1. UVIS Icy Satellites Update
Amanda Hendrix
January 2007

2. topics Phoebe results Iapetus results Hyperion results In the works
FUV water ice paper
Enceladus plume against Saturn disk?
H2O2 - VIMS/UVIS comparison
Future work

3. General procedure Do this for entire image (1024,i,j)
- scattered light
data_cal = smooth(data(*,i,j) x FF(*,i)/int.per.,3,/NaN) x 99cal(*,i) x redpatch(*,i)
x1.05
x0.91
Do this for entire image (1024,i,j)
Use nightside rows (if possible) as background and subtract off
Need to test scattered light correction; may need to add this step

4. Spectral Models Hapke Model
Bidi. ref=(w/4)(0/(+0))[(1+B)*p+H()*H(0)-1]*R()
Emphasis on how to correctly model single-scatter albedo w
For H2O, non-H2O species
Use Enceladus as object against which we compare the H2O model -- but need to make sure we get Enceladus reflectance absolutely right
Depends on FF
Depends on scattered light correction (?)
Apply to Phoebe, Iapetus, inner icies

5. Update on Phoebe paper Submitted to Icarus in September
Reviews back, revisions needed
Focus on this when Iapetus paper is submitted (next 1-2 wks)
Hope to apply new red patch before final submission
Main results in paper:
Demonstration of Hapke models
Areal, intimate
H2O + carbon, tholins, kerogen, poly-HCN etc.
Intimate mixture models work better overall
But it’s pretty hard to distinguish meaningfully between the different non-ice species
Disk-resolved spectra show compositional variations across surface
More H2O ice in high southern latitude region
Possibly corresponding to rim of a large crater
Upper limits on O, C; H distribution off-body (or lack thereof)

7. Sample Phoebe models average Phoebe reflectance

9. Phoebe disk-resolved reflectance spectra
High S. latitude bright region - more H2O
mid-latitude dark region

10. Update on Iapetus paper
For submission to Icarus as part of special issue
Hopefully within next 1-2 weeks
Will apply new red patch later (after reviews)
Main results in paper:
We can use VIMS models (Buratti et al. 2005) for average light terrain and average dark terrain to match UVIS spectra
Light terrain: 78% H2O + 22% Triton tholin
Dark terrain: 5% H2O + 55% poly-HCN + 40% Triton tholin
Within dark material,
Apex region (centered on 90°W) is spectrally different from non-apex (more H2O ice?)
Could suggest compositional differences related to emplacement of dark material
Or could suggest compositional differences due to meteoritic bombardment of dark material
Comparisons with Phoebe, Hyperion

11. Iapetus images
3-color
Long-

12. Analysis of different regions on Iapetus LH

13. Intimate Mixture Model Fits to Iapetus Bright Terrain and
Average Dark Terrain
New red patch should help here (make reflectance flatter)
Intimate mixture model fits to light terrain and average dark region are consistent with VIMS results
(Buratti et al., 2005)

14. Spectral variations within dark terrain
Apex: °W longitude
Spectral models are in progress; it appears that more H2O ice is present
in apex region compared to non-apex region

15. That darn star
Light from way off-limb star (rows 26-27) contaminated data from
disk of Iapetus (32-33)

16. Update on Hyperion Results
Nature paper in preparation (Cruikshank et al.)
Some UVIS results were given to Dale C.
Awaiting status of manuscript

17. Models of Hyperion spectra
Intimate Mixture Model results:
Bright:
~50% H2O plus ~50% organic material
Average:
~35% H2O plus ~65% organic material
Dark:
~10% H2O plus ~90% organic material
Cannot pull out a dark terrain spectrum that is H2O-free

18. In progress: Water Ice paper
Possible improvement of optical constants over Warren (1984)
Include new data since Warren (1984)
Dependence in optical constants on hexagonal vs amorphous ice
Hapke modeling of water ice in FUV
Comparisons to icy satellites
My models (so far) generally need H2O grain sizes much smaller than those modeled by VIMS
Is this real?
Two (+) populations of H2O grain sizes?
Or does UVIS detect asperities on larger H2O grain surfaces?
New red patch will help at longest wavelengths
Need to try Bill’s scattered light correction, especially for Enceladus

19. Models of H2O for different grain sizes

20. Use Enceladus reflectance spectrum to check H2O spectral models
New red patch should help here
Is refl really this bright here?
Do scattered long- (>1700 Å) photons contaminate short- <1500 Å) spectrum?

21. (From July 2006 team meeting) Enceladus scattering issue for filled slit, bright source, does signal at bright long  contaminate short ?
**At the end of this observation, when we are very close and the slit is ~filled, there is a lot of scattering of light at the shorter wavelengths and the reflectance shape is not accurate. **

22. Is it possible to detect Enceladus plume against Saturn disk?
Or do we only measure variations in Saturn reflectance?
3-color image
004EN Icymap007_cirs 2 3 1
LW image
Geometer image

23. Need more integration time to clean up spectra before we can do this right

24. H2O2 - VIMS/UVIS comparison
Preliminary results from Sarah Newman/Bonnie Buratti

25. H2O2 at FUV wavelengths
This is what H2O2 gas looks like - in the NUV, H2O2 in H2O ice (e.g. Europa) looks like H2O2 gas. So we may want to look for this signature in icy satellite reflectance spectra

26. Future Work Io paper!! (with Don)
Look into images of Io torus neutrals
Icy satellite phase curves, models
Surface structure
Any spatial variability in surface structure?
Icy satellites - EUV spectra