1. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 1 ENA diagnostics of the solar wind interaction with planetary bodies Stas Barabash Swedish Institute of Space Physics (IRF), Kiruna, Sweden

2. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 2 Outline ENA introduction Sci. objectives of planetary ENA imaging. What can one achieve by ENA imaging? Global ion distribution inside magnetospheres: Mercury, Earth Plasma distributions in the interaction region: Mars, Venus, MEX data Outflowing planetary ions: Mars Global neutral gas / dust distribution: Europe, Phobos torus, Saturn rings Surface interaction. Sputtered ENAs. Precipitation maps: Mercury, Moon Atmosphere interaction. Backscattered ENAs. Precipitation maps: Mars, MEX data Global dynamics: Mercury, Earth Conclusion Planetary ENA experiments New frontiers for planetary ENA imaging

3. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 3 Planetary ENA experiments (out side the Earth) PlanetMission / InstrumentRemark MarsMars Express, 2003 ASPERA-3 100 eV - few keV VenusVenus Express, 2005 ASPERA-4 100 eV - few keV JupiterCassini, 1997/INCA Voyager E > 20 keV Non-ENA dedicated (Kirsch et al., 1981) SaturnCassini, 1997/INCA Voyager E > 20 keV Non-ENA dedicated (Kirsch et al., 1981) MoonChandrayaan-1, 2008 SARA 10 eV - 3 keV Sputtering and backscattered ENAs MercuryBepi Colombo, 2013 MPO / SELENA MMO / ENA Shutter techn. 20 eV - 1.5 keV Replica of SARA

4. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 4 ENA introduction (1) No gravitation banding: E >> E escape, i.e., E escape (O) = 2.4 eV for Mars Processes resulting in ENA production in planetary environments Neutralization: charge - exchange on neutral gas and dust Surface (upper atmosphere) interaction: backscattering, sputtering, and recoil B0B0 A+A+ A0A0 neutral gas A+A+ A0A0 dust A+A+ A0A0 surface / atmosphere A+A+ B0B0 surface (B) / atmosphere Ion neutralization Surface / atmosphere interaction A+A+ C0C0 surface (B) / atmosphere

5. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 5 ENA introduction (2) ENAs propagate as photons: imaging of populations resulting in ENAs Neutralization (CX): Advantages: Provides ion or neutral gas (dust) global distribution Drawback: line-of-sigh integrals => inversion problem, extra assumptions Surface interaction: Advantages: Provides the integral flux at the surface (cm -2 s -1 eV -1 ), no inversion. Surface (upper atmosphre) works a display Drawback: Loss spectral information

6. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 6 ENA introduction. Non magnetized planets (3) Direct interaction with the upper atmosphere/ionosphere: Venus/Mars. ENA diagnostic to reveal: Morphology of the interaction region Global dynamics of the interaction region Precipitation onto the upper atmosphere (backscattering) Direct interaction with the surface: Moon. ENA diagnostic to reveal: Morphology of the interaction region Space weather effects

7. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 7 DIAGNOSTIC OF THE INTERACTION REGION MORPHOLOGY (MARS/VENUS)

8. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 8 ENAs at Mars

9. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 9

10. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 10

11. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 11

12. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 12 Shocked SW ENAs. NPI observations

13. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 13 NPI ENA observations vs. simulations ENA signal

14. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 14 Inversion results // Solar wind parameters (non-fitted) pars[0] = 2.5; // Solar wind proton density [#/cm^3] pars[1] = 400e3; // Solar wind speed [m/s] pars[2] = 10; // Solar wind temperature [eV] // Geometry parameters (fiitted) pars[3] = 0.1667; // alpha, magnetopause penetration pars[4] = 0.55; // x_0, Bow shock position [Rm] pars[5] = 1.35; // x_nose, magnetopause position [Rm]

15. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 15 Futaana, et al, 2006

16. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 16 Subsolar jet (cone) Futaana, et al, 2006

17. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 17 Non-observation of O-ENAs Oxygen ENAs have NOT been observed by ASPERA-3: fluxes below the instrument limit (2.5·10 4 cm -2 sr -1 s -1 ) Galli et al.,. 2006). Scaling the escape rate gives Q(O+) < 10 23 s -1. In agreement with the direct escape measurements.

18. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 18 GLOBAL DYNAMICS

19. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 19 Response to an interplanetary shock (1) Futaana, Barabash et al., 2006

20. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 20 Response to an interplanetary shock (2) Futaana, Barabash et al., 2006

21. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 21 Response to an interplanetary shock (3) Futaana, Barabash et al., 2006

22. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 22 Response to an interplanetary shock (4) Futaana, Barabash et al., 2006

23. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 23 ENA jet oscillations TT Oscillation periods: 50 and 300 sec Depth ~20-30% Grigoriev et al., Space Science Rev.,, 2006

24. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 24 Diagnostic of the dynamics Time scale of the interaction region reconfiguration against interplanetary disturbances. Time scale of the local instabilities at the induced magnetospehere boundary / plasma oscillations in the magnetospheath.

25. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 25 DIAGNOSTIC OF THE PLASMA PRECIPITATION

26. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 26 Backscattering ENAs. Simulations (1) Monte Carlo simulation of proton / ENA backscattering (Kallio and Barabash, 2000)

27. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 27 Backscattering ENAs. Simulations (2) Backscattering hydrogen velocity distribution (Kallio and Barabash, 2000) Albedo ~60%, Energy loss ~40%

28. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 28 Backscattering H-ENAs. ENA albedo Backscattered hydrogen (ENA albedo) Precipitating particles (ENAs and protons) experience elastic and non- elastic (CX, excitation) collisions with the upper atmosphere gases (mostly O and CO 2 ) Kallio and Barabash (2001) predicted backscattering H atoms caused by hydrogen ENA precipitation onto the upper atmosphere. ENA energy ≈ 0.6 x precipitating energy ENA albedo ≈ 0.6

29. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 29 Backscattering H-ENAs. Observations (1) Backscattering H-ENAs H-ENAs from subsolar region

30. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 30 H atom Energy: Subsolar ENAs: 2.14 keV Backscattering: 1.36 keV Compare with ~2 keV shocked solar wind as measured by IMA in the magnetosheath Flux: (8 - 14)·10 6 cm -2 sr -1 s -1 Backscattering H-ENAs. Observations (2) 160 ns 200 ns Backscattering H-ENAs. ENA albedo H-ENAs from subsolar region. ENA jet 27 Feb. 1948 - 1958 TOF, ns

31. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 31 Backscattering H-ENAs. Precipitation maps Backscattered ENAs flux is proportional to the precipitation flux and can be used to construct precipitation maps NPD FoV longitude - latitude coverage. Orbit 500. July 11 1840 - 1900 Precipitation map NPD1 - Dir0. Orbit 500. July 11 1840 - 1900

32. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 32 DIAGNOSTIC OF THE INTERACTION REGION MORPHOLOGY (THE MOON)

33. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 33

34. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 34 Sputtered atoms (Johnson and Baragiola, 1991)

35. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 35 Minimagnetosphere (Lin et., 1998)

36. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 36 Imaging magnetic anomalies Orbit motion FoV (channels)

37. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 37 Sputtered atoms Angular distribution does not depend on the impinging ion flux angular distribution (statistically). Atoms are not affected by electromagnetic forces and gravitation (E >> E escape = 1.7 eV for Fe). Sputtered atoms: O, Na, Al, Si, K, Ca, Ti, Mn, Fe Atom sputtering conserves stoichiometry - an analytical tool in the lab. Thomson - Siegmund spectrum:

38. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 38

39. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 39 DIAGNOSTIC OF SPACE WEATHERING (THE MOON)

40. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 40 Space weathering Space weathering: changing albedo (visible, IR) under space environment effects, e.g., particle and photon flux, mmicrometeor bombardment Swirl - like albedo marking in Crisium impact basin antipodal region (Reiner Gamma region, Lin et al., 1988, Hood et al. 1999)

41. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 41 ENA emissions at Mars: simulations and observations on Mars Express Stas Barabash and Mats Holmström Swedish Institute of Space Physics, Kiruna, Sweden

42. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 42 ENA production at Mars Charge - exchange on the exosphere (extended due to low gravity!) Upstream solar wind Shocked solar wind Planetary oxygen ions Backscattering of the solar wind protons

43. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 43 CX SW ENAs. Simulations (1) Highest neutral gas density Plasma distribution? Bow shock The boundary CX: undisturbed solar wind on the extended exosphere CX: shocked solar wind on the exosphere SW void Mars Solar wind Typical morphology: neutral solar wind, ENA fluxes tangential to flow lines

44. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 44 CX SW ENAs. Simulations (2) Holmström et al., 2002

45. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 45 CX oxygen ENAs. Simulations (1) Oxygen ion distribution (Test partciles in the empirical model, Kallio, 1997; Barabash et al., 2002)

46. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 46 CX oxygen ENAs. Simulations (2) O - ENA fluxes 0.1 - 1.65 keV (Barabash et al., 2002) Typical morphology: subsolar jet and tailward flux

47. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 47 MEX ENA sensors NPD NPI

48. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 48 MEX ENA observations Global structure of the solar wind interaction region Shape of the solar wind void (NPI, Herbert Gunell et al., 2005) Subsolar ENA jet (NPD, Futaana et al., 2005) Oscillations of the ENA jet (NPD, Futaana et al., 2005) Solar wind - atmosphere interaction Occultation of the neutral solar wind at Mars (NPI, Klas Brinkfeld et al., 2005) Solar wind proton precipitation onto the atmosphere: ENA albedo (backscattered ENAs) (NPD, Futaana et al., 2005) Oxygen ENAs are not yet identified in the available data.

49. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 49 Ion distributions inside magnetospheres. Pretty ENA images Earth’s ring current, outer vantage point IMAGE / HENA, courtesy D. Mitchell, APL Earth’s ring current, low altitude polar vantage point Astrid-1 / PIPPI, Barabash et al., 1999 Earth’s ring current, from below Astrid-1 / PIPPI, C:son Brand et al., 2001 Mercury magnetosphere, 30 keV protons, polor vantage point, Simulations, Barabash et al., 2001

50. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 50 Ion distributions inside magnetospheres. Science Ring current physics Dynamics Global morphology during different conditions Composition (H, He, O) variations Storm / substorm relations Ion dynamics during substorms injections Plasma sheet depolarization M - I coupling (from deduced ion distribution) Microphysics though P/A distribution reconstruction. Yet, it requires high angular resolution IMAGE / HENA Movie, courtesy Pontus C:son Brandt, APL

51. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 51 Plasma distributions in the interaction region ENA imaging non-magnetized planets, Mars and Venus. Simulations by Kallio et al., 1998; Holmström et at, 2002; Mura et al., 2002; Lammer et al., 2002; Gunell et al., 2004. The main scientific objective: determined the structure of the interaction region ENA detector ENA

52. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 52 Plasma distributions in the interaction region. Mars Simulations by Holmström et al., 2002

53. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 53 Plasma distributions in the interaction region. Venus Simulations by Gunell et al., 2004

54. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 54 ENA Occultation at Mars (1) v Mars Photon flux Solar wind / ENA flux  ~ 4°  0 12 3456 7 x10 7 Simulated ENA flux at SZA=160° Holmström et al [2001] Interaction with the upper atmosphere - scattering

55. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 55 ENA Occultation at Mars (2) Scattered photons ENA Background noise S/C in Mars umbra S/C in Mars penumbra 40 Sector 21 Observed flux 2·10 5 cm -2 s -1 is consistent with 0.3% of the solar wind flux

56. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 56 Imaging outflowing planetary ions Planetary ions escaping the non-magnetic atmospheric bodies (Mars, Venus, comets) charge - exchange with the exospheric neutrals and are converted to ENAs. O-ENAs images visualize the instantaneous distribution of O + ions. ENA imaging is the most promising way to determine the total escape rate, the key number for understanding solar wind effects on the atmospheric evolution. In-situ measurements require assumptions on global distributions. O- ENA imaging is being attempted on Mars Express / ASPERA-3.

57. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 57 Neutral gas distribution (1). Europa torus Neutral gas immersed in the background of charged particles shines in ENAs. Mauk et al., 2003 observed the Europa torus around Jupiter in ENAs (Cassini/INCA). Main finding: Europa gas cloud (most probable from ice sputtering) is comparable with the one from the volcanic moon Io. The Titan exosphere immersed inside the Saturn radiation belts is also shining in ENAs (simulations by Dandouras and Amsif, 1999 in preparation for the Cassini / INCA experiment). Raw image Point source (calibration) Deconvolved image Europa torus Jupiter

58. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 58 Neutral gas distribution (2). Phobos torus Weakly outgassing (mostly water, Q~10 23 s -1 ) Phobos results in a torus immersed in the solar wind flowing around Mars. The torus is a possible source of low energy ( < 1 keV) ENAs (Mura et al., 2001). Mars Express / ASPERA-3 will attempt imaging to constrain the outgassing rate and obtain the radial profile. Only Mars exosphereOnly Phobos torus Mars + Phobos Obstacle

59. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 59 Ion / dust neutralization. Saturn radiation belts / rings Mauk et al., 1998. Simulations of ENA signal from F-ring of Saturn in the frame Cassini / INCA experiment. F - ring looks like a circular line source. Science: Trapped ion radial diffusion rate Particle size constraining from energy spectrum Efficiency of ion / ring interactions H+H+ H 0, ~ 50 keV, > 50% dust particle ~0.5  m

60. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 60 Surface interaction. Sputtered / Backscattered ENA Energy spectrum follows the Thompson - Sigmund formula: Typical fluxes (input flux dependent, integrate within 10% energy band, 10 - 100 eV): 10 3 - 10 4 cm -2 s -1 sr -1 Mass composition reflects the surface elemental composition. For Mercury: O, Na, K, Ca, Mg, Al, Si Precipitating ions (H+) can be also backscattered as H-ENAs. Sputtered / backscattered ENA imaging reveals: Precipitation maps similarly to auroral display (ENA - “aurora”) Inputs to surface - bound exospheres (Mercury, Moon) Na image by Potter and Morgan, 1990. Hot spots: precipitation regions or minerological feature?

61. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 61 Surface interaction. ENA - aurora on Mercury Ion precipitation maps Sputtered Na - ENA images (10 - 40 eV) H+, solar windH+, Tail source, 30keV Na+, photoions

62. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 62 Surface interaction. Minimagnetospshres on the Moon The Moon surface is exposed to the solar wind flux except areas of strong remanent magnetic fields, minimagnetopsheres (Lin et al., 1998). The minimagnetospheres will be “visible” on sputtered / backscattered ENA images as voids. ENA imaging is the only technique capable of visualizing minimagnetospsheres. Simulations by Futaana, Barabash, and Holmström, 2004 for a void of 100 km diameter and a virtual ENA detector at 100 km height.

63. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 63 Atmosphere interaction. Backscattering H-ENAs Backscattered hydrogen (ENA albedo) Precipitating protons and ENA from SW Kallio and Barabash (2001) predicted backscattering H atoms caused by hydrogen ENA and solar wind proton precipitation onto the upper atmosphere of Mars (at Venus the similar process operates). E bs /E nsw ≈ 0.6 F bs /F nsw ≈ 0.6

64. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 64 Atmosphere interaction. Mars Express results Subsolar point NPD1 FoV NPD2 FoV

65. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 65 H atom Energy: 1.69 - 2.14 keV (160 - 180 ns) Compare with ~2 keV shocked solar wind as measured by IMA in the magnetosheath Flux: (8 - 14)·10 6 cm -2 sr -1 s -1 Only direct precipitation of the solar wind down to the exobase altitude (250 km) can be accounted for such high fluxes! In agreement with IMA ion observations of the deep solar wind penetration. Stong energy and momentum deposition to the upper atmosphere. Atmosphere interaction. Mars Express results 160 ns 180 ns

66. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 66 Global dynamics. D st and total ENA production ENA flux at a vantage point is a function of the global ion (neutral gas) contain => global dynamics of the system. Jorgensen et al., 1997 POLAR / IPS observations (17.5 …~ 100 keV) ENA signal time variation follows moderate storm dynamics. The characteristic time scales can be determined from a single point ENA measurements. Jorgensen et al., 2001 also reported short-lived ENA bursts associated with substorm signatures D st index and POLAR ENA signal Recovery phase Main phase

67. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 67 Global dynamics (2). Fine time variations Ebihara, Barabash, Ejiri, 1999. Simulation of total ENA production ENA production for E < 30 keV follows D st quite precisely High energy ENA variations reflect particle motion in the inner magnetosphere Variations with drift angular frequency (~1 hour) and beatings caused by finite energy window

68. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 68 Global dynamics. Application to Mercury Problem of distinguishing spatial and temporal variations in compact magnetospheres (small size, short reconfiguration time): necessity of global techniques. Mercury case: substorm time ~1 min, one substorm per 5 min (Siscoe et at., 1975) ENA signal profile is a sequence of flashes lasting for ~ 1min each. For studies of global dynamics the details of the generation mechanisms are not important. Time ENA signal intensity How often? 5 min? How long is recovery? How fast is injection? How long? 1 min?

69. EuroPlanet, Sept. 22, 2006Stas Barabash, Page 69 New frontiers for planetary ENA imaging Priorities for new investigations and new experimental challenges Earth High angular resolution (~1° x 1° / pixel) for all energy ranges: pitch - angle effects and microphysics Non-atmospheric bodies (Mercury, Moon, asteroids) ENA imaging mass spectroscopy (M/  M ~ 20…40): surface - plasma interactions Non-magnetic atmospheric bodies (Mars, Venus, comets) Low energy ENA imaging (tens eV) with moderate mass resolution: escape processes