p.#a.#delamere# university#of#colorado#con/ioworkshop2012/program... · 2012. 7. 13. ·...
TRANSCRIPT
Io’s plasma interac0ons: 101
P. A. Delamere University of Colorado
Issues for plasma interac0ons • Energy input for neutral escape (forma4on of corona and extended neutral clouds)
• Diagnos4c of atmospheric composi4on, distribu4on, and possible asymmetry
• Io’s aurora…diagnos4c of Io’s atmosphere
• Torus variability linked to volcanic ac4vity (JAXA EXCEED mission)
Steffl et al., 2008
Delamere et al., 2004
Types of interac0ons • Magne4zed (internally generated magne4c field) – Mini-‐magnetosphere (Ganymede)
• Non-‐magne4zed – Inert, no induced magne4c field and no neutral source (e.g. moon).
– Induced magne4c field due to 4me-‐varying external magne4c field (e.g. Europa and Io)
– Magne4c perturba4on due to interac4on with neutral source (.e.g. Io, Enceladus)
Pickup=source of energy
(at 60 km/s)
Tpu(O+)=270 eV
Tpu(S+)=540 eV
Tpu(SO2+)= 1080 eV
Interac0on processes
Momentum loading (pickup) • Ioniza4on
• Charge exchange
– Ioniza4on adds mass – Charge exchange does not add mass (usually) – Pickup involves two parts:
• Accelera4on to corota4on speed • Hea4ng at local flow speed (on 4me scale of gyromo4on)
– Both transfer momentum from ambient plasma to new ions
Ioniza0on and Charge Exchange
• .CharCharge
Ioniza4on limited by electron temperature [Saur et al., 1999; Dols et al., 2008]
Charge exchange amplified by “seed” ioniza4on. Results in an avalanche of reac4ons [Fleshman et al., 2011]
Io’s (par0al) neutral torus
M. Burger
Electrodynamic consequences
• Momentum loading generates currents
€
M•v = J ×BdV∫
€
J =∇ ×B
µo
Ioniza4on + charge exchange
Flow around a conduc0ng obstacle
Dols et al., 2008
Ring Beam (pickup) distribu0on
B
Momentum transfer • Magne4c field perturba4on due to “pick up” (e.g. ioniza4on and charge exchange)
• Alfven characteris4c determined plasma mass density and magne4c field.
vcor
vA
€
vcorvA
=δBx
Bz
Momentum transfer
• Alfven wing magne4c field topology results in forces on charged par4cles via Maxwell stresses. – Accelera4on of iogenic plasma at the expense of torus plasma.
– Ul4mately, Jupiter’s atmospheric is the source of momentum and energy.
Es0mate of momentum loading • Maxwell stress
• Plasma mass coupling rate
• Momentum balance requires (ignoring upstream input, chemical processes)
€
dpxdt
= 2(δBx )BzA /µo = (2ρtorusvAA)vx
•
MAlfven = 2ρtorusvAA =2PdAMAvcor
•
MAlfven =•
Mionization +•
Mchex ≈ 300 kg/s
Momentum transfer
€
•
MAlfven
€
•
Mtorus€
•
MAlfven
€
•
Mionization
€
•
Mchex
€
•
Mtorus•
MAlfven
<1
Electron Beams
Galileo
Fresh hot ions
Flow
Magnetic field
Galileo Io Flyby -‐ 1995
Flux
NeV
x (10
10 c
m-2
s-1
)"
Y (RIo)"
Bagenal, [1997]
• Is the local interaction ionosphere-like (elastic collision dominated), or comet-like (mass loading dominated)? • Bagenal, [1997]: 200-500 (kg/s) • Saur et al., [2003]: 50-200 (kg/s)
Y (RIo)
Bagenal, [1997]
€
I = JA = JπRIo2 = 3×106(A)
€
V ≈ vB(2RIo) = 400(kV)
€
P =VI =1.2 ×1012(W)
Energe0cs
Power (Alfven wave) per hemisphere: 5x1011 W
Io Interac4on: ~1012 W
IR+UV auroral spots: 109-‐1010 W
Io-‐DAM: 109-‐1010 W
Precipita4ng electrons (100-‐1000 eV): ~1010-‐1011 W
B
Analysis of mass loaded systems
Analysis of mass loaded systems
Analysis of mass loaded systems
Ion Cyclotron Waves B
Ion Cyclotron Waves
SO+ SO2
+
Ion Cyclotron Waves
Russell and Kivelson, 2001
Huddleston et al., 1997
Galileo Magnetometer Data
0.4 0.6 0.8 10
10
20
30
40
Frequency (Hz)
Pow
er/fr
eque
ncy
(Arb
itrar
y lo
g sc
ale)
32 amu 48 amu 64 amuA
Freq
uenc
y (H
z)
1.3 (C.A.) 2 3 4 RIo 32 amu
48 amu
64 amu
A BA B04:35 04:40 04:450.25
0.50
0.75
1.00
0.4 0.6 0.8 10
10
20
30
40
Frequency (Hz)
Pow
er/fr
eque
ncy
(Arb
itrar
y lo
g sc
ale)
32 amu 48 amu 64 amuB
Analysis of plasma data in Io’s wake Upstream Wake
Frank and Paterson, 2002
Hybrid Simula0ons (“synthe0c par0cle data”)
Energy (e
V)
Time
Hybrid simula0ons (upstream)
Hybrid simula0ons (wake)
Io’s electrodynamic interac0on with Jupiter’s magnetosphere
• Complex! – Induced Dipole – Thermal plasma -‐> neutral atmosphere
• Ioniza4on and Charge Exchange, auroral emissions? – Electron beams from Alfvenic interac4on
• Ioniza4on, auroral emissions? – Escaping neutrals
• Charge exchange, electron impact dissocia4on – Plasma data analysis difficult due to non-‐Maxwellian distribu4ons!