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?