12053( 5) - 21-Jan-2010 13:09:35 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12053 Version: 5 Check-in Time: 21-Jan-2010 13:09:35 STScI Edit Number: 0 Title Hubble Investigation of the Unusual Object P/2010 A2 ------------------------------------------------------------------------------------ Type Cycle GO/DD 17 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. David Jewitt University of California - Los Angeles CoI: Dr. Harold A. Weaver The Johns Hopkins University Applied N Physics Laboratory CoI: Dr. Michal Drahus University of California - Los Angeles N CoI: Mr. Max Mutchler Space Telescope Science Institute Y ------------------------------------------------------------------------------------ Abstract On 2010 January 6, the LINEAR survey telescope detected an extremely unusual-looking object (P/2010 A2) that appears to be either: (1) the most remarkable member of a new dynamical class known as the main-belt comets (MBCs), or (2) a manifestation of a collision between two asteroids in the Flora family. In either case, this discovery could have profound implications for planetary science. We propose a 5-orbit Hubble investigation of P/2010 A2, executed within the next week if possible, to determine the nature of this strange, quickly-evolving object. Deep WFC3 (or ACS/WFC) images taken over a 6 hr period will be used to measure the size, shape, and rotational period of the nucleus, to characterize the near-nucleus environment, and to perform a deep search for any decameter-sized fragments. We will also measure the color of the nucleus in 3 different bands for comparison with asteroids and other cometary nuclei. With its high spatial resolution and high sensitivity, Hubble is uniquely suited to this investigation. ------------------------------------------------------------------------------------ Observations Description ------------------------ At its declination of +28 , P/2010 A2 will have an HST visibility window of 54 min per orbit. We are working closely with the JPL Horizons group to ensure we have knowledge of the object?s ephemeris to an accuracy of 10??, or better, for the HST observations, which is more than adequate for planning these imaging observations. (The WFC3 has a field-ofview of 162?? ? 162??, and the ACS/WFC has a field-of-view of 202?? ? 202??.) At the time of the Hubble observations, the object?s heliocentric distance will be 1.9 AU, the geocentric distance will be 1 AU (corresponding to 29 km/pixel at the comet for the WFC3), the solar elongation angle will be 160?, the solar phase angle will be 10?, and the 12053( 5) - 21-Jan-2010 13:09:35 - [ 2] galactic latitude (which aects the level of background star contamination) will be 13?. All of these geometric parameters are currently favorable for Hubble observations, but the conditions get progressively worse over time. The target?s apparent rate of motion is 35??/hr, which is easily within Hubble?s tracking capabilities. This rate of motion is also slow enough to keep a single pair of guide stars within the FGS pickles for an entire visibility window. This program requires both high spatial resolution and high sensitivity. The former drives us to the WFC3 (0.??4/pix vs 0.??5/pix), but the latter argues for use of the ACS/WFC3 (with 2x the throughput at visible wavelengths). We have tentatively selected WFC3 for this submission (partly because of its higher spatial resolution and partly because we figure the degraded CTE and increased noise of the ACS/WFC might negate some of its perceived advantage in sensitivity), but we plan to consult with the relevant STScI experts before making a final decision on which camera to use for this investigation. We request 5 consecutive orbits utilizing the newly commissioned WFC3. Our choice of 5 orbits is a compromise between the desire to characterize the temporal evolution of the object and the need to minimize the impact on Hubble?s observing schedule. Our planned observations would cover a clock time of 6 hours, which should be sufficient to include an entire sinusoid of a dual-peaked light curve for a ?typical? rotational period of 12 hours. During orbits #1, #3, and #5, we tentatively plan to take images in 3 different filters (here we assume WFC3): F390W (or possibly F475W), F606W, and F814W. Orbits #2 and #4 will be used entirely for F606W. This strategy balances our attempt to go as deep as possible, yet also obtain some color information for comparison with previously observed asteroids and cometary nuclei. Our nominal observing strategy will be to use a standard 2-point dither, taking a series of images (e.g., 1-2 long F606W images and 1 long exposure each using F390W and F814W) at one location near the center of one of the CCD chips, and an identical series at the second dither location. Dithering mitigates the effects of bad pixels and cosmic ray events. We will shift and add the resultant images, reaching a limiting magnitude (S/N5) of V 27.5 for the F606W images, as determined from the WFC3 ETC assuming a total exposure 12053( 5) - 21-Jan-2010 13:09:35 - [ 3] time of 2000 sec and a solar-type spectrum. This latter limit corresponds to an object having a diameter of 25-30 m, assuming an albedo of 10% and a phase law of 0.04 mag/deg. For the F390W and F814W filters, we only require reaching S/N10 for V 24, which can be accomplished using exposure times of 320 sec and 120 sec, respectively. We expect to use exposure times of at least 347 sec for all of our images to ?hide? the overhead associated with dumping the data storage buffer. We understand that we will have essentially no control over the spacecraft roll angle, which means we won?t be able to optimize the orientation of the dust tail on the CCD (i.e., to orient the tail along the longest dimension of the detector). The field-of-view of the camera is large enough that we should obtain excellent data on a portion of the tail, no matter what spacecraft roll angle is used. The proposed observing plan features the following properties: We will probe the spectral properties of the main component; these include the spectral slope between the F390W and F606W bands, and the prominent silicate absorption band in F814W ? a signature of S-type asteroids. A sensitive search for fragments in F606W. Mitigation of the brightness modulation from the body rotation; this eect will be largely averaged-out if we change filters in the suggested manner. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- Observations at the earliest opportunity, possibly next week, are highly desired, since material in P/2010 A2 is dispersing and fading. We request that observations be taken no later than the end of January in order to connect the HST-observed morphology with the initial morphology obtained from the ground (albeit at 10 times poorer resolution). ------------------------------------------------------------------------------------ 12053( 5) - 21-Jan-2010 13:09:35 - [ 4] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: P2010-A2 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET Main-belt comet or collision between two asteroids ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=2.0112975, E=0.1231870, I=5.28995, O=320.13138, W=133.28380, T=04-DEC-2009:07:05:09, EQUINOX=J2000, EPOCH=25-NOV-2009:00:00:00 ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 24 +/- 1 Ephemeris Center: EARTH Ephemeris Uncertainty: 7250 KM Acquisition Uncertainty: 10 " ------------------------------------------------------------------------------------------------------------------------------------ 12053( 5) - 21-Jan-2010 13:09:35 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: duplicate of visit 11 to see if it can go earlier than day 29. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F606W CR-SPLIT=NO 1 537 S REQ EPHEM CORR PA2V01 S ------------------------------------------------------------------------------------------------------------------------------------ 2 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F814W CR-SPLIT=NO 1 537 S REQ EPHEM CORR PA2V01 S ------------------------------------------------------------------------------------------------------------------------------------ 3 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F814W CR-SPLIT=NO 1 537 S POS TARG 0.2, 0.2; REQ S EPHEM CORR PA2V01 ------------------------------------------------------------------------------------------------------------------------------------ 4 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F606W CR-SPLIT=NO 1 537 S POS TARG 0.2, 0.2; REQ S EPHEM CORR PA2V01 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ P2010-A2 1 WFC3/UVI ACCUM UVIS1-FI F606W none none none none 1 N/A S X P2010-A2 2 WFC3/UVI ACCUM UVIS1-FI F814W none none none none 1 N/A S X P2010-A2 3 WFC3/UVI ACCUM UVIS1-FI F814W none none none none 1 N/A S X P2010-A2 4 WFC3/UVI ACCUM UVIS1-FI F606W none none none none 1 N/A S X 12053( 5) - 21-Jan-2010 13:09:35 - [ 6] Visit: 11 Visit Requirements: 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| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F606W CR-SPLIT=NO 1 537 S REQ EPHEM CORR PA2V11 S ------------------------------------------------------------------------------------------------------------------------------------ 2 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F814W CR-SPLIT=NO 1 537 S REQ EPHEM CORR PA2V11 S ------------------------------------------------------------------------------------------------------------------------------------ 3 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F814W CR-SPLIT=NO 1 537 S POS TARG 0.2, 0.2; REQ S EPHEM CORR PA2V11 ------------------------------------------------------------------------------------------------------------------------------------ 4 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F606W CR-SPLIT=NO 1 537 S POS TARG 0.2, 0.2; REQ S EPHEM CORR PA2V11 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ P2010-A2 1 WFC3/UVI ACCUM UVIS1-FI F606W none none none none 1 N/A S X P2010-A2 2 WFC3/UVI ACCUM UVIS1-FI F814W none none none none 1 N/A S X P2010-A2 3 WFC3/UVI ACCUM UVIS1-FI F814W none none none none 1 N/A S X P2010-A2 4 WFC3/UVI ACCUM UVIS1-FI F606W none none none none 1 N/A S X 12053( 5) - 21-Jan-2010 13:09:35 - [ 7] Visit: 12 Visit Requirements: 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| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F606W CR-SPLIT=NO 1 537 S REQ EPHEM CORR PA2V12 S ------------------------------------------------------------------------------------------------------------------------------------ 2 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F814W CR-SPLIT=NO 1 537 S REQ EPHEM CORR PA2V12 S ------------------------------------------------------------------------------------------------------------------------------------ 3 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F814W CR-SPLIT=NO 1 537 S POS TARG 0.2, 0.2; REQ S EPHEM CORR PA2V12 ------------------------------------------------------------------------------------------------------------------------------------ 4 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F606W CR-SPLIT=NO 1 537 S POS TARG 0.2, 0.2; REQ S EPHEM CORR PA2V12 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ P2010-A2 1 WFC3/UVI ACCUM UVIS1-FI F606W none none none none 1 N/A S X P2010-A2 2 WFC3/UVI ACCUM UVIS1-FI F814W none none none none 1 N/A S X P2010-A2 3 WFC3/UVI ACCUM UVIS1-FI F814W none none none none 1 N/A S X P2010-A2 4 WFC3/UVI ACCUM UVIS1-FI F606W none none none none 1 N/A S X 12053( 5) - 21-Jan-2010 13:09:35 - [ 8] Visit: 13 Visit Requirements: 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| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F606W CR-SPLIT=NO 1 537 S REQ EPHEM CORR PA2V13 S ------------------------------------------------------------------------------------------------------------------------------------ 2 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F814W CR-SPLIT=NO 1 537 S REQ EPHEM CORR PA2V13 S ------------------------------------------------------------------------------------------------------------------------------------ 3 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F814W CR-SPLIT=NO 1 537 S POS TARG 0.2, 0.2; REQ S EPHEM CORR PA2V13 ------------------------------------------------------------------------------------------------------------------------------------ 4 P2010-A2 WFC3/UVI ACCUM UVIS1-FIX F606W CR-SPLIT=NO 1 537 S POS TARG 0.2, 0.2; REQ S EPHEM CORR PA2V13 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ P2010-A2 1 WFC3/UVI ACCUM UVIS1-FI F606W none none none none 1 N/A S X P2010-A2 2 WFC3/UVI ACCUM UVIS1-FI F814W none none none none 1 N/A S X P2010-A2 3 WFC3/UVI ACCUM UVIS1-FI F814W none none none none 1 N/A S X P2010-A2 4 WFC3/UVI ACCUM UVIS1-FI F606W none none none none 1 N/A S X 12053( 5) - 21-Jan-2010 13:09:35 - [ 9] Summary Form for Proposal 12053 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG 0.2, 0.2, REQ EPHEM CORR PA2V01, REQ EPHEM CORR PA2V11, REQ EPHEM CORR PA2V12, REQ EPHEM CORR PA2V13 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names P2010-A2 ------------------------------------------------------------------------------------------------------------------------------------