ENA generation mechnism

2. ENA generation mechnism Krimigis et al, 2004

3. Some Questions about the Interaction between Trapped Particles and Neutrals • What is the source of trapped particles? • How are they accelerated to high energies? • What is the principal loss mechanism? • How do particles respond in the rotating magnetic field of Saturn? • Are particle collisions with ring and icy moon surfaces important?

4. Rev 0

5. Charge Energy Mass Spectrometer (CHEMS) on Cassini records “fingerprints” of ion composition at Earth, Jupiter, and Saturn Saturn Earth Jupiter mass (amu) Plotted: 2/25/05 mass per charge (amu/e)

6. Some Questions about the Interaction between Trapped Particles and Neutrals • What is the source of trapped particles? • How are they accelerated to high energies? • What is the principal loss mechanism? • How do particles respond in the rotating magnetic field of Saturn? • Are particle collisions with ring and icy moon surfaces important?

7. Energetic Neutral Atom (ENA) Imaging O+fast+ H  Ofast + H+ ENA generation mechnism

8. Grid outlines INCA FOV

9. ENA PERIODICITIES Hydrogen ENA emission modulated at Saturn’s rotation period Oxygen

10. With what else does this ENA oscillation correlate? B-field SKR Energetic (25-200keV) e-

11. Oxygen ENA modulation is time-dispersed in energy--high energies lead low, due to grad-B drifts

12. 7 Rs At what radial distance is the corotating ENA emission concentrated?

15. Hydrogen Geocorona Rairden et al. (1986) Earth Ring Current The density of OH in the 6-10 Rs region is comparable to H density in the Geocorona. O is probably about the same as OH. O+ lifetime in the Earth’s ring current is ~ 8h. O+ lifetime in the inner Saturn magnetosphere could be much shorter, depending on its radial placement (O, OH charge-exchange cross-section is larger than H) Highest ENA production Devoid of energetic ions

16. Modulation persistence and phase lock suggest an “active” longitude (could be a quadrant) coupled with a preferred local time for ion injection Gas Hot H+, O+ Ion Dispersion Event Neutral Gas? Saturn Cassini (Mauk et al, GRL, June 2005)

17. Modulation persistence and phase lock suggest an “active” longitude (could be a quadrant) coupled with a preferred local time for ion injection Gas Hot H+, O+ Ion Dispersion Event Neutral Gas? Saturn Cassini

18. Modulation persistence and phase lock suggest an “active” longitude (could be a quadrant) coupled with a preferred local time for ion injection Gas Hot H+, O+ Ion Dispersion Event Neutral Gas? Saturn Cassini

19. Modulation persistence and phase lock suggest an “active” longitude (could be a quadrant) coupled with a preferred local time for ion injection Gas Hot H+, O+ Ion Dispersion Event Neutral Gas? Saturn Cassini

20. Modulation persistence and phase lock suggest an “active” longitude (could be a quadrant) coupled with a preferred local time for ion injection Gas Hot H+, O+ Ion Dispersion Event Neutral Gas? Saturn Cassini

21. Modulation persistence and phase lock suggest an “active” longitude (could be a quadrant) coupled with a preferred local time for ion injection Gas Hot H+, O+ Ion Dispersion Event Neutral Gas? Saturn Cassini

22. Modulation persistence and phase lock suggest an “active” longitude (could be a quadrant) coupled with a preferred local time for ion injection Gas Hot H+, O+ Ion Dispersion Event Neutral Gas? Saturn Cassini

23. Modulation persistence and phase lock suggest an “active” longitude (could be a quadrant) coupled with a preferred local time for ion injection Gas Hot H+, O+ Ion Dispersion Event Neutral Gas? Saturn Cassini

24. Modulation persistence and phase lock suggest an “active” longitude (could be a quadrant) coupled with a preferred local time for ion injection Gas Hot H+, O+ Ion Dispersion Event Neutral Gas? Saturn Cassini

25. Modulation persistence and phase lock suggest an “active” longitude (could be a quadrant) coupled with a preferred local time for ion injection Gas Hot H+, O+ Ion Dispersion Event Neutral Gas? Saturn Cassini

26. Modulation persistence and phase lock suggest an “active” longitude (could be a quadrant) coupled with a preferred local time for ion injection Gas Hot H+, O+ Ion Dispersion Event Neutral Gas? Saturn Cassini

27. How do these events look from an off-equatorial vantage point?

28. Same event, higher energy H

29. Watch the rotating blob…

30. Summary of Observations on Periodicities • Brightest ENA emission from interface between dense gas cloud in vicinity of E-Ring, and energetic ions just outside that region. • Large scale ion injections are commonly seen as corotating brightenings in ENA. • Ion injections are well correlated with SKR, including when they are seen repeating at Saturn’s rotational period. • Oxygen ENA emission shows more pronounced, and more regular, rotation modulation than hydrogen. • Energetic oxygen lifetime in the inner magnetosphere should be no longer than hours, given the density of the water-product cloud in the vicinity of the E-ring. The repeated, un-damped rotational modulation therefore requires nearly continual replenishment of the energetic oxygen ions. • The synchronicity of the modulated ENA emission, as well as the unchanging energy dispersion, requires repeated injections preferentially at the same Saturn IAU longitude --possibly the same ‘clock’ that drives the SKR.