0Assigned ID: 2719
----- Attempting Submission 1 (Mon Mar 07 21:59:35 GMT 2022) -----Could not find ephemeris for target 16929-04-C2021-A1-BThis resubmission updates visit 4 to utilize new JPL orbital elements for the target. I also added a small POS TARG to move the target to the geometric center of the 2k subarray. I removed the small dither because there is no chip gap and bad pixels are a much smaller concern than being able to reliably stack all 5 images, reject the many star trails we will get in the Milky Way background, and try to detect an extended diffuse feature. -- Max Mutchler1677438443----- Attempting Submission 1 (Mon Mar 21 21:24:55 GMT 2022) -----
----- Attempting Submission 2 (Tue Mar 22 14:59:15 GMT 2022) -----
----- Attempting Submission 3 (Mon May 16 20:10:44 GMT 2022) -----Visit Planner had processed visit 4 just fine, but when I ran it for all 4 visits (including the 3 already executed) it said it could not find the ephemeris? I don't think this is really a problem.Disintegration of Long-Period Comet C/2021 A1Long-period comet nuclei are volatile rich products of accretion in the protoplanetary disk of the Sun, preserved at about 10 K in the Oort cloud. They include some of the most primitive macroscopic objects in the solar system. We now know that comet nuclei spontaneously and suddenly disintegrate and that disintegration probably dominates sublimation as the main destructive process operating on these bodies when in the inner solar system. Crucially, disintegration may account for the long-recognized ``fading problem'' discovered by Oort in 1950: comets fade because they fall apart, not because they run out of ice. Unfortunately, our confidence that disintegration is important is not matched by an understanding of the process or its cause. This is because disintegrations are unpredictable, sudden, and difficult to observe. Proposed models center around internal pressure build-up, explosion of amorphous ice, and centripetal disruption caused by outgassing torques, but we do not possess the high quality (resolution, sensitivity and temporal resolution) data needed to determine what is really happening. C/2021 A1 began disintegration in early 2022 March, providing a rare opportunity to study a disintegration with the full power of HST. We propose an efficient, 4 orbit DDT observation, with 3 orbits scheduled early to assess the fragment field and measure size, velocity and acceleration distributions, and a single orbit in June to examine the distribution of material perpendicular to the orbit plane. Only by obtaining this type of high resolution, high sensitivity, time-resolved data can we hope to characterize and understand cometary disintegration.We request 4 orbits with WFC3 to examine the disintegration of C/2021 A1. Our basic observing strategy is to take multiple long exposures (348-400 s) using WFC3 and a wide bandpass filter (F350LP) for maximum sensitivity. We use F350LP because the F350LP count rate is 1.6x higher for a target with a solar-type spectrum than other commonly used broadband filters (e.g., F606W). We also plan to dither the exposures to mitigate the effects from bad pixels, cosmic rays, and the inter-chip gap. The sampling of the observations is a principal concern. HST observations of disin- tegrating comet P/2010 V1 (Ikeya-Murakami) show that fragments evolve photometrically and morphologically on a 1 day timescale and that they cannot be linked unambiguously on timescales > 2 days. For example, in P/2010 V1, fragments in January 2016 could not be connected to fragments observed 3 weeks later, impeding the ability to measure non- gravitational accelerations and to reach conclusions about the ice content and activity states of the fragments. However, with approximately daily sampling, the linkage problems would largely disappear. Accordingly, we request 3 orbits distributed with approximately 1 to 2 day spacing, for a total of 3 to 6 days coverage, to be scheduled as soon as practical. Three orbits (as opposed to two) are the minimum needed to confirm astrometric linkages between fragments, including the possibility of non-linear motions due to outgassing acceleration. Early scheduling of these 3 orbits is needed to sample the disintegration before the small fragments have faded to invisibility. We request immediate scheduling, but not disruptive scheduling for this purpose, with a nominal desired observing window in early to mid-April. We request 1 additional orbit on UT 2022 June 7, this being the date on which the Earth passes through the projected orbit plane of C/2021 A1. Observations from within the orbit plane provide a model-free perspective on the distribution of material above and below the plane, including the best possible measure of the out-of-plane ejection velocity of the material. We do not know what fraction of the comet material will remain observable in June but, given the sensitivity mentioned below, we expect to detect the larger surviving fragments. The WFC3 Exposure Time Calculator indicates that, for a point source, solar-type spectrum, a signal-to-noise ratio of 6 is reached in 348 s at V = 26.5 in the F350LP filter (ETC request ID WFC3UVIS.im.765972; optimal extraction yields SNR=13). For example, at opposition and heliocentric distance R = 1 AU, magnitude V = 26.5 corresponds to an object radius 20 m (geometric albedo 0.04 assumed). These are upper limits to the point source thresholds because at least some of the fragments are embedded in their own dust comae. However, it is clear that HST offers unprecedented sensitivity to faint fragments.This team is experienced in the acquisition, interpretation and publication of solar system target HST data. Jewitt has a long record in ground- and space-based planetary astronomy. Max Mutchler is an expert in the optimal application of HST to solar system science targets. Jing Li is experienced with image reduction and author of a paper on disintegration of Comet Elenin. Yoonyoung Kim and Jessica Agarwal are dust dynamics experts with numerous HST publications.Solar System Astronomy0falseSUPPORTEDSOLAR SYSTEMYESCOMETdisintegrating cometTYPE=COMET,Q=0.6152301521444987,E=1.000100458487891,I=132.685813010451
,O=255.8891005421364,W=225.0877142804849,T=03-JAN-2022:07:01:27,TTimeScale=TDB,EQUINOX=J2000,EPOCH=11-JUL-2021:00:00:00,EpochTimeScale=TDB,R0=2.808
,DT=0.
,A1=5.805860996246E-8,A2=-2.026799678802E-8,A3=1.105900406837E-8
,ALN=0.1112620426,NM=2.15,NN=5.093,NK=4.6142,AMRAT=0.EARTHSOLAR SYSTEMYESCOMETdisintegrating cometTYPE=COMET,Q=0.6152301549244599,E=1.000100476563864,I=132.6858128893857
,O=255.8891027444656,W=225.0877146079479,T=03-JAN-2022:07:01:27,TTimeScale=TDB,EQUINOX=J2000,EPOCH=11-JUL-2021:00:00:00,EpochTimeScale=TDB,R0=2.808
,DT=0.
,A1=5.810580730438E-8,A2=-2.030660629272E-8,A3=1.103076815605E-8
,ALN=0.1112620426,NM=2.15,NN=5.093,NK=4.6142,AMRAT=0.EARTHWFC3/UVISImagingNoNoF350LP/private/var/folders/tj/27ygn_756lz3w1z19s6wtgtm0006vh/T/OPVisit17591109005210678121.xmlUsing ephemeris for target 16929-01-C2021-A1ephemeris data for target 16929-01-C2021-A1 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 22.064 to 23.121. ephemeris interval: 22.120 to 24.122Timing link suitability includes constraints ([02 After 01 by 1.0 to 3.0 days] [03 After 01 by 4.0 to 8.0 days])The scheduling data was generated by CASM 29.2.CASM was run in Phase II mode.1649201093000250.40999999999997(Tic-Visit
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)true10/private/var/folders/tj/27ygn_756lz3w1z19s6wtgtm0006vh/T/OPVisit11556982831228932853.xmlUsing ephemeris for target 16929-02-C2021-A1ephemeris data for target 16929-02-C2021-A1 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 22.064 to 23.121. ephemeris interval: 22.120 to 24.122Timing link suitability includes constraints ([02 After 01 by 1.0 to 3.0 days])The scheduling data was generated by CASM 29.2.CASM was run in Phase II mode.1649286690000246.92511870405326(Tic-Visit
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