0Assigned ID: 3837
----- Attempting Submission 1 (Fri Oct 21 15:32:33 GMT 2022) -----
HST Phase I Proposal 3837 successfully submitted.
Receipt: # 3837-1
----- Attempting Submission 2 (Fri Oct 21 18:02:15 GMT 2022) -----
HST Phase I Proposal 3837 successfully submitted.
Receipt: # 3837-2
----- Attempting Submission 3 (Fri Oct 21 23:11:03 GMT 2022) -----Unsupported characters were found in Observing Description and replaced with |*|
ORBITAL VISIBILITY OVERRUN
ORBITAL VISIBILITY OVERRUN
ORBITAL VISIBILITY OVERRUN
ORBITAL VISIBILITY OVERRUNIn this resubmission, we switched to the 2k subarray and shorter exposure times (6 x 220s). An offset is applied to better place the nucleus and tail within the subarray at the orient expected on Dec 19, and a small dither is also folded in between orbits. We understand new alignments must still be inserted, and may require us to reduce exposure times a bit further (or drop to 5 exposures). -- Max Mutchler-1337062215----- Attempting Submission 1 (Thu Dec 01 15:35:53 GMT 2022) -----
----- Attempting Submission 2 (Fri Dec 02 16:43:05 GMT 2022) -----We may have to make more changes to avoid orbit overruns.Macroscopic Debris from the DART impactThe NASA DART impact into one component of the Didymos/Dimorphos binary asteroid occurred on UT 2022 September 26. Images taken at the impact time show a spectacular, structured cloud of ejecta and, on later dates, the emergence of a long, radiation-pressure swept tail of particles. Here, we propose a 4 orbit program to observe the DART-produced debris some 10 weeks after the impact, from a perspective within the projected orbit plane of the system. This observing geometry, in conjunction with an existing dynamics model, will provide a unique measure of the quantity and of the size and velocity distributions of the larger ejecta particles, and we also expect to detect individual macroscopic fragments (boulders) in the ejecta trail. The measurement is highly complementary to the 19 orbit HST program GO 16674, whose final observation was taken on October 15. The proposed observation will extend the time base of data from less than three weeks to ten, and provide the strongest ejection constraints and the ultimate record of this unique impact experiment. Having an exactly known impact time and projectile energy, the DART impact also provides an important means to interpret existing and future observations of colliding asteroids, which are also known to produce structured ejecta fields and long trails of debris.The science objectives can be met using 4 orbits on HST with WFC3, scheduled to occur as the Earth crosses the projected orbital plane. We considered a larger request for time at additional, later epochs. However, the syndynes and synchrones collapse together at later dates, providing little additional information, and the Didymos system will become progres- sively fainter as the distances from Sun and Earth increase. We are confident that ours is an efficient program focused on a necessary measurement. We propose to use the F350LP filter for these observations. This long-pass filter has very broad spectral coverage (FWHM >4000 A) and provides maximum sensitivity to con- tinuum sources. It has become the standard filter for numerous Hubble GO observations of faint solar system targets, from asteroids and comet nuclei to Kuiper belt objects. Our plan is to obtain dithered images (to escape the effects of bad pixels and the inter-chip gap) with five images per orbit having exposure times of 300 s each. Because the impact-associated dust trail is expected to be very long, we will use the full WFC3 CCD readout, providing a 160 160 arcsec field of view (about 20,000 km if observations are taken at the optimum epoch of UT 2022 December 5). Use of the online WFC3 Exposure Time Calculator indicates that this procedure will yield a point source 5 sensitivity for objects at magnitude V = 26.8. Depending on the unknown dust trail surface brightness distribution, the obtained sensitiv- ity might be slightly degraded relative to the model value owing to added noise. A V = 26.8 magnitude object at the observing geometry of December 5 and having the 15 percent albedo of Dimorphos would have spherical equivalent radius 2.5 m, similar to the sizes of the larger boulders imaged on the surface by DART. Prior observations of moving objects from archived data show that the limiting magni- tude is in practice set by interference from trailed field objects, a problem which does not af- fect observations of stars and galaxies where no trailing is involved. The non-sidereal RA motion of Didymos on UT December 5, for instance, varies from -200 hour 1 to +160 hour 1, as seen from HST. The non-sidereal DEC motion is of the same order. At 200 hour 1, field objects are dragged across the CCD by 400 pixels in 300s. Galaxies are a particular nuisance, since their diffuse, large-scale and structured brightness is impossible to mask. The best protection from degradation of the sensitivity by trailed objects in the background is provided by obtaining more data with different and uncorrelated backgrounds. Repeated detection of fragments in different orbits, for example, provides rock solid confidence that these objects are real and not noise peaks in the data. For this reason, and given the singular nature of this opportunity to observe the DART produced ejecta distribution, we request 4 orbits with WFC3 and the F350LP filter. The requested orbits represent a 20% addition to Hubble time already allocated to the study of the debris field, and provide unique information on the properties of the largest particles ejected by the spacecraft impact. Use of the same filter also provides continuity with the near-impact data obtained under GO 16674. The ephemeris uncertainties are well below 1 arcsec and have no impact on the planned observations. The Earth crosses the projected orbit plane of the Didymos pair on two occasions before the solar elongation shrinks into the HST Sun exclusion zone of 55 deg. The first crossing, on UT 2022 December 5, is preferable for two reasons; 1) the earlier observation will sample the debris some 70 days after impact, from a geometry not very different from that at the impact epoch (other than the smaller out-of-plane angle), 2) the later crossing, on UT 2023 June 5, will suffer from substantial loss of sensitivity as a result of the larger heliocentric and geocen- tric distances (rH 2 AU vs. 1.1 and 0.2 AU on December 5). We estimate this loss at about 3.3 magnitudes. The linear resolution corresponding to the 0.08 arcsec HST PSF will also be considerably worse at the later plane crossing (116 km vs. 10 km on December 5). For these reasons, we request observations as near as possible to the UT 2022 December 5 plane crossing. The out-of-plane angle is <1 from December 2 to 9, and observations in this period are requested. At earlier and later dates, the unique projection-free perspective on the vertical distribution of material in the trail and on the fragments, will be progressively degraded. Therefore, we request 4 orbits in the UT 2022 December 2-9 window, preferably scheduled close to December 5.Our team has a strong record in the use of HST for challenging solar system observations. Jessica Agarwal is an expert in dust dynamics and the motions of boulders near 67P. PI Jewitt is a planetary astronomer using ground- and space-based telescopes to explore the small-body populations. Yoonyoung Kim wrote the Monte Carlo model used to interpret the dust and debris observations. Jing Li is experienced with software and data reduction. Max Mutchler is an expert in planning HST observation programs that maximally exploit the science capabilities of HST.Solar System Astronomy3falsefalsefalsefalsefalsetruefalseSUPPORTEDSOLAR SYSTEMNOASTEROIDBinary asteroid (65803) DidymosTYPE=ASTEROID,A=1.643401186439353,E=0.3836403201185644,I=3.413079835162661
,O=73.0031688833396,W=319.5500495128057,M=1.263702528507169,EQUINOX=J2000,EPOCH=24-OCT-2022:12:00:00,EpochTimeScale=TDB,R0=1.
,A1=0.,A2=-1.101805196413E-14,A3=0.
,ALN=1.,NM=2.,NN=0.,NK=0.,AMRAT=0.Didymos itself is V=16. The trail and fragments we seek will be of order 10 mags fainter.EARTHWFC3/UVISImagingNoNoF350LP/System/Volumes/Data/solaris/user1/sherwin/17289/OP-cache/17289-v01.xmlUsing ephemeris for target 17289-01-DIDYMOSephemeris data for target 17289-01-DIDYMOS does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 22.213 to 24.182. ephemeris interval: 22.334 to 24.336Timing link suitability includes constraints ([Sequence (01 02 03 04) within 0.5 days])Hst Same orient constraint links visits (01 02 03 04)The scheduling data was generated by CASM 30.3.CASM was run in Phase II mode.(Tic-Visit
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)false10Using ephemeris for target 17289-02-DIDYMOSephemeris data for target 17289-02-DIDYMOS does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 22.213 to 24.182. ephemeris interval: 22.334 to 24.336Timing link suitability includes constraints ([Sequence (01 02 03 04) within 0.5 days])Hst Same orient constraint links visits (01 02 03 04)The scheduling data was generated by CASM 30.3.CASM was run in Phase II mode./System/Volumes/Data/solaris/user1/sherwin/17289/OP-cache/17289-v02.xml(Tic-Visit
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