messenger observations of extreme space weather at mercury

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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