1. BC/MPO/SERENA Scientific Objectives Anna Milillo and the SERENA team

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

3. Instrument package on board BepiColombo/MPO SERENA NPA-IS Search for Exospheric Refilling and Emitted Natural Abundances Neutral Particle Analysers - Ion Spectrometers Units: ELENA : Emitted Low-Energy Neutral Atoms STROFIO : Start from a ROtating FIeld spectrOmeter MIPA : Miniature Ion Precipitation Analyser PICAM : Planetary Ion CAMera SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

4. Main scientific objectives of each unit NPA: ELENA investigates the Hermean escaping neutral gas (strongly linked to its surface), and the processes responsible of such a population. ELENA investigates the Hermean escaping neutral gas (strongly linked to its surface), and the processes responsible of such a population. STROFIO investigates the exospheric gas composition. STROFIO investigates the exospheric gas composition. IS: MIPA investigates the plasma precipitation toward the surface of Mercury. MIPA investigates the plasma precipitation toward the surface of Mercury. PICAM investigates the exo-ionosphere extension and composition. PICAM investigates the exo-ionosphere extension and composition. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

5. SERENA vs Hermean environment SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

6. Targets Exosphere composition and spatial distribution and dynamics Search for exo-ionosphere and its relation with neutral atmosphere Surface release processes Atmosphere/magnetosphere exchange and transport processes Escape, source/sink balance, geochemical cycles SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

7. SERENA scientific objectives 1.Chemical and elemental composition of the exosphere 2.Exo-ionosphere composition and distribution 3.Surface emission rate and release processes 4.Plasma precipitation rate 5.Particle loss rate from Mercury’s environment 6.Gas density anisotropies Remote sensing of the surface composition Magnetosphere structure and dynamics Planetary response to SW variations ENA imaging (comparative solar-planetary relationship) Heavy ion sputtering products SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

8. Exosphere composition The estimate of the exospheric densities is derived from observations and models. The scale height for each species is derived by assuming a temperature T=500 K for volatiles and T=5000 K for refractory (Leblanc et al., 2004) Sc. Obj:1 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

9. Expected range of the ion/neutral densities in Mercury's close-to-planet environment Sc. Obj:1 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

10. Neutral density asymmetries Sc. Obj:6 The measurements of the spatial distributions of the neutrals as well as ions are a possible way to understand the ejection processes that lead to these distributions and to have information about the history of the particles during their trajectories. Moreover, asymmetries induced by strong thermal variations, between different latitudes, day/night, dawn/dusk sides and perihelion/aphelion are expected in the Hermean exospheric density. STROFIO will observe these asymmetries. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

11. Sodium observations variability tail Sc. Obj:1 Dawn-dusk asymmetries SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008 (Schleicher et al. A&A, 2004) (Potter et al., 1999) (Potter et al., 2002)

12. Summary of scientific requirements (1) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

13. Summary of instrument performances (1) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

14. Exo-ionosphere composition Ions of planetary origin have been observed by MESSENGER in the magnetospheric tail. They are likely generated in the dayside hemisphere due to photoionisation and ion-sputtering processes. Sc. Obj:2 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

15. Expected range of the ion/neutral densities in Mercury's close-to-planet environment Sc. Obj:2 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

16. Exo-ionosphere distribution Na + distribution model by Leblanc foresees strong asimmetries Sc. Obj:2 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008 (Leblanc et al., 2004)

17. Summary of scientific requirements (2) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

18. Summary of instrument performances (2) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

19. Surface release processes Different release processes can have different efficiencies as a function of latitude and longitude/LT at Mercury due to surface compositions and mineralogy togheter with external conditions, as solar irradiance or plasma precipitation. Among the release processes the ion-sputtering is particularly intriguing since the involved energies induce escape from the planet, with possible implication on its evolution. Sc. Obj: 3 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

20. Particle release processes SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008 TD PSD IS MIV Sc. Obj: 3 (Environment Simulation Tool (EST) at IFSI)

21. SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008 Energy distribution of sputtered particles Energy distribution of sputtered particles by Wurz et al, SERENA Meeting in Pejo, 2006 H escape O escape Ca escape Fe escape CaOHFe ELENASTROFIO Sc. Obj: 3

22. Why we require detection of neutrals at energies >10 eV SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008 (EST@IFSI)

23. Ion-sputtering process ELENA will map the location of the sputtering process on the surface and will image of the surface loss rate Sc. Obj: 3 Surface sputtered signal obtainable by ELENA when MPO pericentre is in the day side (Mura et al, PSS, 2005) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

24. Impulsive event (meteoroid 0.1 m) Frequency ~ 2 events/day (Marchi et al, A&A, 2005) Duration ~ 10-30 min Amplitude ~ 2000 km (Mangano et al., PSS, 2007) Sc. Obj: 3 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

25. Intensifications, durations and spatial dimensions of a 10 cm MIV exosphere SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008 METEORITE OF 10 cm Altitude: SpeciesNaMgAlSiSOK (*) Ca Intensification I / d ~ 3 n ~ 10 3 10 3 10> 10 ---- < 10 4 Duration Δt 0 d 300 n 19002000~2500800~900 ---- 3500 Extension d - d 0º n 40º50º45º25º30º - d - n 50º Altitude: SpeciesNa (*) MgAlSiS (*) OK (*) Ca Intensification I ---- < 10 2 10 2 -< 10 ---- > 10 2 Duration Δt ---- 2700~ 2200~ 3200-1200 ---- 3500 Extension d - d - n 100º70º80º20º - d - n 90º

26. Probability to detect 10 cm MIV exosphere SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008 Species Duration NaMgAlSiSOKCa 400km 1 day / d / n 15.5%21% 5%6.8% / d / n 30% 1 month / d / n 99.3%99.9% 77.8%87.8% / d / n 99.9% 1500km 1 day / d / n 20%22.5%27%/4.7% / d / n 58% 1 month / d / n 99.8%99.9% /76.3% / d / n 99.9% average 1 day / d / n 17.7%21.7%24%0-5%5.7% / d / n 44% 1 month / d / n 99.5%99.9% 0- 77.8% 82% / d / n 99.9%

27. Summary of scientific requirements (3) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

28. Summary of instrument performances (3) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

29. SW precipitation The SW ions (at energy about 1 keV) entering in the magnetosphere partially reach the planet surface causing ion sputtering, hence producing neutral atoms and ions. MIPA will monitor the SW precipitation. Sc. Obj: 4 (Massetti et al., 2003) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

30. (Delcourt et al., 2003) Planetary ions precipitating from the magnetosphere (Seki et al., 2006) Planetary heavy ions precipitate toward the planet in the day side high latitudes and in the night side mid/low latitudes The precipitating planetary heavy ion fluxes are expected to be lower than the precipitating solar wind fluxes. Thus, they will be observed by MIPA and PICAM in the night side where the solar wind contribution is expected to be negligible. Sc. Obj: 4 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

31. Loss cone angle The particle precipitates when V // /V n is high (i.e. the pitch angle is lower than the loss cone angle) (Nilsson et al. 1997) Sc. Obj: 4 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

32. Summary of scientific requirements (4) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

33. Summary of instrument performances (4) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

34. Loss rate from Hermean environment The high-energy neutral products of the release processes as well as the charge-exchange ENA, are mainly created close to the surface and carried outward of the planetary environment due to their high velocity that exceeds the escape velocity (v esc = 4 km/s). Directional neutral measurements by ELENA will contribute in evaluating the mass loss from the Hermean environment. Sc. Obj: 5 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008 (Mura et al., 2006)

35. Loss rate from Hermean environment The ions produced at thermal energies are energised and become part of the magnetospheric ion populations. Part of the magnetospheric plasma is eventually lost to the SW. PICAM high energy resolution will allow such an investigation. Sc. Obj: 5 (Delcourt et al., 2003) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

36. Summary of scientific requirements (5) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

37. Summary of instrument performances (5) SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

38. Summary of ELENA scientific performances Energy range<0.02- 5 keV (mass dependent) Velocity resolution  v/v Down to 15% Viewing angle2 o x76 o Nominal angular resolution2 o x2 o Mass resolution M/  M H and heavy species Optimal temporal resolution18 s Geometric factor G1. 10 – 5 cm 2 sr Integral Geometric factor4 10 – 4 cm 2 sr SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

39. Summary of STROFIO scientific performances Energy range< eV Viewing angle [deg]20 o x 20 o Mass resolution M/  M 60 Mass range1-64 dalton (AMU) Sensitivity0.14 (counts/s)/ (particles/cm 3 ) Temporal resolution10 s SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

40. Summary of MIPA scientific performances Energy range 10 eV – 15 keV Energy resolution  E/E 7% Viewing angle9 o x 180 o Angular resolution (FWHM) 4.5° x 22.5° (inherent 4.5° x 8°) Mass range, amu 1 – 50 Mass resolution, M/  M ~5 Time resolution, sec 8 s, Full Azimuth – Energy cycle (8A x 32E) Efficiency, e 1 – 10% (adjustable to decrease GF) Geometrical factor 1.8 · 10 -3 cm 2 sr eV/eV w/o efficiency SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

41. Summary of PICAM scientific performances Energy range1 eV - 3 keV Energy resolution  E/E 7% Viewing angle 3 ‑ D, 2  Angular resolution~22.5 o Mass resolution M/  M >50 Mass range1... ~132 AMU (Xe) Time resolution1 s... 32 s Geometric factor G = S  3.4 x 10 – 3 cm 2 sr SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

42. SERENA new webpage: Home SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008 http://www.ifsi-roma.inaf.it/enagroup/serena/index.php?categoryid=1

43. SERENA new web site: Science SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

44. SERENA new web site: Team SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

45. SERENA new web site: Resources SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

46. SERENA Science team and thematic WGs SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008 The SERENA science team is involved in the Hermean Environment WG. It has recently coordinated and participated to the paper on HE for the PSS special issue. It has participated also to the Surface and Composition paper in the same special issue

47. Thank you SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

48. BepiColombo key questions Which are the composition, the origin and the dynamics of Mercury’s exosphere and polar deposits? Which are the structure and the dynamics of Mercury’s magnetosphere ? SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

49. Sodium and Potassium observations Sc. Obj:1 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008 (Killen et al. SSR, 2007)

50. Oxygen The small amount of observed atmospheric oxygen relative (<4. 10 4 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. Sc. Obj:1 SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008

51. 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 by Ly  photons, giving the Ca atom excess energy as observed (Killen et al., 2005). SERENA-HEWG meeting, Santa Fe, 12-14 May, 2008