18215( 4) - 18-Nov-2025 15:56:51 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18215 Version: 4 Check-in Time: 18-Nov-2025 15:56:51 STScI Edit Number: 3 Title Supporting the JUICE mission through HST astrometry of Kallichore ------------------------------------------------------------------------------------ Type Cycle GO/DD 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Juan Luis Rizos Instituto de Astrofisica de Andalucia Y (IAA) CoI: Dr. Benjamin Proudfoot University of Central Florida Board of Y Trustees CoI: Dr. Simon Bernard Porter Southwest Research Institute N CoI: Prof. Jose Maria Gomez-Limon Instituto de Astrofisica de Andalucia N Gallardo (IAA) CoI: Alvaro Alvarez-Candal Instituto de Astrofisica de Andalucia N (IAA) CoI: Dr. Altair Ramos Gomes-Junior Universidade Federal de Uberlandia N CoI: Prof. Luisa Maria Lara Instituto de Astrofisica de Andalucia N (IAA) CoI: Dr. Olivier Witasse European Space Agency - ESTEC N CoI: Dr. Paul Hartogh Max Planck Institute for Solar System N Research ------------------------------------------------------------------------------------ Abstract Kallichore (Jupiter XLIV) is a faint irregular satellite of Jupiter and the closest of the outer moons to the nominal JUICE trajectory. Refining its poorly constrained orbit is essential to assess the feasibility of a potential close JUICE flyby. On December 15, 2025, Kallichore will occult a relatively bright star along a well-placed ground track across Europe. We request two single-orbit HST/WFC3-UVIS visits to obtain high-precision astrometry of Kallichore in the days preceding this event. These observations will reduce the predicted shadow-path uncertainty from hundreds to a few tens of kilometers, enabling a coordinated ground-based campaign and providing key input for JUICE navigation and mission planning. Moreover, the ultra-precise astrometry will further improve our understanding of the dynamical evolution and physical properties of Jupiter's irregular satellites. ------------------------------------------------------------------------------------ Observations Description ------------------------ We request two single-orbit visits with WFC3/UVIS, scheduled for November 30 and December 4, 2025, separated by four days to maximize temporal coverage. Each visit will obtain eight 97-s exposures using the UVIS2-2K2C-SUB aperture and the F606W filter, selected for its combination of high throughput and well-characterized PSF. Observations will be executed in non-sidereal tracking mode, following the predicted motion of Kallichore. A box-dither pattern will be applied between exposures to improve PSF sampling and mitigate detector artifacts. Simulations with the HST Exposure Time Calculator (G2V spectrum, high background) indicate an SNR > 14 per frame, including a post-flash level of 17 18215( 4) - 18-Nov-2025 15:56:51 - [ 2] electrons to mitigate charge-transfer efficiency losses. We verified with the HST Exposure Time Calculator that stars fainter than magnitude 17 will not be saturated. The fields include at least three non-saturated Gaia DR3 stars suitable for differential astrometry. ------------------------------------------------------------------------------------ 18215( 4) - 18-Nov-2025 15:56:51 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: KALLICHORE ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE irregular ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=JUPITER STD=KALLICHORE ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS NOT OCC OF KALLICHORE BY JUPITER FROM EARTH, SEP OF KALLICHORE IO FROM EARTH GT 10", SEP OF KALLICHORE EUROPA FROM EARTH GT 10", SEP OF KALLICHORE GANYMEDE FROM EARTH GT 10", SEP OF KALLICHORE CALLISTO FROM EARTH GT 10" ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 23.6 The V-magnitude flux was obtained from the Minor Planet Center's Natural Satellites Ephemeris Service. From November 27, 2025 onward, the flux is below 23.6. Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ 18215( 4) - 18-Nov-2025 15:56:51 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 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 ------------------------------------------------------------------------------------------------------------------------------------ 18215( 4) - 18-Nov-2025 15:56:51 - [ 5] Visit: 01 Visit Requirements: 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 KALLICHORE WFC3/UVI ACCUM UVIS2-2K2 F606W FLASH=17 1 97 S (388 PATTERN 1 1 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 KALLICHORE WFC3/UVI ACCUM UVIS2-2K2 F606W FLASH=17 1 97 S (388 PATTERN 1 2 S C-SUB 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 | ------------------------------------------------------------------------------------------------------------------------------------ KALLICHORE 1 WFC3/UVI ACCUM UVIS2-2K F606W 1 none none none 1 N/A S 2C-SUB KALLICHORE 1 WFC3/UVI ACCUM UVIS2-2K F606W 2 none none none 1 N/A S 2C-SUB KALLICHORE 1 WFC3/UVI ACCUM UVIS2-2K F606W 3 none none none 1 N/A S 2C-SUB KALLICHORE 1 WFC3/UVI ACCUM UVIS2-2K F606W 4 none none none 1 N/A S 2C-SUB KALLICHORE 2 WFC3/UVI ACCUM UVIS2-2K F606W 1 none none none 1 N/A S 2C-SUB KALLICHORE 2 WFC3/UVI ACCUM UVIS2-2K F606W 2 none none none 1 N/A S 2C-SUB KALLICHORE 2 WFC3/UVI ACCUM UVIS2-2K F606W 3 none none none 1 N/A S 2C-SUB KALLICHORE 2 WFC3/UVI ACCUM UVIS2-2K F606W 4 none none none 1 N/A S 2C-SUB 18215( 4) - 18-Nov-2025 15:56:51 - [ 6] Visit: 02 Visit Requirements: BETWEEN 2025.339:04:40:00 AND 2025.339:05:50:00; 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 KALLICHORE WFC3/UVI ACCUM UVIS2-2K2 F606W FLASH=17 1 97 S (388 SEQ 1-2 NON-INT; PATTERN S C-SUB S) 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 KALLICHORE WFC3/UVI ACCUM UVIS2-2K2 F606W FLASH=17 1 97 S (388 PATTERN 1 2 S C-SUB 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 | ------------------------------------------------------------------------------------------------------------------------------------ KALLICHORE 1 WFC3/UVI ACCUM UVIS2-2K F606W 1 none none none 1 N/A S 2C-SUB KALLICHORE 1 WFC3/UVI ACCUM UVIS2-2K F606W 2 none none none 1 N/A S 2C-SUB KALLICHORE 1 WFC3/UVI ACCUM UVIS2-2K F606W 3 none none none 1 N/A S 2C-SUB KALLICHORE 1 WFC3/UVI ACCUM UVIS2-2K F606W 4 none none none 1 N/A S 2C-SUB KALLICHORE 2 WFC3/UVI ACCUM UVIS2-2K F606W 1 none none none 1 N/A S 2C-SUB KALLICHORE 2 WFC3/UVI ACCUM UVIS2-2K F606W 2 none none none 1 N/A S 2C-SUB KALLICHORE 2 WFC3/UVI ACCUM UVIS2-2K F606W 3 none none none 1 N/A S 2C-SUB KALLICHORE 2 WFC3/UVI ACCUM UVIS2-2K F606W 4 none none none 1 N/A S 2C-SUB 18215( 4) - 18-Nov-2025 15:56:51 - [ 7] Summary Form for Proposal 18215 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-2K2C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=17 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 2025.339:04:40:00 AND 2025.339:05:50:00, PATTERN 1 1, PATTERN 1 2, SEQ 1-2 NON-INT, VISIBILITY INTERVAL NO GYRO BIAS UPDATE ON MOVING TARGET ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names KALLICHORE ------------------------------------------------------------------------------------------------------------------------------------