17835( 8) - 29-Apr-2025 18:01:44 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17835 Version: 8 Check-in Time: 29-Apr-2025 18:01:44 STScI Edit Number: 6 Title Improving the masses of the Pluto Small Satellites ------------------------------------------------------------------------------------ Type Cycle GO 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Simon Bernard Porter Southwest Research Institute Y ------------------------------------------------------------------------------------ Abstract This program would measure astrometry for the small satellites of Pluto to update and improve their dynamical mass estimates. All four small satellites of Pluto were discovered by HST, and WFC3 has been the primary source of astrometry for them both before and after the New Horizons flyby in 2015. Styx and Keberos have only ever been observed with WFC3 due their extreme faintness (V~26-27). The proposed observations, which would be no earlier than Spring 2025, six years after the last HST observations of Pluto, would enable significant improvement in the orbits of Styx and Kerberos. Recently published dynamical studies of the Pluto small satellites (Kenyon & Bromley, 2022, Porter & Canup 2023) show that the much smaller Styx and Kerberos are sufficiently perturbed by Nix and Hydra that Styx and Kerberos can be used to constrain the mases of Nix and Hydra. This improvement in the orbits of Styx and Keberos would then directly help to better constrain the masses of Nix and Hydra, while also enabling the long-term monitoring of Styx and Kerberos that is critical to determine their masses. The masses of the small satellites of Pluto provide important constraints on the formation of the Pluto system. This in turn helps to constrain the moon-forming process after a giant impact, critical to understanding planet formation in general. The proposed observations would use proven published techniques to measure the absolute astrometry of the small satellites relative to the background Gaia DR3 stars, eliminating the problem of historical anaylses that Pluto and Charon are barely resolved in WFC3 and make poor astrometric references. ------------------------------------------------------------------------------------ Observations Description ------------------------ These are observations of the Pluto system to measure the positions of the satellites relative to background stars in order to improve their mass estimation (see Porter & Canup 2023 for desciption of the analysis to be performed). Some amount of background stars are expected and useful, and that's also why the observations are full frame, both chips. However, as noted in the proposal, we will need to check each visit to make sure there isn't a direct star collision with any of the satellites. Pluto is in a dense star field, so there is a chance of that happening. The timing requirements for the three visits are that they are sufficiently far apart to see significant motion of the satellites. The orbital period of Hydra is 38 days, so a separation between the orbits of at least 14 days (~1/3 of a Hydra orbit) is preferable, but any amount larger is fine, and the exact timing 17835( 8) - 29-Apr-2025 18:01:44 - [ 2] of the observations is not constrained. If needed, smaller timing separation are possible, but check with the PI. All observations are 4 images in a box dither, with the F350LP filter, to maximize their throughput and efficiency. ------------------------------------------------------------------------------------ 17835( 8) - 29-Apr-2025 18:01:44 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: PLUTO ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: DWARF-PLANET Pluto system ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=PLUTO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 14 Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ 17835( 8) - 29-Apr-2025 18:01:44 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type LINE Pattern_Purpose OTHER Number_Of_Points 5 Point_Spacing 0.030 Line_Spacing Coordinate_Frame CELESTIAL Pattern_Orient 0 Angle_Between_Sides Center_Pattern YES Pattern_Comments: Objects will naturally dither themselves in a predominantly east-west direction. This dither pattern uses offsets perpendicular to the mean motion of the objects with a two-level pattern so that the dither cannot lead to a false detection with coherent motion. The overall pattern is six positions with 0.75 pixel spacing. ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 17835( 8) - 29-Apr-2025 18:01:44 - [ 5] Visit: 01 Visit Requirements: BETWEEN 01-MAY-2025:00:00 AND 07-MAY-2025:04:05; BETWEEN 14-MAY-2025:06:30 AND 18-MAY-2025:11:25; BETWEEN 18-MAY-2025:14:10 AND 30-MAY-2025:19:50; BETWEEN 30-MAY-2025:21:00 AND 31-MAY-2025:12:30; BETWEEN 31-MAY-2025:14:15 AND 04-JUN-2025:10:40; BETWEEN 04-JUN-2025:11:50 AND 04-JUN-2025:23:10; BETWEEN 05-JUN-2025:00:30 AND 05-JUN-2025:01:05; BETWEEN 05-JUN-2025:02:20 AND 05-JUN-2025:20:30; BETWEEN 05-JUN-2025:21:35 AND 10-JUN-2025:23:45; BETWEEN 11-JUN-2025:01:05 AND 22-JUN-2025:00:45; BETWEEN 22-JUN-2025:01:50 AND 24-JUN-2025:00:00 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 PLUTO WFC3/UVI ACCUM UVIS2 F350LP 1 400 S SEQ 1 NON-INT; PATTERN 2 S (1600 S) 1 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 1 none none none 1 N/A S PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 2 none none none 1 N/A S PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 3 none none none 1 N/A S PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 4 none none none 1 N/A S 17835( 8) - 29-Apr-2025 18:01:44 - [ 6] Visit: 02 Visit Requirements: AFTER 01 BY 14 D TO 1000 D; BETWEEN 01-MAY-2025:00:00 AND 07-MAY-2025:04:05; BETWEEN 14-MAY-2025:06:30 AND 18-MAY-2025:11:25; BETWEEN 18-MAY-2025:14:10 AND 30-MAY-2025:19:50; BETWEEN 30-MAY-2025:21:00 AND 31-MAY-2025:12:30; BETWEEN 31-MAY-2025:14:15 AND 04-JUN-2025:10:40; BETWEEN 04-JUN-2025:11:50 AND 04-JUN-2025:23:10; BETWEEN 05-JUN-2025:00:30 AND 05-JUN-2025:01:05; BETWEEN 05-JUN-2025:02:20 AND 05-JUN-2025:20:30; BETWEEN 05-JUN-2025:21:35 AND 10-JUN-2025:23:45; BETWEEN 11-JUN-2025:01:05 AND 22-JUN-2025:00:45; BETWEEN 22-JUN-2025:01:50 AND 23-JUN-2025:03:35 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 PLUTO WFC3/UVI ACCUM UVIS2 F350LP 1 400 S SEQ 1 NON-INT; PATTERN 2 S (1600 S) 1 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 1 none none none 1 N/A S PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 2 none none none 1 N/A S PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 3 none none none 1 N/A S PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 4 none none none 1 N/A S 17835( 8) - 29-Apr-2025 18:01:44 - [ 7] Visit: 03 Visit Requirements: AFTER 02 BY 14 D TO 1000 D; BETWEEN 05-JUN-2025:21:35 AND 10-JUN-2025:23:45; BETWEEN 11-JUN-2025:01:05 AND 22-JUN-2025:00:45; BETWEEN 22-JUN-2025:01:50 AND 23-JUN-2025:02:35; BETWEEN 23-JUN-2025:04:00 AND 26-JUN-2025:00:10; BETWEEN 26-JUN-2025:02:10 AND 26-JUN-2025:15:50; BETWEEN 26-JUN-2025:16:55 AND 29-JUN-2025:19:35; BETWEEN 29-JUN-2025:21:05 AND 02-JUL-2025:08:15; BETWEEN 02-JUL-2025:09:25 AND 03-JUL-2025:13:00 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 PLUTO WFC3/UVI ACCUM UVIS2 F350LP 1 400 S SEQ 1 NON-INT; PATTERN 2 S (1600 S) 1 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 1 none none none 1 N/A S PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 2 none none none 1 N/A S PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 3 none none none 1 N/A S PLUTO 1 WFC3/UVI ACCUM UVIS2 F350LP 4 none none none 1 N/A S 17835( 8) - 29-Apr-2025 18:01:44 - [ 8] Summary Form for Proposal 17835 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 14 D TO 1000 D, AFTER 02 BY 14 D TO 1000 D, BETWEEN 01-MAY-2025:00:00 AND 07-MAY-2025:04:05, BETWEEN 02-JUL-2025:09:25 AND 03-JUL-2025:13:00, BETWEEN 04-JUN-2025:11:50 AND 04-JUN-2025:23:10, BETWEEN 05-JUN-2025:00:30 AND 05-JUN-2025:01:05, BETWEEN 05-JUN-2025:02:20 AND 05-JUN-2025:20:30, BETWEEN 05-JUN-2025:21:35 AND 10-JUN-2025:23:45, BETWEEN 11-JUN-2025:01:05 AND 22-JUN-2025:00:45, BETWEEN 14-MAY-2025:06:30 AND 18-MAY-2025:11:25, BETWEEN 18-MAY-2025:14:10 AND 30-MAY-2025:19:50, BETWEEN 22-JUN-2025:01:50 AND 23-JUN-2025:02:35, BETWEEN 22-JUN-2025:01:50 AND 23-JUN-2025:03:35, BETWEEN 22-JUN-2025:01:50 AND 24-JUN-2025:00:00, BETWEEN 23-JUN-2025:04:00 AND 26-JUN-2025:00:10, BETWEEN 26-JUN-2025:02:10 AND 26-JUN-2025:15:50, BETWEEN 26-JUN-2025:16:55 AND 29-JUN-2025:19:35, BETWEEN 29-JUN-2025:21:05 AND 02-JUL-2025:08:15, BETWEEN 30-MAY-2025:21:00 AND 31-MAY-2025:12:30, BETWEEN 31-MAY-2025:14:15 AND 04-JUN-2025:10:40, PATTERN 2 1, SEQ 1 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names PLUTO ------------------------------------------------------------------------------------------------------------------------------------