5830( 2) - 07/28/95 14:15 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5830 Version: 2 Check-in Date: ********** 1.Proposal Title: THE SMALL ICY PARTICLES OF THE A AND B RINGS OF SATURN ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Solar System GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Michel C. FESTOU Observatoire Midi-Pyrenees CoI: S. Alan STERN Southwest Research Institute, San Antonio N CoI: Don E. Shemansky Univ. of Southern Calif., L.A. N ------------------------------------------------------------------------------------ 6. Abstract Near 1650 Angstrom, a strong absorption attributed to small water ice particles, and possibly water vapor, has been seen in Voyager and IUE spectra of the two main rings of Saturn. These small particles are not seen at longer wavelengths, even in forward scattering, except in the form of spokes, because of the masking effects of the dominant large particles. All the fainter rings, however, show that small particles are produced in large amounts, and thus indicate that they should be present in every ring. No constraining observations exist that allow a description of the production of icy grains and water molecules in the Saturn rings, and to evaluate the effects of their transport and subsequent destruction in OH radicals and H atoms. GHRS FUV spectra of the A and B rings, to be obtained at or near the time of the 1995-96 ring crossing, will allow us to distinguish the properties of solid state vs gaseous absorbers. When the opening angle of the rings will be small, the front side of the rings will occult the far side of the same rings and will permit a complete characterization of the cloud of water that surrounds the icy blocks. Later, when the rings opening angle will be larger, only the solid particles will absorb and their properties will be derived. All these observations, address the important question of the role of the source of H atoms and OH radicals inside the Saturnian system, with important consequences for the planning of the observing sequences of some of the CASSINI instruments. ------------------------------------------------------------------------------------ 5830( 2) - 07/28/95 14:15 - [ 2] Observations Description ------------------------ Offset acq. of Rhea, then GHRS spectra of the near and far edges of the Saturnian rings. Do once in Oct. and then in May (when rings are more open). Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS __Diagnosti Email: , ------------------------------------------------------------------------------------ 5830( 2) - 07/28/95 14:15 - [ 3] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: Rhea ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: satellite Rhea ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | STD=RHEA | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG OF RHEA FROM EARTH Between 200 340 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V=12.9 B-V=0.67 | ACQ TARGET. OLG CONSTRAINTS | APPROXIMATE. | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: FARSIDE ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: RING SATURN ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | TYPE=TORUS,LONG=153,LAT=0,RAD=1.9E5,POLE | _LAT=90 | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V=12.9 B-V=0.67 | EDGE OF RING ON FAR SIDE OF SATURN, | TOWARDS WEST. Mean radius of rings | taken as 190,000 km, a near limb | observation at 1 arcsec from that | limb corresponds to degrees a value | of 156. With 153 degrees, the line | of sight passes at 2.23 arc sec from | the limb. | ------------------------------------------------------------------------------------------------------------------------------------ 5830( 2) - 07/28/95 14:15 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 | TARGET NAME: NEARSIDE ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: RING SATURN ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | TYPE=TORUS,LONG=27,LAT=0,RAD=1.9E5,POLE_ | LAT=90 | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V=12.9 B-V=0.67 | EDGE OF RING ON NEAR SIDE OF SATURN, | TOWARDS WEST. See above. | ------------------------------------------------------------------------------------------------------------------------------------ 5830( 2) - 07/28/95 14:15 - [ 5] Visit: 01 Visit Requirements: BETWEEN 01-OCT-1995 AND 20-OCT-1995 On Hold Comments: Additional Comments: BEST IF ORIENTED SO THAT RINGS ALIGN WITH GHRS X AXIS Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 RHEA HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN, 1 18S ONBOARD ACQ FOR 20-35 LOCATE=EXTENDED Comments: STEP-TIME=2.0 sec ------------------------------------------------------------------------------------------------------------------------------------ 20 FARSIDE HRS ACCUM 2.0 G140L 1650 1 1604.8S ------------------------------------------------------------------------------------------------------------------------------------ 25 FARSIDE HRS ACCUM 2.0 G140L 1850 1 1523.2S ------------------------------------------------------------------------------------------------------------------------------------ 30 NEARSIDE HRS ACCUM 2.0 G140L 1650 1 1604.8S ------------------------------------------------------------------------------------------------------------------------------------ 35 NEARSIDE HRS ACCUM 2.0 G140L 1850 1 1523.2S Comments: all numbers checked by mcf ------------------------------------------------------------------------------------------------------------------------------------ 5830( 2) - 07/28/95 14:15 - [ 6] Visit: 02 Visit Requirements: BETWEEN 14-May-1996 AND 30-Jun-1996 On Hold Comments: Additional Comments: BEST IF ORIENTED SO THAT RINGS ALIGN WITH GHRS X AXIS Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 RHEA HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN, 1 18S ONBOARD ACQ FOR 20-35 LOCATE=EXTENDED Comments: STEP-TIME=2.0 sec ------------------------------------------------------------------------------------------------------------------------------------ 20 FARSIDE HRS ACCUM 2.0 G140L 1650 1 1604.8S ------------------------------------------------------------------------------------------------------------------------------------ 25 FARSIDE HRS ACCUM 2.0 G140L 1850 1 1523.2S ------------------------------------------------------------------------------------------------------------------------------------ 30 NEARSIDE HRS ACCUM 2.0 G140L 1650 1 1604.8S ------------------------------------------------------------------------------------------------------------------------------------ 35 NEARSIDE HRS ACCUM 2.0 G140L 1850 1 1523.2S ------------------------------------------------------------------------------------------------------------------------------------ 5830( 2) - 07/28/95 14:15 - [ 7] Summary Form for Proposal 5830 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN LOCATE=EXTENDED ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Solar System ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-OCT-1995 AND 20-OCT-1995 ONBOARD ACQ FOR 20-35 BETWEEN 14-May-1996 AND 30-Jun-1996 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names RHEA FARSIDE NEARSIDE ------------------------------------------------------------------------------------------------------------------------------------