Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5385 Report Date: 18-Jul-95:17:16 Version: ********** Check-in Date: ********** 1.Proposal Title: DETECTING THE HYDROXYL RADICAL IN THE JOVIAN MAGNETOSPHERE ------------------------------------------------------------------------------------ 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 We propose to observe the Jupiter magnetosphere to determine the presence and abundance of the hydroxyl radical(OH). OH has been seen in the region of the icy moons of Saturn by the HST/FOS instrument (GO3644-Cycle 2, August, 1992). The observed abundance implied a source rate 20 times higher than predicted on the basis of ion surface sputtering of H_2O. Plasma content at the orbit of Europa is greater than at Saturn. Sputtering source rates of 3x10^26 mol/s are predicted, or about 1/6 to 1/3 the rate inferred at Saturn's icy satellites. OH may contribute a substantial fraction of OII to the outward moving Io torus plasma. Our physical chemistry model predicts that for a 40% contribution to local plasma density, the Europan sourced OH number density may approach an average of 3 cm^-3. Assuming a path length of 10 R_j, with an OH emission probability of 2.3x10^-5 s^-1 in the OH A-X (0,0) band near 3085 Angstroms the intensity is 5 Rayleighs. This should be observable by the HST/FOS. If the high source rate of OH at Saturn is driven by micrometeoritic gardening of the satellite surfaces, then the same process may be active at Europa, producing a commensurately higher signal. Direct estimates of OH densities along with physical chemistry modeling will provide definitive constraints on possible surface erosion rates of Europa's surface. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 10.00 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5385 PI: Donald E. Shemansky Proposal Title: DETECTING THE HYDROXYL RADICAL IN THE JOVIAN MAGNETOSPHERE ------------------------------------------------------------------------------------ 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 ------------------------------------------------------------------------------------ 3. Description of proposed observations. The observations consists of 8 hours signal integration time at 670000km (9.4R_J) from Jupiter's center on the dusk side in the equatorial-satellite orbital plane. This is the location of Europa's orbit. Ganymede, Callisto or Europa, itself, will be used for onboard aquisition to remove the zero-point error in the ephermeris with respect to the guide stars. The aperture will then be offset to the desired location. The observation is to be made with when no satellites are in the field of view. The FOS Red Digicon will be used with the G270H grating and the 2.0-Bar aperture. The Red Digicon with the G270H yields the greatest detection efficiency at the OH 3085A band. The 2.0-bar aperture is the largest available for our desired resolution and is selected here because a maximal field of view is necessary to enhance the signal-to-noise ratio (SNR). The experience of our last HST observation (GO3644, Cycle-2) suggests that to achieve a SNR of ~5 for the expected 5 Rayleigh OH 3085A band, an exposure of at least 8 hours is necessary. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. Our previous experience (GO3644 Cycle-2) shows that the HST provides an excellent platform for the detection of extremely faint UV signals. An extraterrestrial OH A-X (0,0) feature cannot be detected with ground based apparatus because of strong airglow foreground signals and atmospheric absorption. The IUE spacecraft has detected the OH band in comets, but the intensity expected for Jupiter's magnetosphere lies below its detection threshold. The HST is the only currently operating platform from which these observations can be performed. CYCLE-2 GO 3644 observation a 37 Rayleigh OH A-X (0,0) emissions at Saturn was obtained with the HST FOS with a SNR ~ 5 with 3.5 hours of exposure time. The HST instrument configuration was identical to that proposed here. Solar scattering from Saturn's rings was the dominant source of signal in the detector. The signal strength of the OH 3085A feature near the orbit of Europa at 9.4 R_j is expected to be 5 R, with source filling the 2.0-bar aperture, so the throughput is comparable to that of non-occulting apertures at 3100 Angstroms. The peak source brightness is anticipated to be f_lambda=0.26 Rayleighs per angstrom at 3085A. For a throughput of 0.04 the required exposure time to obtain a SNR ~ 5 is 7 hours. Estimates of the noise are complicated by the lack of estimates of solar scattering from the planet. However, CYCLE-2 GO 3644's experience of separating solar scattering off the nearby rings from the 37 Rayleighs signal 120000 away convinces us scattering from Jupiter at a distance of 671000 km will be much less severe. Dark count from the dectectors will be the leading noise term. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. The observations should take place between the time window of April 20 and May 10, 1994, constrained by maintenance of a small zenith angle in the dark Earth atmosphere. No Jovian satellites should be in the field of view of the detector during the exposure, since it the magnetospheric gas that is to be detected. Page 3 ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. No special calibration required. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. ------------------------------------------------------------------------------------ 9. Description of previous HST work. CYCLE-2 GO3644, with title, ``A Search for the Hydroxyl Radical in Saturn's Magnetosphere'' detected 37 Rayleigh emission in the OH A-X (0,0) band at 3085A. The current proposal is related to the earlier HST observation only in that the surprisingly large OH signal seen at Saturn prompted the consideration of the existance of OH at Europa. The source rate at Saturn for the production of OH was found to be 20 times larger than that predicted by ion sputtering of the icy satellites alone. If the production of OH was enhanced by an extraplanetary source, such as micrometeoritic erosion of the icy moon's surfaces, then such a mechanism may be likely at Jupiter as well, with Europa the likely candidate for observation of the effect. Otherwise, the program proposed here is independent of the previous observation. The successful detection of OH in Saturn's magnetosphere by GO3644 was the first remote detection of a molecular species in a planetary atmosphere. The observation has significant impact upon both theoretical and observational studies of the Saturn system. The detected brightness of 37 Rayleighs implied much larger quantities of neutral particles in the magnetosphere than had previously been inferred. The result does agree well with the prediction of Shemansky and Hall (1992) based upon their analysis of the magnetospheric energy budget and upon establishment of the distribution of atomic hydrogen by analysis of Voyager UVS observations of H Lyman-alpha emission. The results of the observations of GO3644 were published in: The Hydroxyl Radical in the Saturn Magnetosphere, D. E. Shemansky, P. L. Matheson, D. T. Hall, H-Y. Hu, and T. M. Tripp, in Nature, vol. 363, pages 329-331, 1993. Further analysis is in process and will appear in a more extensive article. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Several SUN SparcStations, with substantial disk capacity are available at the University of Southern California at minimal cost to the department. Within our group, IRAF/STSDAS has been installed and is operational on one dedicated machine which also contains an extensive set of atomic and ion electronic model structures and accompanying analytical codes necessary to reduce complex spectra. This database and software collection has been developed over the past 15 years. The CPU time required to reduce and analyze the HST data associated with this research program are anticipated to have minimal impact on the current computing load. ------------------------------------------------------------------------------------ 11. Address Information Name: DONALD 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 = 5385 [ 4] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: EURTOR ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: OFFSET JUPITER ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = JUPITER, ACQ=1.5 | TYPE = TORUS, | LONG = 90, | LAT = 0, | RAD = 6.6E+05, | POLE_LAT = +90 | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | WND1 = 01-APR-94 TO 31-MAY-1994 | SEP OF EURTOR EUROPA FROM EARTH GT 10" | SEP OF EURTOR IO FROM EARTH GT 10" | SEP OF EURTOR CALLISTO | FROM EARTH GT 10" | SEP OF EURTOR GANYMEDE | FROM EARTH GT 10" | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | | | ESTIMATED BAND BRIGHTNESS 5 | | RAYLEIGHS CONTINUUM IS SKY | | BACKGROUND NO SATELLITES IN FIELD OF | | VIEW SEP OF LOS EUROPA FROM EARTH GT | | 10 SEP OF LOS IO FROM EARTH GT 10 | | SEP OF LOS CALLISTO FROM EARTH GT 5 | | SEP OF LOS GANYMEDE FROM EARTH GT 5 | ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5385 [ 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 EURTOR FOS/RD IMAGE 4.3 G270H 3090 Y-SIZE=1 1 64M 1 2 3 CYCLE 4 COMB=YES GUID TOL 0.2" SUB-STEP=4 AT 1-AUG-94 +/- 7D Comments: SINGLE GUIDE STAR OK BLIND POINTING ACQUISITION. MERGE TO PRODUCE 4 APPROX EQUAL LENGTH ALIGNMENTS. EXPAND TO FILL 2 ORBITS. ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5385 [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters Y-SIZE COMB SUB-STEP ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 10.00 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category GIANT PLANETS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4; GUID TOL 0.2"; AT 1-AUG-94 +/- 7D; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G270H ------------------------------------------------------------------------------------------------------------------------------------ Target Names EURTOR ------------------------------------------------------------------------------------------------------------------------------------