9 May 2008 1

MESSENGER First Flyby Magnetospheric Results

J. A. Slavin and the MESSENGER Team

BepiColombo SERENA Team Meeting

Santa Fe, New Mexico11 May 2008

9 May 2008 2

Mariner 10 View of Magnetosphere

Miniature Terrestrial-type Magnetosphere according to Mariner 10 measurements (mid-1970’s) with some Exospheric Neutrals from ground-based telescopic

observations (mid-1980’s)

9 May 2008 3

Christon (1989)

Mariner 10 Energetic Particle Events

Mariner 10 Measurements Strongly Suggest Earth-like Substorms, but with durations of only a few minutes – consistent with the

Dungey Cycle T ~ 1 min for Mercury due to Siscoe et al. (1975)

9 May 2008 4

Other Mariner 10 Substorm Phenomena

Similarity to Terrestrial-type Substorms includes Near-Tail Dipolarization and SCW Field-Aligned Currents

Slavin et al. (1997)

9 May 2008 5

MESSENGER First Fly-by Trajectory

Low Latitude Near-Tail Encounter

9 May 2008 6

First Flyby Overview

IMF Bz > 0, so No Substorms, but Planetary Ions Everywhere!

9 May 2008 7

Not resolved?

4 6 8 10 30 50

mqhist_1843_1914 1 1:10:03 PM 4/6/08

cnts_wt_normSUMO+Na+ (23)28 (Si+ CO N2 C2H4)34 (H2S)K+Ca+H2OC+

10

20

30

40

50

60

70

80

Mass/Charge (amu/e)

Cou

nts

per

bin

MESSENGER EPPS-FIPS

12

16

23

28

34

39

40

O++C++

He+

18

Mg++

C+

First Ion Composition Measurements at Mercury!

Zurbuchen et al. (2008)

Mercury’s Surface and Atmosphere provide a Compositionally Rich Source of Photo-Ions throughout the Magnetosphere and the Near-by Solar Wind.

Na+

9 May 2008 8

Can Mercury’s Magnetosphere Thermalize Heavy Ions?

Boardsen and Slavin (2007)

Small Magnetospheric Dimensions may prevent significant Photo-Ion Thermalization – e.g., No ICW’s in Mariner 10 data

Potter et al. (2002)

9 May 2008 9

BS & MP Boundary Models

Bow Shock indicates M ~ 3; Magnetopause is Terrestrial in Shape with Factor of ~ 8 Spatial Scaling

9 May 2008 10

Large Flux Transfer Event

Russell and Elphic (1978)

Magnetosheath FTE following Bz < 0; Diameter is ~ 1200 km or about 30% of Rmp as compared with ~ 10% at Earth (supporting predictions by Kuznetsova and Zeleny,1986)

9 May 2008 11

Flank Region Vortex Signatures

Fujimoto et al. (1998)

Spatial scale lengths for individual rotation signatures are ~ 1 RM or ~ 0.7 – 1 Rmp as compared to ~ 2 – 3 Rmp at the Earth.

9 May 2008 12

“Double Magnetopause” and ULF Waves

Na+ ionized in the flank magnetosheath will have an energy of ~ 6 keV and a depth of penetration into the magnetosphere of ~ 1 gyro-radius or ~ 1000 km – which is comparable to the scale of the “double” magnetopause. ULF waves with frequencies below H+ gyro-frequency are common and appear to map out closed field line region.

9 May 2008 13

What is our estimate of the dipole?

External field Moment(nT-RM

3)Pole tilt(North H)

Pole lon (North H)

RMS Cond No

1. TS04 -229 9º 19º 28 nT 1 nT

2. SHA: 1 fit -247 12º 42º 26 nT 10 nT

3. SHA: 3 fits -290 5º 51º 14 nT 17 nT

13 24% Dir: 5.4º

23 16% Dir: 7.1º

Anderson et al. (2008)

9 May 2008 14

Summary of Initial Results

Has Mercury’s magnetic field changed since Mariner 10?- Less than ~10% moment and 20º in direction. - Smaller than variations between different analysis techniques.

What is our current best estimate for the main field?- Moment: -290 nT-RM

3, 5º tilt, 51º lon.

Is there evidence for higher order structure?- Best fit to data requires a g20 term with g20/g10 in the range 0.2 to 0.4.- Driven by equatorial field that is lower than a dipole would give. - Could be due to plasma pressure.

2nd and 3rd encounters near equator at ~180º opposite longitude:- will help resolve longitude asymmetry;- will determine prevalence of plasma pressures.

Anderson et al. (2008)

9 May 2008 15

Post - MESSENGER First Flyby View

Magnetosphere Immersed in a Comet-Like Planetary Ion Coma.

9 May 2008 16

MESSENGER (2011) & BepiColombo (2019)

MESSENGER Orbit BepiColombo MPO & MMO Orbits

9 May 2008 17

Second Mercury Encounter will be October 6th, 2008!