1. XXM Status, Priorities, Plans, and Activities Icy Satellite Science
C. J. Hansen, A. Hendrix
January 2011

2. XXM Status Icy satellite flybys since last team meeting
Rev 131 Enceladus 18 May 2010
Solar occultation
Paper submitted to Science – rejected
Nature wants us to combine with CDA paper
Go to GRL?
Icy satellite flybys since last team meeting
Rev Enceladus (E11) August 2010
ORS but no UVIS primes
Rev Enceladus (E12) November 2010
Gravity pass
Rev Enceladus (E13) December 2010
INMS pass
Continuing to collect icy satellite observations, ICYLONs and ICYMAPs, as ride-alongs
particularly on Rev 139
Mimas, Dione, Rhea

3. XXM Planning Status Requested PIEs for all occultations by:
Dione and Tethys
Look for volatiles being released, supplying E ring
Rhea
Look for rings or other evidence of volatile release
15 occs requested
8 in as occ PIEs
2 “in” but in conflict
3 out
2 not scheduled yet
Iapetus in apoapsis Rev 196
One in proximal orbit

4. Solstice Mission Enceladus Flybys
E14 – E16 coming up in next year
Requested assignment of Enceladus flyby E15 (Rev 155) on 19 October 2011 for dual stellar occultation
We got it

5. XXM SM7a Tweak
Opportunity for dual stellar occ by Enceladus’ plume tweaked in,
19 October 2011, epsilon Orionis (blue) and zeta Orionis (white)

6. Backup Slides

7. Observation Suite
System scans show variable atomic oxygen in Saturn’s system
Localized scans across Enceladus give higher resolution picture of the distribution of oxygen

8. Enceladus mini- System Scan

9. Variability of Oxygen Emission Feature
Note: Units are Rayleighs / 10 pixels because summed over spectral channels 237 to 246
This plot shows the variability observed in the observations analyzed to-date. The range is 0.3 to 2.3 Rayleighs/pixel
But, differing geometries have not been accounted for

10. ICYSTARE Oxygen spatial distribution
Units should be rayleighs
Rhea Rev018
Range = 131,036 km
Phase = 170
Duration = 178 records x 30 sec = 89 min
# spatial pixels = 64

11. The Source
We now know that these molecules are the dissociation products of the water vapor in Enceladus’ plume
4 days: H2O  H + OH via photo-dissociation
12 days: OH  O + H via electron dissociation
37 days: O average loss rate via charge exchange, depending on location and amount of time spent in the plasma sheet
UVIS observations show that neutral oxygen is “smeared out” into a torus that peaks at Enceladus’ orbit but is not symmetric about it
Additional sources???
UVIS system scans give us the mass budget of O in the system
E ring particles are 0.3 to 3 microns
Lifetime of 1 micron grains is ~50 yrs
Estimate of required re-supply rates, water molecules/sec:
1.3 x Melin, H., et al., PSS
Water supplied by Enceladus: ~1028 molecules / sec

12. Rev 129 Dione ICYMAP