16199( 13) - 17-Jul-2025 11:49:29 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16199 Version: 13 Check-in Time: 17-Jul-2025 11:49:29 STScI Edit Number: 11 Title Exploiting the fortunate Jupiter transit geometry to probe Ganymede's and Callisto's atmospheres ------------------------------------------------------------------------------------ Type Cycle GO 28 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Lorenz Roth Royal Institute of Technology Y CoI: Dr. Kurt David Retherford Southwest Research Institute N CoI: Dr. Joachim Saur Universitat zu Koln N CoI: Dr. Tracy M Becker Southwest Research Institute N CoI: Dr. Jens Hoeijmakers Lund University N CoI: Dr. Pippa Molyneux Southwest Research Institute N ------------------------------------------------------------------------------------ Abstract Ganymede and Callisto are primary targets of ESA's JUpiter Icy Moon Explorer (JUICE) and NASA's Europa Clipper mission: Callisto will be visited with a total of about 20 flybys. Ganymede will be the first planetary moon to be orbited by a spacecraft (JUICE). Today, the atmospheres of the two icy moons are only loosely constrained by observations. Oxygen, the domimant atmospheric species, is observable only through faint electron-excited emissions, complicating derivation of reliable neutral gas abundances or distribution due to poorly constrained electron properties. STIS spectral imaging has recently proven to be a sensitive tool for investigating Io and Europa while in transit of Jupiter: Atmospheres and plume abundances are probed through extinction of the bright Jupiter Ly-alpha background - independently of electron properties. The observing geometry now during HST Cycle 28 provides optimal conditions to also observe Ganymede and Callisto in transit of Jupiter. Both moons have long (>3.5 h) transits near the Ly-alpha-bright equator of the planet, a condition that is fulfilled only every ~6 years. We propose to observe Ganymede and Callisto during one transit of Jupiter each with two consecutive HST orbits. The observations will provide the most precise measurements of the H atmospheres and the first ever spatially resolved constraints on atmospheric H2O - from sublimation or outgassing - for the two largest moons of Jupiter. The transit geometry provides the unique opportunity to measure hemispheric differences in the atmospheres, which likely arise from the moons' surface volatile distributions as known via albedo dichotomies between the trailing and leading sides. ------------------------------------------------------------------------------------ Observations Description ------------------------ We observe Ganymede and Callisto during one visit per target with two contiguous HST orbits each. We use STIS in the spectral mode with the G140L grating and the unsupported 6"x6" aperture. The use of this aperture is required: Both Ganymede's and Callisto's disks (~1.6" and 1.8") almost fill the widest available slit (2"), preventing a characterization of (a) the several moon radii extended H coronae and (b) the Jovian background. To minimize the geocorona signal and to maximize the moon size in the apertures the observations are to be taken max 2 month befor or after Jupiter opposition 16199( 13) - 17-Jul-2025 11:49:29 - [ 2] on August 20, 2021. The period +/-3 days around opposition is yet excluded to avoid phase angles below 1 deg and thus avoid the shadow of the respective moon on Jupiter to be in the background image. Target acqusition is omitted to save science exposure time. The pointing accurary of HST is sufficient to ensure the moons to be within the 6"x6" aperture. ------------------------------------------------------------------------------------ 16199( 13) - 17-Jul-2025 11:49:29 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: GANYMEDE-TRANSIT ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE Ganymede in transit of Jupiter ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=JUPITER STD=GANYMEDE ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS NOT OCC OF GANYMEDE-TRANSIT BY JUPITER FROM EARTH, SEP OF GANYMEDE-TRANSIT IO FROM EARTH GT 10", SEP OF GANYMEDE-TRANSIT EUROPA FROM EARTH GT 10", SEP OF GANYMEDE-TRANSIT CALLISTO FROM EARTH GT 10", TRANSIT OF GANYMEDE ACROSS JUPITER FROM EARTH, CML OF JUPITER FROM EARTH BETWEEN 250 200 ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 4.6 +/- 0.4 Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 TARGET NAME: GANYMEDE-TRANSIT-COPY ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE Ganymede in transit of Jupiter ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=JUPITER STD=GANYMEDE ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS NOT OCC OF GANYMEDE-TRANSIT-COPY BY JUPITER FROM EARTH, SEP OF GANYMEDE-TRANSIT-COPY IO FROM EARTH GT 10", SEP OF GANYMEDE-TRANSIT-COPY EUROPA FROM EARTH GT 10", SEP OF GANYMEDE-TRANSIT-COPY CALLISTO FROM EARTH GT 10", TRANSIT OF GANYMEDE ACROSS JUPITER FROM EARTH, CML OF JUPITER FROM EARTH BETWEEN 340 240 ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 4.6 +/- 0.4 This is a copy of the Ganymede target to change the CML of Jupiter in the observing windows for the HOPR repeat visits, 3-4. Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ 16199( 13) - 17-Jul-2025 11:49:29 - [ 4] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 TARGET NAME: CALLISTO-TRANSIT ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE Callisto in transit of Jupiter ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=JUPITER STD=CALLISTO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS NOT OCC OF CALLISTO-TRANSIT BY JUPITER FROM EARTH, SEP OF CALLISTO-TRANSIT IO FROM EARTH GT 10", SEP OF CALLISTO-TRANSIT GANYMEDE FROM EARTH GT 10", TRANSIT OF CALLISTO ACROSS JUPITER FROM EARTH, CML OF JUPITER FROM EARTH BETWEEN 340 200 ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 5.6 +/- 0.5 Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 4 TARGET NAME: CALLISTO-TRANSIT2 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE Callisto in transit of Jupiter ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=JUPITER STD=CALLISTO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS NOT OCC OF CALLISTO-TRANSIT2 BY JUPITER FROM EARTH, SEP OF CALLISTO-TRANSIT2 IO FROM EARTH GT 10", SEP OF CALLISTO-TRANSIT2 GANYMEDE FROM EARTH GT 10", TRANSIT OF CALLISTO ACROSS JUPITER FROM EARTH, CML OF JUPITER FROM EARTH BETWEEN 310 200 ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 5.6 +/- 0.5 Used with HOPR visit 52. Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ 16199( 13) - 17-Jul-2025 11:49:29 - [ 5] Visit: 01 (Ganymede visit) Visit Requirements: BETWEEN 20-JUN-2021:00:00:00 AND 17-AUG-2021:00:00:00; BETWEEN 06-SEP-2021:01:30:00 AND 06-SEP-2021:02:20:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GANYMEDE-TR STIS/FUV TIME-TA 6X6 G140L 1425 BUFFER-TIME=500 1 2400 S ANSIT -MAMA G see below (2030 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 GANYMEDE-TR STIS/FUV TIME-TA 6X6 G140L 1425 BUFFER-TIME=500 1 2400 S ANSIT -MAMA G see below (2353 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GANYMEDE-TRANSIT 1 STIS/FUV TIME-TA 6X6 G140L 1425 none none none none 1 2030.0 S -MAMA G GANYMEDE-TRANSIT 2 STIS/FUV TIME-TA 6X6 G140L 1425 none none none none 2 2353.0 S -MAMA G 16199( 13) - 17-Jul-2025 11:49:29 - [ 6] Visit: 02 (Callisto visit) Visit Requirements: BETWEEN 20-JUN-2021:00:00:00 AND 17-AUG-2021:00:00:00; BETWEEN 04-OCT-2021:07:45:00 AND 04-OCT-2021:08:45:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CALLISTO-TR STIS/FUV TIME-TA 6X6 G140L 1425 BUFFER-TIME=500 1 2400 S ANSIT -MAMA G see below (2390 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 CALLISTO-TR STIS/FUV TIME-TA 6X6 G140L 1425 BUFFER-TIME=500 1 2400 S ANSIT -MAMA G see below (2680 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ CALLISTO-TRANSIT 1 STIS/FUV TIME-TA 6X6 G140L 1425 none none none none 1 2390.0 S -MAMA G CALLISTO-TRANSIT 2 STIS/FUV TIME-TA 6X6 G140L 1425 none none none none 2 2680.0 S -MAMA G 16199( 13) - 17-Jul-2025 11:49:29 - [ 7] Visit: 03 (Ganymede visit - repeat orbit 1) Visit Requirements: BETWEEN 27-SEP-2021:11:00:00 AND 27-SEP-2021:15:00:00; VISIBILITY INTERVAL 45 M On Hold Comments: Additional Comments: HOPR repeat of orbit 1 of visit 1 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GANYMEDE-TR STIS/FUV TIME-TA 6X6 G140L 1425 BUFFER-TIME=500 1 2400 S ANSIT-COPY -MAMA G see below (1948 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GANYMEDE-TRANSIT-CO 1 STIS/FUV TIME-TA 6X6 G140L 1425 none none none none 1 1948.0 S PY -MAMA G 16199( 13) - 17-Jul-2025 11:49:29 - [ 8] Visit: 04 (Ganymede visit - repeat orbit 2) Visit Requirements: AFTER 03 BY 0.8 Orbits TO 1.2 Orbits; VISIBILITY INTERVAL 53 M On Hold Comments: Additional Comments: HOPR repeat of orbit 2 of visit 1 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GANYMEDE-TR STIS/FUV TIME-TA 6X6 G140L 1425 BUFFER-TIME=500 1 2400 S ANSIT-COPY -MAMA G see below (2428 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GANYMEDE-TRANSIT-CO 1 STIS/FUV TIME-TA 6X6 G140L 1425 none none none none 1 2428.0 S PY -MAMA G 16199( 13) - 17-Jul-2025 11:49:29 - [ 9] Visit: 52 (Callisto visit) Visit Requirements: SCHED 70%; VISIBILITY INTERVAL NO GYRO BIAS UPDATE ON MOVING TARGET On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CALLISTO-TR STIS/FUV TIME-TA 6X6 G140L 1425 BUFFER-TIME=500 1 2390 S ANSIT2 -MAMA G see below (2266 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 CALLISTO-TR STIS/FUV TIME-TA 6X6 G140L 1425 BUFFER-TIME=500 1 2400 S ANSIT2 -MAMA G see below (2588 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ CALLISTO-TRANSIT2 1 STIS/FUV TIME-TA 6X6 G140L 1425 none none none none 1 2266.0 S -MAMA G CALLISTO-TRANSIT2 2 STIS/FUV TIME-TA 6X6 G140L 1425 none none none none 2 2588.0 S -MAMA G 16199( 13) - 17-Jul-2025 11:49:29 - [ 10] Summary Form for Proposal 16199 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 6X6 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=500 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 03 BY 0.8 Orbits TO 1.2 Orbits, BETWEEN 04-OCT-2021:07:45:00 AND 04-OCT-2021:08:45:00, BETWEEN 06-SEP-2021:01:30:00 AND 06-SEP-2021:02:20:00, BETWEEN 20-JUN-2021:00:00:00 AND 17-AUG-2021:00:00:00, BETWEEN 27-SEP-2021:11:00:00 AND 27-SEP-2021:15:00:00, SCHED 70%, VISIBILITY INTERVAL 45 M, VISIBILITY INTERVAL 53 M, VISIBILITY INTERVAL NO GYRO BIAS UPDATE ON MOVING TARGET ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names CALLISTO-TRANSIT, CALLISTO-TRANSIT2, GANYMEDE-TRANSIT, GANYMEDE-TRANSIT-COPY ------------------------------------------------------------------------------------------------------------------------------------