XXM Status, Priorities, Plans,
and Activities
Icy Satellite Science
C. J. Hansen, A. Hendrix
June 2011
XXM Status
•
Rev 131
Enceladus
18 May 2010
• Solar occultation
• Paper published in GRL 38:L11202, June 9, 2011
•
Icy satellite flybys since last team meeting
– Rev 149
Helene
• Upcoming icy satellite flybys
– Rev 154 Enceladus (E14)
– Rev 155 Enceladus (E15)
1 October 2011
19 October 2011
• This is the flyby with the plume dual stellar occ
• Will practice with planned instrument configuration on Rhea occ
August 1
– Rev 156 Enceladus (E16)
– Rev 158 Dione (D3)
6 November 2011
12 December 2011
• Continuing to collect icy satellite observations, ICYPLU, ICYLONs
and ICYMAPs, as ride-alongs
– Rev 144 Mimas
– Enceladus’ plume at high phase angles
Hello
Helene!
• Helene is
Dione’s
leading coorbital one of 4
of Saturn’s
moons in the
Lagrangian L4
point
• Phoebe-size:
36 x 32 x 30
km
• Sub-Saturnian
side
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” SOST but in conflict
4 out
1 not scheduled yet
• Iapetus in apoapsis Rev 196
• Now looking at occs in
proximal orbit
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 whethe
Dione exhibits low-level activ
by looking for volatiles via ab
of starlight from uv-bright st
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 whet
is ring material orbiting Rhea
continuing to look for volatile
Rhea's vicinity that could exp
MAPS data now attributed to
TETHYS
TETHYS
TETHYS
TETHYS
TETHYS
Kap_Ori
Eps_Ori
Alp_Vir
Alp_Vir
Bet_Ori
Priority 2: Determine whethe
contributes to the E ring by lo
for volatiles in Tethys' vicinit
Gam_Ori
Eps_Ori
Priority 1: Identify long-term
secular and seasonal change
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
Solstice
Mission
Enceladus
Flybys
• E14 – E16 coming up
• 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)
Objectives from the Traceability Matrix
#
Summary
IC1a
Identify long-term secular and seasonal changes at Enceladus, through
observations of the south polar region, jets, and plumes. Also focus on wellilluminated N. pole to understand why it is so fundamentally different from S. pole.
(Opportunity is ideal because illumination conditions are reversed from the
primary mission.)
IN1a
Test for the presence of an ocean at Enceladus as inferred from plume composition, and
constrain the mechanisms driving the endogenic activity by long-term remote sensing of
plumes and thermal emission.
IC2a
Determine whether Dione exhibits evidence for low-level activity, now or in recent
geological time.
IN2b
Determine whether Tethys contributes to the E-ring and the magnetospheric ion and
neutral population.
IN2a
Explore the mechanisms behind the unique thermal and optical properties of Mimas
discovered by Cassini with remote sensing, especially the N. pole, at the highest
resolution possible.
IN1b
Observe selected small satellites to quantify the movement of Enceladus material
through the system, the history and formation of satellites, including collisions/breakup,
interaction with ring material as indicated by surface properties/composition, and
cratering rates and geologic history deep in the Saturnian system
Comments
Green = nature of prox.
orbit; Red=illumination;
Blue=long baseline
Get rid of
Solstice Mission Priorities
• The main priority for UVIS are the Dione stellar
occ opportunities
• MAG sees mass-loading in the magnetosphere at
~7 kg/sec (Enceladus supplies ~200 kg/sec)
• Dione plume won’t go as high or lose as much gas
(escape velocity is higher because Dione is larger,
gravity higher)
• So we need to look close to the limb and be very
very lucky!
– 6 occs in XXM plus 4 in proximal orbits
Events in F-Ring/Proximal Mission Phases
Object
Rhea occ
Daphnis
Pandora
Mimas
Epimetheus
Prometheus
Dione occ
Pan
Dione occ
Janus
Pan
Enceladus
Janus
Atlas
Enceladus
Tethys
Hyperion
Dione
Rhea
Dione
Enceladus
Enceladus
Enceladus
Dione
Time (2017)
10 Jan 14:39
16 Jan 13:22
23 Jan 17:17
30 Jan 21:06
30 Jan 21:07
30 Jan 21:28
8 Feb 21:16:31
7 Mar 18:09
9 Mar 1:52:01
22 Mar 01:50
22 Mar 02:23
29 Mar 05:46
12 Apr 13:45
12 Apr 13:45
3 May 00:45
15 May 00:24
25 May 01:14
29 May 00:01
6 June 22:21:08
14 Jun 13:47:59
17 June
13 July
27 Aug
14 Sep 8:10:49
C/A (km)
γ-Ori
17,600
19,000
40,385
5900
50,250
γ-Ori
25,350
γ-Ori
43,950
55,200
93,046
9060
13,170
174,730
193,000
285,000
200,000
κ-Ori
β-CMa
195,000
173,000
146,000
β-CMa
Uniqueness
Comments
UVIS occ – 1 min
Closest ever by > order of mag
Closest by a factor of 3
Close flyby of N. Pole
One of closest, but not unique
One of closest, but not unique
Map N. Pole
Closest by factor of 2
UVIS occ – 3 min
Low phase angle
UVIS occ – 2 min
Second best (see below)
Equal to best yet
Last VGR class flyby
Best by an order of magnitude
Best by almost factor of 2
Last look at Hyperion
Last look at Dione
UVIS occ – 2 min
UVIS occ – 2 min
UVIS occ – 2 min
Notes: Compiled from the SOST PIE list, Digit, and Horizons Pink is must have; orange is should have.
Blue are occs – don’t need Rhea
Last four of Enceladus are of equal priority – don’t need all?
Observations of small satellites would give estimate of amplitude of libration
System Scan Observations
Objective: map neutral species in the Saturn system out to 5 –
10 Rs
–
–
Specifically atomic H and O
Oxygen maps support ISWG priority 1 objectives IC1a and IN1a
• UVIS team recommended 128 hr system scan 4x per year to
get oxygen
– Fewer hours required for H
• Project subsequently agreed to 256 hr per year (4 x 64 hr)
– (that is what we have been getting)
– Concern was whether this would be enough time to map O
The Good News
• 64 hrs is enough to map O in the system out to 5 Rs
• Data shown is from 64 hr system scan acquired in 2010
However…
• When we get into inclined orbits line-of-sight density drops
• System scan duration will need to double-triple to
compensate with longer integration times
128 hr
256 hr
256 hr
256 hr
64 hr
Summary of Request
167-168
OR 169-170
17 June 2012
2 August 2012
256 hr
196-197
5 August 2013
256 hr
206-207
3 August 2014
256 hr
211-212
25 January 2015
resume 4 per
year 64 hr cadence
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
Variability of Oxygen Emission near Enceladus
25
20
Rayleighs/pixel/sec
Note: Units are
Rayleighs / 10
pixels because
summed over
spectral
channels 237 to
246
15
10
5
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Observation
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
• 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