H3 and the Planets

1
H3 and the Planets
Steve Miller

• H3
• - the
• driver of
• planetary
• atmospheres

2
H3 and the Planets
Steve Miller

• H3 in planetary atmospheres

Formed above the homopause - thermosphere/ionosph
ere Na(h) Na0 exp-h/Ha Ha kT/mag Pressure
lt 1mbar Number density lt 1018m-3 Temperatures
Jupiter 900-1100K Saturn 400K Uranus 500-750K
3
H3 and the Planets
Steve Miller

• H3 chemistry

Formation H2 hn / e- ? H2 e-
e- H2 H2 ? H3 H Charge
exchange H2(vgt4) H ? H2
H Destruction H3 e- ? H2 H / 3H
Protonation H3 X ? XH H2 In
planetary atmospheres, X CH4, C2H2, C2H6
4
H3 and the Planets
Steve Miller

• What we observe

5
H3 and the Planets
Steve Miller

• Medium resolution spectroscopy

Uranus 1999 L window spectrum H3 n2 fundamental
Temperature 600K H3 column density 5x1015
m-2 Total emission 10-5 W m-2
6
H3 and the Planets
Steve Miller

• High resolution spectroscopy

Jupiter 1998 Doppler shifting of Q(1,0-)
vion 1 - 3km s-1
7
H3 and the Planets
Steve Miller

• A Big Question

Exospheric temperatures Calculated Measured
Jupiter 203K 940K Saturn
177K 420K Uranus 138K
800K Neptune 132K 600K
Why are they so hot?
8
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 mechanisms that cause this?
Connerney et al.
9
H3 and the Planets
Steve Miller

• Planetary aurorae

10
H3 and the Planets
Steve Miller

• The H3 thermostat

• 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

This does NOT help the high temperature problem
BUT
11
H3 and the Planets
Steve Miller

• H3 in exoplanets

Many large exoplanets found close to central
star lt 0.5a.u. Solar radiation gt100 x
jovian Will atmosphere heat up uncontrollably
and boil off? More hn creates more H3 More H3
more cooling
Detection?
Becomes less effective at dlt0.4a.u. due to H2 ? H
H
12
H3 and the Planets
Steve Miller

• H3 heating - Joule heating

HJ Eeq2 SP SP ? N(H3)
Typical values Eeq 1-3 Vm-1 SP 1-10mho BUT

13
H3 and the Planets
Steve Miller

• H3 heating - ion winds

vion -Eeq x BJ / BJ2
Typical values BJ 10-3 Tesla vion 1-2 km
s-1 BUT
14
H3 and the Planets
Steve Miller

• H3 heating - ion winds and ion drag

vneut k vion k 0.5 HJ (1-k)Eeq2
SP Hdrag k(1-k)Eeq2 SP Helec HJ Hdrag
Typical values Helec gt 1014W planetwide
15
H3 and the Planets
Steve Miller

• Heating/cooling in an auroral event

Sept. 8, 1998 Sept. 11, 1998
T(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.
16
H3 and the Planets
Steve Miller

• H3 heating - Saturn I

17
H3 and the Planets
Steve Miller

• H3 heating - Saturn II

Wion 0.34 WSat E(r ) WSat- Wionr x BSat
Typical values Helec n x 1012W planetwide
18
H3 and the Planets
Steve Miller

• Uranus

Solar cycle control of total H3 emission
Effect of Sun-Magnetic Pole angle?
19
H3 and the Planets
Steve Miller

• Jupiter Saturn Uranus
• Energy Tracer v v v
• Thermostat v v
• Conductivity v v v
• Heating v v ?

20
H3 and the Planets
Steve Miller
George Millward Alan Aylward Tom Stallard
Makenzie Lystrup Henrik Melin Chris
Smith Bob Joseph Jonathan Tennyson Tom
Geballe Larry Trafton
Oka

• H3
• - the
• driver of
• planetary
• atmospheres