18364( 2) - 14-Aug-2026 11:48:50 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18364 Version: 2 Check-in Time: 14-Aug-2026 11:48:50 STScI Edit Number: 0 Title Testing the Collision-Color-Satellite Connection in the Trojans ------------------------------------------------------------------------------------ Type Cycle GO 34 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Keith S. Noll Planetary Science Institute Y CoI: Dr. Ian Wong Space Telescope Science Institute N ------------------------------------------------------------------------------------ Abstract Large asteroids with small satellites are frequently associated with collisional families. Among the Trojans the Eurybates family is the largest of only six known families. (3548) Eurybates, the largest member of this family, is the first Trojan target of the Lucy Discovery mission. Eurybates also has a satellite and, intriguingly, is a spectrally neutral C-type in a population where more than 90% are redder P- or D-type objects. C-type collisional family asteroids with satellites are known in the Main Belt where C-types are common. But with just a single example of the apparent connection between collisions, satellite formation and unusual color in the Trojans, it is difficult to reach a conclusion about the causal nature of these correlated properties. However, there are two ideal candidates for testing this correlation - the C-type Trojan asteroids (4709) Ennomos and (9799) Thronium - both have recently been shown to have collisional families and both are less-red than the vast majority of Trojans. By using HST to search for satellites, we propose to test the hypothesis that all three properties are causally related. If satellites are found, the likelihood of chance correlation is significantly reduced. Identifying the processes at work as "normal" will enhance the value of the upcoming Lucy encounter with Eurybates by allowing discoveries in that system to be extrapolated to other objects and populations. If no satellites are identified, we will tighten constraints on the outcomes and subsequent evolution of collisional processing in the Trojans. ------------------------------------------------------------------------------------ Observations Description ------------------------ This proposal will execute two visits each to two Trojan asteroid that are possible analogs to Eurybates. Both are largest members of collisional families and both are unusually neutral in color, like Eurybates. Each visit will have six exposures in the F350LP filter to go as deep as possible in order to search for satellites that might have resulted from the family forming collision. The two visits for each object will be separated by a minimum time calculated to give even very wide possible satellites enough time to have moved at least 1/4 of an orbit to improve the chance of detection at at least one epoch. A line dither pattern will be used with an offset between each iteration of the dither to achieve sub pixel dithering. 18364( 2) - 14-Aug-2026 11:48:50 - [ 2] ------------------------------------------------------------------------------------ 18364( 2) - 14-Aug-2026 11:48:50 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: ENNOMOS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: ASTEROID Trojan Asteroid (4709) Ennomos ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=ASTEROID, A=5.274586528852086, E=0.02264257597954345, I=25.41386995274401, O=253.0588450054122, W=83.67865706597865, M=92.72663675193036, EQUINOX=J2000, EPOCH=09-JUN-2026:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 16.0 +/- 0.3 Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 TARGET NAME: THRONIUM ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: ASTEROID Trojan Asteroid (9799) Thronium ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=ASTEROID, A=5.191110558168659, E=0.04685583179040113, I=30.51270344780228, O=259.5593137497432, W=115.3240300704947, M=159.6742252254411, EQUINOX=J2000, EPOCH=09-JUN-2026:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 17.2 +/- 0.3 Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ 18364( 2) - 14-Aug-2026 11:48:50 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE-3PT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.135 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18364( 2) - 14-Aug-2026 11:48:50 - [ 5] Visit: 01 Visit Requirements: BETWEEN 30-SEP-2026:00:00:00 AND 26-FEB-2027:00:00:00 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 ENNOMOS WFC3/UVI ACCUM UVIS2-C51 F350LP 2 350 S SEQ 1 NON-INT; PATTERN 1 S 2C-SUB (2100 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 | ------------------------------------------------------------------------------------------------------------------------------------ ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 1 none 1 none 1 N/A S 12C-SUB ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 1 none 2 none 1 N/A S 12C-SUB ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 2 none 1 none 1 N/A S 12C-SUB ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 2 none 2 none 1 N/A S 12C-SUB ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 3 none 1 none 1 N/A S 12C-SUB ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 3 none 2 none 1 N/A S 12C-SUB 18364( 2) - 14-Aug-2026 11:48:50 - [ 6] Visit: 02 Visit Requirements: AFTER 01 BY 12 D TO 120 D 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 ENNOMOS WFC3/UVI ACCUM UVIS2-C51 F350LP 2 350 S SEQ 1 NON-INT; PATTERN 1 S 2C-SUB (2100 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 | ------------------------------------------------------------------------------------------------------------------------------------ ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 1 none 1 none 1 N/A S 12C-SUB ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 1 none 2 none 1 N/A S 12C-SUB ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 2 none 1 none 1 N/A S 12C-SUB ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 2 none 2 none 1 N/A S 12C-SUB ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 3 none 1 none 1 N/A S 12C-SUB ENNOMOS 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 3 none 2 none 1 N/A S 12C-SUB 18364( 2) - 14-Aug-2026 11:48:50 - [ 7] Visit: 11 Visit Requirements: BETWEEN 11-JAN-2027:00:00:00 AND 02-JUL-2027:00:00:00 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 THRONIUM WFC3/UVI ACCUM UVIS2-C51 F350LP 2 350 S SEQ 1 NON-INT; PATTERN 1 S 2C-SUB (2100 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 | ------------------------------------------------------------------------------------------------------------------------------------ THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 1 none 1 none 1 N/A S 12C-SUB THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 1 none 2 none 1 N/A S 12C-SUB THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 2 none 1 none 1 N/A S 12C-SUB THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 2 none 2 none 1 N/A S 12C-SUB THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 3 none 1 none 1 N/A S 12C-SUB THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 3 none 2 none 1 N/A S 12C-SUB 18364( 2) - 14-Aug-2026 11:48:50 - [ 8] Visit: 12 Visit Requirements: AFTER 11 BY 20 D TO 120 D 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 THRONIUM WFC3/UVI ACCUM UVIS2-C51 F350LP 2 350 S SEQ 1 NON-INT; PATTERN 1 S 2C-SUB (2100 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 | ------------------------------------------------------------------------------------------------------------------------------------ THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 1 none 1 none 1 N/A S 12C-SUB THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 1 none 2 none 1 N/A S 12C-SUB THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 2 none 1 none 1 N/A S 12C-SUB THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 2 none 2 none 1 N/A S 12C-SUB THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 3 none 1 none 1 N/A S 12C-SUB THRONIUM 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 3 none 2 none 1 N/A S 12C-SUB 18364( 2) - 14-Aug-2026 11:48:50 - [ 9] Summary Form for Proposal 18364 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C512C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 12 D TO 120 D, AFTER 11 BY 20 D TO 120 D, BETWEEN 11-JAN-2027:00:00:00 AND 02-JUL-2027:00:00:00, BETWEEN 30-SEP-2026:00:00:00 AND 26-FEB-2027:00:00:00, PATTERN 1 1, SEQ 1 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names ENNOMOS, THRONIUM ------------------------------------------------------------------------------------------------------------------------------------