This is a resubmission, correcting a reference.442479524Assigned ID: 653
----- Attempting Submission 1 (Fri Apr 07 17:13:30 GMT 2017) -----
HST Phase I Proposal 653 (APT-Cy25PhaseI-RFrench.apt) successfully submitted.
Receipt: # 653-1
----- Attempting Submission 2 (Fri Apr 07 21:57:00 GMT 2017) -----Sensitive exposures should have an ETC run number provided.
Sensitive exposures should have an ETC run number provided.
Sensitive exposures should have an ETC run number provided.
Sensitive exposures should have an ETC run number provided.
Sensitive exposures should have an ETC run number provided.
Sensitive exposures should have an ETC run number provided.This version splits the original four-orbit visit for IAPETUS-LEADING into two visits of two orbits each, separated by 1 to 2 orbits, due to STSCI-mandated restrictions on the number of consecutive orbits for a
a moving target.
The first of the two new visits retains the first two orbits of the original visit.
The second of the two new visits follows the previous one by 1 to 2 orbits. Each orbit contains a single long G230L exposure of the IAPETUS-LEADING.521752604----- Attempting Submission 1 (Tue Jul 18 01:08:20 GMT 2017) -----
Your proposal could not be saved.
Submission aborted.
----- Attempting Submission 2 (Tue Aug 01 15:15:57 GMT 2017) -----
HST Phase II Proposal 15167 (15167-Rfrench-PhaseII-V4.apt) successfully submitted.
Receipt: # 15167-2
----- Attempting Submission 3 (Tue Aug 01 15:19:59 GMT 2017) -----
----- Attempting Submission 4 (Wed Jun 27 20:37:06 GMT 2018) -----All errors/warnings relate to long G230L exposures - we have confirmed that the expected signal from Iapetus is so low that we will not saturate at any wavelength withing this aperture.Unmasking the Dark Side of IapetusWe propose to take advantage of the unique capabilities of STIS in a UV-intensive series of observations to obtain high-SNR spectra of the bright and dark hemispheres of Iapetus over a critical near-UV range where Cassini instruments lack coverage (190-350 nm). The leading face of Iapetus acts a sort of canvas, painted with material from Saturn's captured moon Phoebe, itself an interloper from the Kuiper Belt, that may provide important clues to the composition and processing history of primordial material from the early stages of planet formation. This underscores the long-recognized importance of identifying the composition of the dark material on Iapetus and placing it in the context of other primitive Solar System objects. In spite of extensive Cassini observations, this has proven to be an elusive goal because of the lack of unique spectral signatures of possible dark materials in the wavelengths observed by Cassini. Each proposed darkening agent (nanoiron/hematite, aromatic and aliphatic tholins, NH3) has a distinctive signature within this previously unobserved spectral window. STIS observations will provide a critical test of proposed compositions for the dark material and its origin. We will draw on our team's extensive experience with STIS observations, Cassini UVIS and VIMS spectra, Earth-based near-IR spectroscopy, and radiative transfer scattering models to compare the observed spectra with predictions for a variety of candidate materials. The Iapetus results will complement recent STIS observations of other icy Saturn satellites (Program 13694 Hendrix) and the STIS-based investigation of the mysterious redness of Saturn's rings (Program 12478 Cuzzi).Our scientific goal is to observe the near-UV to visible spectrum of the dark (leading) and bright (trailing) hemispheres of Iapetus, unique among Saturn's moons in having such a strong global asymmetry in reflectivity. The dark (leading) hemisphere may be sweeping up dust from outer regions of the Saturn system, such as particles from the Phoebe ring, but the composition of the dark material has not yet been securely established. Using STIS near-UV and visible measurements, we will obtain high-SNR spectra that include a particularly diagnostic wavelength range between 200-350 nm that is not accessible to Cassini instruments. The two leading proposed contaminants of the dark side -- iron nanoparticles and tholins -- have distinctly different spectra in this range. Based on previous STIS results for the spectra of Saturn's rings, we expect to be able to discriminate between these two possibilities, which would have important implications for the cosmogony of the Saturn satellite system.
Our observing strategy is to maximize the SNR of the low-albedo dark hemisphere by allocating 4 of our 6 orbits to the dark side. To minimize time spent on guide star and target acquisition, we will make use of contiguous orbits for each of two visits. For each visit, the first orbit will begin with a G750L STIS/CCD spectrum (and the necessary flat field images to enable correction for fringing), followed by a G430L STIS/CCD spectrum; the remainder of the first orbit will be devoted to a long STIS/MAMSA G230L exposure. The remainging three orbits of the IAPETUS_LEADING (dark hemisphere) visit will be exclusively devoted to long G230L exposures to enhance the total SNR of the UV-starved low albedo spectrum of the dark side of Iapetus. For the bright hemisphere visit, the second orbit will be devoted to a single long G230L exposure. We use a slit of 52x0.5 (as was used for Rhea in PID 13694; comparable in diameter to Iapetus) because the angular diameter of Iapetus from Earth for this observing window is 0.19 - 0.21 arcsec, uncomfortably large for the 52x0.2 slit; this obviates the need for ACQ/PEAK exposures.
In short, we will observe using all spectral elements (G750L, G430L, and G230L) for full wavelength coverage on the first orbit of each visit, then a G230L exposure for remaining orbit(s) for each visit. We request four continguous orbits for IAPETUS-LEADING (the dark hemisphere) in order to maximize the exposure time of the G230L element on this low-albedo side of Iapetus by minimizing the overhead in guide star acquisition and ACQ. We have restricted the observing geometry to be within +/- 5 degrees of the central meridian centered on the bright and dark hemispheres. (WFPC2 observations of Saturn's rings show a variation in the magnitude and width of the opposition surge, and similar results have been found for Saturn satellites).
Because of the long orbital period of Iapetus (79 days), there are relatively few windows of opportunity for this restricted geometry. We have removed the restriction from previous Phase II submissions on the minimum phase angle at the time of observation, to ease schedulability, as recommended by Crystal Manfolk. If the requested observing windows cannot be scheduled within the Cycle 25 observation period, we understand that the next provisional window for the leading hemisphere observations would be in October 2018. This would be ideal from our point of view, since it could preserve the strict requirement that the CML be within 5 degrees of 90 for the dark leading hemisphere, which would ensure the least possible contamination of the dark hemisphere spectrum by encroaching bright material visible from a small crescent of the bright hemisphere. Expanding the range of allowed CML to +/- 20 degrees of 90 degrees would result in about 20% contamination of the spectrum by the bright material, significantly complicating our analysis.
*** Warnings about long G230L exposures are benign because there will be no saturation even for the longest possible exposure within a single orbit. ***Solar System6falsefalsetruefalsefalsefalsefalseSUPPORTEDSOLAR SYSTEMSATELLITELeading (Dark) hemisphere of Iapetus - near eastern elongationSTD=SATURNSTD=IAPETUSETC runs use STIS data of Saturn's C ring scaled to Iapetus sizeSEP OF IAPETUS-LEADING SATURN FROM EARTH GT 45",
SEP OF IAPETUS-LEADING RHEA FROM EARTH GT 10",
SEP OF IAPETUS-LEADING TITAN FROM EARTH GT 10",
CML OF IAPETUS-LEADING FROM EARTH BETWEEN 85 95EARTHSOLAR SYSTEMSATELLITETrailing (bright) hemisphere of Iapetus near western elongationSTD=SATURNSTD=IAPETUSETC runs use STIS data of Saturn's C ring scaled to Iapetus sizeSEP OF IAPETUS-TRAILING SATURN FROM EARTH GT 45",
SEP OF IAPETUS-TRAILING RHEA FROM EARTH GT 10",
SEP OF IAPETUS-TRAILING TITAN FROM EARTH GT 10",
CML OF IAPETUS-TRAILING FROM EARTH BETWEEN 265 275EARTHSTIS/CCDSpectroscopicNoNoG430L4300STIS/NUV-MAMASpectroscopicNoNoG230L2376STIS/CCDSpectroscopicNoNoG750L7751STIS/CCDSpectroscopicNoNoG430L4300STIS/NUV-MAMASpectroscopicNoNoG230L2376STIS/CCDSpectroscopicNoNoG750L7751STIS/NUV-MAMASpectroscopicNoNoG230L2376STIS/NUV-MAMASpectroscopicNoNoG230L2376Using ephemeris for target 15167-01-IAPETUS-LEADINGephemeris data for target 15167-01-IAPETUS-LEADING does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 18.130 to 19.152. ephemeris interval: 18.151 to 20.153Timing link suitability includes constraints ([04 After 01 by 0.2 to 0.3 days])The scheduling data was generated by CASM 26.0.CASM was run in Phase II mode./private/var/folders/8k/sxlgy5ts2xdbykzf_vw6jrfw0001c5/T/OPVisit6265240548357245112.xmlUse all spectral elements for full wavelength coverage on first orbit, then G230L exposure for the second orbit of this visit. The second visit of two orbits for Iapetus-Leading follows this visit by one to two orbits because of restrictions on the number of successive moving target orbits for a single visit.
*** Warnings about long G230L exposures are benign because there will be no saturation even for the longest possible exposure within a single orbit. ***(Tic-Visit
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)true20Flatfield necessary to remove fringing of G750LUsing ephemeris for target 15167-04-IAPETUS-LEADINGephemeris data for target 15167-04-IAPETUS-LEADING does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 18.130 to 19.152. ephemeris interval: 18.151 to 20.153Timing link suitability includes constraints ([04 After 01 by 0.2 to 0.3 days])The scheduling data was generated by CASM 26.0.CASM was run in Phase II mode./private/var/folders/8k/sxlgy5ts2xdbykzf_vw6jrfw0001c5/T/OPVisit9136849121672950490.xmlThis is the second visit of two orbits for Iapetus leading. It should follow the first visit of two orbits for the same target after 1 to two orbits.
*** Warnings about long G230L exposures are benign because there will be no saturation even for the longest possible exposure within a single orbit. ***(Tic-Visit
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