astrochemistry applied to planets: cosmic-ray...
TRANSCRIPT
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ASTROCHEMISTRY APPLIED TO PLANETS:
COSMIC-RAY IONIZATION AND HAZES ON HOT-JUPITERS
Paul B Rimmer (University of St Andrews)Catherine Walsh (QUB, Leiden Observatory)Christiane Helling (University of St Andrews)
Thursday, 18 April 13
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ASTROCHEMISTRY AND ATMOSPHERIC CHEMISTRY
• Astrochemistry
• Hydrogen dominated
• Gas and surface chemistry
• 10 - 1000 K, 100 - 1010 cm-3
• Dominated by ion-neutral chemistry
• Lots of radicals, unsaturated carbon chains
• Atmospheric Chemistry
• Hydrogen dominated, or not
• Possible surface chemistry?
• 500 - 3000 K, 108 - 1019 cm-3
• Three-body, neutral-neutral reactions
• Carbons are saturated, aromatic
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ASTROCHEMISTRY AND ATMOSPHERIC CHEMISTRY
•Astrochemistry •Atmospheric Chemistry
Bean et al. (2010)Bergin et al. (2010)Thursday, 18 April 13
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ASTROCHEMISTRY AND ATMOSPHERIC CHEMISTRY
•Astrochemistry
•Complex species have N > 6
•Things like CH2OHCHO
•Atmospheric Chemistry
•Complex species have more than one carbon.
•C2H2, C2H4, anything with three carbons or more!
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WHY APPLY ASTROCHEMISTRY TO ATMOSPHERES?
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THE HAZY CASE OF HD 189733 b
• Pont & Sing observed a haze in the upper atmosphere of HD 189733 b.
• Equilibrium gas-phase chemistry can’t account for hazes.
• Non-equilibrium dust formation (nucleation + growth) can, but not that high up in the atmosphere.
• Where is the haze coming from, and what is it made of?
C. Carreau (ESA)
Thursday, 18 April 13
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PARTS OF A GIANT GAS PLANET’S ATMOSPHERE
Thermosphere
Stratosphere
Troposphere
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JUPITER
Thursday, 18 April 13
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HD 209458 b
European Space Agency and Alfred Vidal-Madjar
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NON-EQULIBRIUM CHEMISTRY:WHAT CAUSES IT?
• Effects within the Atmosphere
• Large-scale motion (Convection)
• Small-scale motion (Turbulence)
• Dust nucleation and growth [Woitke & Helling (2003),(2004)]
• Alfven ionization, grain discharges, lightning, [Helling (2012), Stark, Helling & Rimmer, Submitted]
• Effects outside the Atmosphere
• Cosmic Rays [Rimmer & Helling, Submitted]
• UV Photons
• IR Photons, X-Rays, Gamma Rays
• Meteorites, infalling dust, etc.
Thursday, 18 April 13
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OUR ION-NEUTRAL NON-EQUILIBRIUM NETWORK
• Over 100 species
• Up to C2H6
• Includes Cations, some Anions
• Treats atmospheric mixing
• Cosmic rays via atmospheric transport model
• Analytic radiative transfer
• Over 2000 Reactions
• Reversible: Neutral-Neutral, Three Body, Ion-Neutral
• Combustion Reactions and Capture Reactions
• Non-Reversible: Photodissociation, Photoionization, Cosmic Ray Ionization
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THE EFFECT OF COSMIC RAY AND UV PHOTOCHEMISTRY
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RETURNING TO HD 189733 b
• The questions we set out to address: what causes the haze and what is it made of?
• Our results hint at cosmic ray ionization as a way to produce hazes in free-floating planets.
• Hazes run into a potential problem with hot Jupiters. UV photons seem to destroy hydrocarbons, and may impede PAH production.
• Maybe silicate grains account for this signature, and the winds are sufficiently strong to get the silicate grains high enough in the atmosphere...
• ... but have we really addressed the question at all?
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WHAT ABOUT HD 189733 b?
•We looked at a Jupiter-like planet and an HD 209458 b-like planet.
•Why not model HD 189733 b?
•Maybe cosmic rays and UV photons conspire to produce a PAH haze in hot Jupiters?
•This is the natural next step.
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