15343( 17) - 13-Nov-2017 19:37:15 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15343 Version: 17 Check-in Time: 13-Nov-2017 19:37:15 STScI Edit Number: 0 Title Phaethon Near Earth ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. David Jewitt University of California - Los Angeles Y CoI: Max Mutchler Space Telescope Science Institute Y CoI: Dr. Jing Li University of California - Los Angeles N CoI: Dr. Jessica Agarwal Max Planck Institute for Solar System Y Research ------------------------------------------------------------------------------------ Abstract Planet-crossing asteroid (3200) Phaethon, source of the Geminid meteoroid stream, will pass close to Earth in December 2017. Observations with HST are proposed to image debris ejected from this object at 1 AU heliocentric distance, to estimate the ejection velocities as the Earth passes through the orbit plane, and to estimate the dust production rate for comparison with the rates needed to sustain the Geminid stream in steady-state. These measurements will help determine the mechanism behind the ejection of the Geminids, a long-standing puzzle. While the release of micron-sized particles (probably by thermal fracture) has been recorded at Phaethon's perihelion (0.14 AU), mass loss has never been detected otherwise, raising the puzzle of the ejection mechanism and duration. The close approach (0.07 AU) on December 17 gives a once-in-a-lifetime opportunity to observe Phaethon at high sensitivity with a resolution of a few kilometers. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose a sequence of imaging observations with WFC3 based on similar satellite-search observations of 1 Ceres (deMario et al. 2016), 4 Vesta (McFadden et al. 2012) and Pluto (e.g. Weaver et al. 2006). Phaethon will have V = 11.5 at closest approach on UT December 17. We will take short, unsaturated exposures to probe the near-nucleus environment along with long integrations in which the nucleus is allowed to saturate in order to obtain sensitivity at larger projected distances. The 2 km pixels of WFC3 (when at the minimum distance, (0.07 AU) will give marginal resolution of the 5 km diameter nucleus, although this is not a primary objective of our proposal, since the nucleus itself is already well-characterized. More usefully, we will have sufficient resolution to detect satellites to the edge of the Hill sphere of Phaethon (radius rH = 65 km, at perihelion). Scaling from deMario et al. (2016) we expect a limiting magnitude Vlim = 24 in 4s integrations in the 50 to 100 pixel (200 to 400) radius range, corresponding to object radii 8 m (at the same albedo as Phaethon). Deeper, stacked integrations will reach Vlim = 28.4 at radii > 400, corresponding to object radii 1 m. We will employ the F350LP broadband filter (a cut-off filter, with effective wavelength 6230A and full width at half maximum 4760A, when imaging a sun-like spectrum) because it conveys maximum sensitivity to faint sources. What is the relation between 15343( 17) - 13-Nov-2017 19:37:15 - [ 2] trail photometry and the mass production rate from Phaethon? The most useful metric for a linear structure is the flux density (or magnitude) per arcsecond along the trail. We convert from photometry to scattering cross-section in the usual way, assuming an albedo (0.05) for the trail particles (Agarwal et al. 2010). In this way, we can connect the photometry (per unit length of trail) to the cross-section in the same length, C, to the mass production rate. Thus we can easily detect or place valuable limits to the mass loss given observations near closest approach. The trail brightness at more usual geocentric distances 1 AU is fainter by a factor 200, or nearly 6 magnitudes. Suppression of the background is key to these observations. As with Ceres and Vesta, both about 3.5 magnitudes brighter than Phaethon, this is to be achieved by azimuthal difference imaging (ADI). This uses observations taken at different position angles in order to vary the relative locations of obscuring artifacts such as diffraction spikes, window and filter ghosts, PSF wings, and saturation/bleeding. This strategy was employed for similar Ceres observations in HST program 13503, designed by Co-I Mutchler. For this purpose, we request observations on 3 consecutive orbits, with one position angle per orbit. For the deeper full-frame images, we will place our target at the UVIS-CENTER aperture location (slightly oset from the chip gap). We will align the chip gap to be approximately perpendicular to the direction of the projected orbit of Phaethon and then rotate the position angle to achieve the background suppression. A typical sequence will consist of 180s x 3, 30s x 3 (both full frame) and 4s x 6 (partial frame, to gain readout speed) integrations. For our shortest subarray exposures, we will utilize post-flash and enforce the use of shutter blade A for greatest sensitivity and stability. We will combine images to remove cosmic rays and suppress noise and the larger obscuring artifacts mentioned above. The ADI subtraction technique requires three or more different role position angles, and these must necessarily be obtained one per orbit. Therefore, we request three orbits for this measurement. In view of the spectacular successes demonstrated with direct WFC3 imaging of Ceres, Vesta and Pluto and the unique, time-critical nature of the Phaethon fly-by, we elected to employ the tested method. The observations should be scheduled as close as is possible to plane-crossing of Phaethon, which occurs on UT 2017 December 17d 05h 44m. Geocentric distance (0.0691 AU), is also a minimum at this time. Plane-crossing gives us maximum sensitivity to extended dust structures because of projection along the line of sight, and also enables a measurement of the perpendicular extent (and ejection velocity) that is not possible otherwise. The plane angle changes by approximately 0.25 degrees per hour around plane crossing, so observations within 2 hours of plane crossing will keep the plane angles < 0.5 degrees. The geocentric distance is constant at the sub-percent level over this interval and is not an important consideration for the scheduling. ------------------------------------------------------------------------------------ 15343( 17) - 13-Nov-2017 19:37:15 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: PHAETHON ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: ASTEROID Asteroid near perihelion ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=ASTEROID, A=1.27112887628073, E=0.8899326468811029, I=22.1844138570854, O=265.3899157874748, W=322.0167282759962, M=220.5660987379586, EQUINOX=J2000, EPOCH=07-MAY-2010:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 11.3 Ephemeris Center: HUBBLE ------------------------------------------------------------------------------------------------------------------------------------ 15343( 17) - 13-Nov-2017 19:37:15 - [ 4] Visit: 01 Visit Requirements: ORIENT 52D TO 52 D; BETWEEN 17-DEC-2017:02:00:00 AND 17-DEC-2017:11:15:00; SEQ 01, 02, 03 WITHIN 3 Orbits 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 PHAETHON S/C POINTIN V1 1 1 S (1 S) POS TARG -0.2727, G -5.4941; SAA CONTOUR 29; GSPAIR NBIN000289F1NBIN000367F2 ; GS ACQ SCENARIO BASE1B3; SEQ 1-6 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 PHAETHON WFC3/UVI ACCUM UVIS-CENT F350LP 1 348 S (348 POS TARG 0, -1; NEW S ER S) OBSET; EXP PCS MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 3 PHAETHON WFC3/UVI ACCUM UVIS-CENT F350LP 1 348 S (348 POS TARG 0, -1; NEW S ER S) ALIGNMENT; EXP PCS MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 4 PHAETHON WFC3/UVI ACCUM UVIS-CENT F350LP 1 348 S (348 POS TARG 0, -1; NEW S ER S) ALIGNMENT; EXP PCS MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 5 PHAETHON WFC3/UVI ACCUM UVIS2-2K2 F350LP 3 30 S (90 NEW ALIGNMENT; EXP PCS S C-SUB S) MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 6 PHAETHON WFC3/UVI ACCUM UVIS2-M1K F350LP FLASH=12 4 4 S (16 S) NEW ALIGNMENT; EXP PCS S 1C-SUB MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHAETHON 1 S/C POINTIN V1 none none none none 1 N/A G PHAETHON 2 WFC3/UVI ACCUM UVIS-CEN F350LP none none none none 1 N/A S TER PHAETHON 3 WFC3/UVI ACCUM UVIS-CEN F350LP none none none none 1 N/A S TER PHAETHON 4 WFC3/UVI ACCUM UVIS-CEN F350LP none none none none 1 N/A S TER PHAETHON 5 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 15343( 17) - 13-Nov-2017 19:37:15 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHAETHON 5 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB PHAETHON 5 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 1 none 1 N/A S K1C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 2 none 1 N/A S K1C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 3 none 1 N/A S K1C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 4 none 1 N/A S K1C-SUB 15343( 17) - 13-Nov-2017 19:37:15 - [ 6] Visit: 02 Visit Requirements: ORIENT 20D TO 25D FROM 01; BETWEEN 17-DEC-2017:02:00:00 AND 17-DEC-2017:11:15:00 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 PHAETHON S/C POINTIN V1 1 1 S (1 S) POS TARG -0.2727, G -5.4941; SAA CONTOUR 29; GSPAIR NBI9000031F10000000000F0 ; GS ACQ SCENARIO ONEB1B3; SEQ 1-6 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 PHAETHON WFC3/UVI ACCUM UVIS-CENT F350LP 1 348 S (348 POS TARG 0, 3; NEW S ER S) OBSET; EXP PCS MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 3 PHAETHON WFC3/UVI ACCUM UVIS-CENT F350LP 1 348 S (348 POS TARG 0, 3; NEW S ER S) ALIGNMENT; EXP PCS MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 4 PHAETHON WFC3/UVI ACCUM UVIS-CENT F350LP 1 348 S (348 POS TARG 0, 3; NEW S ER S) ALIGNMENT; EXP PCS MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 5 PHAETHON WFC3/UVI ACCUM UVIS2-2K2 F350LP 3 30 S (90 NEW ALIGNMENT; EXP PCS S C-SUB S) MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 6 PHAETHON WFC3/UVI ACCUM UVIS2-M1K F350LP FLASH=12 4 4 S (16 S) NEW ALIGNMENT; EXP PCS S 1C-SUB MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHAETHON 1 S/C POINTIN V1 none none none none 1 N/A G PHAETHON 2 WFC3/UVI ACCUM UVIS-CEN F350LP none none none none 1 N/A S TER PHAETHON 3 WFC3/UVI ACCUM UVIS-CEN F350LP none none none none 1 N/A S TER PHAETHON 4 WFC3/UVI ACCUM UVIS-CEN F350LP none none none none 1 N/A S TER PHAETHON 5 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 15343( 17) - 13-Nov-2017 19:37:15 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHAETHON 5 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB PHAETHON 5 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 1 none 1 N/A S K1C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 2 none 1 N/A S K1C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 3 none 1 N/A S K1C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 4 none 1 N/A S K1C-SUB 15343( 17) - 13-Nov-2017 19:37:15 - [ 8] Visit: 03 Visit Requirements: ORIENT 40D TO 45D FROM 01; BETWEEN 17-DEC-2017:02:00:00 AND 17-DEC-2017:11:15:00 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 PHAETHON S/C POINTIN V1 1 1 S (1 S) POS TARG -0.2727, G -5.4941; SAA CONTOUR 29; GSPAIR NBI8000275F20000000000F0 ; GS ACQ SCENARIO ONEB1B3; SEQ 1-6 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 PHAETHON WFC3/UVI ACCUM UVIS-CENT F350LP 1 348 S (348 POS TARG 0, -1; NEW S ER S) OBSET; EXP PCS MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 3 PHAETHON WFC3/UVI ACCUM UVIS-CENT F350LP 1 348 S (348 POS TARG 0, -1; NEW S ER S) ALIGNMENT; EXP PCS MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 4 PHAETHON WFC3/UVI ACCUM UVIS-CENT F350LP 1 348 S (348 POS TARG 0, -1; NEW S ER S) ALIGNMENT; EXP PCS MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 5 PHAETHON WFC3/UVI ACCUM UVIS2-2K2 F350LP 3 30 S (90 NEW ALIGNMENT; EXP PCS S C-SUB S) MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 6 PHAETHON WFC3/UVI ACCUM UVIS2-M1K F350LP FLASH=12 4 4 S (16 S) NEW ALIGNMENT; EXP PCS S 1C-SUB MODE GYRO ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHAETHON 1 S/C POINTIN V1 none none none none 1 N/A G PHAETHON 2 WFC3/UVI ACCUM UVIS-CEN F350LP none none none none 1 N/A S TER PHAETHON 3 WFC3/UVI ACCUM UVIS-CEN F350LP none none none none 1 N/A S TER PHAETHON 4 WFC3/UVI ACCUM UVIS-CEN F350LP none none none none 1 N/A S TER PHAETHON 5 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 15343( 17) - 13-Nov-2017 19:37:15 - [ 9] 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHAETHON 5 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB PHAETHON 5 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 1 none 1 N/A S K1C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 2 none 1 N/A S K1C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 3 none 1 N/A S K1C-SUB PHAETHON 6 WFC3/UVI ACCUM UVIS2-M1 F350LP none none 4 none 1 N/A S K1C-SUB 15343( 17) - 13-Nov-2017 19:37:15 - [ 10] Summary Form for Proposal 15343 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS-CENTER, UVIS2-2K2C-SUB, UVIS2-M1K1C-SUB, V1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations S/C, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, POINTING ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=12 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 17-DEC-2017:02:00:00 AND 17-DEC-2017:11:15:00, EXP PCS MODE GYRO, GS ACQ SCENARIO BASE1B3, GS ACQ SCENARIO ONEB1B3, GSPAIR NBI8000275F20000000000F0, GSPAIR NBI9000031F10000000000F0, GSPAIR NBIN000289F1NBIN000367F2, NEW ALIGNMENT, NEW OBSET, ORIENT 20D TO 25D FROM 01, ORIENT 40D TO 45D FROM 01, ORIENT 52D TO 52 D, POS TARG -0.2727, -5.4941, POS TARG 0, -1, POS TARG 0, 3, SAA CONTOUR 29, SEQ 01, 02, 03 WITHIN 3 Orbits, SEQ 1-6 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names PHAETHON ------------------------------------------------------------------------------------------------------------------------------------