Compressibility of Mercury's dayside magnetosphere

Zhong, Jun; Wan, Weixing; Wei, Yong; Slavin, J. A.; Raines, J. M.; Rong, Zhaojin; Chai, Lihui; Han, Xinyi

doi:10.1002/2015gl067063

Cited by 37 publications

(48 citation statements)

References 28 publications

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“…For higher solar wind pressures and/or more intense dayside reconnection, such as solar wind structures accompanied by lower upstream Alfvénic Mach numbers, lower plasma beta in the magnetosheath and southward interplanetary magnetic fields, the dayside magnetosphere would be expected to lie at such low altitudes as to "disappear" from the MESSENGER data set. Indeed, throughout its mission MESSENGER Journal of Geophysical Research: Space Physics 10.1029/2018JA026166 did observe several events in which the dayside magnetosphere appears to have "disappeared", and those events are discussed by Zhong et al (2015).…”

Section: Discussionmentioning

confidence: 99%

“…For instance, when Mercury's magnetosphere is compressed by the solar wind due to enhanced pressure, the induced field generated in the conducting core adds to the internal field and effectively provides a shield for the magnetosphere limiting the direct access of solar wind particles to the planetary surface. Indeed, the effects of the induction currents on the large‐scale configuration of Mercury's magnetosphere have been inferred from the MESSENGER data for cases of strong (Slavin et al, ) and modest (Johnson et al, ; Zhong et al, ) variations in solar wind pressure.…”

Section: Introductionmentioning

confidence: 99%

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MESSENGER Observations and Global Simulations of Highly Compressed Magnetosphere Events at Mercury

et al. 2019

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We identify and examine all MErcury Surface Space ENvironment, GEochemistry, and Ranging (MESSENGER) crossings of Mercury's dayside magnetopause with magnetospheric field intensities ≥300 nT. The eight such events, which occurred under highly compressed magnetosphere conditions, are analyzed in the identical manner utilized by Slavin et al. (2014, https://doi.org/10.1002/2014JA020319). The results suggest that the eight highly compressed magnetosphere events represent the highest solar wind dynamic pressures for which the MESSENGER's orbit still passed below the magnetopause and provided measurements of the dayside magnetosphere. Using the magnetohydrodynamic model by Jia et al. (2015, https://doi.org/10.1002/2015JA021143) that electromagnetically couples Mercury's interior with its magnetosphere, a series of global simulations are conducted to quantitatively characterize the response of Mercury's magnetosphere to solar wind forcing. Combining the MESSENGER observations with the simulations, we have obtained a consistent picture of how Mercury's dayside magnetospheric configuration is controlled, separately and in combination, by induction‐driven shielding and reconnection‐driven erosion. For solar wind pressures of ∼40–90 nPa, compared with the average ∼10–15 nPa at Mercury's orbit, the shielding effects of induction in Mercury's core in standing‐off the solar wind typically exceed the erosion of the dayside magnetosphere due to reconnection for these events, most of which occurred under low magnetic shear conditions. For high magnetic shear across the magnetopause our simulation predicts that reconnection would dominate. Mercury's effective magnetic moment as inferred from magnetopause standoff distance ranges from 170 to 250 nT−RM3 for these events. These findings are of crucial importance for understanding the space weathering at Mercury and its contribution to the generation of Mercury's exosphere.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

MESSENGER Observations and Global Simulations of Highly Compressed Magnetosphere Events at Mercury

et al. 2019

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“…Figure a shows that crossings were observed approximately equally in all MLT sectors in the dayside magnetosphere and that on average the magnetopause crossings occurred near to the location given by the Winslow et al () model for the majority of orbits considered here. There appears to be a substantial spread in the distance of the observed crossings from the model location, which is likely due to crossings occurring during a range of Hermean seasons, resulting in significant changes to the compression of the magnetosphere by the solar wind between aphelion and perihelion (Zhong et al, ). The location of the FTEs identified in this study are presented in Figures c and d as red circles, with the magnetopause crossings indicated in gray for context.…”

Section: Discussionmentioning

confidence: 99%

The Influence of IMF Clock Angle on Dayside Flux Transfer Events at Mercury

Leyser

Imber

Milan

et al. 2017

Geophysical Research Letters

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Analysis of MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) data has shown for the first time that the orientation of the interplanetary magnetic field (IMF) in the magnetosheath of Mercury plays a crucial role in the formation of flux transfer events (FTEs) at the dayside magnetopause. During the first 4 Hermean years of MESSENGER's orbit around Mercury, we have identified 805 FTEs using magnetometer data. Under conditions of near-southward IMF, at least one FTE was detected on nearly 70% of passes through the magnetopause but the observation rate during northward IMF was less than 20%. FTEs were also observed preferentially in the prenoon sector. FTEs have been observed at Earth at all locations on the magnetopause under a wide range of solar wind conditions by single spacecraft such as

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“…A major question after Mariner 10 was whether the entire dayside is ever exposed to direct solar wind impact, either because of severe compression of the magnetosphere and/or erosion of dayside magnetic flux by reconnection [ Hood and Schubert , ; Slavin and Holzer , ]. MESSENGER observations have shown that this indeed can occur but is rare, occurring only about 5% of time for MESSENGER orbital observations, during extreme solar wind conditions, More typically, reconnection‐driven erosion effects are offset by magnetic fields induced in the planetary core [ Slavin et al , ; Zhong et al , ; Johnson et al , ]. The detection of induced core fields is important because it has allowed a determination of Mercury's core radius independently of traditional geodetic techniques [ Johnson et al , ], and demonstrates that changes in solar wind conditions are sensed by the planet's iron core.…”

Section: Modern‐day Mercury Inside and Out: Not Quite So “Dead”mentioning

confidence: 99%

A whole new Mercury: MESSENGER reveals a dynamic planet at the last frontier of the inner solar system

Johnson

Hauck

2016

JGR Planets

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The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission yielded a wealth of information about the innermost planet. For the first time, visible images of the entire planet, absolute altimetry measurements and a global gravity field, measurements of Mercury's surface composition, magnetic field, exosphere, and magnetosphere taken over more than four Earth years are available. From these data, two overarching themes emerge. First, multiple data sets and modeling efforts point toward a dynamic ancient history. Signatures of graphite in the crust suggest solidification of an early magma ocean, image data show extensive volcanism and tectonic features indicative of subsequent global contraction, and low‐altitude measurements of magnetic fields reveal an ancient magnetic field. Second, the present‐day Mercury environment is far from quiescent. Convective motions in the outer core support a modern magnetic field whose strength and geometry are unique among planets with global magnetic fields. Furthermore, periodic and aperiodic variations in the magnetosphere and exosphere have been observed, some of which couple to the surface and the planet's deep interior. Finally, signatures of geologically recent volatile activity at the surface have been detected. Mercury's early history and its present‐day environment have common elements with the other inner solar system bodies. However, in each case there are also crucial differences and these likely hold the key to further understanding of Mercury and terrestrial planet evolution. MESSENGER's exploration of Mercury has enabled a new view of the innermost planet, and more importantly has set the stage for much‐needed future exploration.

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Compressibility of Mercury's dayside magnetosphere

Cited by 37 publications

References 28 publications

MESSENGER Observations and Global Simulations of Highly Compressed Magnetosphere Events at Mercury

MESSENGER Observations and Global Simulations of Highly Compressed Magnetosphere Events at Mercury

The Influence of IMF Clock Angle on Dayside Flux Transfer Events at Mercury

A whole new Mercury: MESSENGER reveals a dynamic planet at the last frontier of the inner solar system

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