6817( 4) - 07/08/96 13:01 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6817 Version: 4 Check-in Date: 08-Jul-1996 12:58:29 1.Proposal Title: The Ultraviolet Spectrum of Callisto ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle SOLAR SYSTEM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: KEITH NOLL SPACE TELESCOPE SCIENCE INSTITUTE CoI: Arthur Lane Jet Propulsion Laboratory N CoI: Deborah Domingue Lunar and Planetary Institute N CoI: Robert Johnson University of Virginia N ------------------------------------------------------------------------------------ 6. Abstract Ultraviolet spectra of Jupiter's icy satellites Europa and Ganymede have revealed the presence of contaminants in surface ices produced by ion irradiation. \SOt\ ice has been identified on the trailing hemisphere of Europa at 280 nm and \oz\ on the trailing hemisphere of Ganymede in a broad band at 260 nm. Recalibrated IUE spectra now suggest the presence of a broad absorption band on Ganymede's trailing hemisphere. We will complete our survey of the ultraviolet spectra of these objects by measuring the UV spectrum of Callisto with the HST FOS. ------------------------------------------------------------------------------------ 6817( 4) - 07/08/96 13:01 - [ 2] Observations Description ------------------------ In our cycle 5 FOS observations of Europa and Ganymede we used a novel target acquisiton technique that allowed us to complete a UV spectroscopic observation of these satellites in 1 orbit. We plan to use the same observing sequence for this observation. Acquisition with the FOS is normally problematic for the Galilean satellites. However, the GHRS has a mode, LOCATE=EXTENDED designed specifically for acquisition of bright objects up to 2 arcsec in diameter. Including overheads, this procedure allows an pointing accurate to 0.1 arcsec in 11 minutes. The relative position of the GHRS and FOS apertures are also known to this precision. This accuracy is more than sufficient since Callisto will overfill the FOS 0.86 arcsec diameter aperture. In the remaining portion of the orbit we will obtain a 130 second exposure in the G270H grating and a 1080 second exposure in the G190H grating. The resultant S/N will be comparable to that of Ganymede shown in figure 1. This is more than sufficient to identify surface contaminants in the spectrum. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6817( 4) - 07/08/96 13:01 - [ 3] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: CALLISTO ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: satellite Callisto ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=CALLISTO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG OF CALLISTO FROM EARTH BETWEEN 250 | 290 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 5.65 | HRS acq for FOS science B-V = 0.86 | | ------------------------------------------------------------------------------------------------------------------------------------ 6817( 4) - 07/08/96 13:01 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CALLISTO HRS ACQ 2.0 MIRROR-N2 BRIGHT = RETURN,LOCATE = EXTENDED 1 1.8 S ONBOARD ACQ FOR 2-3 ,SEARCH-SIZE = 3 ------------------------------------------------------------------------------------------------------------------------------------ 2 CALLISTO FOS/BL ACCUM 1.0 G270H 1 130 S ------------------------------------------------------------------------------------------------------------------------------------ 3 CALLISTO FOS/BL ACCUM 1.0 G190H 1 1080 S ------------------------------------------------------------------------------------------------------------------------------------ 6817( 4) - 07/08/96 13:01 - [ 5] Summary Form for Proposal 6817 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT = RETURN LOCATE = EXTENDED SEARCH-SIZE = 3 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2-3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G270H G190H ------------------------------------------------------------------------------------------------------------------------------------ Target Names CALLISTO ------------------------------------------------------------------------------------------------------------------------------------