Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 3862c Report Date: 09-May-96:18:53 Version: ********** Check-in Date: ********** 1.Proposal Title: THE EXCITATION OF THE ATMOSPHERES OF PLANETARY SATELLITES ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID SOLAR SYSTEM GO Sub Category ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Dr. John T. Clarke MICHIGAN, UNIVERSITY OF USA 313-747-3540 ------------------------------------------------------------------------------------ 7. Abstract We will observe Io at near and far UV wavelengths in a set of observa- tions designed to study the excitation of Io's atmosphere. The distin- guishing element of this program is the design of the observations to separate the following processes: resonant scattering of solar emission, charged particle excitation by magnetospheric plasma, and the decay in surface. Io will be observed with the FOS/HST in the near-UV over a period of time centered Io emerging from eclipse to separate the solar emissions (sunlit) from particle excited emissions (while in shadow) and the near UV SO2 aurora will be observed while Io is in shadow. Two far- UV multiplets of O and S will be observed with GHRS as Io goes into eclipse to determine the light curve by which these lines rapidly decrease in intensity when Io is in shadow, discovered in Cycle 1. The far UV lines of atomic sulfur and oxygen come from an extended atmosphere, and are produced by a combination of ionospheric currents and torus plasma impact relatively high in the atmosphere. The near-UV bands of SO reflect particle impact on SO2, the parent molecule believed to be driven by sublimation vapor pressure from the surface, and may be excited relatively closer to Io's surface (due to three times smaller scale height) by incident plasma and/or ionospheric processes. ------------------------------------------------------------------------------------ 8. Scientific Key Words: PLANETARY SATELLITE, PLASMA TORUS, AURORA ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 4.11 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: HRS FOS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 3862c PI: Dr. John T. Clarke Proposal Title: THE EXCITATION OF THE ATMOSPHERES OF PLANETARY SATELLITES ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi John T. Clarke MICHIGAN, UNIVERSITY OF USA Janet Luhmann CALIFORNIA, UNIVERSITY OF, LOS USA ANGELES Joe Ajello JET PROPULSION LABORATORY USA Nick Schneider UNIVERSITY OF COLORADO USA ------------------------------------------------------------------------------------ 2. Scientific Justification. ------------------------------------------------------------------------------------ 3. Description of proposed observations. The proposed observations are: i) two GHRS G160M LSA exposures of Io (at 1300 and 1910 A) with 1 minute readouts roughly centered on the time of eclipse disappearance for a period of 40 min. (or as long as possible in one dark orbit), ii) one FOS G270H 4.3 arc sec aperture exposure of Io with 1 minute readout time centered on the time of eclipse re-appearance for one dark orbit: the total is 3 dark orbits. Because we will be using large apertures, we request coarse track only (no fine lock) to decrease the acquisition time and avoid any chance of loss of lock. Acquisition will be accomplished by: GHRS - on-board acq. of Io, and FOS - acquiring a satellite in sunlight (listed as Ganymede, but could be any), interactive acq. of that sat., and then blind offset to Io in shadow. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The line emissions excited by the impact of magnetospheric plasma at Io are radiated chiefly in the FUV, and require a space-based instrument with high sensitivity and angular resolution to be detected. Ground-based instruments today have great difficulty in detecting atmospheric line emissions from Io. Emissions from the extended atmosphere of Io are just detectable with the IUE, but higher sensitivity and angular resolution will be required to determine the source region and spatial distribution. We have successfully performed observation (ii) above with the IUE, although the low sensitivity of IUE did not permit a positive detection of SO emission. Only the HST is fast enough to detect changes in emission brightness through the eclipse events. Io is believed to be the initial source of the plasma in Jupiter's magnetosphere, and we are proposing to observe the source region of that plasma localized in the atmosphere of Io. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. The observations of Io must be centered (+/- 15 min.) on the time of eclipse re - or dis- appearance, and must occur at the time of year when the orbital longitude of Jupiter 30 to 70 degrees for the GHRS (ingress) spectra, and 250 to 300 degrees for the FOS (egress) spectra. These constraints can be relaxed somewhat if necessary to allow scheduling. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. None. Page 3 ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. J. Ajello has recently performed laboratory studies of electron excita- tion of SO2 and N2 gases, measuring the electron impact induced fluorescence spectrum of SO2 in the UV (400-2000 A). The results of these studies show that the strongest features in the wavelength range of GHRS occur between 1200-1500A and include resonance lines of SI, SII, SIII, and OI. For these features we have measured excitation functions from 0-400 eV for modelling the excitation rates at Io. The analysis of the HST spectra will be greatly aided by our laboratory studies of electron excitation of SO2 and N2 gases. The relative strengths of the various lines will allow us to estimate the bulk composition and vertical thickness of Io's atmosphere, and the absolute intensity of the observed emission can be related to the total ionization rate and therefore the mass supply rate into the plasma torus. Through the measurements of solar scattering, particle excitation, and the several time scales for atmospheric collapse, we hope to obtain a definitive picture of the production and excitation of Io's atmosphere. Through comparison of leading and trailing face spectra, we hope to determine the process by which Titan's atmosphere is excited. The UV spectra will be reduced using standard routines. The temporal variation of the emission features in the Io data before and after eclipse re- appearance will be interpreted in terms of a model for the various emission processes discussed above. We hope to separate the strengths of the different processes by fitting components with different time scales to the measured variation in brightness of each individual line, and then compare the different ------------------------------------------------------------------------------------ 8. Additional comments or special requests. None. ------------------------------------------------------------------------------------ 9. Description of previous HST work. GO 2602 - "The Excitation of the Atmospheres of Planetary Satellites", J. Clarke PI - directly related to the proposed observations. Observations were performed on 17 January 1992 with FOS G270H and 4.3 aper. as Io entered into eclipse shadow, and on 26 January 1992 with FOS G130H and 4.3 aper. as Io entered into eclipse shadow. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Complete computing facilities are in place and available within the Space Physics Research Lab. at the University of Michigan for use on this project. Two VAX 750's and a VAX 8600 are accessible via a local area network, in addition to the Michigan network MERIT, SPAN, and Internet. A SUN 4/110 workstation with IDL is available for use, and a SUN IPX with IDL has been procured with cycle 1 GO funding. All Co-I's also have complete computing facilities at their institutions for use on this project. In addition, N. Schneider has proposed undertaking ground-based observations of Io in eclipse, to study the O[I] 6300 A emission changes for comparison with the HST UV data. ------------------------------------------------------------------------------------ 11. Address Information Name: JOHN T. CLARKE Category: PI Institution: UNIVERSITY OF MICHIGAN Address: AOSS DEPT. City: ANN ARBOR State: MI Zip Code: 481092143 Country: USA Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 3862c [ 4] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: IO-ACQ-GHRS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = JUPITER | STD = IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | | | IO-ACQ-GHRS = IO IN SUNLIGHT FOR ON- | | BOARD ACQUISITION WITH GHRS. | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: IO-INGRESS ------------------------------------------------------------------------------------------------------------------------------------ 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 30 70, | 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" | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | 1 |SURF(V) = 5.8 +/- 0.5 | OBSERVE IO GOING INTO ECLIPSE BEHIND 2 |SIZE = 1.0 +/- .2 | JUPITER; BEGIN GHRS SERIES 10-15 3 |SURF-CONT(2700) = 2 +/- 1 E-13 | MIN. BEFORE ECLIPSE DISAPPEARANCE | | AND SCHEDULE WHEN ORBITAL LONGITUDE | | OF JUPITER IS 30 TO 70 DEGREES (~FEB | | -MARCH 1993). PLEASE NOTE THAT THE | | WINDOWS CAN BE EXPANDED IF NEEDED TO | | SCHEDULE. | ------------------------------------------------------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 3862c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 | TARGET NAME: IO-ACQ-FOS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: OFFSET EUROPA ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = JUPITER | STD = EUROPA | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | 1 |SURF(V) = 5.5 +/- 0.5 | STRATEGY IS TO ACQUIRE EUROPA AND 2 |SIZE = 2.0 +/- .2 | THEN BLIND OFFSET TO IO, BOTH IN 4.3 3 |SURF-CONT(2700) = 2 +/- 1 E-13 | APERTURE. TO ACQUIRE EUROPA WITH | | FOS, TAKE A SET OF 5 SPECTRA AT | | DIFFERENT Y-DEFLECTIONS TO DETERMINE | | CENTERING IN X AND Y (FROM OBSERVED | | WAVELENGTH) THEN UPLINK HST POINTING | | CORRECTION. | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 4 | TARGET NAME: IO-EGRESS ------------------------------------------------------------------------------------------------------------------------------------ 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 250 300, | 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 EUROPA IO FROM EARTH LT 2' | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | 1 |SURF(V) = 5.8 +/- 0.5 | OBSERVE IO COMING OUT OF ECLIPSE 2 |SIZE = 1.0 +/- .2 | BEHIND JUPITER; BEGIN FOS SERIES 10- 3 |SURF-CONT(2700) = 2 +/- 1 E-13 | 15 MINUTES BEFORE IO ECLIPSE | | REAPPEARANCE AND SCHEDULE WHEN | | ORBITAL LONGITUDE OF JUPITER IS 250 | | TO 300 DEGREES. PLEASE NOTE THAT THE | | WINDOWS CAN BE EXPANDED IF NEEDED TO | | SCHEDULE. | ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 3862c [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 IO-ACQ-GHRS HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=5 1 10S 3 1 CYCLE 2 / 1-14 BRIGHT=RETURN PCS MODE C /1-14 ONBOARD ACQ FOR 4 SEQ 1-4 NO GAP Comments: ON-BOARD ACQ OF IO WITH N2. PLEASE USE INFO. FROM EARLIER IO ACQ'S FOR STEP-TIME: I ESTIMATE STEP-TIME = 0.4. ------------------------------------------------------------------------------------------------------------------------------------ 2 IO-ACQ-GHRS HRS ACQ/ 2.0 MIRROR-N2 1 40.8S 1 1 ONBOARD ACQ FOR 4 PEAKUP Comments: STEP-TIME=0.4; NEED 0.25 ARC SEC CENTERING OF IO IN LSA. PLEASE ADJUST TIME_PER_EXP IF NECESSARY. ------------------------------------------------------------------------------------------------------------------------------------ 3 IO-ACQ-GHRS HRS IMAGE 2.0 MIRROR-N2 1 96.8S 3 1 Comments: IMAGE OF IO IN LSA AFTER CENTERING. I ESTIMATE 100 COUNTS/DWELL POINT FROM IO DISK. ------------------------------------------------------------------------------------------------------------------------------------ 4 IO-INGRESS HRS RAPID 2.0 G160M 1301.0 SAMPLE- 1 25M 1 1 DARK TIME TIME=12.75 Comments: BEGIN GHRS SPECTRA AFTER IMAGE AND 10-15 MINUTES BEFORE IO PASSES INTO JUPITER'S SHADOW. SCHEDULE IN DARK TIME DUE TO 1304 AIRGLOW. ------------------------------------------------------------------------------------------------------------------------------------ 5 IO-ACQ-GHRS HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=5 1 10S 3 1 ONBOARD ACQ FOR 8 BRIGHT=RETURN SEQ 5-8 NO GAP PCS MODE C Comments: ON-BOARD ACQ OF IO WITH N2. PLEASE USE INFO. FROM EARLIER IO ACQ'S FOR STEP-TIME: I ESTIMATE STEP-TIME = 0.4. ------------------------------------------------------------------------------------------------------------------------------------ 6 IO-ACQ-GHRS HRS ACQ/ 2.0 MIRROR-N2 1 40.8S 1 1 ONBOARD ACQ FOR 8 PEAKUP Comments: STEP-TIME=0.4; NEED 0.25 ARC SEC CENTERING OF IO IN LSA. PLEASE ADJUST TIME_PER_EXP IF NECESSARY. ------------------------------------------------------------------------------------------------------------------------------------ 7 IO-ACQ-GHRS HRS IMAGE 2.0 MIRROR-N2 1 96.8S 3 1 Comments: IMAGE OF IO IN LSA AFTER CENTERING. I ESTIMATE 100 COUNTS/DWELL POINT FROM IO DISK. ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 3862c [ 7] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 8 IO-INGRESS HRS RAPID 2.0 G200M 1910.0 SAMPLE- 1 25M 1 1 TIME=12.75 Comments: BEGIN GHRS SPECTRA AFTER IMAGE AND 10-15 MINUTES BEFORE IO PASSES INTO JUPITER'S SHADOW. ------------------------------------------------------------------------------------------------------------------------------------ 9 IO-ACQ-FOS FOS/BL IMAGE 4.3 G270H Y-SIZE=5 1 300 S 3 1 SEQ 9-11 NO GAP Y-SPACE=128 RT-ANALYSIS COMB=YES SUB-STEP=4 Comments: SPECTRA OF EUROPA FOR INT. ACQ. REQUIRES REAL-TIME UPLINK FOR S /C MOTIONS IN X AND Y DURING EARTH OCCULTATION. AFTER CENTERING ON EUROPA, OFFSET TO IO, WHICH IS IN SHADOW. ------------------------------------------------------------------------------------------------------------------------------------ 10 IO-EGRESS FOS/BL RAPID 4.3 G270H STEP-PATT=DEF 1 30 M 1 1 REQ UPLINK READ-TIME=60. Comments: FOS EXPOSURES OF IO: BEGIN 10- 15 MINUTES BEFORE IO REAPPEARS IN SUNLIGHT FROM ECLIPSE. ------------------------------------------------------------------------------------------------------------------------------------ 11 IO-EGRESS FOS/BL IMAGE 4.3 G270H STEP-TIME=1.0 1 4.0 S 1 2 SUB-STEP=1 Y-SIZE=4 Y-SPACE=64 COMB=NO Comments: IMAGE OF 4.3 APERTURE FOR POST- UPLINK POINTING INFORMATION, PERFORMED AFTER IO COMES BACK INTO SUNLIGHT. ------------------------------------------------------------------------------------------------------------------------------------ 12 IO-ACQ-FOS FOS/BL IMAGE 4.3 G270H Y-SIZE=5 1 300 S 3 1 SEQ 12-14 NO GAP Y-SPACE=128 RT-ANALYSIS COMB=YES SUB-STEP=4 Comments: SPECTRA OF EUROPA FOR INT. ACQ. REQUIRES REAL-TIME UPLINK FOR S /C MOTIONS IN X AND Y DURING EARTH OCCULTATION. AFTER CENTERING ON EUROPA, OFFSET TO IO, WHICH IS IN SHADOW. ------------------------------------------------------------------------------------------------------------------------------------ 13 IO-EGRESS FOS/BL RAPID 4.3 G190H STEP-PATT=DEF 1 30 M 1 1 REQ UPLINK READ-TIME=60. Comments: FOS EXPOSURES OF IO: BEGIN 10- 15 MINUTES BEFORE IO REAPPEARS IN SUNLIGHT FROM ECLIPSE. SAME AS OTHER SET, BUT WITH G190H. ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 3862c [ 8] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 14 IO-EGRESS FOS/BL IMAGE 4.3 G270H STEP-TIME=1.0 1 4.0 S 1 2 SUB-STEP=1 Y-SIZE=4 Y-SPACE=64 COMB=NO Comments: IMAGE OF 4.3 APERTURE FOR POST- UPLINK POINTING INFORMATION, PERFORMED WHEN IO IS IN SUNLIGHT. ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 3862c [ 9] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP IMAGE RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE=5 BRIGHT=RETURN SAMPLE-TIME Y-SIZE=5 Y-SPACE=128 COMB=YES SUB-STEP=4 STEP-PATT=DEF READ-TIME=60. STEP-TIME=1.0 SUB-STEP=1 Y-SIZE=4 Y-SPACE=64 COMB=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 4.11 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 2 / 1-14; PCS MODE C /1-14; ONBOARD ACQ FOR 4; SEQ 1-4 NO GAP ONBOARD ACQ FOR 4 DARK TIME ONBOARD ACQ FOR 8; SEQ 5-8 NO GAP; PCS MODE C ONBOARD ACQ FOR 8 SEQ 9-11 NO GAP; RT-ANALYSIS; REQ UPLINK; SEQ 12-14 NO GAP; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M G200M G270H G190H ------------------------------------------------------------------------------------------------------------------------------------ Target Names IO-ACQ-GHRS IO-INGRESS IO-ACQ-FOS IO-EGRESS ------------------------------------------------------------------------------------------------------------------------------------