! +====================+ ! | PED OUTPUT PRODUCT | ! +====================+ ! ! /spectre/data1/aroman/proposals/6840.prop ! Generated by PREPROCESSOR, version 6.3 ! Date: Tue May 28 14:47:11 EDT 1996 Proposal_Information Title: Determining the Crustal Composition of Io through Atmospheric Spectroscopy Proposal_Category: GO Scientific_Category: SOLAR SYSTEM Cycle: 6 Investigators PI_Name: Michael Brown PI_Institution: Caltech CoI_Name: Melissa McGrath CoI_Institution: Space Telescope Science Institute Contact: 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. Questions Observing_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: Fixed_Targets Solar_System_Targets Target_Number: 10 Target_Name: IO-ACQ Description: SATELLITE Io Level_1: STD=JUPITER Level_2: STD=IO Level_3: Window: OLG OF IO BETWEEN 59 73 Flux: F-CONT(2800)=5+/-1e-15 SURF(V) = 5+/-.5 SIZE=1 Comments: Io acquisition for target 20-42 Target_Number: 20 Target_Name: IO-OFFSET-1 Description: SATELLITE Io Level_1: STD=JUPITER Level_2: STD=IO Level_3: TYPE=POS_ANGLE,RAD=1,ANG=276,REF=NORTH,EPOCH=01-Jan-1902 Window: Flux: F-CONT(2800)=5+/-1e-15 SURF(V) = 5+/-.5 SIZE=1 Comments: Target_Number: 30 Target_Name: IO-OFFSET-2 Description: SATELLITE Io Level_1: STD=JUPITER Level_2: STD=IO Level_3: TYPE=POS_ANGLE,RAD=2,ANG=276,REF=NORTH,EPOCH=01-Jan-1902 Window: Flux: F-CONT(2800)=5+/-1e-15 SURF(V) = 5+/-.5 SIZE=1 Comments: Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: On_Hold_Comments: Visit_Comments: This visit takes 3 orbits, which should be scheduled without any breaks. Exposure_Number: 11 Target_Name: IO-ACQ Config: FOS/RD Opmode: ACQ/PEAK Aperture: 4.3 Sp_Element: G270H Wavelength: 2223-3277 Optional_Parameters: SEARCH-SIZE-Y=3,SCAN-STEP-Y=1.23,SCAN-STEP-X=0,SEARCH-SIZE-X=1 Number_of_Iterations: 1 Time_Per_Exposure: 1 S Special_Requirements: ONBOARD ACQ FOR 12-42 SEQ 11-21 NON-INT Comments: Inital acquisition of Io into 4.3 aperture Exposure_Number: 12 Target_Name: IO-ACQ Config: FOS/RD Opmode: ACQ/PEAK Aperture: 1.0 Sp_Element: G270H Wavelength: 2223-3277 Optional_Parameters: search-size-x=6,SEARCH-SIZE-Y=2,SCAN-STEP-Y=.61,scan-step-x=.61 Number_of_Iterations: 1 Time_Per_Exposure: 1 S Special_Requirements: ONBOARD ACQ FOR 13-42 Comments: Peakup in 1.0 arcsec aperture Exposure_Number: 13 Target_Name: IO-ACQ Config: FOS/RD Opmode: ACQ/PEAK Aperture: 1.0 Sp_Element: G270H Wavelength: 2223-3277 Optional_Parameters: search-size-x=3,SEARCH-SIZE-Y=3,SCAN-STEP-Y=.29,scan-step-x=.29 Number_of_Iterations: 1 Time_Per_Exposure: 1 S Special_Requirements: ONBOARD ACQ FOR 14-42 Comments: Exposure_Number: 14 Target_Name: IO-ACQ Config: FOS/RD Opmode: IMAGE Aperture: 1.0 Sp_Element: G270H Wavelength: 2223-3277 Optional_Parameters: Y-SPACE=32 Number_of_Iterations: 1 Time_Per_Exposure: 1 S Special_Requirements: 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. Exposure_Number: 21 Target_Name: IO-ACQ Config: FOS/RD Opmode: RAPID Aperture: 1.0 Sp_Element: G270H Wavelength: 2223-3277 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 4 M Special_Requirements: END ORBIT Comments: Take one short spectrum of Io to use for continuum subtraction of other spectra. Exposure_Number: 31 Target_Name: IO-OFFSET-1 Config: FOS/RD Opmode: RAPID Aperture: 1.0 Sp_Element: G270H Wavelength: 2223-3277 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 1040 S Special_Requirements: MAX DUR 18 M SEQ 31-32 NON-INT Comments: Offset 1" from the center of Io to take spectrum of atmosphere. Exposure_Number: 32 Target_Name: IO-OFFSET-2 Config: FOS/RD Opmode: RAPID Aperture: 1.0 Sp_Element: G270H Wavelength: 2223-3277 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 1080 S Special_Requirements: END ORBIT EXPAND Comments: Offset 2" from the center of Io to map atmosphere Exposure_Number: 41 Target_Name: IO-OFFSET-1 Config: FOS/RD Opmode: RAPID Aperture: 1.0 Sp_Element: G270H Wavelength: 2223-3277 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 1040 S Special_Requirements: MAX DUR 18 M SEQ 41-42 NON-INT Comments: Offset 1" from the center of Io. Exposure_Number: 42 Target_Name: IO-OFFSET-2 Config: FOS/RD Opmode: RAPID Aperture: 1.0 Sp_Element: G270H Wavelength: 2223-3277 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 1040 S Special_Requirements: END ORBIT EXPAND Comments: Data_Distribution ! Defaults indicated; change if desired Medium: 8MM Blocking_Factor: 10 Ship_To: PI_Address Ship_Via: UPS Recipient_Email: ! 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