15678( 7) - 04-Mar-2019 17:58:12 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15678 Version: 7 Check-in Time: 04-Mar-2019 17:58:12 STScI Edit Number: 0 Title Comet or break-up? The physical nature of Gault's dust trail ------------------------------------------------------------------------------------ Type Cycle GO/DD 26 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Karen J. Meech University of Hawaii Y CoI: Dr. Larry Denneau University of Hawaii N CoI: Dr. Ken Smith The Queen's University of Belfast N CoI: Prof. Alan Fitzsimmons The Queen's University of Belfast N CoI: Dr. Robert Weryk University of Hawaii N CoI: Dr. Jan Kleyna University of Hawaii N CoI: Dr. Richard Wainscoat University of Hawaii N CoI: Dr. Harald Ebeling University of Hawaii N CoI: Dr. Jacqueline Keane University of Hawaii Y ------------------------------------------------------------------------------------ Abstract The past two decades have shown that the main asteroid belt contains a number of asteroids exhibiting mass loss. Main-belt comets show regular activity due to the excavation of revealed subsurface ices, either through intra-asteroid collisions which result in the explosive ejection of a debris cloud, or through rotational spin up due to thermal torques (the YORP effect) that can disrupt rubble-pile asteroids. As only some 20 such bodies have been detected so far, many physical aspects of their origin and subsequent evolution remain uncertain. On 5 January 2019 we detected a dust tail / trail associated with the 5-10 km main belt asteroid (6478) Gault in images obtained by the ATLAS project; this is only the third discovery of a dust coma around a known main-belt asteroid. Archival data from ATLAS and Pan-STARRS show the Gault tail / trail already in early December 2018, but not in images taken between 2010 and January 2018. The tail / trail has significantly changed over one month; it is not clear whether this is due to pure dynamical evolution and changes in observing geometry, or because of continuous sublimation. We propose a DD programme of WFPC3 imaging over four orbits. A two-orbit observation is requested as soon as possible to image the asteroid coma and near-asteroid dust structures at high angular resolution (about 40 km at the asteroid). The remaining two orbits would be used in February and March. Only HST will allow us to study the changing morphology of the dust structures and thus differentiate between continuous mass-loss and an impulsive event, and for the latter to decide between an impact and spin-up origin for this surprising discovery. ------------------------------------------------------------------------------------ Observations Description ------------------------ Optical imaging observations to explore the dust surrounding asteroid Gault. We request a total time baseline for observations of approximately two months, with visits spaced roughly equally, to enable robust measurements of the 15678( 7) - 04-Mar-2019 17:58:12 - [ 2] evolution of the dust structure and of the velocity of any detected fragments. While we would like to observe Gault as soon as possible, disruptive scheduling is not warranted. ------------------------------------------------------------------------------------ 15678( 7) - 04-Mar-2019 17:58:12 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: GAULT ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: ASTEROID Active asteroid ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=ASTEROID, A=2.305298349567425, E=0.1942278713804378, I=22.79993887779855 , O=183.6161875622978, W=83.12121545138562, M=33.45120536282601, EQUINOX=J2000, EPOCH=30-APR-2013:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 27 +/- 5 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 15678( 7) - 04-Mar-2019 17:58:12 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 15678( 7) - 04-Mar-2019 17:58:12 - [ 5] Visit: 01 (Visit 1-WFC3/UVIS) Visit Requirements: ORIENT 315D TO 328 D; BETWEEN 19-JAN-2019:00:00:00 AND 07-FEB-2019:00:00:00 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 GAULT WFC3/UVI ACCUM UVIS1 F350LP CR-SPLIT=NO 1 380 S POS TARG 65, 0; SEQ 1-2 S (1520 S) NON-INT; PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 GAULT WFC3/UVI ACCUM UVIS1 F350LP CR-SPLIT=NO 1 380 S (380 POS TARG 65, 0 S 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 | ------------------------------------------------------------------------------------------------------------------------------------ GAULT 1 WFC3/UVI ACCUM UVIS1 F350LP 1 none none none 1 N/A S GAULT 1 WFC3/UVI ACCUM UVIS1 F350LP 2 none none none 1 N/A S GAULT 1 WFC3/UVI ACCUM UVIS1 F350LP 3 none none none 1 N/A S GAULT 1 WFC3/UVI ACCUM UVIS1 F350LP 4 none none none 1 N/A S GAULT 2 WFC3/UVI ACCUM UVIS1 F350LP none none none none 1 N/A S 15678( 7) - 04-Mar-2019 17:58:12 - [ 6] Visit: 02 (Visit 2-WFC3/UVIS) Visit Requirements: ORIENT 2D TO 23 D; AFTER 01 BY 20 D TO 27 D; VISIBILITY INTERVAL 50 M 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 GAULT WFC3/UVI ACCUM UVIS1 F350LP CR-SPLIT=NO 1 355 S POS TARG 60, -5; SEQ 1-2 S (1420 S) NON-INT; PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 GAULT WFC3/UVI ACCUM UVIS1 F350LP CR-SPLIT=NO 1 355 S (355 POS TARG 60, -5 S 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 | ------------------------------------------------------------------------------------------------------------------------------------ GAULT 1 WFC3/UVI ACCUM UVIS1 F350LP 1 none none none 1 N/A S GAULT 1 WFC3/UVI ACCUM UVIS1 F350LP 2 none none none 1 N/A S GAULT 1 WFC3/UVI ACCUM UVIS1 F350LP 3 none none none 1 N/A S GAULT 1 WFC3/UVI ACCUM UVIS1 F350LP 4 none none none 1 N/A S GAULT 2 WFC3/UVI ACCUM UVIS1 F350LP none none none none 1 N/A S 15678( 7) - 04-Mar-2019 17:58:12 - [ 7] Visit: 03 (Visit 3-WFC3/UVIS) Visit Requirements: ORIENT 65D TO 80 D; AFTER 02 BY 20 D TO 27 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 GAULT WFC3/UVI ACCUM UVIS2 F350LP CR-SPLIT=NO 1 378 S POS TARG 55, -10; SEQ S (1512 S) 1-2 NON-INT; PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 GAULT WFC3/UVI ACCUM UVIS2 F350LP CR-SPLIT=NO 1 378 S (378 POS TARG 55, -10 S 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 | ------------------------------------------------------------------------------------------------------------------------------------ GAULT 1 WFC3/UVI ACCUM UVIS2 F350LP 1 none none none 1 N/A S GAULT 1 WFC3/UVI ACCUM UVIS2 F350LP 2 none none none 1 N/A S GAULT 1 WFC3/UVI ACCUM UVIS2 F350LP 3 none none none 1 N/A S GAULT 1 WFC3/UVI ACCUM UVIS2 F350LP 4 none none none 1 N/A S GAULT 2 WFC3/UVI ACCUM UVIS2 F350LP none none none none 1 N/A S 15678( 7) - 04-Mar-2019 17:58:12 - [ 8] Summary Form for Proposal 15678 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS1, UVIS2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 20 D TO 27 D, AFTER 02 BY 20 D TO 27 D, BETWEEN 19-JAN-2019:00:00:00 AND 07-FEB-2019:00:00:00, ORIENT 2D TO 23 D, ORIENT 315D TO 328 D, ORIENT 65D TO 80 D, PATTERN 1 1, POS TARG 55, -10, POS TARG 60, -5, POS TARG 65, 0, SEQ 1-2 NON-INT, VISIBILITY INTERVAL 50 M ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names GAULT ------------------------------------------------------------------------------------------------------------------------------------