! +====================+ ! | PED OUTPUT PRODUCT | ! +====================+ ! ! /spectre/data1/aroman/proposals/6786.prop ! Generated by PREPROCESSOR, version 6.3g ! Date: Fri Jul 26 13:48:43 EDT 1996 Proposal_Information Title: HST observations of Io's atmosphere coordinated with GALILEO Proposal_Category: GO Scientific_Category: SOLAR SYSTEM Cycle: 6 Investigators PI_Name: Gilda Ballester PI_Institution: University of Michigan CoI_Name: John Clarke CoI_Institution: University of Michigan Contact: CoI_Name: Joe Ajello CoI_Institution: Jet Propulsion Laboratory Contact: CoI_Name: Darrell Strobel CoI_Institution: Johns Hopkins University Contact: CoI_Name: Nick Schneider CoI_Institution: University of Colorado Contact: CoI_Name: Melissa McGrath CoI_Institution: Space Telescope Science Institute Contact: CoI_Name: Mike Combi CoI_Institution: University of Michigan Contact: Abstract: The main molecular component of Io's atmosphere, SO_2, has been detected in its strong absorption bands around 2000 Angstroms with HST reflectance spectra. SO_2 is produced by sublimation of frost deposits and direct outgassing from volcanoes. Although modeling of the HST data has set valuable constraints, the nature of these sources remains to be unambiguously determined. We propose to separate the sublimation and volcanic SO_2 components with 3 HST orbits to obtain FOS G190H disk-integrated spectra with the best possible S/N as a function of time as Io comes out of eclipse and its SO_2 frost deposits warm up by sunlight and build up the sublimation component. Two additional orbits are requested for SO_2 observations of Io at east and west elongation for comparison of the leading, trailing and Jupiter-facing hemispheres, and against previous east/west observations to measure variations associated with volcanic activity. A second set of 3 HST orbits are requested for observations of Io coming out of eclipse in support of GALILEO UVS eclipse observations during its third approach to Jupiter (G2). Both instruments would take nearly simultaneous disk-integrated spectra of the far-UV emissions by the main atomic atmospheric components O and S, the excitation of which is somehow controlled by the atmosphere-torus interaction. Although farther from Io and with a smaller spectral coverage, GHRS G140L would provide higher S/N and better temporal and spectral resolution, which would be very valuable for interpretation of the GALILEO data. Questions Observing_Description: Four Visits will be made for a total of 8 HST orbits. Visits 2,3 and 4 should be nearly contiguous. Visit 1: Three orbits for GHRS observations of the O and S atmospheric emissions as Io comes out of eclipse. These observations should be simultaneous with GALILEO observations of Io coming out of eclipse planned for 04 Sep 1996 from 11:18 to 12:40 UT (outside lunar avoidance). In case this observing time is absolutely unfeasible, e.g. because of HST orbit constraints or SAA problems, we will observe the closest possible in time either after (or before) the eclipse, which would still provide valuable information. The first orbit will consist of the guide star acquisition, on-board acquisition of another Galilean satellite with GHRS side 2, and a GHRS image of the satellite for pointing information. (An exposure of the acquisition satellite was added to fill up this orbit and obtain a solar-like spectrum.) During Earth occultation we will switch from GHRS side 2 to side 1. In the second orbit we will slew to Io and observe it as it comes out of eclipse, taking consecutive G140L spectra centered at 1370 Angstroms with 0.5 min integration time. Similar spectra will be taken in the third orbit, but will cover the whole 1100-1900 Angstroms region of O and S emissions. Visit 2: Three orbits for FOS observations as Io comes out of eclipse and afterwards, to measure changes in the SO_2 atmospheric abundance due to sublimation of SO_2 frost by sunlight. The first orbit will consist of the guide star acquisition and a GHRS (side 2) assisted acquisition of Europa or Ganymede. (An exposure of the acquisition satellite was added to fill up this orbit and obtain a solar-like spectrum.) In the second orbit we will then the slew to Io and center it in the FOS/BL 4.3" aperture to observe it as it just comes out of eclipse and afterwards, taking consecutive G190H spectra of 2.0 min of integration in RAPID readout mode. Similar spectra will be taken in the third orbit, plus a G270H image for pointing information. The main constraint when choosing the observing date for this Visit is to observe Io in the second orbit for the maximum possible amount of time (eg, 30-40 minutes) after it has just come out of eclipse, so that we can measure the rate of buildup of the SO_2 sublimation component after shadow. (Ie, rather than splitting the observation half and half in shadow and sunlight, best to take roughly ~5 minutes in shadow or during eclipse exit, and over roughly ~30 minutes in sunlight.) Visits 3 and 4: Visit 3 will consist of one orbit for FOS/BL G190H 4.3" aperture observations of the SO_2 atmosphere on Io's leading hemisphere when near eastern elongation. A GHRS assisted acquisition of Io will be made, and then FOS G190H blue side spectra will be obtained. Visit 4 will be similar but will be to observe the trailing hemisphere when near western elongation. Io can be observed near eastern or western elongation (respectively at OLG of 90 and 270 degrees) within about +/- 30 degrees or +/- 3.5 hours from elongation. We would like Visit 4 to either precede or follow Visit 3 by roughly half an Io orbit (roughly 22 hours), in order to observe the two hemispheres the closest possible in time for comparison to the similar east/west pair of observations made in 1994. Ideally, we would benefit from scheduling Visits 3 and 4 in conjunction with Visit 2, by scheduling Visit 3 just some hours after Visit 2. The purpose is to measure the SO_2 abundance on the leading hemisphere (OLG ~ 90 degrees) just after the Jupiter-facing hemisphere (OLG > 15 degrees) has been observed in Visit 2, and to do the further comparison with the trailing hemisphere (OLG ~ 270 degrees). We realize that this additional constraint may complicate the scheduling. If this arrangement is impossible, then the pair of Visits 3 and 4 could be scheduled at another time, though we would still benefit if they are scheduled the closest possible in time to Visit 2. The alternative of scheduling Visits 2, 3 and 4 within about week may also give useful results. Real_Time_Justification: The second orbit of Visit 1 should overlap the GALILEO observations of Io coming out of eclipse currently planned for 4 Sep 1996 11:18--12:40 UT. However, this date may change, perhaps to about a week earlier, and we will keep the program coordinator informed as soon we find out. In case an HST orbit cannot overlap the GALILEO observation, we should observe the closest possible after (or before), in which case the Phase 2 will need to be modified (eg, we may be able to acquire Io directly instead of offsetting from Europa). The second orbit of Visit 2 should be chosen to observe Io the longest possible (eg, 30-40 minutes) just after it comes out of eclipse. The purpose is to measure the rate at which the atmospheric SO_2 builds up by sublimation of SO_2 frost from sunlight. The visit's window is 20 Aug - 20 Oct 1996, when Io is separated by at least about 20" from Jupiter's limb at eclipse exit. Calibration_Justification: Additional_Comments: Fixed_Targets Solar_System_Targets Target_Number: 1 Target_Name: IO-EGRESS-GHRS Description: SATELLITE IO Level_1: STD=JUPITER Level_2: STD=IO Level_3: Window: OLG OF JUPITER BETWEEN 260 330, OLG OF IO BETWEEN 0 60, ECL U OF IO BY JUPITER, SEP OF EUROPA IO FROM EARTH GT 10", SEP OF GANYMEDE IO FROM EARTH GT 10", SEP OF CALLISTO IO FROM EARTH GT 10" Flux: SURF(V) = 5.0+/-0.5 SIZE=1.0+/-.2 SURF-CONT(1900)=1.5+/-1e-15 F-LINE(1304)=2.1+/-1e-13 W-LINE(1304)=0.01 Comments: GHRS observation of Io coming out of eclipse coordinated with GALILEO. Target_Number: 2 Target_Name: IO-ACQ-EGRESS Description: OFFSET EUROPA Level_1: STD=JUPITER Level_2: STD=EUROPA Level_3: Window: Flux: SURF(V) = 5.3+/-0.5 SIZE=2.0+/-.2 SURF-CONT(2700)=2+/-1e-12 Comments: Acquisition of Europa while Io is in shadow for egress observations. Target_Number: 3 Target_Name: IO-EGRESS-FOS Description: SATELLITE IO Level_1: STD=JUPITER Level_2: STD=IO Level_3: Window: OLG OF JUPITER BETWEEN 260 330, OLG OF IO BETWEEN 0 60, ECL U OF IO BY JUPITER, SEP OF EUROPA IO FROM EARTH GT 10", SEP OF GANYMEDE IO FROM EARTH GT 10", SEP OF CALLISTO IO FROM EARTH GT 10", SEP OF JUPITER IO FROM EARTH GT 20" Flux: SURF(V) = 5.0+/-0.5 SIZE=1.0+/-.2 SURF-CONT(1900)=1.5+/-1e-15 F-LINE(1304)=2.1+/-1e-13 W-LINE(1304)=0.01 Comments: FOS observation of Io just coming out of eclipse. Target_Number: 4 Target_Name: IO-EAST-FOS Description: SATELLITE IO Level_1: STD=JUPITER Level_2: STD=IO Level_3: Window: OLG OF IO BETWEEN 60 120 Flux: SURF(V) = 5.3+/-0.5 SIZE=2.0+/-.2 SURF-CONT(2700)=2+/-1e-13 Comments: Io at eastern elongation within about 30 degrees. Target_Number: 5 Target_Name: IO-WEST-FOS Description: SATELLITE IO Level_1: STD=JUPITER Level_2: STD=IO Level_3: Window: OLG OF IO BETWEEN 240 300 Flux: SURF(V) = 5.3+/-0.5 SIZE=2.0+/-.2 SURF-CONT(2700)=2+/-1e-13 Comments: Io at western elongation within about 30 degrees. Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: BETWEEN 04-Sep-1996:09:00:00.0 AND 04-Sep-1996:10:00:00.0 On_Hold_Comments: Visit_Comments: Coordinated with GALILEO observations of Io coming out of eclipse, planned for 04 SEP 1996 11:18 - 12:40 UT (outside lunar avoidance). Three HST orbits to observe Io with GHRS as it comes out of eclipse, or the closest possible to the GALILEO observations. Exposure_Number: 111 Target_Name: IO-ACQ-EGRESS Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N2 Wavelength: Optional_Parameters: SEARCH-SIZE=5,LOCATE=EXTENDED Number_of_Iterations: 1 Time_Per_Exposure: 10 S Special_Requirements: ONBOARD ACQ FOR 112-133 SEQ 111-113 NON-INT Comments: STEP-TIME = 0.2S On-board acquisition of Europa (or Ganymede) while Io is in eclipse. Exposure_Number: 112 Target_Name: IO-ACQ-EGRESS Config: HRS Opmode: IMAGE Aperture: 2.0 Sp_Element: MIRROR-N2 Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 51.2 S Special_Requirements: Comments: Image of Europa in LSA for pointing information. Estimated counts/dwell_point = 100. Exposure_Number: 113 Target_Name: IO-ACQ-EGRESS Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G200M Wavelength: 1795. Optional_Parameters: STEP-PATT=1 Number_of_Iterations: 5 Time_Per_Exposure: 207.2 S Special_Requirements: Comments: G200M observation of Europa for solar-like spectra for analysis of Io exposure 133. Added to use last portion of acq. orbit. Offset to Io in next orbit. Exposure_Number: 121 Target_Name: IO-EGRESS-GHRS Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1370. Optional_Parameters: STEP-PATT=1 Number_of_Iterations: 32 Time_Per_Exposure: 29.6 S Special_Requirements: SEQ 121,122 NON-INT Comments: Exposure_Number: 122 Target_Name: IO-EGRESS-GHRS Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1370. Optional_Parameters: STEP-PATT=1 Number_of_Iterations: 34 Time_Per_Exposure: 29.6 S Special_Requirements: END ORBIT Comments: Exposure_Number: 131 Target_Name: IO-EGRESS-GHRS Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1370. Optional_Parameters: STEP-PATT=1 Number_of_Iterations: 22 Time_Per_Exposure: 29.6 S Special_Requirements: SEQ 131-133 NON-INT Comments: Exposure_Number: 132 Target_Name: IO-EGRESS-GHRS Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1542. Optional_Parameters: STEP-PATT=1 Number_of_Iterations: 4 Time_Per_Exposure: 118.4 S Special_Requirements: Comments: Exposure_Number: 133 Target_Name: IO-EGRESS-GHRS Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1370 Optional_Parameters: STEP-PATT=1 Number_of_Iterations: 4 Time_Per_Exposure: 207.2 S Special_Requirements: Comments: Visit_Number: 02 Visit_Requirements: BETWEEN 20-Aug-1996 AND 20-Oct-1996 On_Hold_Comments: Visit_Comments: Three orbits to observe Io with FOS coming out of eclipse. In the 2nd orbit Io should be observed for the longest possible after eclipse exit. During the given window Io will be separated by at least about 20" from Jupiter's limb when exiting eclipses. Exposure_Number: 211 Target_Name: IO-ACQ-EGRESS Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N2 Wavelength: Optional_Parameters: SEARCH-SIZE=5,LOCATE=EXTENDED Number_of_Iterations: 1 Time_Per_Exposure: 10 S Special_Requirements: ONBOARD ACQ FOR 212 SEQ 211-212 NON-INT Comments: STEP-TIME = 0.2S GHRS assisted on-board acquisition of Europa (or Ganymede) while Io is eclipsed. Switch to FOS/BL --- KEEP SAME GUIDE STARS. Exposure_Number: 212 Target_Name: IO-ACQ-EGRESS Config: FOS/RD Opmode: ACQ/PEAK Aperture: 1.0 Sp_Element: G270H Wavelength: Optional_Parameters: SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3,SCAN-STEP-X=0.29,SCAN-STEP-Y=0.29 Number_of_Iterations: 1 Time_Per_Exposure: 1 S Special_Requirements: ONBOARD ACQ FOR 221-233 Comments: FOS ACQ PEAKUP of Europa after HRS ASSISTED ACQ (C1 pattern with the 1.0 aperture). Optimizes the pointing and provides information. Exposure_Number: 221 Target_Name: IO-EGRESS-FOS Config: FOS/RD Opmode: RAPID Aperture: 4.3 Sp_Element: G190H Wavelength: Optional_Parameters: READ-TIME=120 Number_of_Iterations: 1 Time_Per_Exposure: 20 M Special_Requirements: SEQ 221-222 NON-INT Comments: G190H spectra of Io coming out of eclipse. Exposure_Number: 222 Target_Name: IO-EGRESS-FOS Config: FOS/RD Opmode: RAPID Aperture: 4.3 Sp_Element: G190H Wavelength: Optional_Parameters: READ-TIME=120 Number_of_Iterations: 1 Time_Per_Exposure: 18 M Special_Requirements: MAX DUR 150% END ORBIT Comments: G190H spectra of Io coming out of eclipse. Exposure_Number: 231 Target_Name: IO-EGRESS-FOS Config: FOS/RD Opmode: RAPID Aperture: 4.3 Sp_Element: G190H Wavelength: Optional_Parameters: READ-TIME=120 Number_of_Iterations: 1 Time_Per_Exposure: 20 M Special_Requirements: SEQ 231-233 NON-INT Comments: G190H spectra of Io after eclipse. Exposure_Number: 232 Target_Name: IO-EGRESS-FOS Config: FOS/RD Opmode: RAPID Aperture: 4.3 Sp_Element: G190H Wavelength: Optional_Parameters: READ-TIME=120 Number_of_Iterations: 1 Time_Per_Exposure: 10 M Special_Requirements: MAX DUR 150% Comments: G190H spectra of Io after eclipse. Exposure_Number: 233 Target_Name: IO-EGRESS-FOS Config: FOS/RD Opmode: IMAGE Aperture: 4.3 Sp_Element: G270H Wavelength: Optional_Parameters: STEP-TIME=1.0,SUB-STEP=4,Y-SIZE=5,Y-SPACE=128,COMB=YES Number_of_Iterations: 1 Time_Per_Exposure: 300 S Special_Requirements: MAX DUR 100% END ORBIT Comments: Image of Io in 4.3 FOS aperture for pointing information. Visit_Number: 03 Visit_Requirements: AFTER 02 BY 3 H TO 1 D On_Hold_Comments: Visit_Comments: One orbit for FOS observations of Io near eastern elongation (+/- 3.5 hours or +/- 30 degrees from elongation). Would benefit from scheduling just some hours after Visit 2, and close in time to Visit 4. (See details in Observing_Description.) Exposure_Number: 311 Target_Name: IO-EAST-FOS Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N2 Wavelength: Optional_Parameters: SEARCH-SIZE=5,LOCATE=EXTENDED Number_of_Iterations: 1 Time_Per_Exposure: 10 S Special_Requirements: NO SPLIT ONBOARD ACQ FOR 312 Comments: STEP-TIME = 0.4S On-board acquisition of Io with GHRS. Switch to FOS/RD --- KEEPING SAME GUIDE STARS. Exposure_Number: 312 Target_Name: IO-EAST-FOS Config: FOS/RD Opmode: RAPID Aperture: 4.3 Sp_Element: G190H Wavelength: Optional_Parameters: READ-TIME=120 Number_of_Iterations: 1 Time_Per_Exposure: 16 M Special_Requirements: NO SPLIT END ORBIT MAX DUR 200% Comments: G190H spectra of Io near eastern elongation. Visit_Number: 04 Visit_Requirements: AFTER 03 BY 20 H TO 24 H On_Hold_Comments: Visit_Comments: One orbit for FOS observations of Io near western elongation (+/- 3.5 hours or +/- 30 degrees from elongation). Would benefit from scheduling roughly 22 hours before or after Visit 3. (See details in Observing_Description.) Exposure_Number: 411 Target_Name: IO-WEST-FOS Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N2 Wavelength: Optional_Parameters: SEARCH-SIZE=5,LOCATE=EXTENDED Number_of_Iterations: 1 Time_Per_Exposure: 10 S Special_Requirements: NO SPLIT ONBOARD ACQ FOR 412 Comments: STEP-TIME = 0.4S On-board acquisition of Io with GHRS. Switch to FOS/RD --- KEEP SAME GUIDE STARS. Exposure_Number: 412 Target_Name: IO-WEST-FOS Config: FOS/RD Opmode: RAPID Aperture: 4.3 Sp_Element: G190H Wavelength: Optional_Parameters: READ-TIME=120 Number_of_Iterations: 1 Time_Per_Exposure: 16 M Special_Requirements: NO SPLIT MAX DUR 200% END ORBIT Comments: G190H spectra of Io near western elongation. Data_Distribution ! Defaults indicated; change if desired Medium: 8MM Blocking_Factor: 10 Ship_To: University of Michigan, AOSS - Space Physics Research Lab, 2455 Hayward St., Ann Arbor, MI 48109-2143 Ship_Via: UPS Recipient_Email: ! 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