XM Status and Plans, XXM Activities Icy Satellite Science C. J. Hansen, A. Hendrix, D. Shemansky 8 June 2009

XM Status, Priorities, Plans To a major extent XM planning is complete for icy satellites Still polishing icy satellite flyby timelines Rev 127 Rhea 1 March 2010 Rev 129 Dione 6 April 2010 Close Enceladus flybys on revs 120, 121, 130, 131 Rev 120 2009 November 2 Rev 121 2009 November 21 Rev 130 2010 April 28 Rev 131 2010 May 18 Rev 120 has high resolution UVIS observation of plume with Saturn in the background Will acquire solar occ on Rev 131 Continuing to collect icy satellite observations: ICYLONs, ICYMAPs, ICYECLs, ICYATMs, ICYOCCs…

Enceladus Flybys March 12, 2008

Rev 120 Enceladus’ Plume against Saturn

Solar Occultation Rev 131 We have the opportunity to observe an occultation of the sun on Rev 131 New results are in the EUV, which gives us access to a different wavelength range than the FUV The big scientific payoff is the chance to definitively detect / measure nitrogen in the plume - important for models of chemistry-driven dynamics in the interior

SM-7a Tweaked a little closer?

Nitrogen in Enceladus’ Plume? Why is that important to know? Evidence for liquid water in the interior Compositional evidence for a hot interior: ammonia (Matson et al, 2007) Existence of N2 implies decomposition of NH3 Titan data (lack of argon) implies NH3 is primordial material from Saturn’s disk Decomposition of NH3 requires temperatures well above the melting point of water Clathrate reservoir hypothesis (Kieffer et al, 2006) CH4 and N2 trapped in water ice clathrates could decompose explosively when exposed to near-vacuum Advective heat transfer, redistribution of latent heat is driving source of energy

XXM Status Requested PIEs for all occultations by: Dione and Tethys Look for volatiles being released, supplying E ring Rhea Look for ring or other evidence of volatile release SOST accepted all of these as PIEs, now going through integration process with other TWTs Enceladus flyby allocations Requested assignment of Enceladus flyby on 19 October 2011 for stellar occultation No contest

SOST Occultation PIEs

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 Execute routinely to monitor Enceladus’ activity remotely

XM Enceladus Flybys Executed in 2008: Enceladus Rev 80 August 11 50 km Enceladus Rev 88 October 9 25 km Enceladus Rev 91 October 31 196 km UVIS collected high resolution surface maps, but no more stellar occs

XM Status, Priorities, Plans To a major extent XM planning is complete for icy satellites Still polishing icy satellite flyby timelines Collecting icy satellite observations: ICYLONs, ICYMAPs, ICYECLs, ICYATMs, ICYOCCs… Amanda is working on reflectance spectroscopy, and what that tells us about E ring coatings on the surfaces of inner satellites, age of ice around the tiger stripes, thermal migration of volatiles on Iapetus Candy is working on oxygen in Enceladus’ vicinity and whether that can be used as a proxy for plume activity, and analyzing stellar occs Un-analyzed data continues to accumulate

Solar Occultation How well can UVIS measure N2 with a solar occultation? Abundance of H2O measured by UVIS = 1.5 x 1016 cm-2 Mixing ratio of mass 28 in the INMS experiment at Enceladus was [M28]/[H2O]=0.036 A solar occultation has been simulated for our H2O optical depth assuming a commingled mixture of H2O and N2 in the spectral region of the H Ly line The ability to measure N2 in a mixing ratio of [N2]/[H2O] = 0.005 is indicated, for an abundance of N2 = 1 x 1014 cm-2 How do we know? N2 was measured above the exobase in the UVIS T10 solar occultation observation using the measured extinction of the sol H Ly line by the N2 b(3,0) band.

Solar Occultation

Solar Occultation Reduced amount of water vapor simulation (Further from source so need to take this into account)

Solar Occultation This is a simulation of the results we could get from a solar occultation by Enceladus’ plume UVIS can detect N2 absorption near 972 Ang Mixing ratio for blue curve, showing clear absorption, is 0.05, close to the INMS derived value of [M28/H2O] = 0.036 Green curve shows likely detection limit with an order of magnitude less nitrogen, or [M28/H2O] = 0.005