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Hermean environment

BepiColombo : a tool for Hermean Environment investigation Anna Milillo ( INAF/ Istituto di Fisica dello Spazio Interplanetario ).

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Hermean environment

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  1. BepiColombo: a tool for Hermean Environment investigationAnna Milillo(INAF/IstitutodiFisicadelloSpazioInterplanetario)

  2. This topic has been submitted for publication in the Bepicolombo special issue of Planetary Space Science:Milillo, A., M. Fujimoto, E. Kallio, S. Kameda, F. Leblanc, Y. Narita, G. Cremonese, H. Laakso, M. Laurenza, S. Massetti, S. McKenna-Lawlor, A. Mura, R. Nakamura, Y. Omura, D.A. Rothery, K Seki, M. Storini, P. Wurz, W. Baumjohann, E. Bunce, Y. Kasaba, J. Helbert , A. Sprague and Hermean Environment WG SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  3. Hermean environment (from Milillo et al., SSR, 2005) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  4. NASA-MESSENGER • The environment is one of the high-priority scientific target of the mission: • What is the nature of Mercury's magnetic field? • What are the unusual materials at Mercury's poles? • What volatiles are important at Mercury? MESSENGER’s instruments devoted to the environment are: Magnetometer (MAG) Energetic Particle and Plasma Spectrometer (EPPS) Mercury Atmospheric and Surface Composition Spectrometer (MASCS) X-Ray Spectrometer (XRS) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  5. ESA-JAXA BepiColombo • The mission has among its major scientific objectives • Determination of the composition, origin and dynamics of Mercury's exosphere and polar deposits and • Investigation of the structure and dynamics of Mercury's magnetosphere. BepiColombo is composed by two spacecraft: the MMO is completely devoted to environment, while MPO has different instruments devoted to the environment. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  6. Instrument for environment SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  7. INTERPLANETARY SPACE MPO/SERENA Energetic Neutrals Energetic Neutrals MPO/SERENA MPO/SIXS MMO/MDM MMO/MPPE MPO/MIXS MPO/MERTIS MMO/PWI Solar wind MPO/MAG MMO/MGF Magnetospheric Ions Electromagetic fields Low-Energy Neutrals MPO/SERENA MPO/SERENA MMO/MSASI MPO/PHEBUS MPO/SimbioSys Planetary Surface MAGNETOSPHERE EXOSPHERE HEWG - Padova, 29 September, 2006

  8. A two spacecraft mission The inter-instrument collaborations planned onboard each spacecraft and the opportunities afforded to perform two-point simultaneous measurements at Mercury constitute exciting features of the mission. A 1:4 resonant orbit configuration for the two spacecraft is currently considered so that the closest approach between the two satellites will be a few 1000 km. Before that during the first two weeks in orbit, the two spacecraft will have a few close encounters SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  9. What do we know about the Hermean Environment?What can we reasonably assume?What can we learn by coordinated observations? SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  10. ... from outside:the solar wind and Mercury’s magnetosphere SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  11. The Solar wind and IMF at Mercury • The Parker spiral forms an angle of about 20° with the solar wind radial direction, less than half of the value at the Earth’s orbit (~45°); this implies a change of the relative ratio of the Interplanetary Magnetic Field (IMF) components with respect to the near-Earth conditions, and an increase of the weight of the IMF Bx component. • The average solar wind density is about ten times higher than that at the Earth, but this value varies considerably due to the high eccentricity of the orbit of the planet (from 32 cm-3 to 73 cm-3). B v B v • The IMF intensity changes by a similar factor. • Which are the effects of these different conditions? SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  12. Mercury has an internal magnetic field • The Mariner 10 observations seem to proove the existence of an internal dipolar-like magnetic field (Ness et al, 1975). • The estimated dipole moment ranges between 284 and 358 nT RM3, Nothward oriented, (confirmed by recent MESSENGER results). • Hermean magnetosphere is only 5% of that of the Earth. In a zero order analysis, the spatial dimensions must be scaled by a factor of ~7. (Milillo et al, 2005) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  13. Typicalscalemagnitudes. • The time scale variations of the magnetospheric processes are few minutes at Mercury (compared with 1 hour at the Earth) • The field variation length scale of the Hermean magnetosphere is comparable to the gyroradii of the heaviest ions. • Adiabaticity parameter< 3 in the cusp regions where the B field is lower; thus, the SW can enter in a non-adiabatic manner inside the magnetosphere (Massetti et al., 2006) k map at the magnetopause (Massetti et al., 2006) • Effects of the ExB drift paths curvature are no more negligible (Delcourt et al., 2002) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  14. Direct entry through the cusps (Kallio et al, 2008) • The IMF orientation and intensity and the weak internal magnetic field of Mercury likely produce a direct entry through the cusps inside the Hermean dayside magnetosphere. • Solar wind plasma circulates inside the magnetosphere and eventually may hit the surface. (Kallio et al, 2003) (Mura et al, 2005) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  15. SW precipitation: high SW pressure (Vsw= 1100 km/s) (Vsw= 860 km/s) (Kabin et al., 2000) (Kallio and Janhunen, 2003) • Extreme events produce precipitation in the whole dayside hemisphere The observations of SEPs from the Sun by MPO/SIXS could provide a useful index for a kind of near-real-time forecast of solar activity that could be used to alert other MPO instruments, such as SERENA, MIXS and PHEBUS (which aim to evaluate the planet’s response to solar disturbances) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  16. SERENA SIXS MAG MGF MPPE PWI Dayside coordinated measurements 1 Joint measurements of MPPE-MEA and MIA, MGF and PWI, on the MMO spacecraft and SIXS, SERENA-MIPA and PICAM and MAG on the MPO spacecraft, will confirm plasma penetration inside the magnetosphere. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  17. SW Plasma circulation inside the magnetosphere (Mura et al., 2005) (Mura et al, PSS, 2005) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  18. Energetic electrons flow inside the magnetosphere (Christon et al, 1986) • Energetic electron fluxes are registered by Mariner 10. • Are they magnetic fluxes as observed during substorms at the Earth or direct solar wind coupling? Dipolarization event ? • Are there also solar wind protons and heavy ions of planetary origin circulating inside the Hermean magnetosphere? Is any ionosphere present there? SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  19. MAG MGF MPPE PWI SERENA To catch a substorm event by two spacecraft in the night-side magnetosphere First the magnetic field measurements of MMO/MGF and MPO/MAG will register signatures of stretching and dipolarization of the magnetic field lines as well as disturbances related to magnetotail reconnection plasmoids, and field-aligned currents. Also, the ion and electron sensors of MMO/MPPE will provide important information about the time-scale of substorms, carriers of field-aligned currents and the effects of heavy ions. Plasma injections will be monitored at two points, MMO/MPPE and MPO/SERENA, during its evolution. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  20. ...to inside:the Mercury’s exosphere related to the plasma environment and surface SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  21. Exosphere Oxygen H, He, and O were detected in the atmosphere by the onboard UV spectrometer (Broadfoot et al., 1974). Later, Na, K, and Ca were detected through ground-based observations (Potter and Morgan, 1985, 1986; Bida et al., 2000). The small amount of observed atmospheric oxygen relative (<4. 104 cm-3) relative to the surface stoichiometry (≈50%) may indicate that atmospheric oxygen is bound in molecules, or it may indicate inefficient release (Morgan and Killen, 1997), or it may efficiently charge exchange with solar wind and magnetospheric protons. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  22. Sodium and Potassium observations The mid latitudes intensification of exospheric Na and K seems to be related to solar wind precipitation through the cusp. Another possible explanation is the association of Na and K with radar and visible bright spots on Mercury's surface (Sprague et al. 1998; Sprague and Massey 2007). (Killen et al. SSR, 2007) However, the images of Na emission obtained from 1997 to 2003 by Potter et al. (2006) showed no evidence of a topographic effect. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  23. Calcium The neutral Calcium was observed by Bida et al. (2000). It is likely that Ca is released in the molecular form, possibly as CaO. If so, CaO could be dissociated in the atmosphere, for instance by Ly photons, giving the Ca atom excess energy as observed (Killen et al., 2005). SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  24. (Potter et al., 2002) variability Sodium observations tail (Potter et al., 1999) Dawn-dusk asymmetries (Schleicher et al. A&A, 2004) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  25. SERENA PHEBUS MSASI Exospheric coordinated measurements The exospheric configuration and composition will be measured by MPO/PHEBUS, and MMO/MSASI and MPO/SERENA-STROFIO in terms of column density, composition and profile variations. STROFIO, in particular, will be the only instrument able to determine the night side exospheric composition. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  26. SERENA MIXS PHEBUS MSASI Dayside coordinated measurements 2 Together with plasma penetration measurements described above, other dedicated instruments will observe the response of the planet in term of radiation and particles release. MIXS will observe the X-Ray emission of planetary aurorae while SERENA-ELENA will monitor the emission of neutral atoms. SERENA-STROFIO and PHEBUS and MSASI will observe the exospheric response of Mercury in terms of column density, composition and profile variations. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  27. Remote sensing the surfacepropertiesfromexosphericmeasurements Due to the strong link between the exosphere and the surface it is possible by measuring neutrals and ions at relatively low altitudes to obtain information regarding the composition of the upper surface of the regolith. However, some release processes are non-stoichiometric and involve only selected species. Eventually, to be able to successfully infer a source composition from exospheric measurements, it is really important to know the mechanism of ejection and the properties of the particular surface. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  28. Particle release processes invesigation PSD TD IS MIV (Environment Simulation Tool (EST) at IFSI) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  29. Ion sputtering analysis SERENA-ELENA will produce a kind of mapping of ion sputtering action on the surface of the planet (Orsini et al. 2008). This measurement correlated with the observation of ion flux to the surface seen by MPO/SERENA-MIPA will provide the surface efficiency in particle releasing via IS SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  30. Impulsive event (meteoroid 0.1 m) Frequency ~ 2 events/day (Marchi et al., 2005) Duration ~ 10-30 min Amplitude ~ 2000 km (Mangano et al., 2007) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  31. MPO/MIXS MPO/SERENA MPO/PHEBUS MMO/MSASI MMO/MDM MPO/SimbioSys Planetary Surface Surface signature in the environment nearby the surface: The surface elemental abundances mapped by MIXS, the surface mineralogy mapped by MERTIS and the surface cratering mapped by SIMBIO-SYS will allow released exospheric atoms to be related to the constitution of the surface. EXOSPHERE MPO/MERTIS SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  32. Exo-ionosphere The photo-ionisation of exospheric atoms creates an ionised thermal plasma population, especially on the dayside. Confirmed by MESSENGER observation. The ions produced at thermal energies are energised and become part of the magnetospheric ion populations. Part of this plasma is eventually lost to the SW. (Leblanc et al., 2004) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  33. MPO/SERENA MMO/MPPE MMO/PWI Planetaryionscirculation The close-to-planet observations of SERENA-PICAM will provide the composition and velocity distribution of planetary ions. Electron and ion phase space densities by MPPE-HEP-e and MEA can be obtained at different distances from the planet. Magnetic fields observations at two vantage points by MAG and MGF and of the electric fields (PWI) will complement the measurements of particle dynamics and currents (Delcourt et al., 2003) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  34. BepiColombo: anoutstandingtoolforHermeanenvironmentinvestigstion • Co-ordinated measurements made by different onboard instruments will answer important key questions regarding the planet’s environment. • The opportunity offered by the BC mission to perform two-point simultaneous measurements provides a powerful and unique investigative tool at a location other than the Earth. • The interaction processes acting at Mercury are present also in other interplanetary environments. For example, the plasma-surface interaction is present wherever a body in the Solar System lacks an atmosphere (Moon, asteroids, Jupiter’s satellites and many other satellites of the giant planets). SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

  35. Thankyou SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

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