Where is Saturn’s Deuterium Hiding?
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Where is Saturn’s Deuterium Hiding? J Roberts-Pierel; C Nixon; E Lellouch; L Fletcher; G Bjoraker; B Hesman; R Achterberg; L Fletcher; F M Flasar 11/4/16 1
Transcript of Where is Saturn’s Deuterium Hiding?
WhereisSaturn’sDeuteriumHiding?
JRoberts-Pierel;CNixon;ELellouch;LFletcher;GBjoraker;BHesman;RAchterberg;LFletcher;FMFlasar
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Outline
• IntroducOontoCassini-Huyguens– Specs– Instruments
• TheCompositeInfraredSpectrometer
• Whydowecare?• Methodology• Results
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Cassini-HuygensTimeline
• October1997:Cassini-Huygensislaunched• December2000:FlybyofJupiter• July2004:ArrivalatSaturnianSystem• January2005:HuygensprobereachesTitan• 2004-Present:OrbiOngSaturniansystemgatheringdata
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ImageCredit:NASAJPL
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SpecificaOons
• 700Wa^sofpower– RadioisotopeThermoelectricGenerators(RTGs)
• Cassini:12scienceinstruments• Huygens:6scienceinstruments• 27scienceinvesOgaOons
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CompositeInfraredSpectrometer(CIRS)
• 2interferometers– Mid-Infrared– Far-Infrared
• Rangeof10-1400cm-1
• AverageoperaOngpower:26.37W• PeakDataRate:6KB/sec
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ImageCredit:ESA
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Methodology:AtmosphericModeling• Mustmodelatmosphereswhenlackingin-situatmosphericprobes
• ObserveabsorpOon,reflecOonandemissionspectraremotely
• Twoapproachestomodelingplanetaryatmospheres
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Method1
• “Simple”approach• ComparetheobservaOonstoarepresentaOverangeofsyntheOcspectra
• Bestfor:– Fewatmosphericparameters– Fewspectra
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Method2• Retrievalalgorithm– ProcesseslargequanOOesofdataandreturnsfi^edatmosphericstates
– ExtractthemaximumamountofatmosphericinformaOonfromfinitesetsofdata
• RadiaOvetransfer(forward)model– CalculatessyntheOcspectrafromassumedparameters
• Inversion(retrieval)model– ComparessyntheOctomeasured– Variesparameterstominimizediscrepancy
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NEMESIS(Method2)
• OriginallyonlyobservaOonsofSaturnandTitanfromCIRS
• Generallyapplicabletoanyplanetaryatmosphere
• Visible/near-infraredtomicrowave• Reflectedsunlightorthermalemission– sca^eringornon-sca^ering
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Saturn:NEMESISModeling
• Mainabsorbers– NH3,PH3,CH4
• Temperature• H2Ortho-ParaFracOon(NuclearSpinState)– Ortho=Twoprotonspinsalignedparallel– Para=TwoprotonspinsalignedanOparallel
• HD
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IniOalNEMESISRetrievalCondiOons-NoHD
𝑋= 𝑋↓0 (𝑝/𝑝↓0 )↑1⁄𝑓−1
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Phosphine
Methane
AmmoniaHD
B
A
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178cm-1R(1)lineregion
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Saturn R1 HD Foward Models, Latitude=41°N
176.5 177.0 177.5 178.0 178.5 179.0
Wavenumber (cm-1
)
635
640
645
650
655
660
665R
adia
nce (
nW
cm
-2
sr-1
/cm
-1
)
2.1x10-5
2.6x10-5
3.5x10-5
4.4x10-5
4.6x10-5
Data
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This Work D/H (Saturn)
-60 -40 -20 0 20 40 60Planetographic Latitude
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0De
uter
ium
/Hyd
roge
n Ra
tio (x
10-5
)
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ModelAssurances• ISO/SWS– ReproducedthemodelingeffortsofLellouch2001– Wereabletoachievethesameresulttowithin8%– UOlizedanimprovedmethodandfoundalowerresult
• GalileoProbe– MeasuredD/HinJupiterin-situ– CIRSresultinexcellentagreement
Conclusion:NosystemaOcmodelingerrors
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Jupiter and Saturn D/H in Molecular Hydrogen
0
1
2
3
4
De
ute
riu
m/H
ydro
ge
n R
atio
(x1
0-5)
JUPITER SATURN SATURN INFERREDFROM CH3D
GalileoProbe13 ISO
SWS4 CIRS(This Work)
ISOSWS
(This Work)
ISOSWS4
ISOLWS6
CIRS(This Work)
Range ofProtosolar Value13
ISOSWS4
CIRS8
IRTFTEXES14
PREDICTED
Guillot7Guillot7
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Discussion• WeareabletomeasureD/HraOointheCIRSdataaccuratelywithNEMESIS
• CurrentmodelsdonotaccuratelypredictSaturn’sD/HraOo– PredictedSaturn/JupiterD/HraOo~1.05-1.15– MeasuredSaturn/JupiterD/HraOo:
• PotenOalexplanaOon:DeuteriumRain
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