6840( 21) - 05/28/96 14:52 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6840 Version: 21 Check-in Date: 28-May-1996 15:48:04 1.Proposal Title: Determining the Crustal Composition of Io through Atmospheric Spectroscopy ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle SOLAR SYSTEM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Michael Brown Caltech CoI: Melissa McGrath Space Telescope Science Institute N ------------------------------------------------------------------------------------ 6. Abstract Although silicate minerals are hypothesized to be the main component of the crust of Io and the primary carrier of the heat flow from the interior to the surface, no evidence for silicates has ever been seen on the surface of Io. Instead, the surface is dominated by sulfur, oxygen, and their compounds. If silicates are the primary consitutent of Io's crust, they must be almost totally covered. Voyager images do allow the possibility that a few bare silicate exposures exist near calderas and hot -spots, however. Sputtering of these bare silicates may inject silicon into Io's atmosphere in the same manner that trace amounts of sodium and potassium are sputtered into the atmosphere. We estimate that 2516 Angstrom silicon emissions could be detected by the FOS even if the surface coverage of exposed silicates were as low as 0.3% making such atmospheric spectroscopy the most sensitive method of detecting evidence for silicates on Io. We propose to search the atmosphere of Io for Si. Assuming reasonable abundances, these observations will also almost certainly produce the first detections of neutral and ionized magnesium from Io, at 2852Angstrom\ and 2795 and 2809Angstrom, respectively. Magnesium would be the first non- alkali trace element detected on Io, and its abundance will provide important clues to the distribution of trace materials on the satellite and ions in the magnetosphere. ------------------------------------------------------------------------------------ 6840( 21) - 05/28/96 14:52 - [ 2] Observations Description ------------------------ The observing program proposed here consists of a sequence of observations with the FOS and G270H grating of the atmosphere of Io, each with 45 minute exposures taken of two positions off the disk of the satellite. Si, Mg, and Mg^+ will be searched for in the 2516, 2852, and 2795 and 2809 Angstrom lines, respectively. A spectrum of the disk of Io must also be obtained in order to accurately subtract scattered light in those spectra obtained close to the limb of the satellite. The 3 orbits (assumed to have 45 minutes of usable time after guide star acquisition/reaquisition) are to be used as follows: Orbit 1: Acquisition of Io into aperture 1.0 using ACQ/PEAK and the A+B1+C1 search strategy, 29 minutes. The remaining 16 minutes will be used for a confirmatory ACQ to map the location of Io in the aperture and a spectrum of Io to assist in subtracting the scattered light from the other spectra. Orbit 2: Spectrum offset 1 arcsec from Io center, 45 minutes. Orbit 3: Spectrum offset 2 arcsec from Io center, 45 minutes. Real Time Justification ----------------------- For all observations, Io must be near eastern elongation for maximum separation from the glare of Jupiter and to doppler shift the exciting emission out of deep absorption lines in the solar spectrum. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6840( 21) - 05/28/96 14:52 - [ 3] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 10 | 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 | | OLG OF IO BETWEEN 59 73 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | F-CONT(2800)=5+/-1e-15 | Io acquisition for target 20-42 SURF(V) = 5+/-.5 | SIZE=1 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 20 | TARGET NAME: IO-OFFSET-1 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE Io ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | TYPE=POS_ANGLE,RAD=1,ANG=276,REF=NORTH,E | POCH=01-Jan-1902 | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | F-CONT(2800)=5+/-1e-15 | SURF(V) = 5+/-.5 | SIZE=1 | | ------------------------------------------------------------------------------------------------------------------------------------ 6840( 21) - 05/28/96 14:52 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 30 | TARGET NAME: IO-OFFSET-2 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE Io ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=JUPITER | STD=IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | TYPE=POS_ANGLE,RAD=2,ANG=276,REF=NORTH,E | POCH=01-Jan-1902 | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | F-CONT(2800)=5+/-1e-15 | SURF(V) = 5+/-.5 | SIZE=1 | | ------------------------------------------------------------------------------------------------------------------------------------ 6840( 21) - 05/28/96 14:52 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: This visit takes 3 orbits, which should be scheduled without any breaks. 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 2223-32 SEARCH-SIZE-Y=3,SCAN-STEP-Y=1.23, 1 1 S ONBOARD ACQ FOR 12-42 SEQ K 77 SCAN-STEP-X=0,SEARCH-SIZE-X=1 11-21 NON-INT Comments: Inital acquisition of Io into 4.3 aperture ------------------------------------------------------------------------------------------------------------------------------------ 12 IO-ACQ FOS/RD ACQ/PEA 1.0 G270H 2223-32 search-size-x=6,SEARCH-SIZE-Y=2, 1 1 S ONBOARD ACQ FOR 13-42 K 77 SCAN-STEP-Y=.61,scan-step-x=.61 Comments: Peakup in 1.0 arcsec aperture ------------------------------------------------------------------------------------------------------------------------------------ 13 IO-ACQ FOS/RD ACQ/PEA 1.0 G270H 2223-32 search-size-x=3,SEARCH-SIZE-Y=3, 1 1 S ONBOARD ACQ FOR 14-42 K 77 SCAN-STEP-Y=.29,scan-step-x=.29 ------------------------------------------------------------------------------------------------------------------------------------ 14 IO-ACQ FOS/RD IMAGE 1.0 G270H 2223-32 Y-SPACE=32 1 1 S 77 Comments: Map location of Io in 1.0" aperture so that we will know precisely where we are pointing for the offsets in the next few exposures. ------------------------------------------------------------------------------------------------------------------------------------ 21 IO-ACQ FOS/RD RAPID 1.0 G270H 2223-32 1 4 M END ORBIT 77 Comments: Take one short spectrum of Io to use for continuum subtraction of other spectra. ------------------------------------------------------------------------------------------------------------------------------------ 31 IO-OFFSET-1 FOS/RD RAPID 1.0 G270H 2223-32 1 1040 S MAX DUR 18 M SEQ 31-32 77 NON-INT Comments: Offset 1" from the center of Io to take spectrum of atmosphere. ------------------------------------------------------------------------------------------------------------------------------------ 32 IO-OFFSET-2 FOS/RD RAPID 1.0 G270H 2223-32 1 1080 S END ORBIT EXPAND 77 Comments: Offset 2" from the center of Io to map atmosphere ------------------------------------------------------------------------------------------------------------------------------------ 41 IO-OFFSET-1 FOS/RD RAPID 1.0 G270H 2223-32 1 1040 S MAX DUR 18 M SEQ 41-42 77 NON-INT Comments: Offset 1" from the center of Io. ------------------------------------------------------------------------------------------------------------------------------------ 42 IO-OFFSET-2 FOS/RD RAPID 1.0 G270H 2223-32 1 1040 S END ORBIT EXPAND 77 ------------------------------------------------------------------------------------------------------------------------------------ 6840( 21) - 05/28/96 14:52 - [ 6] Summary Form for Proposal 6840 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK IMAGE RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE-Y=3 SCAN-STEP-Y=1.23 SCAN-STEP-X=0 SEARCH-SIZE-X=1 scan-step-x=.61 scan-step-x=.29 Y-SPACE=32 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 12-42 SEQ 11-21 NON-INT ONBOARD ACQ FOR 13-42 ONBOARD ACQ FOR 14-42 END ORBIT MAX DUR 18 M SEQ 31-32 NON-INT END ORBIT EXPAND MAX DUR 18 M SEQ 41-42 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G270H ------------------------------------------------------------------------------------------------------------------------------------ Target Names IO-ACQ IO-OFFSET-1 IO-OFFSET-2 ------------------------------------------------------------------------------------------------------------------------------------