0Assigned ID: 832
----- Attempting Submission 1 (Fri Apr 08 21:06:58 GMT 2016) -----
HST Phase I Proposal 832 (europa_all.apt) successfully submitted.
Receipt: # 832-1My moving targets cannot go through visit planner, but I keep getting this error. I am submitting with error.Resubmission to hide the wavelength calibrations during the occultation.1756102838----- Attempting Submission 1 (Wed Jul 20 23:19:33 GMT 2016) -----
HST Phase II Proposal 14650 (europa_final_phase2.apt) successfully submitted.
Receipt: # 14650-1
----- Attempting Submission 2 (Fri Aug 19 20:37:29 GMT 2016) -----A simple definitive test for chloride salts on EuropaEuropa is a prime location for exploring our concepts of habitability throughout the solar system. As importantly, Europa is a case study for how liquid water drives the geochemistry and geophysics in a world very different from our own. One of the keys to understanding the liquid water's effect on habitability, geochemistry, and even on geophysics is understanding the chemistry of the internal ocean. Evaporites on the surface of Europa provide a window into this ocean chemistry.
Recent observations have overturned 15 years worth of assumptions about the chemistry of Europa's ocean and have suggested that chloride salts -- rather than sulfate salts -- could be the most abundant constituent in the ocean and in the surface evaporites. The possibility of chloride salts has major implications for geophysics and habitability, but, because chloride salts are basically featureless, definitive spectral evidence was thought impossible.
New laboratory data now shows, however, that electron irradiation with Europa-like fluxes imparts distinct spectral absorption features on chloride salts. These spectral features, in specific bands between 430 and 830 nm, are uniquely accessible to high spatial resolution HST spectroscopy. We propose a very simple program to obtain four separate high spatial resolution STIS slit scans across the disk of Europa to construct a global spectral map which will detect and map these surface salts. These observations can definitively identify chloride salts on Europa and fundamentally change our understanding of this world. Rarely can such a simple and short program with HST have the possibility of obtaining such conclusive and transformative results.We consider four factors in designing our observation sequence: spectral coverage, signal-to-noise, spatial resolution, and observing efficiency. STIS low resolution CCD spectroscopy perfectly covers the wavelengths of the NaCl and KCl color centers. The G430L mode will cover 460 nm NaCl and most of the broad 550 nm KCl color centers, while the G750L mode will cover the remainder of the 550 nm KCl (with significant overlap to stitch the two together) as well as the 647 and 830 nm color centers due to KCl and the strong 723 NaCl color center. Even at low resolution, there will be ~30 resolution elements across these ~50 nm wide spectral features. We estimate that if the spectrum is similar to that of the ocean brine, but diluted with pure ice by a factor of 50% as suggested by Fischer et al., we would require a S/N of 200 across the band to make a 10% detection of the ~5% absorption feature, or a S/N of approximately 25 per pixel across these bands. In the short wavelength band, this S/N is achieved in a 2 second (!) exposure (with a 140 second exposure required for saturation). In the long wavelength band, the required exposure time is 1.6 seconds (with 48 seconds until saturation). Clearly, these observations will be dominated by overhead rather than integration time. We discuss how to efficiently scan the spatial slit across Europa after first determining the number of visits required, which is set by the spatial resolution required.
The spatial resolutions of Keck near-infrared AO and HST optical imaging are well matched. Our goal is to obtain visible spectral maps with spatial resolution comparable to our existing infrared data. The highest spatial resolution is achieved only at the sub-observer point (the equator at the central longitude of the observation). All other locations at the disk will be foreshortened in each observation. A four visit sequence is the optimal trade-off between full disk spatial resolution and observing efficiency. With four visits sequenced ~90 degrees of longitude apart on the satellite, the worst spatial resolution achieved on the equator will be 45 degrees off of each sub-observer point and will be degraded by 40% compared to the sub-observer resolution. Such a degradation appears acceptable compared to the sizes of the features seen in Figure 1. (A sequence of only 3 visits would lead to resolution degradations of 100%, comparable to the size of some of the features we are attempting to detect).
Within each visit, we seek an observational sequence that efficiently observes both spectral settings while scanning the slit across the surface of Europa with steps small enough to maximize spatial resolution. The observing window for these ecliptic observations is 54 minutes. After a six minute guide star acquisition, we will require a 6 minute STIS peak up, leaving 42 minutes for observation. Our ideal sequence would then be 26 separate spatial positions with 0.025 arcseconds spacing across the ~0.65 arcsecond central region of Europa which contains the 90 degree sub-observer quadrant (we need not scan to the limb as those regions are better covered at other phases). Each of the two spectral setups requires a 4 minute overhead (plus subsequent readout), so, if we complete one full spectral sequence before switching, we have 40 minutes total remaining for exposure, readout, and dither of 52 spectra. If we assume 20 seconds for each dither and obtain a readout of 7 seconds by using a 256 column subaperture, we can expose each spectrum for 20 seconds. We will obtain ~3 times the required S/N, while staying well below saturation. In addition, the use of subapertures should guarantee that we do not need to pause for STIS buffer dump.
We are mapping the entire surface of Europa. The four visits should occur at Europa phases which are ~90 degrees apart. To stay as far from Jupiter as possible, the visits should be centered at phases of 45, 135, 225, and 315 degrees (with an acceptable range of ~5 degrees). The observations need not occur within a single Europa orbit. The other Galilean satellites should each be greater than 5 arcseconds away during each observation.Solar System12falsefalsefalsefalsefalsefalseAVAILABLESOLAR SYSTEMYESSATELLITECentered near phase=45 degree (longitude 45 W)STD=JUPITERSTD=EUROPASEP OF EUROPA-45 JUPITER FROM EARTH GT 30",
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CML OF EUROPA-45 FROM EARTH BETWEEN 40 50EARTHSOLAR SYSTEMYESSATELLITECentered near phase=135 degree (longitude 135 W)STD=JUPITERSTD=EUROPASEP OF EUROPA-135 JUPITER FROM EARTH GT 30",
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CML OF EUROPA-135 FROM EARTH BETWEEN 130 140EARTHSOLAR SYSTEMYESSATELLITECentered near phase=225 degree (longitude 225 W)STD=JUPITERSTD=EUROPASEP OF EUROPA-225 JUPITER FROM EARTH GT 30",
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SEP OF EUROPA-225 IO FROM EARTH GT 10",
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CML OF EUROPA-225 FROM EARTH BETWEEN 220 230EARTHSOLAR SYSTEMYESSATELLITECentered near phase=315 degree (longitude 315 W)STD=JUPITERSTD=EUROPASEP OF EUROPA-315 JUPITER FROM EARTH GT 30",
SEP OF EUROPA-315 CALLISTO FROM EARTH GT 10",
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CML OF EUROPA-315 FROM EARTH BETWEEN 310 320EARTHSTIS/CCDSpectroscopicNoNoG430L4300STIS/CCDSpectroscopicNoNoG750L7751STIS/CCDSpectroscopicNoNoG430L4300STIS/CCDSpectroscopicNoNoG750L7751STIS/CCDSpectroscopicNoNoG430L4300STIS/CCDSpectroscopicNoNoG750L7751STIS/CCDSpectroscopicNoNoG430L4300STIS/CCDSpectroscopicNoNoG750L7751POS-TARGMOSAICDITHER0.06STIS-ALONG-SLITfalsetrue150.0POS-TARGSTIS-PERP-TO-SLIT90.03falseUsing ephemeris for target 14650-12-EUROPA-45ephemeris data for target 14650-12-EUROPA-45 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 16.214 to 18.089. ephemeris interval: 16.244 to 18.244The scheduling data was generated by CASM 24.2.CASM was run in Phase II mode./private/var/folders/ny/y2rfgxpn4k37g754z2ph3gd00001bc/T/OPVisit5216910499282234893.xml(Tic-Visit
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)true10Using ephemeris for target 14650-13-EUROPA-135ephemeris data for target 14650-13-EUROPA-135 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 16.214 to 18.089. ephemeris interval: 16.244 to 18.244The scheduling data was generated by CASM 24.2.CASM was run in Phase II mode./private/var/folders/ny/y2rfgxpn4k37g754z2ph3gd00001bc/T/OPVisit9090653820384317493.xml(Tic-Visit
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)true10Using ephemeris for target 14650-14-EUROPA-225ephemeris data for target 14650-14-EUROPA-225 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 16.214 to 18.089. ephemeris interval: 16.244 to 18.244The scheduling data was generated by CASM 24.2.CASM was run in Phase II mode./private/var/folders/ny/y2rfgxpn4k37g754z2ph3gd00001bc/T/OPVisit795284091376130553.xml(Tic-Visit
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)true10Using ephemeris for target 14650-15-EUROPA-315ephemeris data for target 14650-15-EUROPA-315 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 16.214 to 18.089. ephemeris interval: 16.244 to 18.244The scheduling data was generated by CASM 24.2.CASM was run in Phase II mode./private/var/folders/ny/y2rfgxpn4k37g754z2ph3gd00001bc/T/OPVisit5420427458687631473.xml(Tic-Visit
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