5. Heliosphere and Intersteller gas

1. 5. Heliosphere and Intersteller gas

2. Outline • Global Heliosphere; • Neutral Intersteller gas; • ENA imaging; • IBEX mission and observation • CASSINI mission and observation • Summary

3. The Sun and Local Interstellar Medium (LISM) Image courtesy of L. Huff/P. Frisch

4. Our Heliosphere

5. Heliosphere

6. Complicated Heliosphere – LISM Interaction • Indirect observations • Anomalous Cosmic Rays (ACR) • Radio emissions • Inferred complications • Inner/Outer heliosheaths • Hydrogen wall • Until ~1 year ago, everything we thought we knew had been from models and indirect observations Simulation courtesy of G. Zank.

7. J.D. Richardson et al 2009

8. Lyα spectrum of α Cen B, showing broad H I absorption at 1215.6 Å and D I absorption at 1215.25 Å. Linsky and Wood (1996).

9. ENAs Illuminate the Global Termination Shock • Supersonic solar wind must slow down and heat before it reaches the interstellar medium • Large numbers of interstellar neutrals drift into heliosphere • Ly-  backscatter • interstellar pickup ions • Hot solar wind charge exchanges with interstellar neutrals to produce ENAs • Substantial ENA signal from outside the termination shock guaranteed from first principles

10. Energetic Particles and ACRs • Energetic particle spectra just past TS • Low energy particles fit power law • High Energy ACRs • Still modulated below ~100 MeV • ACR spectrum not “unfolded” into single power law as predicted Decker et al., 2005

11. Energetic particle flux looks like from Sun? J.D. Richardson et al 2009

12. Possible reason J.D. Richardson et al 2009

13. IBEX mission Routine Operations • Nominal orbit – 25-50 Re x 7000 km altitude, 3-8 days per orbit • Sun-pointing spinning S/C (4 rpm) • Science Observations > 10 Re • Engineering < 10 Re • Data download and command upload • Adjust spin axis ~5° (Earth’s orbital motion) • Nearly full sky viewing each 6 months Earth’s Magnetosphere

14. Orbit of IBEX

15. How ENA Sensors Work

16. IBEX Payload IBEX-Hi: • Energy range: 0.3-6 keV • Team: LANL (Lead), UNH, SwRI IBEX-Lo: • Energy range: 0.01-2 keV • Team: LMATC (Lead), UNH, GSFC, APL CEU: • Provides electronic support and control for payload • Developed by SwRI

17. IBEX’s Sole, Focused Science Objective • IBEX’s sole, focused science objective is to discover the global interaction between the solar wind and the interstellar medium. • IBEX achieves this objective by taking a set of global energetic neutral atom (ENA) images that answer four fundamental science questions: • What is the global strength and structure of the termination shock? • How are energetic protons accelerated at the termination shock? • What are the global properties of the solar wind flow beyond the termination shock and in the heliotail? • How does the interstellar flow interact with the heliosphere beyond the heliopause?

18. Low energy interstellar neutral gas E. Moebius 2009

19. E. Moebius 2009

20. E. Moebius 2009

21. Interstellar Neutral Oxygen: Question • Question -Interstellar Flow and interaction • First direct measurements of filtered interstellar neutral oxygen • Measure speed, direction and temperature of the interstellar oxygen inside TS • Compare to unfiltered He • Provide information about filtration and the interstellar interaction further out, beyond the heliopause Neutral O flux as a function of velocity angle measured during optimum times twice each year. The filtered secondary population is slower, hotter and more strongly deflected than the primary population.

22. S.A. Fuselier 2009

23. Recent IBEX observation Energetic Neutral Atoms Heating by Termination Shock

24. Recent IBEX observation

25. Energetic Neutral Atom (ENA) imaging

26. Cassini-Huygens mission

27. ENA imaging (INMS)

28. Fig. 1 Conventional concept of the heliosphere [(adapted from (3)]: The Sun is at the center, the region of the supersonic solar wind being asymmetric and compressed in the direction facing the interstellar wind flow (nose). S M Krimigis et al. Science 2009;326:971-973 Published by AAAS

30. Fig. 2 (A) Image of heliospheric ENAs in the range of 5.2 to 13.5 keV (data from day 265, 2003, to day 184, 2009) plotted in ecliptic coordinates. S M Krimigis et al. Science 2009;326:971-973 Published by AAAS

31. Fig. 3 Pressure contributed by protons beyond the TS computed from spectra deduced from the ENA observations in pPa (1 pPa = 10−11 dynes cm–2). S M Krimigis et al. Science 2009;326:971-973 Published by AAAS

32. Fig. 4 Annotated summary of basic findings from the ENA maps of the heliosheath; the dominant interaction between the nonthermal heliosheath pressure with the ISMF tends to produce a diamagnetic bubble, as envisioned by Parker (15), who neglected the effects of the ram pressure of the interstellar plasma. S M Krimigis et al. Science 2009;326:971-973 Published by AAAS

34. ENA imaging • ENA imaging is the only way to globally observe the interaction between the solar wind and the interstellar medium (structures, dynamics, energetic particle acceleration and charged particle propagation) in the complex region that separates our solar system from the galactic environment.

35. For plasma sheet of the Earth’s magnetosphere

36. Summary • ENA观测对星际间物质研究可以不受行星际磁场的影响； • ENA的观测帮助我们了解Termination shock的离子加速机制及其本身的拓扑结构； • 通过ENA的观测了解heliosphere的结构。