18071( 4) - 28-Aug-2025 14:40:12 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18071 Version: 4 Check-in Time: 28-Aug-2025 14:40:12 STScI Edit Number: 0 Title Confirming distantly-active long period comets on retrograde orbits beyond 20 au ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Bryce Bolin Eureka Scientific Inc. Y CoI: Dr. James M Bauer University of Maryland N CoI: Dr. Christine Chen The Johns Hopkins University N CoI: Dr. Yanga Fernandez University of Central Florida Board of N Trustees CoI: Dr. Dean C. Hines Space Telescope Science Institute N CoI: Laura-May Abron Griffith Observatory N CoI: Dr. Carey Michael Lisse The Johns Hopkins University Applied N Physics Laboratory CoI: Prof. Alessandro Morbidelli Observatoire de la Cote d'Azur N CoI: Dr. Keith S. Noll NASA Goddard Space Flight Center N CoI: Dr. Ian Wong Space Telescope Science Institute N CoI: Dr. Ludmilla Kolokolova University of Maryland N ------------------------------------------------------------------------------------ Abstract The vast majority of comets show maximum amounts of activity when they cross the ice sublimation line between 4-5 au. Bodies that show activity beyond the ice sublimation line are thought to be driven by the sublimation of hypervolatiles such as CO2 and CO, which begin to sublimate well beyond 10 au. Recently, a class of objects known as distantly active comets, such as long-period comets C/2017 K2 and C/2014 UN271, and Centaur 95P/Chiron, have shown activity well beyond this distance, strongly supporting the hypervolatile activity hypothesis. However, additional examples of distantly active comets are rare. In this proposal, we have identified two candidate comets located more than ~20 au from the Sun and show evidence of being active by having significant non-gravitational accelerations. We propose to use the exceptional sensitivity and angular resolution of HST/WFC3 to test or set stringent limits on the activity of two distantly active comet candidates, (336756) 2010 NV1 and (523797) 2016 NM56. Our observations will test these candidate comets' activity by using the high sensitivity and resolution of HST to constrain their extendedness relative to point sources and mass loss below the limit implied by their non-gravitational accelerations. By testing these candidates for distant activity, we will dramatically increase the sample of distantly active comets, which will be used to test the predictions of planet formation models used to describe the formation and early evolution of cometary bodies in the solar system. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will acquire images in the F350LP filter for a maximum throughput of a Solar-like source, which is expected for our targets. Each visit will consist of six 320-s exposures using the F350LP filter and the UVIS2-C1K1C-SUB detector setup for a total integration time of 1920 s. The UVIS2-C1K1C-SUB is used 18071( 4) - 28-Aug-2025 14:40:12 - [ 2] because it provides a field of view large enough to contain our targets, which all have ephemeris uncertainties of less than 1 arcsec and have a low data volume to allow us to take six exposures without a serial dump penalty. Each of our visits will only consist of a single orbit. Therefore, we will not need to use a gyro bias update. The F350LP filter provides the maximum throughput enabled by WFC3/UVIS in the 300 nm - 800 nm wavelength range for a Solar-like source expected of solar system objects while allowing for a 0.04 pixel scale. We will use the methodology of Jewitt et al. 2020 for color calibrations of the F350LP filter observations. We will use line dithering to reduce the noise from flat-field calibration errors, cosmic rays, and residual images. ------------------------------------------------------------------------------------ 18071( 4) - 28-Aug-2025 14:40:12 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: 336756 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET distant comet ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=9.418643768523664, E=0.969512448983736, I=140.8078454726423 , O=136.1979282539766, W=132.9680938874039, T=14-DEC-2010:12:00:53, TTimeScale=TDB, EQUINOX=J2000, EPOCH=22-JUN-2013:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 24.8 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 TARGET NAME: 523797 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET distant comet ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=10.52698864463187, E=0.8578637261172851, I=144.0483239884555 , O=350.0186370149513, W=345.6683665580405, T=14-OCT-2015:02:49:09, TTimeScale=TDB, EQUINOX=J2000, EPOCH=22-NOV-2015:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 24.4 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 18071( 4) - 28-Aug-2025 14:40:12 - [ 4] Visit: 01 (336756_Visit_1) Visit Requirements: BETWEEN 05-FEB-2026:18:00:00 AND 06-FEB-2026:18:00:00; BETWEEN 08-FEB-2026:00:00:00 AND 11-FEB-2026:18:00:00; BETWEEN 12-FEB-2026:12:00:00 AND 16-FEB-2026:00:00:00; BETWEEN 17-FEB-2026:06:00:00 AND 18-FEB-2026:06:00:00; BETWEEN 19-FEB-2026:18:00:00 AND 24-FEB-2026:00:00:00; 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 336756 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG 0.1, 0.1 S 1C-SUB see below (311 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 336756 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG -0.5, 0.3 S 1C-SUB see below (311 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 336756 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG -0.2, 0.1 S 1C-SUB see below (311 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 336756 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG 0.2, -0.2 S 1C-SUB see below (311 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 336756 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG 0.2, 0.2 S 1C-SUB see below (311 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 336756 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG -0.1, 0.1 S 1C-SUB see below (311 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 | ------------------------------------------------------------------------------------------------------------------------------------ 336756 1 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 336756 2 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 336756 3 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 336756 4 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 18071( 4) - 28-Aug-2025 14:40:12 - [ 5] 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 | ------------------------------------------------------------------------------------------------------------------------------------ 336756 5 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 336756 6 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 18071( 4) - 28-Aug-2025 14:40:12 - [ 6] Visit: 02 (523797_Visit_1) Visit Requirements: BETWEEN 04-MAR-2026:00:00:00 AND 06-MAR-2026:06:00:00; BETWEEN 06-MAR-2026:12:00:00 AND 08-MAR-2026:12:00:00; BETWEEN 08-MAR-2026:18:00:00 AND 09-MAR-2026:18:00:00; BETWEEN 10-MAR-2026:06:00:00 AND 11-MAR-2026:06:00:00; BETWEEN 12-MAR-2026:00:00:00 AND 12-MAR-2026:12:00:00; BETWEEN 16-MAR-2026:06:00:00 AND 17-MAR-2026:12:00:00; 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 523797 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG -0.5, 0.3 S 1C-SUB see below (311 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 523797 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG -0.2, 0.1 S 1C-SUB see below (311 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 523797 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG 0.2, -0.2 S 1C-SUB see below (311 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 523797 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG 0.2, 0.2 S 1C-SUB see below (311 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 523797 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG -0.1, 0.1 S 1C-SUB see below (311 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 523797 WFC3/UVI ACCUM UVIS2-C1K F350LP 1 240 S POS TARG 0.1, 0.1 S 1C-SUB see below (311 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 | ------------------------------------------------------------------------------------------------------------------------------------ 523797 1 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 523797 2 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 523797 3 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 523797 4 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 18071( 4) - 28-Aug-2025 14:40:12 - [ 7] 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 | ------------------------------------------------------------------------------------------------------------------------------------ 523797 5 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 523797 6 WFC3/UVI ACCUM UVIS2-C1 F350LP none none none none 1 311.0 S S K1C-SUB 18071( 4) - 28-Aug-2025 14:40:12 - [ 8] Summary Form for Proposal 18071 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C1K1C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 04-MAR-2026:00:00:00 AND 06-MAR-2026:06:00:00, BETWEEN 05-FEB-2026:18:00:00 AND 06-FEB-2026:18:00:00, BETWEEN 06-MAR-2026:12:00:00 AND 08-MAR-2026:12:00:00, BETWEEN 08-FEB-2026:00:00:00 AND 11-FEB-2026:18:00:00, BETWEEN 08-MAR-2026:18:00:00 AND 09-MAR-2026:18:00:00, BETWEEN 10-MAR-2026:06:00:00 AND 11-MAR-2026:06:00:00, BETWEEN 12-FEB-2026:12:00:00 AND 16-FEB-2026:00:00:00, BETWEEN 12-MAR-2026:00:00:00 AND 12-MAR-2026:12:00:00, BETWEEN 16-MAR-2026:06:00:00 AND 17-MAR-2026:12:00:00, BETWEEN 17-FEB-2026:06:00:00 AND 18-FEB-2026:06:00:00, BETWEEN 19-FEB-2026:18:00:00 AND 24-FEB-2026:00:00:00, POS TARG -0.1, 0.1, POS TARG -0.2, 0.1, POS TARG -0.5, 0.3, POS TARG 0.1, 0.1, POS TARG 0.2, -0.2, POS TARG 0.2, 0.2, VISIBILITY INTERVAL NO GYRO BIAS UPDATE ON MOVING TARGET ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names 336756, 523797 ------------------------------------------------------------------------------------------------------------------------------------