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
• Rev 129
Rhea
Dione
1 March 2010
6 April 2010
• Close Enceladus flybys on revs 120, 121, 130, 131
•
•
•
•
Rev 120
Rev 121
Rev 130
Rev 131
2009 November 2
2009 November 21
2010 April 28
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
Enceladus’ Plume against Saturn
Rev 120
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
UV stellar occultations
Orbit
158
158
158
158
170
200
211
217
217
217
217
217
217
220
220
220
220
252
264
266
278
290
DOY
346
346
346
346
225
1
22
167
167
167
167
167
167
229
229
229
229
349
68
80
160
241
Year
2011
2011
2011
2011
2012
2014
2015
2015
2015
2015
2015
2015
2015
2015
2015
2015
2015
2016
2017
2017
2017
2017
Date
DEC
DEC
DEC
DEC
AUG
JAN
JAN
JUN
JUN
JUN
JUN
JUN
JUN
AUG
AUG
AUG
AUG
DEC
MAR
MAR
JUN
AUG
12
12
12
12
12
1
22
16
16
16
16
16
16
17
17
17
17
14
9
21
9
29
9:36:40
9:37:18
9:38:04
9:38:27
21:45:22
3:03:42
6:22:15
19:57:36
20:06:49
20:06:54
20:07:12
20:08:52
20:09:50
18:36:20
18:36:33
18:36:49
18:39:36
0:05:13
1:51:55
19:23:32
2:20:31
22:40:54
Egress
9:38:33
9:38:54
9:39:22
9:40:10
21:46:11
3:06:24
6:22:42
20:05:38
20:09:33
20:09:21
20:09:26
20:10:58
20:12:14
18:39:29
18:39:33
18:39:43
18:42:48
0:05:54
1:52:44
19:24:36
2:21:46
22:42:24
135
139
143
143
183
183
183
183
211
245
250
277
293
205
290
11
11
68
68
68
68
23
287
334
157
256
2010
2010
2011
2011
2013
2013
2013
2013
2015
2016
2016
2017
2017
JUL
OCT
JAN
JAN
MAR
MAR
MAR
MAR
JAN
OCT
NOV
JUN
SEP
24
17
11
11
9
9
9
9
23
13
29
6
13
18:54:51
7:11:35
4:56:43
4:57:10
18:03:46
18:03:58
18:05:05
18:06:55
16:30:03
20:41:41
9:57:57
22:21:50
19:51:54
18:56:21
7:14:40
4:58:47
5:01:41
18:05:57
18:05:29
18:07:43
18:08:57
16:32:13
20:43:33
10:01:09
22:24:44
19:55:48
UVIS
UVIS
UVIS
UVIS
UVIS
151
170
178
225
291
213
225
7
315
248
2011
2012
2013
2015
2017
AUG
AUG
JAN
NOV
SEP
1
12
7
11
5
7:22:52
17:28:57
1:07:44
14:21:41
9:00:15
7:24:06
17:29:45
1:08:12
14:26:13
9:01:42
UVIS
UVIS
155 292 2011 OCT
233
71 2016 MAR
19
11
9:23:21
11:57:46
9:24:30 ENCELADUS
11:58:58 ENCELADUS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
UVIS
Ingress
Target Moon Star
DIONE
Alp_Lyr
DIONE
Zet_Oph
DIONE
Eta_UMa
DIONE
Alp_Vir
DIONE
Kap_Ori
DIONE
Alp_Vir
DIONE
Alp_CMa
DIONE
Alp_Vir
DIONE
Bet_Cen
DIONE
Bet_Cru
DIONE
Alp1Cru
DIONE
Alp_Pav
DIONE
Alp_Eri
DIONE
Bet_Cen
DIONE
Bet_Cru
DIONE
Alp1Cru
DIONE
Alp_Eri
DIONE
Zet_Ori
DIONE
Gam_Ori
DIONE
Lam_Sco
DIONE
Eps_CMa
DIONE
Kap_Ori
Objective
Priority 1: Determine whether
Dione exhibits low-level activity
by looking for volatiles via absorption
of starlight from uv-bright stellar
source
RHEA
RHEA
RHEA
RHEA
RHEA
RHEA
RHEA
RHEA
RHEA
RHEA
RHEA
RHEA
RHEA
Eps_Ori
Sig_Sgr
Alp_Lyr
Eta_UMa
Zet_Ori
Eps_Ori
Kap_Ori
Bet_CMa
Alp_CMa
Eta_UMa
Gam_Ori
Kap_Ori
Eps_CMa
Priority 1-2: Determine whether there
is ring material orbiting Rhea by
continuing to look for volatiles in
Rhea's vicinity that could explain the
MAPS data now attributed to rings
TETHYS
TETHYS
TETHYS
TETHYS
TETHYS
Kap_Ori
Eps_Ori
Alp_Vir
Alp_Vir
Bet_Ori
Priority 2: Determine whether Tethys
contributes to the E ring by looking
for volatiles in Tethys' vicinity
Gam_Ori
Eps_Ori
Priority 1: Identify long-term
secular and seasonal changes
by observing plume occulting
bright uv stars
NOTE: Colored fill indicates a single block of time
Rhea occ in bold goes through the equatorial plane, thus is best geometry to be occulted by ring material
other occs do not go through the equatorial plane, thus only address whether there are volatiles
XXM SM7a Tweak
• Opportunity for dual stellar occ by Enceladus’ plume tweaked in,
19 October 2011, epsilon Orionis (blue) and zeta Orionis (white)
QuickTime™ and a
H.264 decompressor
are needed to see this picture.
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
Enceladus
Enceladus
Rev 80
Rev 88
Rev 91
August 11
October 9
October 31
50 km
25 km
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