Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5376 Report Date: 18-Jul-95:17:15 Version: ********** Check-in Date: ********** 1.Proposal Title: A SEARCH FOR A MOLECULAR OXYGEN ATMOSPHERE ON EUROPA: CYCLE4 MEDIUM ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID SOLAR SYSTEM GO Sub Category SATELLITES ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Doyle T. Hall 2380 USA 410-516-8784 ------------------------------------------------------------------------------------ 7. Abstract We will use the HST GHRS to search for a molecular oxygen (O2) atmosphere on Jupiter's satellite Europa. The Voyager spacecraft revealed much about Europa's surface characteristics, but failed to perform occultation or airglow observations necessary to constrain its atmosphere. There is observable evidence of energetic particle sputtering on Europa's icy surface, and the sputtered water fragments are thought to reassociate to form molecular hydrogen and oxygen. The oxygen molecules are gravitationally bound to the satellite and could accumulate into a detectable O2 atmosphere. Europa lies in the outer regions of the Io plasma torus, and is subjected to a significant electron flux. If Europa has a tenuous O2 atmosphere, dissociative electron impact excitation would produce significant OI 1356A emission. We will search for this emission using the HST GHRS. The observation will provide the most stringent observational limit on Europa's atmosphere to date, improving the current upper limit by almost two orders of magnitude. Detecting an oxygen atmosphere on Europa would be a significant accomplishment for HST, and would provide invaluable information to use in planning the upcoming Galileo spacecraft encounter with the Jupiter system. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 2.52 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: HRS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5376 PI: Doyle T. Hall Proposal Title: A SEARCH FOR A MOLECULAR OXYGEN ATMOSPHERE ON EUROPA: CYCLE4 MEDIUM ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Doyle T. Hall 2380 USA Paul D. Feldman 2380 USA Melissa A. Mcgrath 3470 USA H. Warren Moos 2380 USA Darrell F. Strobel 2380 USA Harold A. Weaver 3470 USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. One dark-time observation of Europa using the LSA of the HRS centered on wavelength 1356A is requested. If GHRS side 1 is repaired during the HST servicing mission, the grating G140L is requested; otherwise use G160M. Orbital dark-time is required to minimize Earth OI 1356A airglow. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The major objective of this program is to fill in a significant gap left over from the Voyager spacecraft mission: neither Voyager encounter with the Jupiter system provided occultation or airglow measurements to constrain the extent of Europa's atmosphere. Ground-based observations are not feasible because of Earth's pervasive oxygen airglow. Finally, HST is the only operating spacecraft capable of performing the Europa OI 1356A observation. Using the IUE satellite requires prohibitively long exposure times. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. Orbital dark-time is required to minimize terrestrial OI 1356A contamination. The observation is designed to detect 200 Rayleighs of emission from Europa in the OI 1356A doublet. From HST's altitude, observed upward-looking day-time Earth airglow intensities are competitive with this. Orbital dark-time is required to obtain an unambiguous detection, and maximize the signal-to-noise with minimum spacecraft time usage. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. Page 3 ------------------------------------------------------------------------------------ 9. Description of previous HST work. ID# 2442: Cometary Parent Molecules, Feldman PI (not related) ID# 2481: HST Observations of Periodic Comets, Feldman CoI (not rel) ID# 2483: The Volatile Composition of New Comets, Feldman CoI (not rel) ID# 2625: Excitation Processes for Outer Planet UV Emission, Moos PI; McGrath, Strobel CoIs (not rel) ID# 2627: Io's Atmosphere and its Interaction with the Plasma Torus, Moos, PI; Feldman, Mcgrath, Strobel CoIs (not rel) ID# 3064: HST Observations of Comet Levy (1990c), Feldman CoI (not rel) ID# 3482: The Nature of the Variable Infalling Matter on the Star Beta Pictoris, Feldman, Moos, CoIs (not rel) ID# 3617: The UV Emissions of Titan, McGrath PI; Feldman, Moos, Strobel CoIs (not rel) ID# 3618: Excitation Processes for Outer Planet UV Emission - Cycle 2 Cont. of #2625, Moos PI; Feldman,McGrath,Strobel CoIs (not rel) ID# 3644: A Search for the Hydroxy Radical in Saturn's Magnetosphere, Shemansky PI; Hall CoI (not rel) ID# 3707: HST Observations of Periodic Comets, Feldman CoI (not rel) ID# 4513: Volatile Composition of New Comets, Feldman CoI (not rel) ID# 4349: Composition of Comet Enke, Feldman CoI (not rel) ID# 4545: Outgassing from Ceres, Feldman CoI (not rel) ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). The Johns Hopkins University provides partial salary support of the P.I., 80% of graduate student tuition fees, and contributes to the maintenance of the computers and network facilities used in this program. Similar support is provided by the other co-I institutions. ------------------------------------------------------------------------------------ 11. Address Information Name: DOYLE T. HALL Category: PI Institution: 2380 Address: THE JOHNS HOPKINS UNIVERSITY CENTER FOR ASTROPHYSICAL SCI. CHARLES AND 34TH STREETS City: BALTIMORE State: MD Zip Code: 21218 Country: USA Telephone: 410-516-8784 Telex (or e-mail): dthall@pha.jhu.edu ------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 5376 [ 4] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: EUROPA ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE EUROPA ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = JUPITER | STD = EUROPA | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | SEP OF EUROPA JUPITER FROM EARTH GT 15" | OLG OF EUROPA FROM SUN BETWEEN 225 315 | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | 1 |V = 5.3 | OBSERVE EUROPA WHEN SEPARATED FROM 2 |SURF-LINE(1355.6) = 2.4 E-12 | JUPITER BY MORE THAN 15 ARCSEC. AT 3 |W-LINE(1355.6) = 1.8 E-03 | 5AU, EUROPA'S RADIUS OF 1569 KM 4 |SIZE = 0.43 | PROJECTS AN ANGLE OF 0.43 ARCSEC. | | ASSUMING AN EMITTING ATOMIC OXYGEN | | GAS T = 150 K, THE INTRINSIC WIDTH | | OF EACH LINE IN THE DOUBLET IS 1.8 | | MA. THE OBSERVATION IS DESIGNED TO | | DETECT 200 R IN THE DOUBLET OR 158 R | | IN THE 1355.6 A LINE, OR 2.4 E-12 ER | ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5376 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 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 EUROPA HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN 1 1.44S 1 1 CYCLE 4 ONBOARD ACQ FOR 2.0 COND IF HRS SIDE 1 AVAILABLE /4.0-6.0 SELECT 1 OF 1.0- Comments: STEP-TIME = 0.16 S; EXPECT 10, 3.0 OR 4.0-6.0 000 COUNTS IN STEP-TIME; EXPOSURES 1.0-3.0 TO BE DONE IF GHRS SIDE 1 IS INOPERATIVE ------------------------------------------------------------------------------------------------------------------------------------ 2 EUROPA HRS ACQ/ 2.0 MIRROR-N2 1 16.32S 1 1 CYCLE 4 PEAKUP ONBOARD ACQ FOR 3.0 Comments: STEP-TIME = 0.16 S; EXPECT 10, 000 COUNTS IN STEP-TIME; EXPOSURES 1.0-3.0 TO BE DONE IF GHRS SIDE 1 IS INOPERATIVE ------------------------------------------------------------------------------------------------------------------------------------ 3 EUROPA HRS ACCUM 2.0 G160M 1356 FP-SPLIT=STD 1 123M 4.4 2 1 CYCLE 4 STEP-PATT=5 3 DARK TIME 4 Comments: EXPOSURES 1.0-3.0 TO BE DONE IF GHRS SIDE 1 IS INOPERATIVE ------------------------------------------------------------------------------------------------------------------------------------ 4 EUROPA HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN 1 1.44S 1 1 CYCLE 4 ONBOARD ACQ FOR 5.0 Comments: STEP-TIME = 0.16 S; EXPECT 10, 000 COUNTS IN STEP-TIME; EXPOSURES 4.0-6.0 TO BE DONE IF GHRS SIDE 1 IS OPERATIVE ------------------------------------------------------------------------------------------------------------------------------------ 5 EUROPA HRS ACQ/ 2.0 MIRROR-N2 1 16.32S 1 1 CYCLE 4 PEAKUP ONBOARD ACQ FOR 6.0 Comments: STEP-TIME = 0.16 S; EXPECT 10, 000 COUNTS IN STEP-TIME; EXPOSURES 4.0-6.0 TO BE DONE IF GHRS SIDE 1 IS OPERATIVE ------------------------------------------------------------------------------------------------------------------------------------ 6 EUROPA HRS ACCUM 2.0 G140L 1356 FP-SPLIT=STD 1 123M 9.8 2 1 CYCLE 4 STEP-PATT=5 3 DARK TIME 4 Comments: EXPOSURES 4.0-6.0 TO BE DONE IF GHRS SIDE 1 IS OPERATIVE ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5376 [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN FP-SPLIT STEP-PATT ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 2.52 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category SATELLITES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4; ONBOARD ACQ FOR 2.0; COND IF HRS SIDE 1 AVAILABLE /4.0-6.0; SELECT 1 OF 1.0-3.0 OR 4.0-6.0; ONBOARD ACQ FOR 3.0; DARK TIME; ONBOARD ACQ FOR 5.0; ONBOARD ACQ FOR 6.0; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names EUROPA ------------------------------------------------------------------------------------------------------------------------------------