MESSENGER Observationsof Extreme Space Weather at
Mercury
James A. SlavinDepartment of Atmospheric, Oceanic and Space Sciences
University of Michigan
SERENA – HEWGKey Largo May 14, 2013
• Dipolar, axial aligned planetary magnetic field with the magnetic dipole offset 484 km north of the planetary center.
[Anderson et al., 2008; 2011]
• Small magnetosphere drive by reconnection rate 10x Earth; Large flux transfer events at the dayside magnetopause; Plasmoids in the magnetotail. [Slavin et al., 2009; 2010]
• Large-amplitude ULF waves in equatorial magnetosphere and non-linear Kelvin-Helmholtz waves on magnetopause boundary – but only on the dusk-side. [Boardsen et al., 2009; 2010; Sundberg et al., 2011; 2012]
Slavin et al. [2009]
Solar System’s Most Dynamic Magnetosphere
2011_104 Orbit
3August 17, 2011
Example – Tail Crossings
August 17, 2011
Crossing #1λ2/λ1 = 11.13λ3/λ2 = 6.99|BN| = 0.54 nT
Crossing #2λ2/λ1 = 11.38λ3/λ2 = 26.81|BN| = 3.15 nT
Crossing #3λ2/λ1 = 17.40λ3/λ2 = 6.31|BN| = 2.83 nT
Crossing #4λ2/λ1 = 19.70λ3/λ2 = 14.18|BN| = 0.57 nT
Crossing #5λ2/λ1 = 27.75λ3/λ2 = 4.67|BN| = 0.91 nT
Subscript 1 – Normal direction
Dayside Crossing – Rotational Discontinuity
August 17, 2011
λ2/λ1 = 25.18 λ3/λ2 = 17.41 |BN| = 15.94 nTSubscript 1 – Normal direction
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Does Reconnection works differently at Mercury?
Earth: Strong dependence on interplanetary magnetic field direction. [Mozer et al., 2011]
Mercury: Reconnection is most intense when the interplanetary magnetic field is strong, but there is little or no dependence upon its direction [DiBraccio et al., 2012].
FTE identification
FTE identification
FTE Shower on April 11, 2011: IMF Bz > 0
December 15, 2008Slavin et al. (2012)
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Plasmoid Shower in Current Sheet
Example: DOY 2012 135
G. A. DiBraccio
BX(nT)
BY(nT)
BZ(nT)
|B|(nT)
Borg et al. 2012
13 March 2013
MVA: DOY 2012 135
G. A. DiBraccio
λ2/λ1 = 16.34λ3/λ2 = 3.20
13 March 2013B1 (nT)
B2 (nT)
B2 (nT)
B3 (nT)
Mercury Tail Loading/Unloading
November 15th, 2012
Repeated 1-s 40-nT increases in the Bz component, followed by a gradual (~10 s) decrease back are observed in the night-side plasma sheet.
[Sundberg et al., 2012]
Dipolarizations
Ho et al. (2012)
Mystery of Mariner 10 Energetic Particle Bursts Solved:The Particles are 30 – 300 keV Electrons!
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Why are extreme solar wind conditions important?
• Does the magnetopause reach the surface of Mercury when SW ram pressure become extreme? If so, what is the effect on Sputtering and Space Weathering rates?
• Are strong interplanetary magnetic fields with special
orientations required to “erode” the dayside magnetosphere like at Earth?
• Mercury’s metallic core extends to within 400 km of the surface; does electromagnetic induction in outer core play a significant role in shielding Mercury from the solar wind?
• What effects do these extreme conditions have on magnetospheric configuration and dynamics?
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November 23, 2011
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Magnetosphere – Core Coupling at Mercury
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Induction Currents in Outer Layer of Core
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Stronger Solar Wind Inputs Stronger Induction
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Reconnection Vs. Induction
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Effect of Reconnection Vs. Conducting Core on Rss
[Schubert and Hood, 1979][Goldstein and Suess, 1979]
[Slavin and Holzer, 1979]
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Effect of Induction on Magnetopause Altitude
No Induction& No Erosion:Pss ~ 1/Rss**6
Induction
[Winslow et al., 2012] [Glassmeier et al., 2007]
Magnetopause Erosion by
Reconnection
Magnetopause Inflation by Induction
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Reconnection Vs. Induction
Magnetospheric Structure• Northward displacement of
magnetic equator implies substantial N-S asymmetry in the surface field.
• Surface field at north pole is 3.4x larger than at south pole.
• Surface area of open magnetic flux in the southern hemisphere is 4x larger than in the northern hemisphere.
• Weak southern polar field and larger open field area imply greater particle-stimulated surface sputtering in the southern polar regions.
Anderson et al. [this meeting]
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Effect of 0.2 RM Magnetic Dipole Offset
BepiColombo will Explore Mercury’s Exposed Southern Hemisphere!
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