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H 3 + and the Planets

Steve Miller. H 3 + and the Planets. H 3 + - the driver of planetary atmospheres. Steve Miller. H 3 + and the Planets. Formed above the homopause - thermosphere/ionosphere N a (h) = N a0 exp[-h/H a ] H a = [kT/m a g] Pressure < 1 m bar Number density < 10 18 m -3 Temperatures:

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H 3 + and the Planets

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  1. Steve Miller H3+ and the Planets H3+ - the driver of planetary atmospheres

  2. Steve Miller H3+ and the Planets Formed above the homopause - thermosphere/ionosphere Na(h) = Na0 exp[-h/Ha] Ha = [kT/mag] Pressure < 1mbar Number density < 1018m-3 Temperatures: Jupiter 900-1100K Saturn 400K Uranus 500-750K H3+ in planetary atmospheres

  3. Steve Miller H3+ and the Planets Formation: H2 + hn / 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+ chemistry

  4. High-resolution spectroscopy - dynamics, energy production - characterising magnetospheres IRTF Medium-resolution spectroscopy - T, rion mapping, energy flow - variability UKIRT Steve Miller H3+ and the Planets What we observe

  5. Q(1,0-) 3.953mm Steve Miller H3+ and the Planets Uranus 1999 L window spectrum H3+ n2 fundamental Medium resolution spectroscopy Temperature ~600K H3+ column density ~ 5x1015 m-2 Total emission ~10-5 W m-2

  6. Steve Miller H3+ and the Planets Jupiter 1998 Doppler shifting of Q(1,0-) High resolution spectroscopy vion = 1 - 3km s-1

  7. Steve Miller H3+ and the Planets Exospheric temperatures: Calculated Measured Jupiter 203K 940K Saturn 177K 420K Uranus 138K 800K Neptune 132K 600K A Big Question Why are they so hot?

  8. Steve Miller H3+ and the Planets Particles (keV electrons) are accelerated along magnetic field lines H3+ formation occurs Thermalisation then radiation What are the mechanisms that cause this? Connerney et al. H3+ as a tracer of energy inputs

  9. Earth- solar wind control Jupiter - internal, rotation Saturn - solar wind, rotation Steve Miller H3+ and the Planets Planetary aurorae

  10. Steve Miller H3+ and the Planets In some spectral regions, H3+ spectrum dominates - 3-4mm 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 The H3+ thermostat This does NOT help the high temperature problem BUT…

  11. Steve Miller H3+ and the Planets Many large exoplanets found close to central star < 0.5a.u. Solar radiation >100 x jovian Will atmosphere heat up uncontrollably and boil off? More hn creates more H3+ More H3+ more cooling H3+ in exoplanets Detection? Becomes less effective at d<0.4a.u. due to H2 H + H

  12. Downward field-aligned current Upward field-aligned current Equatorward electric field Steve Miller H3+ and the Planets H3+ heating - Joule heating HJ = Eeq2SP SP N(H3+) Typical values: Eeq = 1-3 Vm-1 ; SP = 1-10mho BUT …

  13. Magnetic field Ion drift Equatorward electric field Steve Miller H3+ and the Planets H3+ heating - ion winds vion = -Eeq xBJ / |BJ|2 Typical values: BJ = 10-3 Tesla; vion = 1-2 km s-1 BUT …

  14. Ion drift Neutral wind Steve Miller H3+ and the Planets H3+ heating - ion winds and ion drag vneut = k vion k ~ 0.5 HJ = [(1-k)Eeq]2 SP Hdrag = k(1-k)Eeq2SP Helec = HJ + Hdrag Typical values: Helec > 1014W planetwide

  15. Steve Miller H3+ and the Planets Heating/cooling in an auroral event Henrik Melin et al., Icarus Articles in press, 2006.

  16. Cassini: solar wind control of Saturn’s polar dynamics Steve Miller H3+ and the Planets H3+ heating - Saturn I

  17. Steve Miller H3+ and the Planets H3+ heating - Saturn II Wion = 0.34 WSat E(r ) = [WSat- Wion]r x BSat Typical values: Helec = n x 1012W planetwide

  18. Auroral emission ~20% of total emission Steve Miller H3+ and the Planets Solar cycle control of total H3+ emission Uranus Effect of Sun-Magnetic Pole angle?

  19. Steve Miller H3+ and the Planets Jupiter Saturn Uranus Energy Tracer √ √ √ Thermostat √√ Conductivity √ √ √ Heating √ √ ?

  20. Steve Miller George Millward Alan Aylward Tom Stallard Makenzie Lystrup Henrik Melin Chris Smith Bob Joseph Jonathan Tennyson Tom Geballe Larry Trafton H3+ and the Planets Oka H3+ - the driver of planetary atmospheres

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