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!