Hermean sputtering: SERENA/ELENA Simulated observation

1. ENA measurements in the Solar System and BepiColombo – SERENA Stefano Orsini, and the ENA team @INAF-IFSI, Roma, Italy Hermean sputtering: SERENA/ELENA Simulated observation

2. ENA features in the solar system KeV ENA Solar wind Neutral Solar wind ions Exospheric gas Charge-Exchange eV ENA Surface IonSputtering eV ENA Atomospheric Sputtering Conf. Planetologia, S.Felice irco06/09/2006

3. Astrid (SAC-B) Cassini IMAGE Doble Star Mars Express Venus Express TWINS Chandrayaan ! IBEX ! BepiColombo ! Solar Orbiter !? Kua-Fu ? Laplace (Europa Orbiter) ? MarcoPolo ? Tandem ? PROCESSES INVESTIGATED VIA ENA Remote sensing of: • Magnetized bodies (Earth, Mercury, Jupiter, Saturn…) Magnetospheric Plasma Circulation Charge exchange! • Non-magnetized bodies with atmosphere (Mars, Venus…) Solar wind-induced neutral gas escape Charge exchange & sputtering! • Bodies without atmosphere (Mercury, Moon, Asteroids…) Solar wind-induced surface erosion Sputtering! • Solar wind acceleration region & heliospheric border Neutral SW, SW - interstellar gas interaction Charge exchange!

4. ENVIRONMENTS INVESTIGATED VIA HIGH ENERGY ENA

5. Solar Orbiter / SCENARIO Neutral Solar Wind Detector (NSWD) (S. Orsini, M. Hilchenbach, J.K. Hsieh, A.M. Di Lellis, M. Collier, A. Czechovski, I. Dandouras, R. D’Amicis, M. Gruntmann, G. Ho, S. Habal, E. Kallio, S. Livi, A. Mura, P. Wurz, et al.) Beyond 3 solar radii, the neutral atoms become more and more decoupled from the plasma of the solar corona. The neutral solar wind constitues an in-situ trace particle population of the solar wind plasma. The expected neutral atom flux is about 103 atoms cm-2 s-1, at 0.21 AU, but it could increase up to 104-105 atoms cm-2 s-1 during Coronal Mass Ejections (CME). Angular resolution ~ 1° Field-of-view = 7° Aberration = 9.2° (Vsw = 400 km/s, Vorbiter = 65 km/s) Aberration = 4.6° (Vsw = 800 km/s and Vorbiter = 65 km/s) FUTURE APPLICATIONS Imaging of the SW Expansion Sun and corona traced by NSWD coronal hole SOLAR ORBITER

6. … IMAGING THE NEUTRAL SOLAR WIND Signal simulation vs 2 different sw models FAST WIND SLOW WIND Our approach Lie-Svendsen et al (2003) Allen et al (2000) Our approach Pseudo-color map of ENA differential flux as a function of angle from Sun’s direction (in degrees) for different models. The azimuth angle is along the ecliptic plane and the elevation angle is across the ecliptic plane. Flux is integrated over all energies (upper panel). Bottom panels are for the Solar Orbiter reference frame during the corotation phase (i.e. with the aberration effect included).

7. IonSputtering Production of ENA from bombardment of a surface by energetic ions Energy distribution Lammer and Bauer(1997), Planet. Space Sci., 45, 73-79 Ei incident particle energy 800 - 1600 eV Ebbinding energy  1 eV Ee Energy of the released particle Te Exospheric temperature T Na – 1600 • Ion sputtering products depend on: • the composition and the chemical structure of the surface; • the impinging plasma flux. • The basic quantities of interest are: • the composition of the ejected particles • the space fluxdistribution and the spacedensity distribution of the sputtered particles Na -800

8. Near Earth Object (NEO) : asteroid or comet nucleus in an evolving population with a lifetime limited to a few million years and an orbit with perihelion distance <1.3 AU Current knowledge NEOs appear heterogeneous in shapes, sizes, spin rates and compositions. they offer clues to the chemical mixture from which the planets were formed carry records in the interplanetary space from - the Solar System’s birth and early phases - the geological evolution of small bodies NEO (433) Eros (John Hopkins University)

9. CI chondrite - type NEO surface • Results – Discussion • Particles fluxes (up to 1011 particles m-2 s-1) appear in a region up to 1 km above the NEO surface (in the solar wind direction). • Maximum density (~ 106.5 particles m-3) appears in a region extending from the NEO surface up to an altitude of about 0.7 km above (in the solar wind direction). Results of the MC simulations x particles m-2 s-1 x particles m-3 Sputtering is considered as the only source for neutral particle production

10. The Natural Satellites Emissivity in the Jovian System C-E ENA from auroral regions I-S Directional NA from Europa C-E ENA from plasma – tori interaction

11. EUROPA Surface composed mainly by water ice and other components as Na, K, etc... Na and K atmosphere has been observed (Brown and Hill, Nature, 1996; Brown, Icarus, 2001) Disrupted ice crust in the Conamara region of Jupiter's moon Europa (NASA courtesy)

12. Ion-sputtering . The emitted flux is proportional to the yield, much higher for higher energies and for heavier ions. (Baragiola et al., NIM B, 2003) Ion flux @ Europa H+ O+ S+ Energetic ion fluxes observed by Galileo spacecraft impacting on the surface of Europa. (Paranicas et al., GRL, 2002)

13. The Natural Satellites Emissivity in the Saturnian Sysytem

14. Titan • Exobase ~ 1500 km altitude • Atmosphere ~ mainly N2 • Two different incident particles: • protons H+ deriving from the solar wind and from Saturn’s magnetosphere • nitrogen ions N+ of the Saturn’s magnetosphere. Atmospheric Sputtering Same process as surface sputtering, but acting on atmospheric particles. Particles may escape directly or after a series of bouncing. At Titan, the atmospheric sputtering is the most efficient escape mechanism (Lammer and Bauer, 1993) (Garnier et al., 2007)

15. Our simulation N+ H+ Yields Energy and pitch angle spectra ION ENERGY ION ENERGY ANGLE ANGLE Our analysis of atmospheric sputtering on Titan, using previous theory and newly data, allow us to be confident in a very high efficiency of the process Y ~ 1÷10 for H+ Y >10 for N+ (Shematovich et al. JGR, 2003)

16. GOING TO MERCURY WITH BEPICOLOMBO PROCESSES IN THE HERMEAN ENVIRONMENT

17. …ARE ION SPUTTERING AND PSD RELATED TO EACH OTHER? See presentation from a. mura during this conference

18. New prospect: ENA direct detection BepiColombo / SERENA - ELENA is a Time-of-Flight Detector, based on the state-of-the art of ultra-sonic oscillating micro-shutters (>100 kHz) and mechanical gratings. Energy range:<20eV-5keV.

19. Sputtered O image simulation, polar view Sputtered signal detection by the SERENA/ELENA unit (simulation)

20. S U M M A R Y • Nowadays, more and more interest is growing about the capabilities of investigating crucial aspects of the particle regimes present in the solar system by means of ENA detection. • These studies range form the properties of the expanding corona, to the escape of matter from the planetary surfaces; from the plasma distributions in the magnetospheres to the interaction between solar and interstellar matter; from the characteristics of escaping fractions of the planetary atmospheres, to the transfer of energy to the internal atmospheric regions. • Such an increase of interest in ENA signal detection is pushing the technological community to produce more and more sophisticated devices, able to accomplish the scientific goals over a wide spectrum of energies and mass species.

21. MANY THANKS FOR YOUR ATTENTION!