MESSENGER Observations of Disappearing Dayside Magnetosphere Events at Mercury

Slavin, J. A.; Middleton, H. R.; Raines, J. M.; Jia, Xianzhe; Zhong, Jun; Sun, W.; Livi, S.; Imber, Suzanne M.; Poh, Gangkai; Akhavan‐Tafti, Mojtaba; Jasinski, Jamie M.; DiBraccio, G. A.; Dong, Chuanfei; Dewey, R. M.; Mays, M. L.

doi:10.1029/2019ja026892

Cited by 54 publications

(77 citation statements)

References 90 publications

(279 reference statements)

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“…Finally, we note that of the three parameters in equation (2), the X-line length L is currently the least well constrained. The two-spacecraft BepiColombo mission will hopefully help to constrain this parameter further, both for regular Hermean conditions and extreme events such as those reported by Slavin et al (2019).…”

Section: Discussionmentioning

confidence: 99%

The Contribution of Flux Transfer Events to Mercury's Dungey Cycle

Fear

Coxon

Jackman

2019

Geophysical Research Letters

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Bursty dayside reconnection plays a proportionally larger role in the driving of Mercury's magnetosphere than it does at Earth. Individual bursts of reconnection, called flux transfer events (FTEs), are thought to open up to 5% of Mercury's polar cap; coupled with the much higher repetition rate of FTEs at Mercury and the short Dungey cycle timescale, this makes FTEs the major driver of Mercury's magnetosphere. However, comparison between spacecraft and ionospheric observations at Earth suggests that the terrestrial contribution of FTEs may have been severely underestimated, by making implicit assumptions about FTE structure. In this study, we consider the implications of removing these assumptions at Mercury; by considering FTE mechanisms based on longer reconnection lines, we find that the contribution of FTEs to Mercury's Dungey cycle could be 5 times greater than previously thought and that FTEs may be able to provide sufficient flux transport to drive Mercury's substorm cycle.

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Section: Discussionmentioning

confidence: 99%

The Contribution of Flux Transfer Events to Mercury's Dungey Cycle

Fear

Coxon

Jackman

2019

Geophysical Research Letters

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“…Much of the indentation in the Zhong et al model is unconstrained, as there are no MESSENGER MP crossings in that region (Figure ). Furthermore, several MP crossings in the cusp region occur on orbits with atypical magnetospheric conditions identified in papers as “disappearing dayside events” (Slavin et al, ; Winslow et al, ). These crossings are not the result of a cusp indentation that is on average very deep but occur at their observed locations because the magnetosphere is extremely compressed.…”

Section: Average Magnetopause Shapementioning

confidence: 99%

“…Figure indicates that this is infrequent, and previous studies have shown that this occurs 1.5–4% of the time (Johnson et al, ; Zhong et al, ). Analyses of extreme events have investigated specific orbits where the magnetopause may intersect the surface (e.g., Jia et al, ), or where there appears to be no dayside magnetosphere (Slavin et al, ; Winslow et al, ).…”

Section: Average Magnetopause Shapementioning

confidence: 99%

“…To determine the MP normal direction, we use MVA (Sonnerup & Scheible, ). At Mercury, MVA has previously been used, for example, on a limited set of MESSENGER MP crossings to determine boundary normals and reconnection rates (DiBraccio et al, ) and in analysis of extreme events (Slavin et al, ). The normal to the magnetopause boundary is identified as the direction in which there is the least variance in the magnetic field magnitude, by calculating the eigenvalues and eigenvectors of the magnetic variance matrix (Sonnerup & Scheible, , equation (8.8)).…”

Section: Minimum Variance Analysismentioning

confidence: 99%

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The Shape of Mercury's Magnetopause: The Picture From MESSENGER Magnetometer Observations and Future Prospects for BepiColombo

et al. 2020

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The MErcury Surface, Space Environment, GEochemistry, and Ranging (MESSENGER) spacecraft orbited Mercury between March 2011 and April 2015, typically passing through the magnetosphere, magnetosheath, and interplanetary magnetic field, on each orbit. Using data from the Magnetometer, we identify magnetopause crossings for the complete orbital mission and model the average boundary shape. We find that Mercury's average magnetopause is well modeled by both an axisymmetric shape and a three-dimensional shape containing indentations in the cusp regions and a magnetotail that is wider in the north-south versus east-west direction. Examination of MESSENGER data and the use of simulated crossings show that coverage is very limited in the cusp region. Parameters describing the indentation are poorly constrained, and model fits may be biased due to the combination of orbital geometry and magnetospheric dynamics. The distribution of MESSENGER data inside the magnetopause, together with minimum variance analysis of a representative subset of magnetopause crossings, hints at the presence of a cusp indentation, though likely shallower than that estimated from the observed crossing positions. The BepiColombo spacecraft will arrive at Mercury in 2025. We simulate expected data coverage and magnetopause crossings using both axisymmetric and three-dimensional magnetopause models. BepiColombo will improve our understanding of the magnetopause shape by providing data over the southern hemisphere and regions of the northern cusp indentation not covered by MESSENGER. There is also the potential for simultaneous measurements of the interplanetary magnetic field and magnetopause position. Plain Language SummaryThe MErcury Surface, Space Environment, GEochemistry, and Ranging (MESSENGER) spacecraft orbited the planet Mercury from 2011 to 2015. On every orbit, MESSENGER crossed the boundary between the planet's magnetic field and solar wind, known as the magnetopause. We identify the location of the magnetopause on each orbit using MESSENGER magnetic field data. We use these locations to understand the three-dimensional shape of the boundary in space, including differences in the north-south versus east-west direction. The shape of MESSENGER's orbit means that there is limited information about some parts of this shape. For example, it is expected that the magnetopause has indentations known as "cusps," which occur near the north and south poles. MESSENGER magnetopause crossings provide no information on the southern cusp, and it is not possible to tell how large the northern cusp indentation is, or even whether it exists at all. The BepiColombo mission will arrive at Mercury in 2025, with two spacecraft that will orbit Mercury at different distances. We use our MESSENGER results to simulate where the two BepiColombo spacecraft are likely to cross the magnetopause. We find that BepiColombo will provide data on the shape of the magnetopause in places that MESSENGER did not and thereby provide information on the full three-dimensional sh...

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“…Because the magnetospheric perturbation was strongest during the first orbit, we analyzed this orbit (orbit 2577) in detail (Figure 1a). In a paper published independently of this work, Slavin et al (2019) also analyzed the effect of this ICME on Mercury's magnetosphere. However, their work focused on the second ICME-affected orbit which displayed less extreme solar wind conditions and magnetospheric response than in the first ICME-affected orbit analyzed in this study (Figure 1a).…”

Section: Introductionmentioning

confidence: 99%

Observations of Extreme ICME Ram Pressure Compressing Mercury’s Dayside Magnetosphere to the Surface

Winslow

Lugaz

Philpott

et al. 2020

ApJ

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Mercury's magnetosphere is known to be affected by the enhanced ram pressure and magnetic fields inside interplanetary coronal mass ejections (ICMEs). Here we report detailed observations of an ICME compressing Mercury's dayside magnetosphere to the surface. A fast CME launched from the Sun on November 29 2013 impacted first MESSENGER, which was orbiting Mercury, on November 30 and later STEREO-A near 1 AU on December 1. Following the ICME impact, MESSENGER remained in the solar wind as the spacecraft traveled inwards and northwards towards Mercury's surface until it reached and passed its closest approach to the planet (at 371 km altitude) without crossing into the magnetosphere. The magnetospheric crossing finally occurred 1 minute before reaching the planet's nightside at 400 km altitude and 84 • N latitude, indicating the lack of dayside magnetosphere on this orbit. In addition, the peak magnetic field measured by MESSENGER at this time was 40% above the values measured in the orbits just prior to and after the ICME, a consequence of the magnetospheric compression. Using both a proxy method at Mercury and measurements at STEREO-A, we show that the extremely high ram pressure associated with this ICME was more than high enough to collapse Mercury's weak magnetosphere. As a consequence, the ICME plasma likely interacted with Mercury's surface, evidenced by enhanced sodium ions in the exosphere. The collapse of Mercury's dayside magnetosphere has important implications for the habitability of close-in exoplanets around M dwarf stars, as such events may significantly contribute to planetary atmospheric loss in these systems.

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MESSENGER Observations of Disappearing Dayside Magnetosphere Events at Mercury

Cited by 54 publications

References 90 publications

The Contribution of Flux Transfer Events to Mercury's Dungey Cycle

The Contribution of Flux Transfer Events to Mercury's Dungey Cycle

The Shape of Mercury's Magnetopause: The Picture From MESSENGER Magnetometer Observations and Future Prospects for BepiColombo

Observations of Extreme ICME Ram Pressure Compressing Mercury’s Dayside Magnetosphere to the Surface

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