5837( 7) - 08/14/95 10:18 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5837 Version: 7 Check-in Date: ********** 1.Proposal Title: Ultraviolet Imaging and Spectroscopy of the Icy Galilean Satellites ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Solar System GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Keith S. Noll Space Telescope Science Institute CoI: Bonnie Buratti Jet Propoulsion Laboratory N CoI: Deborah Domingue Lunar and Planetary Institute N CoI: Robert Johnson University of Virginia N CoI: Arthur L. Lane Jet Propulsion Laboratory N CoI: Melissa McGrath Space Telescope Science Institute N CoI: Paola Sartoretti Space Telescope Science Institute N CoI: Harold A. Weaver Space Telescope Science Institute N ------------------------------------------------------------------------------------ 6. Abstract We will obtain the first ultraviolet images of the three icy Galilean satellites, Europa, Ganymede, and Callisto, with the HST WFPC2. No other observatory or spacecraft has been or will be capable of obtaining resolved images of Jupiter's large satellites at wavelengths below 3200 Angstrom . Strong UV bands of SO2 and other spectral features caused by charged particle impacts in ice produce significant albedo effects in this part of the spectrum. Correlation of UV albedo maps to visible geologic features will allow us to investigate both internal and external processes that modify these surfaces. We will also obtain high S/N spectra of all three satellites from 1800-3300 Angstrom , including the first useable spectra ever below 2400 Angstrom . The FOS spectra are of sufficiently high resolution that we will be able to distinguish between different compositional and physical states of the surfaces. The spectra will also improve the interpretation of the images. Our program of imaging and spectroscopy will be coordinated with a series of `final' IUE and groundbased near-UV observations to be executed prior to the Galileo encounter with the Jovian system. The measurements will provide the temporal tie between 15-plus years of IUE spectroscopy and the HST/Galileo epoch and, more importantly, will shape the priorities for the Galileo satellite encounters on that now bandwidth-limited mission. ------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 2] Observations Description ------------------------ The HST is the only instrument capable of obtaining spatially resolved images of Europa, Ganymede, and Callisto in the UV for the forseeable future. The imaging experiments on the Galileo spacecraft which will arrive at Jupiter in 1995 extend only to 3800 Angstrom (Yeates et al. 1985). Ground based observations are limited to the spectral range longer than ~ 3200 Angstrom . The Voyager UV filter was similarly limited to wavelengths longward of 3500 Angstrom . HST is also capable of obtaining high S/N and high spectral resolution UV spectra with short integration times. These data will be used to determine surface composition, help in the analysis of WFPC2 images with filter bandpasses in the UV, and will be conveyed to the Galileo science team in order to assist in difficult decisions regarding data retrieval. Our observing plan is to repeat identical four-orbit observing sequences for Europa, Ganymede, and Callisto. We will use the sequence once for the trailing hemisphere of each satellite (near western elongation) and once for the leading hemisphere of each satellite (near eastern elongation) for a total of twenty four orbits. The four orbit sequence consists of two orbits of WFPC2 observations followed by two orbits of FOS spectroscopy. The observation sequence will begin in the first orbit with a full guide star acquisition followed by exposures in the UV (F255W, F300W, F336W), blue (F439W), green (F555W), and red (F675W) filters. The exposure times needed for S/N >= 100 per pixel are seconds in the cases of the visible wavelength filters which will be used to make composite images required for correlating UV features to visible albedo features. The exposure times needed for the UV filters are given in the table. For the two shortest filters we tabulate the number of electrons collected per pixel in 1000 seconds (F218W) and 100 seconds (F255W). For the two longer UV filters we compute the time to accumulate 15,000 electrons (S/N ~ 122). The key observations in the F218W filter take place in the second orbit in the sequence after a guide star reaquisition, allowing us the maximum integration time. We will obtain two 1000 second integrations at F218W which should yield S/N >= 18 per pixel. Long integrations accumulate many cosmic rays so two are required to allow us to efficiently remove their effects (we will not use CR-SPLIT on individual integrations). The third orbit will begin with a full guide star acquisition and then use the FOS ACQ/PEAK onboard software for target acquisition. ACQ/PEAK has recently been upgraded to allow acquisitions of bright moving targets in the FOS, something that was not possible before. Unfortunately, the search routine is time consuming and uses the remainder of the orbit. After a reacquisition in the fourth orbit, FOS/RD spectra with the G270H and G190H will be obtained. Integration times of 5 minutes (G270H) and 20 minutes (G190H) achieve S/N >= 10 for all wavelengths longer than 1950 Angstrom for all satellites. Because of the steepness of the solar continuum the S/N is considerably higher at the long wavelength end of each grating. For the dark trailing hemisphere of Europa (where we have measured the flux down to 2200 Angstrom ) the S/N in the G190H grating ranges from 5 at 1800 Angstrom to 122 at 2300 Angstrom , in the G270H grating the S/N is 50 at 2200 Angstrom and 350 at 3300 Angstrom . Callisto and Ganymede are fainter, in part because they overfill the aperture. The S/N for the dark leading hemisphere of Callisto, the darkest of all six hemispheres, will be lower by as much as a factor of 0.4 at all wavelengths. Real Time Justification ----------------------- Our highest priority is to execute the observations in time (summer 1995) to assist the Galileo team in deciding priorities for the limited amount of science data that will be returned. We prefer observations near opposition when we obtain the best image scale and in order to obtain low phase angle observations that will complement the higher phase angle observations Galileo will make. Team member A. Lane is the principal investigator for satellite surfaces on the Galileo UVS experiment. He will be the primary point of contact between our investigative team and the Galileo project. We plan to make information available as quickly as possible to aid the Galileo team in selecting target sequences and in prioritizing data retrieval. Team members A. Lane and D. Domingue will also be responsible for leading both IUE and ground based spectroscopic observations that will concentrate on the long wavelength portion of the UV. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: Europa-East ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: satellite Europa ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = Jupiter | STD = Europa | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG of Europa from Earth between 70 110 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 5.29 B-V = 0.87 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: Europa-West ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: satellite Europa ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = Jupiter | STD = Europa | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG of Europa from Earth between 250 290 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 5.29 B-V = 0.87 | | ------------------------------------------------------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 5] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 | TARGET NAME: Ganymede-East ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: satellite Ganymede ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = Jupiter | STD = Ganymede | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG of Ganymede from Earth between 70 | 110 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 4.61 B-V = 0.83 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 4 | TARGET NAME: Ganymede-West ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: satellite Ganymede ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = Jupiter | STD = Ganymede | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG of Ganymede from Earth between 250 | 290 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 4.61 B-V = 0.83 | | ------------------------------------------------------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 6] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 5 | TARGET NAME: Cal-Gany-W ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: satellite Ganymede ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = Jupiter | STD = Ganymede | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG of Ganymede from Earth between 240 | 300 , SEP OF GANYMEDE CALLISTO FROM | EARTH LT 100", A_VEL CALLISTO RELATIVE | GANYMEDE FROM EARTH LT 0.0007 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 4.61 B-V = 0.83 | Both Callisto and Ganymede must be | on WFPC | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 6 | TARGET NAME: Cal-Gany-E ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: satellite Callisto ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = Jupiter | STD = Callisto | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG of Ganymede from Earth between 60 | 120 , SEP OF GANYMEDE CALLISTO FROM | EARTH LT 100", A_VEL CALLISTO RELATIVE | GANYMEDE FROM EARTH LT 0.0007 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 5.65 B-V = 0.86 | Both Callisto and Ganymede must be | on WFPC | ------------------------------------------------------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 7] Visit: 01 Visit Requirements: BEFORE 16-OCT-95 On Hold Comments: Additional Comments: This visit has limited opportunities for scheduling we prefer as close to Jupiter opposition as possible exp-times assume Ganymede = 3x Callisto expect 2000 - 3000 ADU in WF Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 Cal-Gany-E WFPC2 IMAGE PC1 F218W ATD-GAIN=7 2 500S NO SPLIT ------------------------------------------------------------------------------------------------------------------------------------ 12 Cal-Gany-E WFPC2 IMAGE PC1 F255W ATD-GAIN=7 1 40S ------------------------------------------------------------------------------------------------------------------------------------ 13 Cal-Gany-E WFPC2 IMAGE PC1 F410M ATD-GAIN=15 1 3S ------------------------------------------------------------------------------------------------------------------------------------ 14 Cal-Gany-E WFPC2 IMAGE PC1 F953N ATD-GAIN=15 1 10S ------------------------------------------------------------------------------------------------------------------------------------ 15 Cal-Gany-E WFPC2 IMAGE PC1 F675W ATD-GAIN=15 1 0.11S ------------------------------------------------------------------------------------------------------------------------------------ 16 Cal-Gany-E WFPC2 IMAGE PC1 F300W ATD-GAIN=15 1 10S ------------------------------------------------------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 8] Visit: 02 Visit Requirements: BEFORE 16-OCT-95 On Hold Comments: Additional Comments: This visit has limited scheduling opportunities, we prefer as close to Jupiter opposition as possible exp-time calculated from observed Callisto WF images from SL9 campaign Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 21 Cal-Gany-W WFPC2 IMAGE PC1 F218W ATD-GAIN=7 2 500S NO SPLIT ------------------------------------------------------------------------------------------------------------------------------------ 22 Cal-Gany-W WFPC2 IMAGE PC1 F255W ATD-GAIN=7 1 40S ------------------------------------------------------------------------------------------------------------------------------------ 23 Cal-Gany-W WFPC2 IMAGE PC1 F410M ATD-GAIN=15 1 5S ------------------------------------------------------------------------------------------------------------------------------------ 24 Cal-Gany-W WFPC2 IMAGE PC1 F953N ATD-GAIN=15 1 30S ------------------------------------------------------------------------------------------------------------------------------------ 25 Cal-Gany-W WFPC2 IMAGE PC1 F675W ATD-GAIN=15 1 0.2S ------------------------------------------------------------------------------------------------------------------------------------ 26 Cal-Gany-W WFPC2 IMAGE PC1 F300W ATD-GAIN=15 1 10S ------------------------------------------------------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 9] Visit: 03 Visit Requirements: BEFORE 16-OCT-95 On Hold Comments: Additional Comments: as close to Jupiter opposition as possible Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 31 Europa-West WFPC2 IMAGE PC1 F218W ATD-GAIN=7 2 500S NO SPLIT ------------------------------------------------------------------------------------------------------------------------------------ 32 Europa-West WFPC2 IMAGE PC1 F255W ATD-GAIN=7 1 40S ------------------------------------------------------------------------------------------------------------------------------------ 33 Europa-West WFPC2 IMAGE PC1 F410M ATD-GAIN=15 1 8S ------------------------------------------------------------------------------------------------------------------------------------ 34 Europa-West WFPC2 IMAGE PC1 F953N ATD-GAIN=15 1 30S ------------------------------------------------------------------------------------------------------------------------------------ 35 Europa-West WFPC2 IMAGE PC1 F675W ATD-GAIN=15 1 0.3S ------------------------------------------------------------------------------------------------------------------------------------ 36 Europa-West WFPC2 IMAGE PC1 F300W ATD-GAIN=15 1 40S ------------------------------------------------------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 10] Visit: 04 Visit Requirements: BEFORE 16-OCT-95 On Hold Comments: Additional Comments: as close to Jupiter opposition as possible Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 41 Europa-East WFPC2 IMAGE PC1 F218W ATD-GAIN=7 2 500S NO SPLIT ------------------------------------------------------------------------------------------------------------------------------------ 42 Europa-East WFPC2 IMAGE PC1 F255W ATD-GAIN=7 1 40S ------------------------------------------------------------------------------------------------------------------------------------ 43 Europa-East WFPC2 IMAGE PC1 F410M ATD-GAIN=15 1 8S ------------------------------------------------------------------------------------------------------------------------------------ 44 Europa-East WFPC2 IMAGE PC1 F953N ATD-GAIN=15 1 30S ------------------------------------------------------------------------------------------------------------------------------------ 45 Europa-East WFPC2 IMAGE PC1 F675W ATD-GAIN=15 1 0.3S ------------------------------------------------------------------------------------------------------------------------------------ 46 Europa-East WFPC2 IMAGE PC1 F300W ATD-GAIN=15 1 40S ------------------------------------------------------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 11] Visit: 05 Visit Requirements: BEFORE 16-OCT-95 On Hold Comments: Additional Comments: STEP-TIME = 0.2 SECONDS USING HRS ACQ FOR FOS SCIENCE ALL THREE SATELLITES MUST BE DONE IN THREE ORBIT VISIT AFTER HRS ACQ SAME GUIDE STARS THROUGHOUT OR GUIDE STAR HANDOFF MUST BE USED Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 51 Europa-East HRS ACQ 2.0 MIRROR-N2 BRIGHT = RETURN 1 1.8S ONBOARD ACQ FOR 52-53 LOCATE = EXTENDED SEARCH -SIZE = 3 ------------------------------------------------------------------------------------------------------------------------------------ 52 Europa-East FOS/BL ACCUM 1.0 G270H 1 120S ------------------------------------------------------------------------------------------------------------------------------------ 53 Europa-East FOS/BL ACCUM 1.0 G190H 1 900S ------------------------------------------------------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 12] Visit: 06 Visit Requirements: BEFORE 16-OCT-95 On Hold Comments: Additional Comments: STEP-TIME = 0.2 SECONDS USING HRS ACQ FOR FOS SCIENCE ALL THREE SATELLITES MUST BE DONE IN THREE ORBIT VISIT AFTER HRS ACQ SAME GUIDE STARS THROUGHOUT OR GUIDE STAR HANDOFF MUST BE USED Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 61 Europa-West HRS ACQ 2.0 MIRROR-N2 BRIGHT = RETURN 1 1.8S ONBOARD ACQ FOR 62-63 LOCATE = EXTENDED SEARCH -SIZE = 3 ------------------------------------------------------------------------------------------------------------------------------------ 62 Europa-West FOS/BL ACCUM 1.0 G270H 1 120S ------------------------------------------------------------------------------------------------------------------------------------ 63 Europa-West FOS/BL ACCUM 1.0 G190H 1 900S ------------------------------------------------------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 13] Visit: 07 Visit Requirements: BEFORE 16-OCT-95 On Hold Comments: Additional Comments: STEP-TIME = 0.2 SECONDS USING HRS ACQ FOR FOS SCIENCE ALL THREE SATELLITES MUST BE DONE IN THREE ORBIT VISIT AFTER HRS ACQ SAME GUIDE STARS THROUGHOUT OR GUIDE STAR HANDOFF MUST BE USED Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 71 Ganymede- HRS ACQ 2.0 MIRROR-N2 BRIGHT = RETURN 1 1.8S ONBOARD ACQ FOR 72-73 East LOCATE = EXTENDED SEARCH -SIZE = 3 ------------------------------------------------------------------------------------------------------------------------------------ 72 Ganymede- FOS/BL ACCUM 1.0 G270H 1 120S East ------------------------------------------------------------------------------------------------------------------------------------ 73 Ganymede- FOS/BL ACCUM 1.0 G190H 1 900S East ------------------------------------------------------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 14] Visit: 08 Visit Requirements: BEFORE 16-OCT-95 On Hold Comments: Additional Comments: STEP-TIME = 0.2 SECONDS USING HRS ACQ FOR FOS SCIENCE ALL THREE SATELLITES MUST BE DONE IN THREE ORBIT VISIT AFTER HRS ACQ SAME GUIDE STARS THROUGHOUT OR GUIDE STAR HANDOFF MUST BE USED Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 81 Ganymede- HRS ACQ 2.0 MIRROR-N2 BRIGHT = RETURN 1 1.8S ONBOARD ACQ FOR 82-83 West LOCATE = EXTENDED SEARCH -SIZE = 3 ------------------------------------------------------------------------------------------------------------------------------------ 82 Ganymede- FOS/BL ACCUM 1.0 G270H 1 120S West ------------------------------------------------------------------------------------------------------------------------------------ 83 Ganymede- FOS/BL ACCUM 1.0 G190H 1 900S West ------------------------------------------------------------------------------------------------------------------------------------ 5837( 7) - 08/14/95 10:18 - [ 15] Summary Form for Proposal 5837 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 HRS FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=7 ATD-GAIN=15 BRIGHT = RETURN LOCATE = EXTENDED SEARCH-SIZE = 3 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Solar System ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 16-OCT-95 NO SPLIT ONBOARD ACQ FOR 52-53 ONBOARD ACQ FOR 62-63 ONBOARD ACQ FOR 72-73 ONBOARD ACQ FOR 82-83 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F218W F255W F410M F953N F675W F300W MIRROR-N2 G270H G190H ------------------------------------------------------------------------------------------------------------------------------------ Target Names Cal-Gany-E Cal-Gany-W Europa-West Europa-East Ganymede-East Ganymede-West ------------------------------------------------------------------------------------------------------------------------------------