0 Assigned ID: 5254 ----- Attempting Submission 1 (Mon Mar 25 21:54:11 GMT 2024) ----- HST Phase I Proposal 5254 successfully submitted. Receipt: # 5254-1 This pattern is not used in this proposal. 0 ----- Attempting Submission 1 (Mon Aug 19 22:07:45 GMT 2024) ----- Backup 5-image pattern unused (but there for reference) Improving the masses of the Pluto Small Satellites 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. 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 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. Dr. Simon Bernard Porter is an expert in Pluto observation and analysis. He has led several HST proposals investigating binary KBOs (GO-14616 and SNAP-15821) and performing astrometry in support of the New Horizons mission (GO-16183, GO-16924). He is a New Horizons Coinvestigator, led the small satellites chapter in the "Pluto After New Horizons" book (2021), and led the most recent analysis of the astrometry, orbits, and masses of the small satellites of Pluto (Porter & Canup 2023). Solar System Astronomy 6 false false false false false false SUPPORTED SOLAR SYSTEM DWARF-PLANET Pluto system STD=PLUTO EARTH WFC3/UVIS Imaging No No F350LP WFC3/UVIS Imaging No No F350LP WFC3/UVIS Imaging No No F350LP CELESTIAL OTHER 0.030 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. LINE false true 5 0 LINE 1 false POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 2 false Using ephemeris for target 17835-01-PLUTO Timing link suitability includes constraints ([02 After 01 by 14.0 to 1000.0 days]) The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. 1746484870000 243.51326781781552 (Tic-Visit :proposal-id 17835 :visit-id "01" :proposal-version -1 :trans-version "20240604" :date "19-Aug-2024 15:25:22.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17835 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17835 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2258 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2645 :pcs-gap 0 ) true 1 0 Using ephemeris for target 17835-02-PLUTO Timing link suitability includes constraints ([02 After 01 by 14.0 to 1000.0 days] [03 After 02 by 14.0 to 1000.0 days]) The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. 1747747201000 261.1186419767828 (Tic-Visit :proposal-id 17835 :visit-id "02" :proposal-version -1 :trans-version "20240604" :date "19-Aug-2024 15:26:16.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17835 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17835 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2258 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2645 :pcs-gap 0 ) true 1 0 Using ephemeris for target 17835-03-PLUTO Timing link suitability includes constraints ([03 After 02 by 14.0 to 1000.0 days]) The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 17835 :visit-id "03" :proposal-version -1 :trans-version "20240604" :date "19-Aug-2024 15:26:07.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17835 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17835 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2258 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2645 :pcs-gap 0 ) true 1 0