer in Mercury? Evidence from Ti/Al measured by MESSENGER

Cited by 28 publications

References 66 publications

The BepiColombo Planetary Magnetometer MPO-MAG: What Can We Learn from the Hermean Magnetic Field?

The BepiColombo Planetary Magnetometer MPO-MAG: What Can We Learn from the Hermean Magnetic Field?

Rationale for BepiColombo Studies of Mercury’s Surface and Composition

Mercury's Interior Structure Constrained by Density and P‐Wave Velocity Measurements of Liquid Fe‐Si‐C Alloys

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