According to general relativity, the gravitomagnetic Lense-Thirring force of Mars would secularly shift the orbital plane of the Mars Global Surveyor (MGS) spacecraft by an amount of 1.5 m, on average, in the cross-track direction over 5 years. The determi

shiftedby3mbythegravitomagnetic eldofMars,aquantitywhichfallswithinthereachedorbitaccuracy.TheaveragedLense-Thirringshiftover veyearsisthus1.5m.

Tocorroboratethisinterpretationofthedata,itisimportanttonotethatinthesuiteofdynamicalforcemodelsusedtoreducethegatheredobserva-tionsgeneralrelativityis,infact,present,butonlywiththegravitoelectricSchwarzschildpart:thegravitomagneticLense-Thirringpartisnotincluded,sothatitisfullyaccountedforbytheshowedresiduals.Moreover,noem-piricalout-of-planeaccelerationswere ttedinthedatareductionprocess;thiswasdoneonlyforthealong-trackcomponentofMGSorbittoaccountforothernon-gravitationalforceslikethermal,solarradiationpressureanddragmismodelling.Thus,itisunlikelythattheout-of-planeLense-Thirringsignalwasremovedfromthedataintheleast-squareprocedure.Moreover,iftherelativisticsignaturewasremovedsothatthedeterminedout-of-planeresidualswereonly(ormainly)duetoothercauseslikemismodellingorun-modellinginthenon-gravitationalforces,itisdi culttounderstandwhythealong-trackresiduals(middlepanelofFigure3of(Konoplivetal.2006))havealmostthesamemagnitude,sincethealong-trackcomponentoftheMGSorbitismuchmorea ectedbythenon-gravitationalaccelerations(e.g.theatmosphericdrag)thantheout-of-planeone.

4Conclusions

Inthiscommunicationweshowedthatthegeneralrelativisticgravitomag-neticLense-Thirringe ectcanaccommodate94%ofthe1.6maverageerrorinthedeterminedout-of-planeorbitresidualsoftheMartianorbiterMGS.ThecollectionandtheprocessingofmoredatafromMGS,OdysseyandtherecentlylaunchedMROspacecraftwillbeoftheutmostimportanceincorroboratingsuchtest.Forexample,theDopplertrackingdatafromtheMarsExplorationRover(MER)toOdysseywillimprovethedetermina-tionofjusttheout-of-planeportionoftheOdysseyorbit.Anindependentcheckwhichcould,andshould,bedoneistoproduceaparticularsolutioninwhichitisalsointroducedaparameterwhichexplicitlyaccountsfortheLense-Thirringe ectandsolveforit.

Acknowledgments

IgratefullythankA.Konopliv,NASAJetPropulsionLaboratory(JPL),forhavingkindlyprovidedmewiththeentireMGSdataset.Iamalso

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