6786( 18) - 07/26/96 14:11 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6786 Version: 18 Check-in Date: 26-Jul-1996 13:50:10 1.Proposal Title: HST observations of Io's atmosphere coordinated with GALILEO ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle SOLAR SYSTEM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Gilda Ballester University of Michigan CoI: John Clarke University of Michigan N CoI: Joe Ajello Jet Propulsion Laboratory N CoI: Darrell Strobel Johns Hopkins University N CoI: Nick Schneider University of Colorado N CoI: Melissa McGrath Space Telescope Science Institute N CoI: Mike Combi University of Michigan N ------------------------------------------------------------------------------------ 6. 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. ------------------------------------------------------------------------------------ 6786( 18) - 07/26/96 14:11 - [ 2] Observations 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 ------------------- ------------------------------------------------------------------------------------ 6786( 18) - 07/26/96 14:11 - [ 3] Data Distribution Media: 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 Email: , ------------------------------------------------------------------------------------ 6786( 18) - 07/26/96 14:11 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: IO-EGRESS-GHRS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | 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" | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(V) = 5.0+/-0.5 | GHRS observation of Io coming out of SIZE=1.0+/-.2 | eclipse coordinated with GALILEO. SURF-CONT(1900)=1.5+/-1e-15 | F-LINE(1304)=2.1+/-1e-13 | W-LINE(1304)=0.01 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: IO-ACQ-EGRESS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: OFFSET EUROPA ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=EUROPA | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(V) = 5.3+/-0.5 | Acquisition of Europa while Io is in SIZE=2.0+/-.2 | shadow for egress observations. SURF-CONT(2700)=2+/-1e-12 | | ------------------------------------------------------------------------------------------------------------------------------------ 6786( 18) - 07/26/96 14:11 - [ 5] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 | TARGET NAME: IO-EGRESS-FOS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | 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" | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(V) = 5.0+/-0.5 | FOS observation of Io just coming SIZE=1.0+/-.2 | out of eclipse. SURF-CONT(1900)=1.5+/-1e-15 | F-LINE(1304)=2.1+/-1e-13 | W-LINE(1304)=0.01 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 4 | TARGET NAME: IO-EAST-FOS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG OF IO BETWEEN 60 120 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(V) = 5.3+/-0.5 | Io at eastern elongation within SIZE=2.0+/-.2 | about 30 degrees. SURF-CONT(2700)=2+/-1e-13 | | ------------------------------------------------------------------------------------------------------------------------------------ 6786( 18) - 07/26/96 14:11 - [ 6] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 5 | TARGET NAME: IO-WEST-FOS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG OF IO BETWEEN 240 300 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(V) = 5.3+/-0.5 | Io at western elongation within SIZE=2.0+/-.2 | about 30 degrees. SURF-CONT(2700)=2+/-1e-13 | | ------------------------------------------------------------------------------------------------------------------------------------ 6786( 18) - 07/26/96 14:11 - [ 7] Visit: 01 Visit Requirements: BETWEEN 04-Sep-1996:09:00:00.0 AND 04-Sep-1996:10:00:00.0 On Hold Comments: Additional 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. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 111 IO-ACQ-EGRE HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=5,LOCATE=EXTENDED 1 10 S ONBOARD ACQ FOR 112-133 SS SEQ 111-113 NON-INT Comments: STEP-TIME = 0.2S On-board acquisition of Europa (or Ganymede) while Io is in eclipse. ------------------------------------------------------------------------------------------------------------------------------------ 112 IO-ACQ-EGRE HRS IMAGE 2.0 MIRROR-N2 1 51.2 S SS Comments: Image of Europa in LSA for pointing information. Estimated counts/dwell_point = 100. ------------------------------------------------------------------------------------------------------------------------------------ 113 IO-ACQ-EGRE HRS ACCUM 2.0 G200M 1795. STEP-PATT=1 5 207.2 S SS 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. ------------------------------------------------------------------------------------------------------------------------------------ 121 IO-EGRESS-G HRS ACCUM 2.0 G140L 1370. STEP-PATT=1 32 29.6 S SEQ 121,122 NON-INT HRS ------------------------------------------------------------------------------------------------------------------------------------ 122 IO-EGRESS-G HRS ACCUM 2.0 G140L 1370. STEP-PATT=1 34 29.6 S END ORBIT HRS ------------------------------------------------------------------------------------------------------------------------------------ 131 IO-EGRESS-G HRS ACCUM 2.0 G140L 1370. STEP-PATT=1 22 29.6 S SEQ 131-133 NON-INT HRS ------------------------------------------------------------------------------------------------------------------------------------ 132 IO-EGRESS-G HRS ACCUM 2.0 G140L 1542. STEP-PATT=1 4 118.4 S HRS ------------------------------------------------------------------------------------------------------------------------------------ 133 IO-EGRESS-G HRS ACCUM 2.0 G140L 1370 STEP-PATT=1 4 207.2 S HRS ------------------------------------------------------------------------------------------------------------------------------------ 6786( 18) - 07/26/96 14:11 - [ 8] Visit: 02 Visit Requirements: BETWEEN 20-Aug-1996 AND 20-Oct-1996 On Hold Comments: Additional 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. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 211 IO-ACQ-EGRE HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=5,LOCATE=EXTENDED 1 10 S ONBOARD ACQ FOR 212 SEQ SS 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. ------------------------------------------------------------------------------------------------------------------------------------ 212 IO-ACQ-EGRE FOS/RD ACQ/PEA 1.0 G270H SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3, 1 1 S ONBOARD ACQ FOR 221-233 SS K SCAN-STEP-X=0.29,SCAN-STEP-Y=0.29 Comments: FOS ACQ PEAKUP of Europa after HRS ASSISTED ACQ (C1 pattern with the 1.0 aperture). Optimizes the pointing and provides information. ------------------------------------------------------------------------------------------------------------------------------------ 221 IO-EGRESS-F FOS/RD RAPID 4.3 G190H READ-TIME=120 1 20 M SEQ 221-222 NON-INT OS Comments: G190H spectra of Io coming out of eclipse. ------------------------------------------------------------------------------------------------------------------------------------ 222 IO-EGRESS-F FOS/RD RAPID 4.3 G190H READ-TIME=120 1 18 M MAX DUR 150% END ORBIT OS Comments: G190H spectra of Io coming out of eclipse. ------------------------------------------------------------------------------------------------------------------------------------ 231 IO-EGRESS-F FOS/RD RAPID 4.3 G190H READ-TIME=120 1 20 M SEQ 231-233 NON-INT OS Comments: G190H spectra of Io after eclipse. ------------------------------------------------------------------------------------------------------------------------------------ 232 IO-EGRESS-F FOS/RD RAPID 4.3 G190H READ-TIME=120 1 10 M MAX DUR 150% OS Comments: G190H spectra of Io after eclipse. ------------------------------------------------------------------------------------------------------------------------------------ 233 IO-EGRESS-F FOS/RD IMAGE 4.3 G270H STEP-TIME=1.0,SUB-STEP=4,Y-SIZE=5 1 300 S MAX DUR 100% END ORBIT OS ,Y-SPACE=128,COMB=YES Comments: Image of Io in 4.3 FOS aperture for pointing information. ------------------------------------------------------------------------------------------------------------------------------------ 6786( 18) - 07/26/96 14:11 - [ 9] Visit: 03 Visit Requirements: AFTER 02 BY 3 H TO 1 D On Hold Comments: Additional 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.) Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 311 IO-EAST-FOS HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=5,LOCATE=EXTENDED 1 10 S 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. ------------------------------------------------------------------------------------------------------------------------------------ 312 IO-EAST-FOS FOS/RD RAPID 4.3 G190H READ-TIME=120 1 16 M NO SPLIT END ORBIT MAX DUR 200% Comments: G190H spectra of Io near eastern elongation. ------------------------------------------------------------------------------------------------------------------------------------ 6786( 18) - 07/26/96 14:11 - [ 10] Visit: 04 Visit Requirements: AFTER 03 BY 20 H TO 24 H On Hold Comments: Additional 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.) Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 411 IO-WEST-FOS HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=5,LOCATE=EXTENDED 1 10 S 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. ------------------------------------------------------------------------------------------------------------------------------------ 412 IO-WEST-FOS FOS/RD RAPID 4.3 G190H READ-TIME=120 1 16 M NO SPLIT MAX DUR 200% END ORBIT Comments: G190H spectra of Io near western elongation. ------------------------------------------------------------------------------------------------------------------------------------ 6786( 18) - 07/26/96 14:11 - [ 11] Summary Form for Proposal 6786 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ IMAGE ACCUM ACQ/PEAK RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE=5 LOCATE=EXTENDED STEP-PATT=1 SCAN-STEP-Y=0.29 READ-TIME=120 COMB=YES ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 04-Sep-1996 09 00 00.0 AND 04-Sep-1996 10 00 00.0 ONBOARD ACQ FOR 112-133 SEQ 111-113 NON-INT SEQ 121,122 NON-INT END ORBIT SEQ 131-133 NON-INT BETWEEN 20-Aug-1996 AND 20-Oct-1996 ONBOARD ACQ FOR 212 SEQ 211-212 NON-INT ONBOARD ACQ FOR 221-233 SEQ 221-222 NON-INT MAX DUR 150% END ORBIT SEQ 231-233 NON-INT MAX DUR 150% MAX DUR 100% END ORBIT AFTER 02 BY 3 H TO 1 D NO SPLIT ONBOARD ACQ FOR 312 NO SPLIT END ORBIT MAX DUR 200% AFTER 03 BY 20 H TO 24 H NO SPLIT ONBOARD ACQ FOR 412 NO SPLIT MAX DUR 200% END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G200M G140L G270H G190H ------------------------------------------------------------------------------------------------------------------------------------ Target Names IO-ACQ-EGRESS IO-EGRESS-GHRS IO-EGRESS-FOS IO-EAST-FOS IO-WEST-FOS ------------------------------------------------------------------------------------------------------------------------------------