6725( 12) - 06/27/96 12:53 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6725 Version: 12 Check-in Date: 27-Jun-1996 12:50:38 1.Proposal Title: Io's SO2 Atmosphere: Patchy or Not? ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle SOLAR SYSTEM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: MELISSA MCGRATH SPACE TELESCOPE SCIENCE INSTITUTE CoI: Paola Sartoretti National Optical Astronomy Observatories N CoI: Michael Belton National Optical Astronomy Observatories N CoI: John Spencer Lowell Observatory N ------------------------------------------------------------------------------------ 6. Abstract We propose to make the first direct, spatially-resolved measurement of SO2 gas directly from a volcanic plume (Pele) on Io. This measurement, combined with a similar measurement from regions of the atmosphere not thought to contain a dense patch of SO2 gas, will provide the first direct evidence for whether Io's SO2 atmosphere is ``patchy." Previous HST observations of Io have shown that the region surrounding the volcano Pele is very unusual: it is very dark in the UV, possibly implying that it is covered by a dense SO2 gas patch (presumably the volcanic plume), and it has an unusual visible color, possibly implying that the surface composition near Pele is different than elsewhere on the surface of the satellite. Two interpretations of these observations are possible: either a large UV-dark patch of SO2 gas is located over the volcano, or the surface itself is very dark in the UV, confirming the very unusual nature of the surface near Pele. We propose to obtain a spatially-resolved (0.3'' aperture) Faint Object Spectrograph (FOS) spectrum of the Pele volcano using the G190H grating (~1600--2200Angstrom) covering the previously-detected SO2 bands in this wavelength region, to attempt detection of SO2 gas over the volcano. A valuable scientific result will be obtained with EITHER a detection (confirming a patchy atmosphere, and that the dark UV albedo is due to gas) OR a non-detection (confirming the unusual surface properties of the Pele volcano), which is currently impossible with existing data. ------------------------------------------------------------------------------------ 6725( 12) - 06/27/96 12:53 - [ 2] Observations Description ------------------------ Our observing strategy requires an FOS 4-stage peakup designed to center one of the visible bright patches on Io in the 0.3" aperture. For this to work correctly, we require a specific orbital longitude of Io so that the bright patch is near the limb. We realize that this will produce a very narrow scheduling window. However, the window should occur once every 42h (one Io orbit), hopefully providing ample scheduling opportunities. We further require Io to be as large in spatial extent as possible; we therefore request a scheduling window near Jupiter opposition. The observing strategy is designed to peakup on the known location of the acquisition bright spot, and then offset to the first target, which is Pele, observe it for 85m; offset to the second visible bright spot and observe it for 45m; finally offset to the last spot (which is UV-bright, visible dark) and observe for 45m. The program design assumes that the acquisition orbit is done in the Io longitude range of 262- 272. This should make it possible to observe the spots at their various latitudes and longitudes in subsequent orbits as Io rotates with time. Each observation consists of a single integration with the FOS G190H in ACCUM mode. The acquisition is done using grating G270H, since Io is too bright to be acquired with grating G400H or the mirror. We have estimated acquisition count rates of 260 cts/sec/diode at 3200A in the 0.3" aperture assuming a bright spot flux of 6x10^13 ergs/s/cm^2/A. We thus estimate that a one second step time should be adequate, particularly for the larger apertures, and including counts over the entire wavelength range of the grating. The program should execute as follows: orbit 1: Io longitude 262-272, target acq bright spot at 17,222 orbit 2: Io longitude 276-286, target Pele at -18,257 orbit 3: Io longitude 289-299, target Pele at -18,257 orbit 4: Io longitude 303-313, target Pele at -18,257 for 880S; target IO-UVBRITE at -45,300 orbit 5: Io longitude 316-326, target IO -UVBRITE at -45,300 for 1460S; target IO-VISBRITE at -7,318 for 660S orbit 6: Io longitude 330-340, target IO-VISBRITE at -7,318 for 2120S The exact times above are not crucial (i.e., we don't require exactly 2120S in orbit 6), but the longitude coverage is, so that the targets are well visible during the orbit specified. If there are problems with the schedulability, we may need to reconsider this observing plan, and will do so in close consultation with the PC and CS. Real Time Justification ----------------------- None. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6725( 12) - 06/27/96 12:53 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6725( 12) - 06/27/96 12:53 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: IO-ACQ ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | TYPE=PGRAPHIC,LONG=222,LAT=17 | OLG OF IO BETWEEN 242 252 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | F-CONT(3200)=7.5e-13 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: IO-PELE ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | TYPE=PGRAPHIC,LONG=257,LAT=-18 | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | F-CONT(2100)=5.5e-16 | | ------------------------------------------------------------------------------------------------------------------------------------ 6725( 12) - 06/27/96 12:53 - [ 5] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 | TARGET NAME: IO-UVBRITE ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | TYPE=PGRAPHIC,LONG=300,LAT=-45 | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | F-CONT(2100)=16.5e-16 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 4 | TARGET NAME: IO-VISBRITE ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | TYPE=PGRAPHIC,LONG=318,LAT=-7 | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | F-CONT(2100)=16.5e-16 | | ------------------------------------------------------------------------------------------------------------------------------------ 6725( 12) - 06/27/96 12:53 - [ 6] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 5 | TARGET NAME: IO-ACQ-2 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | TYPE=PGRAPHIC,LONG=222,LAT=17 | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | F-CONT(3200)=7.5e-13 | | ------------------------------------------------------------------------------------------------------------------------------------ 6725( 12) - 06/27/96 12:53 - [ 7] 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 IO-ACQ FOS/RD ACQ/PEA 4.3 G270H SEARCH-SIZE-X=1,SEARCH-SIZE-Y=3, 1 1 S ONBOARD ACQ FOR 12 K SCAN-STEP-Y=1.23 ------------------------------------------------------------------------------------------------------------------------------------ 12 IO-ACQ FOS/RD ACQ/PEA 1.0 G270H SEARCH-SIZE-X=6,SEARCH-SIZE-Y=2, 1 1 S ONBOARD ACQ FOR 13 K SCAN-STEP-Y=0.61,SCAN-STEP-X=0.61 ------------------------------------------------------------------------------------------------------------------------------------ 13 IO-ACQ FOS/RD ACQ/PEA 0.3 G270H 3000-32 SEARCH-SIZE-X=5,SEARCH-SIZE-Y=5, 1 1 S ONBOARD ACQ FOR 14 K 70 SCAN-STEP-Y=0.17,SCAN-STEP-X=0.17 ------------------------------------------------------------------------------------------------------------------------------------ 14 IO-ACQ-2 FOS/RD ACQ/PEA 0.3 G270H 3000-32 SEARCH-SIZE-X=6,SEARCH-SIZE-Y=6, 1 2 S ONBOARD ACQ FOR 15 K 70 SCAN-STEP-Y=0.09,SCAN-STEP-X=0.09 ------------------------------------------------------------------------------------------------------------------------------------ 15 IO-PELE FOS/RD ACCUM 0.3 G190H 1 82 M ------------------------------------------------------------------------------------------------------------------------------------ 16 IO-UVBRITE FOS/RD ACCUM 0.3 G190H 1 45 M ------------------------------------------------------------------------------------------------------------------------------------ 17 IO-VISBRITE FOS/RD ACCUM 0.3 G190H 1 45 M ------------------------------------------------------------------------------------------------------------------------------------ 6725( 12) - 06/27/96 12:53 - [ 8] Summary Form for Proposal 6725 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SCAN-STEP-Y=1.23 SCAN-STEP-X=0.61 SCAN-STEP-X=0.17 SCAN-STEP-X=0.09 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 12 ONBOARD ACQ FOR 13 ONBOARD ACQ FOR 14 ONBOARD ACQ FOR 15 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G270H G190H ------------------------------------------------------------------------------------------------------------------------------------ Target Names IO-ACQ IO-ACQ-2 IO-PELE IO-UVBRITE IO-VISBRITE ------------------------------------------------------------------------------------------------------------------------------------