Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5391 Report Date: 18-Jul-95:17:17 Version: ********** Check-in Date: ********** 1.Proposal Title: MAPPING THE HYDROXYL DISTRIBUTION IN THE SATURN MAGNETOSPHERE CYCLE4MEDIUM ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID SOLAR SYSTEM GO Sub Category GIANT PLANETS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Donald E. Shemansky UNIV. OF SOUTHERN CALIFORNIA USA ------------------------------------------------------------------------------------ 7. Abstract A total of 16 hrs primary spacecraft time is requested here in our attempt to confirm and to expand our HST Cycle-2 program of August, 1992 (GO3644). In that program, the HST/FOS was used to discover the presence of neutral OH in the Saturn magnetosphere. This was first observation of a molecular neutral species in a magnetosphere. The observed brightness of 37 Rayleighs in the OH 3085 A band places a lower limit of 160 mol/cm^3 in the region near the orbit of Tethys. This result constrasts sharply with prevailing theories and models of plasma source and transport processes at Saturn, which limit the neutral density in that region to < 10 mol/cm^3. It is necessary to confirm and expand the previous finding to provide constraints for examining source processes from the icy moons and rings. Our model predicts the OH cloud extends beyond Rhea's orbit. A source rate of > 10^27 mol/s is predicted and agrees with the previous HST result, but is more than 10 times estimates based upon ion sputtering of the icy moons and rings. Possibly, micrometeoritic gardening of the icy moons significantly alters the source rate. If so, this result has substantial impact upon understanding of evolutionary processes in the atmospheres of other planets. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 16.00 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5391 PI: Donald E. Shemansky Proposal Title: MAPPING THE HYDROXYL DISTRIBUTION IN THE SATURN MAGNETOSPHERE CYCLE4MEDIUM ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Donald E. Shemansky UNIV. OF SOUTHERN CALIFORNIA USA Philip L. Matheson UNIV. OF SOUTHERN CALIFORNIA USA Hongyao D. Hu UNIV. OF SOUTHERN CALIFORNIA USA Doyle T. Hall JOHNS HOPKINS UNIV. USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. Three observations, evenly divided in 16 hrs of primary spacecraft time, will be conducted at positions ~37 arcsec, ~50 arcsec and ~82 arcsec on the dusk side of Saturn in the equatorial plasma sheet. An offset of 37 arcsec corresponds to 4.5 Saturn radii (R_S). A satellite, probably Titan, will be used for Onboard Acquisition to remove zero point error in the ephemeris with respect to the guide stars. Subsequently the aperture will be offset to the desired observation point. The FOS Red Digicon will be used with the G270H grating and the 0.7x2.0-Bar aperture. The Red Digicon using the G270H yields the greatest detection efficiency at the OH 3085A A-X(0,0) band. The 0.7x2.0-Bar aperture is the largest available for our desired resolution and is selected because a maximal field of view is necessary to enhance the signal to noise ratio (SNR). Our last HST observation showed that to achieve SNR > 5 for the expected 37 R emission at 3085A, exposure durations of at least 3.5 hours are necessary because of strong competative solar scattering from rings, zodiacal and diffuse galactic sky background signals. Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. An extraterrestrial OH A-X(0,0) feature cannot be detected with ground based apparatus because of strong airglow foreground signals and atmos- pheric absorption. The IUE spacecraft has detected OH in comets, but the expected intensity in Saturn's magnetosphere lies below its detect- able threshold. The HST is the only currently operating platform from which these observations can be performed. Although the proposed fixes to HST will improve the signal to noise ratio, we have calculated our required exposure times on the basis of current platform characteristics. For the extended source to be viewed here, improvements in resolution are offset by the smaller field of view of the aperture. Cycle-2 GO3644 established that HST FOS can detect a 37 Rayleigh emission with SNR >5 in 3.5 hours of exposure time under the presence of competitive solar scattering from the rings, zodiacal and diffuse galactic sky background using the FOS Red Digicon and G270H grating. The 0.7x2.0- Bar aperture has the largest field of view commensurate with a desired resolution of > 600. An SNR of ~5 is adequate to establish the quantity of physically significant OH 3085A emissions in Saturn's magnetosphere. Exposures of 5 hours each are requested to account for reasonable variations in source strength. Three observations at 4.5 R_S, 6.0 R_S and 10.0 R_S (37, 50 and 82 arcsec, respectively) in the orbital plane of the satellites will be used to comfirm and map the distribution of OH in the Saturn magneto- sphere. All exposures are to be on the dusk side. The signal at 4.5 R_S is expected to be ~37 Rayleighs as in the Cycle-2 GO3644 discovery observation. Theoretical models of the distribution of OH indicate that emissions 6.0 R_S should be comparable to those at 4.5 R_S, requiring a similar exposure time. An exposure at 10 R_S is to establish the limits of the OH distribution. Our own models do not indicate a signi- amount of OH to be present past the orbit of Rhea (8.8R_S) but we have no way of definitively predicting the detectable edge of the OH neutral cloud. The measurement is intended to place an upper limit on the amount of OH at that location, and provide information on the kinetic distribution of water product neutrals produced in the magnetosphere. The 16 hours of available primary spacecraft time is to be divided equally between the exposures at each location. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. No special calibration required. ------------------------------------------------------------------------------------ 11. Address Information Name: DOANLD E. SHEMANSKY Category: PI Institution: UNIV. OF SOUTHERN CALIFORNIA Address: DEPT. OF AEROSPACE ENGINEERING UNIV. OF SOUTHERN CALIFORNIA City: LOS ANGELES State: CA Zip Code: 90089 Country: USA Telephone: 213-740-7184 Telex (or e-mail): 4720490 USC LSA ------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 5391 [ 4] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: SATH1 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: OFFSET SATURN ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = SATURN, ACQ=1.5 | TYPE = TORUS, | LONG = 90, | LAT = 0, | RAD = 2.7E+05, | POLE_LAT = +90 | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | SEP OF SATH1 TETHYS FROM EARTH GT 10" | SEP OF SATH1 DIONE FROM EARTH GT 10" | SEP OF SATH1 RHEA FROM EARTH GT 12" | SEP OF SATH1 TITAN FROM EARTH GT 14" | SEP OF SATH1 HYPERION FROM EARTH GT 5" | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | | | VALIDATE-BUG REFUSED SOME `SEP' USB- | | TA SAYS INCLUDE REQ. AS COMMENTS: | | SEP OF SATH1 IAPETUS FROM EARTH GT | | 7" SEP OF SATH1 ENCELADUS FROM EARTH | | GT 5" ESTIMATED BRIGHTNESS 35 | | RAYLEIGHS | ------------------------------------------------------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 5391 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: SATH2 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: OFFSET SATURN ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = SATURN, ACQ=1.5 | TYPE = TORUS, | LONG = 90, | LAT = 0, | RAD = 3.6E+05, | POLE_LAT = +90 | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | | | ESTIMATED BRIGHTNESS 35 RAYLEIGHS | | FOR TARGET 1 AND 2. CONTINUUM IS SKY | | BACK GROUND. SATELLITES MUST LIE | | OUTSIDE FIELD OF VIEW AS SPECIFIED | | ABOVE FOR TARGET 1. NOTE COMMENTS | | FOR TARGET 1. FLUX VALUES NOT | | INCLUDED SINCE THROUGHPUT OF 0.7X2- | | BAR AP. IS ESTIMATED FOR EXTENDED | | SOURCE RATHER THAN OCCULTED POINTED | | SOURCE. | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 | TARGET NAME: SATH3 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: OFFSET SATURN ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = SATURN, ACQ=1.5 | TYPE = TORUS, | LONG = 90, | LAT = 0, | RAD = 6.0E+05, | POLE_LAT = +90 | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | | | ESTIMATED FLUX IS UNKNOWN. THIS | | TARGET IS TO ESTABLISH LIMIT ON | | EXTENT OF OH CLOUD AT SATURN | | SATELLITES MUST LIE OUTSIDE FIELD OF | | VIEW AS SPECIFIED FOR TARGET 1 AND 2 | | SEE COMMENT FOR TARGET 1 AND 2. | ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5391 [ 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 SATH1 FOS/RD ACCUM 0.7X2.0 G270H 1 231M 5 1 CYCLE4 / 1-3 -BAR Comments: EXPOSURE TIME BASED UPON PREVIOUS HST OBSERVATION GO- 3644 AND MODEL CALCULATIONS FLUX VALUES NOT INCLUDE SINCE ESTIMATE OF THROUGHPUT FOR AP 0.7X2-BAR IS FOR EXTENDED SOURCE ------------------------------------------------------------------------------------------------------------------------------------ 2 SATH2 FOS/RD ACCUM 0.7X2.0 G270H 1 231M 5 2 -BAR Comments: EXPOSURE TIME BASED UPON MODEL PREDICTING OH AMOUNT AT 6 RS TO BE COMPARABLE TO THAT OBSERVED AT 4.5 RS ------------------------------------------------------------------------------------------------------------------------------------ 3 SATH3 FOS/RD ACCUM 0.7X2.0 G270H 1 231M 5 3 -BAR Comments: EXPOSURE TIME REQUESTED TO SET LIMIT ON DISTRIBUTION OF OH IN SATURN MAGNETOSPHERE. OH IS NOT PREDICTED TO BE DETECTABLE. ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5391 [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 16.00 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category GIANT PLANETS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE4 / 1-3; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G270H ------------------------------------------------------------------------------------------------------------------------------------ Target Names SATH1 SATH2 SATH3 ------------------------------------------------------------------------------------------------------------------------------------