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Mangano V., Massetti S., Milillo A., Mura A., Orsini S., Leblanc F.

Dynamical Evolution of Sodium Anysotropies in the Exosphere of Mercury. Mangano V., Massetti S., Milillo A., Mura A., Orsini S., Leblanc F. INAF-IAPS Roma, Italy, CNRS Paris, France. HEWG-SERENA meeting Key Largo, May 15th 2013. Why Mercury Exosphere ?.

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Mangano V., Massetti S., Milillo A., Mura A., Orsini S., Leblanc F.

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  1. Dynamical Evolution of Sodium Anysotropies in the Exosphere of Mercury Mangano V., Massetti S., Milillo A., Mura A., Orsini S., Leblanc F. INAF-IAPS Roma, Italy, CNRS Paris, France HEWG-SERENA meeting Key Largo, May 15th 2013

  2. Why Mercury Exosphere? • Exosphere is almost ‘nothing’…it is so tenuous! (density < 10−14 bar) • Peculiar because it is directly in contact with the surface • It is the result of many interactions and equilibrium of sources and sinks ...hence, a veryactivedynamics ! (Milillo et al, 2005)

  3. Why Mercury Exosphere? • Itisalmost ‘nothing’…so tenuous! (densitylessthan 10-14 bar) • Peculiarbecauseitisdirectly in contact with the surface • Itis the result of manyinteractions and equilibrium of sources and sinks • For thisreasonithas a veryactivedynamics • Na is a minor speciesBUT... • Thanks to resonantscattering, itis a verygood‘tracer’! WhySodium?

  4. Mercury Variability/1 ...both in time and in space ! Na D2 emission in MR (Potter et al, 1999) Na D2 tail (Potter et al, 2002)

  5. Mercury Variability/2 ...on time-scales of hours and days, with peculiar and recurring morphologies. D2 Na intensityvariability in kR (Leblanc et al., 2009) D1+D2 tailvariability with TAA in R (Schmidt et al, 2012)

  6. N SSP SEP E W SUN S THEMIS 0.90 m Solar Telescope F/16 Ritchey-Chretien telescope in alt-az mounting Helium filled telescope tube MTR mode for multiline spectropolarimetry Spectral range 400 to 1000 nm at : R ~ 220,000 Slit: 0.5" & 120 " long R ~ 400,000 Slit: 0.25" & 70 " long (low and high resolution) Spectral resolution 0.027 Å to 0.016 Å Spectral dispersion 10.2 to 6 mÅ Two individual cameras: D1 Na at 5896 Å & D2 Na at 5889 Å THEMIS – Observatorio del Teide, Tenerife Lat.:  N  28° 18' 12.42" Long.: W 16° 30’ 32.04" Elevation:   2429 m Sixyears of observations (2007-2012): ~ 150 days!

  7. Observations on July13th, 2008 06:52 UT 08:16 UT 09:33 UT 10:50 UT 13:38 UT 16:55 UT • The two-peaksfeatureisvisible for the wholeday related to the magneticcusps • Southern peakintensityishigher • The intensity trend isdecreasing

  8. Dependance on seeing • Comparison is misleading without ‘averaging’ the different seeing values to a single one • Convolution of the observations with a proper gaussian profile degrades all the images to the worse seeing value (1.77’’)

  9. Dependance on TAA Average Intensity Emission vs Time (for the whole 7 days) is also decreasing  this is because of TAA dependance Normalization is needed Leblanc et al., 2010

  10. Final images • Alldegraded to 1.77’’ seeingvalue (the one of 4th scan) • Normalized to the averageintensity trend of the period (TAA)

  11. Exospheric Model (Mura et al., 2009) • Mid-latitudepeaks are the results of a twostepprocess: • 1) IS (ion-sputtering) • 2) PSD (photon-stimulateddesorption) + TD (thermaldesorption) • Simulationsagree in magnitude • Peaks (as the effect of a single ionprecipitationevent) decrease, causing a migration of Na towards the equatorialregion • Unfortunately the model fails in the decreasing time-scale (~2-5 hours)

  12. Magnetospheric Model (Massetti et al., 2007) • Earth-likemagnetospheregenerated by an intrinsicmagneticdipole • MESSENGER foundthatitisshiftednorthward by 0.2 RM • Thismay cause broadening of the southerncuspfootprint • Simulations with IMF=[-10 0 -30] nTfitsremarkablywell with the first observation • High pressure SW can cause a shifttoward the poles of the cuspfootprints

  13. Analysis/1: emissionregions N E S • Eveniferrorbars are quite big, S regionisclearlyhigherthan the rest • A second ‘event’ seem to occurat the fourthscan • A decreasing trend with time can also be hypothesised

  14. Analysis/2: peaksevolution • Going deeper in the analysis 21 thin ‘slices’ along Z axis • Some interesting features are revealed…

  15. Analysis/2: peaksevolution • Going deeper in the analysis 21 thin ‘slices’ along Z axis • Some interesting features are revealed…

  16. Analysis/2: peaksevolution • Intensity in latitude vs time (time increasing bottom to top) • Intensity variations in latitude are evidenced  4th scan

  17. Ourinterpretation • During a quasi-steady reconnection regime solar windprecipitatestoward the cuspfootprints • Additionalpulsedreconnections are superposedcausing more intense localized plasma precipitation • Hence, the plasma impactingonto the surfacewould produce the localizedpeaks of the Na exosphere • In addition, observations show the effects of a discrete sequence of precipitationevents due to pulsedmagneticreconnection, superposed to the precipitation due to quasi-steady reconnection, as a global modulation of Na release averageintensity

  18. Summary • Daily and ~1-hour time-scale observations with THEMIS solar telescopeallow a detailedmonitoring of the highlydynamicexosphere of Mercury • Cusprelatedpeaks in the Na exosphere are observed on July 13th 2008 in high resolution • Analysis of peaksintensityvariations with time alonglatitudeisperformed • Comparison with both the Exospheric Model by A. Mura (2009) and the Magnetospheric Model by S. Massetti (2007) mayexplain the mainfeatures: • 1. peaksbroadening & equatorialenhancement • 2. cuspfootprint • A reasonable scenario with IMF conditions and interactions with the Mercury magneticfieldisgiven. Unfortunatelylocal data of IMF on July 2008 are notavailable to confirmit.

  19. Thankyou ! For details: Mangano V., Massetti S., Milillo A., Mura A., Orsini S., Leblanc F. Dynamical evolution of sodium anysotropies in the exosphere of Mercury Planet. Space Sci. 2013, in press http://www.sciencedirect.com/science/article/pii/S0032063313000597

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