Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5216 Report Date: 18-Jul-95:17:04 Version: ********** Check-in Date: ********** 1.Proposal Title: IO'S VOLCANIC SURFACE AND ATMOSPHERE ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID SOLAR SYSTEM GTO/WF2 Sub Category SATELLITES ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Dr. John Trauger 2370 USA 818-354-9594 PROJECT SCIENTIST ------------------------------------------------------------------------------------ 7. Abstract We propose a series of UV images of Io's trailing hemisphere to determine a) the surface distributions of SO2 frost and SO2 gas absorption, and b) the spatial distribution of the FUV airglow emissions of S and O. Our main scientific goals are to observe Io's atmosphere, both through NUV absorption and FUV emission, and to determine the process by which 1 ton/sec of material is released into the plasma torus. Io's atmosphere is believed to be patchy, with spatial variations of up to 1000 times in surface density, and the airglow emission region extent has just been determined for the first time with FOS and GHRS spectra. With the WFPC2 enhanced UV capabilities, we expect to be able to image the spatial and altitude distributions of the atmosphere, and image the airglow process to study the interaction between Io's atmosphere and the corotating plasma torus. ------------------------------------------------------------------------------------ 8. Scientific Key Words: SATELLITE ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 4.14 par: 0 10. Num targs pri: 2 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: WF/PC ------------------------------------------------------------------------------------ 12. Special sched req: Time Critical obs. ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5216 PI: Dr. John Trauger Proposal Title: IO'S VOLCANIC SURFACE AND ATMOSPHERE ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Dr. John T. Trauger 2370 USA Prof. John T. Clarke 2660 USA Chris Burrows STSCI USA David Crisp JPL USA John Hoessel UNIV. OF WISCONSIN USA Jay Gallagher UNIV. OF WISCONSIN USA Richard Griffiths JOHNS HOPKINS UNIV USA Jeff Hester ARIZONA STATE UNIV. USA John Holtzman LOWELL OBSERVATORY USA Jeremy Mould CALTECH USA James Westphal CALTECH USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. Io's disk is 1 arc sec in diameter, and near-UV and visible images will be obtained with the PC when Io is near western elongation (and the apparent motion is small): this will provide roughly 20 pixels across the diameter of the disk. This is lower resolution than the Voyager visible images, and we will use the Voyager images together with the visible images (F380W) to determine the surface morphology for comparison with the near-UV images. The near-UV images will be taken with filters F218W, F255W, and F336W. The wavelength region covered by F218W is very sensitive to SO2 absorption (2 orders of magnitude more than the 2900 A region previously imaged with FOC), and we may thus resolve the spatial distribution of this most important atmospheric component on Io. Three far-UV images to detect the airglow O and S emissions on Io will be obtained (and co- added) with F160BW. An image with F160BW and F165LP will separate the solar light reflected by Io. (F380W images will identify the limb of the satellite.) The NUV and FUV image sets should be scheduled in ~succesive west elongations of Io (43 hr apart), to correlate the airglow emissions with the SO2 atmospheric distribution, since the airglow may be produced by direct excitation of O and S but also possibly from dissociation/ excitation of SO2 as suggested by the decrease in the emissions as Io goes into eclipse observed with HST. These images should also be scheduled close to the WFPC2 GTO program on the Io plasma torus. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. Io can only be imaged with 20 pixels across the disk and in the UV with the HST. Galileo will have a UV spectrometer, but no UV imaging capability, so that we expect our UV images will complement the high angular resolution spectroscopy to be performed with the Galileo UVS. These images are also a follow-up program with high signal-to-noise of a GO program of FOC imaging over cycles 0-1 and 3: J. Clarke of the WFPC2 science team is a Co-I on the cycle 3 proposal. We are requesting single images of Io near W elongation at 3 NUV wavelengths for discrimination in the SO2 spectrum between surface frost and gas absorption - the spectral region covered by the filters chosen (not availiable with the FOC) are the most sensitive to SO2 gas absorption as recently found with the FOS. The exposure times are estimated based on IUE and HST spectra of the whole disk of Io. Page 3 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. Io images must be scheduled near orbital elongation from Jupiter, as indicated in comments in the Obs. Summ. Form. We also wish to have the Io images taken close in time to the Io Torus images listed in that program. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. Dark time is requested for the FUV exposures series with F160BW. We are imaging very weak oxygen and sulfur FUV emissions and therefore need to minimize background signal from the Earth's H Lyman alpha and oxygen airglow emissions (at 1304 and 1356 A). The exposures cannot be interrupted due to Io's rotation and temporal variability in its atmospheric conditions from its variable volcanic activity. The exposures have been planned accordingly. ------------------------------------------------------------------------------------ 11. Address Information Name: JOHN T. TRAUGER Category: PI Institution: 2370 Address: MS 179-225 4800 Oak Grove Drive City: Pasadena State: CA Zip Code: 91109 Country: USA Telephone: 818-354-9594 Telex (or e-mail): ------------------------------------------------------------------------------------ Name: JOHN T. CLARKE Category: Institution: 2660 Address: City: State: Zip Code: Country: Telephone: 313-747-3540 Telex (or e-mail): ------------------------------------------------------------------------------------ Name: GILDA E. BALLESTER Category: Institution: 2660 Address: City: State: Zip Code: Country: Telephone: 313-747-3670 Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 5216 [ 4] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: IO-WEST ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = JUPITER | STD = IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG OF IO BETWEEN 245 295, | OLG OF JUPITER BETWEEN 300 60, | 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 |V = 5.2 +/- 0.5 | THREE SEQUENTIAL NEAR-UV PC IMAGES 2 |SURF-CONT(2180) = 2 +/- 1 E-14 | OF IO'S TRAILING HEMISPHERE, ONE PER 3 |SURF-CONT(2550) = 4 +/- 1 E-12 | FILTER, TO STUDY DISTRIBUTION OF 4 |SURF-CONT(3360) = 1.3 +/- 1 E-12 | ATMOSPHERIC AND SURFACE SO2. 5 |SURF-CONT(3800) = 4.5 +/- 1 E-12 | SCHEDULE MIDPOINT OF SERIES WHEN IO | | IS NEAR OR AT WESTERN ELONGATION. | | WINDOWS CAN BE EXPANDED SOMEWHAT IF | | NEEDED FOR SCHEDULING. | ------------------------------------------------------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 5216 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: IO-W-FUV ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE IO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = JUPITER | STD = IO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG OF IO BETWEEN 245 295, | OLG OF JUPITER BETWEEN 300 60, | 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 |V = 5.2 +/- 0.5 | LONG WFC FAR-UV EXPOSURES OF IO'S 2 |F-LINE(1304)=2+/-10E-14,W-LINE(1304)=10 | TRAILING HEMISPHERE (PLUS TWO SHORT 3 |F-LINE(1479)=8+/-50E-15,W-LINE(1479)=10 | BACKGROUND EXPOSURES) TO DETECT 4 |F-LINE(1814)=2+/-10E-14,W-LINE(1814)=10 | AIRGLOW EMISSIONS. SCHEDULE MIDPOINT 5 |SIZE = 1.7 +/- 1.5 | OF SERIES WHEN IO IS NEAR OR AT 6 |SURF-CONT-BKG(1900) = 1.5 +/- 1 E-15 | WESTERN ELONGATION. WINDOWS CAN BE 7 |SURF-CONT(3800) = 4.5 +/- 1 E-12 | EXPANDED SOMEWHAT IF NEEDED FOR | | SCHEDULING. FLUXNUM 2 AND 4 INCLUDE | | TWO EMISSION MULTIPLETS. SCHEDULE ON | | DARK TIME. | ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5216 [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 1.1 IO-WEST WFPC2 IMAGE PC1-FIX F380W ATD-GAIN=7 1 3.3 S 60 5 1 CYCLE 4 CR-SPLIT=NO SEQ 1.1 - 1.5 NO GAP GUID TOL 0.2"/ 1.1 -2.4 Comments: TAKE VIOLET IMAGE OF IO'S TRAILING HEMISPHERE WITH SAME GUIDE STARS AS LINENUM 1.2-1.5 TO IDENTIFY LIMB OF SATELLITE AND DEFINE VISIBLE SURFACE. ------------------------------------------------------------------------------------------------------------------------------------ 1.2 IO-WEST WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=7 2 25.0 S 60 4 1 CYCLE 4 CR-SPLIT=NO CR- TOLERANCE=0.1 Comments: TWO F336W IMAGES OF IO'S TRAILING HEMISPHERE (TWO IMAGES FOR CR-SPLIT, WILL BE ADDED TO IMPROVE S/N). TAKE IMAGES DURING THE SAME HST ORBIT TO AVOID BLURRING FROM IO'S ROTATION. ------------------------------------------------------------------------------------------------------------------------------------ 1.3 IO-WEST WFPC2 IMAGE PC1-FIX F255W ATD-GAIN=7 2 500.0 S 15 3 1 CYCLE 4 CR-SPLIT=NO CR- TOLERANCE=0.1 Comments: TWO F255W IMAGES OF IO'S TRAILING HEMISPHERE (TWO IMAGES FOR CR-SPLIT, WILL BE ADDED TO IMPROVE S/N). TAKE IMAGES DURING THE SAME HST ORBIT TO AVOID BLURRING FROM IO'S ROTATION. ------------------------------------------------------------------------------------------------------------------------------------ 1.4 IO-WEST WFPC2 IMAGE PC1-FIX F218W ATD-GAIN=7 3 1020.0 16 2 1 CYCLE 4 CR-SPLIT=NO CR- TOLERANCE=0.1 Comments: THREE F218W IMAGES OF IO'S TRAILING HEMISPHERE (FOR CR- SPLIT, AND ADDI- TION TO IMPROVE S/N). TAKE FIRST TWO IMAGES DURING THE SAME HST ORBIT, AND THIRD ONE IN NEXT HST ORBIT (WITH LINENUM 1.5) TO AVOID BLURRING ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5216 [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 1.5 IO-WEST WFPC2 IMAGE PC1-FIX F380W ATD-GAIN=7 1 3.3 S 60 5 1 CYCLE 4 CR-SPLIT=NO Comments: TAKE VIOLET IMAGE OF IO'S TRAILING HEMISPHERE WITH SAME GUIDE STARS AS LINENUM 1.1-1.3 TO IDENTIFY LIMB OF SATELLITE AND DEFINE VISIBLE SURFACE. ------------------------------------------------------------------------------------------------------------------------------------ 2.1 IO-W-FUV WFPC2 IMAGE WF4-FIX F380W ATD-GAIN=7 1 0.7 S 60 7 1 CYCLE 4 CR-SPLIT=NO POS TARG -17.3, +2.5 Comments: VIOLET IMAGE OF IO'S TRAILING HEMISPHERE WITH SAME GUIDE STARS AS IN LINENUM 2.1-2.2 TO IDENTIFY LIMB OF SATELLITE. ------------------------------------------------------------------------------------------------------------------------------------ 2.2 IO-W-FUV WFPC2 IMAGE WF4-FIX F160BW ATD-GAIN=7 1 1500.0 4 6 1 CYCLE 4 CR-SPLIT=NO POS TARG -17.3, CR- +2.5 TOLERANCE=0.1 Comments: UV IMAGE OF IO'S TRAILING HEMISPHERE TO MEASURE FUV BACKGROUND SCATTERED LIGHT FROM THE DISK. ------------------------------------------------------------------------------------------------------------------------------------ 2.3 IO-W-FUV WFPC2 IMAGE WF4-FIX F160BW ATD-GAIN=7 4 1000.0 4 2 1 CYCLE 4 CR-SPLIT=NO 3 SEQ 2.1 - 2.3 NO CR- 4 GAP TOLERANCE=0.1 5 POS TARG -17.3, +2.5 Comments: THREE LONG FUV EXPOSURES OF IO'S TRAILING HEMISPHERE TO IMAGE AIRGLOW EMISSIONS. THREE IMAGES FOR CR-SPLIT, TO BE ADDED TO IMPROVE S/N. SCHEDULE EXPOSURES CLOSE IN TIME TO SEQUENCE 1.1-1.4 TO CORRELATE DATA. ------------------------------------------------------------------------------------------------------------------------------------ 2.4 IO-W-FUV WFPC2 IMAGE WF4-FIX F380W ATD-GAIN=7 1 0.7 S 60 7 1 CYCLE 4 CR-SPLIT=NO POS TARG -17.3, +2.5 Comments: EXECUTE EXPOSURE 2.4 BEFORE OR AFTER THE LAST EXPOSURE IN LINENUM 2.3 TO CHECK THE POINTING. ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5216 [ 8] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN CR-SPLIT=NO CR-TOLERANCE=0.1 CR-SPLIT ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GTO/WF2 ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 4.14 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category SATELLITES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4; SEQ 1.1 - 1.5 NO GAP; GUID TOL 0.2"/ 1.1-2.4; POS TARG -17.3, +2.5 SEQ 2.1 - 2.3 NO GAP; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F380W F336W F255W F218W F160BW ------------------------------------------------------------------------------------------------------------------------------------ Target Names IO-WEST IO-W-FUV ------------------------------------------------------------------------------------------------------------------------------------