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La#tudinalandseasonalvaria#onsofO2onMarsusingHerschel/HIFI
T.Encrenaz1,R.Moreno1,E.Lellouch1,T.Fouchet1,P.Hartogh2,C.Jarchow2,F.Lefèvre3,T.Cavalié4
1LESIA,ObservatoiredeParis,France2MPSLindau,Germany
3LATMOS‐IPSL,Paris,France4LAB,Bordeaux,France
«TheUniverseexploredbyHerschel»,Noordwijk,Oct.15‐18,2013
Objec#veofthestudy
• Withameanmixingra#oabove0.1%,molecularoxygenis,a_ernitrogenandargon,themostabundantminorspecies.S#ll,itsabundanceandseasonalvaria#onsremainpoorlystudied,becauseoftheweaknessofitsspectroscopicsignatures.Oxygenwasfirstdetectedat0.76µmbyBarker(1972)andCarletonandTraub(1972),withamixingra#oof1300ppm.
• Anewdisk‐averagedmeasurementof1400±120ppmhasbeenrecentlyinferredbyHartoghetal.(A&A521,id.L49,2010)usinghigh‐resolu#onheterodynespectroscopyat774GHzwiththeHIFIinstrumentaboardHerschel(April2010,Ls=76°).
• Asanon‐condensiblespecies,oxygenonMars,likeCO,isexpectedtoshowspa#alandtemporantvaria#ons,butthesemeasurementshavenotbeenperformedyetonO2.
• WehavebeenusingHIFIaboardHerscheltostudythela#tudinalvaria#onsofO2onMarsfortwodifferentseasons,Ls=47°(Dec.23,2011)andLs=108‐115°(May09‐25,2012).Inaddi#on,HDOandH2
18Otransi#onshavebeenmeasuredsimultaneouslyforaretrievalofD/H.13COandC18Otransi#onshavebeenrecordedsimultaneouslytoinferCOmixingra#oandchecktheconsistencyoftheGCMthermalprofile.
• ThepresentreportdescribestheanalysisoftheO2andCOdata.
ThedatasetDates:
Dec22,2011–Ls=47°,MarsDiam=8.3arcsec
May25,2011–Ls=115°,MarsDiam=8–9arcsec
Transi+ons:Simultaneousmeasurements:
‐13CO1870.141GHz,C18O1863.039GHz,O21870.018GHz
‐ O21812.405GHz,HDO1818.519GHz
‐ HDO1625.408GHz,H218O1633.483GHz
HerschelFOV:11.3arcsec@1870GHz,12.9arcsec@1633GHzObserva+onsequence:
Foreachperiod,threeobserva#onsweresuccessivelyrecorded,centeredalongthecentralmeridian,atthesouthlimb,thecenterandthenorthlimb.
Totalobserving+me:27hours
Dataanalysis
• StrongripplesarepresentintherawdatabecauseMarsisastrongcon#nuumsource(Hartoghetal.A&A521,id.L48,2010)
• Ripplehasbeencorrectedfromtheknowninstrumentstandingwavefrequencybyremovingsinusoidalbaselines
• N‐SoffsetshavebeeninferredusingaradiometricmodelofMars
• RTcalcula#onshavebeenmadefortheexactoffsetsoftheobserva#ons,usingtheEMCD‐GCMtemperatureprofiles,fordifferentvaluesoftheCOandO2mixingra#os
• Bestfitsareshowninthenextfigures,forthe13COandC18OlinesandforthetwoO2lines,forthe3diskposi#onsandthetwoseasons.
Herschel/HIFIdataa_erripplecorrec#on Frequency (GHz)1 1863.0 1870.1 1870.0 1818.5 1812.4
22Dec2011Data–Thermalprofiles
HIFI/Herschel,Dec22,2011,South–Ls=47°‐CO=1100ppm
HIFI/Herschel,Dec22,2011,South–Ls=47°‐O2=1600ppm
HIFI/Herschel,Dec22,2011,Center–Ls=47°‐CO=1000ppm
HIFI/Herschel,Dec22,2011,Center–Ls=47°‐O2=1600ppm
HIFI/Herschel,Dec22,2011,North–Ls=47°‐CO=1000ppm
HIFI/Herschel,Dec22,2011,North–Ls=47°‐O2=1600ppm
25May2012Data–Thermalprofiles
HIFI/Herschel,May25,2012,South–Ls=115°‐CO=1100ppm
HIFI/Herschel,May25,2012,South–Ls=115°‐O2=1600ppm
HIFI/Herschel,May25,2012,Center–Ls=115°‐CO=1000ppm
HIFI/Herschel,May25,2012,Center–Ls=115°‐O2=1600ppm
HIFI/Herschel,May25,2012,North–Ls=115°‐CO=1000ppm
HIFI/Herschel,May25,2012,North–Ls=115°‐O2=1600ppm
Conclusions
‐Bestfitsareobtainedforthefollowingmixingra#osofCOandO2(ppm): CO O2
N C S N C S
Dec.2011(Ls=47°) 1000 1000 1100 1600 1600 1600
May2012(Ls=115°) 1000 1000 1000 1600 1600 1600
‐ Forbothseasons,thereisnoevidenceforala#tudinalvaria#oninthemixingra#osofCOandO2
‐ Thereisasystema#cdiscrepancyinthefitsoftheCOlines,withthesynthe#c13COlinebeingstrongerthanthedataandthesynthe#cC18Olinebeingweaker‐ Possibleorigin:UncertaintyinUSB/LSBgains
‐ ForbothCOandO2,theinferredmixingra#ostendtobelargerthanmeasuredbyHartoghetal.(A&A521,id.L48andid.L49,2010)forLs=77°
‐ Possibleorigin:ChangeinT(z)profile?Seasonaleffect?