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

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 136 Enceladus (E11) 13 August 2010 ORS but no UVIS primes Rev 141 Enceladus (E12) 30 November 2010 Gravity pass Rev 142 Enceladus (E13) 21 December 2010 INMS pass Continuing to collect icy satellite observations, ICYLONs and ICYMAPs, as ride-alongs particularly on Rev 139 Mimas, Dione, Rhea

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

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

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

Backup Slides

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

Enceladus mini- System Scan

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

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

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 1028 2009 Melin, H., et al., PSS Water supplied by Enceladus: ~1028 molecules / sec

Rev 129 Dione ICYMAP