h 3 + and the planets steve miller h 3 + - the driver of planetary atmospheres
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H3+ and the Planets Steve Miller
H3+
- thedriver ofplanetary
atmospheres
H3+ and the Planets Steve Miller
H3+ in planetary atmospheres
Formed above the homopause - thermosphere/ionosphere
Na(h) = Na0 exp[-h/Ha]
Ha = [kT/mag]
Pressure < 1barNumber density < 1018m-3
Temperatures:Jupiter 900-1100KSaturn 400KUranus 500-750K
H3+ and the Planets Steve Miller
H3+ chemistry
Formation: H2 + h / e- H2+ + e- [+e-]
H2+ + H2 H3
+ + H
Charge exchange: H2(v>4) + H+ H2+ + H
Destruction: H3+ + e- H2 + H / 3H
Protonation: H3+ + X XH+ + H2
In planetary atmospheres, X = CH4, C2H2, C2H6
H3+ and the Planets Steve Miller
What we observe
IRTF
High-resolution spectroscopy
- dynamics, energy production
- characterising magnetospheres
Medium-resolution spectroscopy
- T, ion mapping, energy flow
- variability
UKIRT
H3+ and the Planets Steve Miller
Medium resolution spectroscopy
Uranus 1999
L window spectrum
H3+2 fundamental
TemperatureTemperature ~600K~600K
HH33++ column density column density ~ 5x10~ 5x101515 m m-2-2
Total emissionTotal emission ~10~10-5-5 W m W m-2-2
Q(1,0-) 3.953m
H3+ and the Planets Steve Miller
High resolution spectroscopyJupiter 1998
Doppler shifting of Q(1,0-)
vvionion = 1 - 3km s = 1 - 3km s-1-1
H3+ and the Planets Steve Miller
A Big Question
Exospheric temperatures:
Calculated MeasuredJupiter 203K 940KSaturn 177K 420KUranus 138K 800KNeptune 132K 600K
Why are they so hot?Why are they so hot?
H3+ and the Planets Steve Miller
H3+ as a tracer of energy inputs
Particles (keV electrons) are accelerated along magnetic field lines
H3+ formation occurs
Thermalisation then radiation
What are the What are the mechanisms that mechanisms that cause this?cause this?
Connerney et al.
H3+ and the Planets Steve Miller
Planetary aurorae
Earth- solar wind control
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are needed to see this picture.
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Saturn - solar wind, rotationSaturn - solar wind, rotation
Jupiter - internal, rotation
H3+ and the Planets Steve Miller
The H3+ thermostat
In some spectral regions, H3
+ spectrum dominates - 3-4m
Particle inputs to upper atmosphere ~ n mW m-2
But increased particle flux creates more H3
+ - H3
+ emission balances this for Jupiter and (probably) Uranus
- but not for Saturn
This does NOT help This does NOT help the high temperature the high temperature problemproblem
BUT…BUT…
H3+ and the Planets Steve Miller
H3+ in exoplanets
Many large exoplanets found close to central star < 0.5a.u.
Solar radiation >100 x jovian
Will atmosphere heat up Will atmosphere heat up uncontrollably and boil off?uncontrollably and boil off?
More h creates more H3+
More H3+ more cooling
Becomes less Becomes less effective at d<0.4a.u. effective at d<0.4a.u. due to Hdue to H22 H + H H + H
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.Detection?Detection?
H3+ and the Planets Steve Miller
H3+ heating - Joule heating
HJ = Eeq2 P
P N(H3+)
Typical values:Typical values:
EEeqeq = 1-3 Vm = 1-3 Vm-1 -1 ; ; PP = 1-10mho = 1-10mho
BUT …BUT …
Downward field-aligned current
Upward field-aligned current
Equatorward electric field
H3+ and the Planets Steve Miller
H3+ heating - ion winds
vion = -Eeq x BJ / |BJ|2
Typical values:Typical values:
BBJJ = 10 = 10-3-3 Tesla Tesla ; v; vionion = 1-2 km s = 1-2 km s-1-1
BUT …BUT …
Magnetic field
Ion drift
Equatorward electric field
H3+ and the Planets Steve Miller
H3+ heating - ion winds and ion drag
vneut = k vion
k ~ 0.5
HJ = [(1-k)Eeq]2 P
Hdrag = k(1-k)Eeq2 P
Helec = HJ + Hdrag
Ion drift
Neutral wind
Typical values: Typical values:
HHelecelec > 10 > 101414W planetwideW planetwide
H3+ and the Planets Steve Miller
Heating/cooling in an auroral event
Sept. 8, 1998 Sept. 11, 1998T(H3
+) 940K 1065K
N(H3+) 1.55x 1016 m-3 1.80x1016 m-3
vion 0.5 km s-1 1.0 km s-1
Helec 67.0 mW m-2 277.0 mW m-2
Precipitation 10.8 mW m-2 12.0 mW m-2
Conduction -0.3 mW m-2 -0.4 mW m-2
E(H3+) -5.1 mW m-2 -10.0 mW m-2
E(CH4) -65.0 mW m-2 -103.3 mW m-2
Net heating 7.4 mW m-2 175.3 mW m-2
Henrik Melin et al., Icarus Articles in press, 2006.
H3+ and the Planets Steve Miller
H3+ heating - Saturn I
Cassini: solar wind control of Saturn’s polar dynamics
H3+ and the Planets Steve Miller
H3+ heating - Saturn II
ion = 0.34 Sat
E(r ) = [Sat- ion]r x BSat
Typical values: HTypical values: Helecelec = n x 10 = n x 101212W planetwideW planetwide
H3+ and the Planets Steve Miller
UranusSolar cycle control of total H3
+ emission QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
Auroral emission ~20% of total emission
Effect of Sun-Magnetic Effect of Sun-Magnetic Pole angle?Pole angle?
H3+ and the Planets Steve Miller
Jupiter SaturnUranus
Energy Tracer √ √ √
Thermostat √ √
Conductivity √ √ √
Heating √ √ ?
H3+ and the Planets Steve Miller
H3+
- thedriver ofplanetary
atmospheres
George Millward Alan AylwardTom Stallard Makenzie LystrupHenrik Melin Chris Smith
Bob Joseph Jonathan TennysonTom Geballe Larry Trafton
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