6818( 3) - 03/04/96 11:03 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6818 Version: 3 Check-in Date: 04-Mar-1996 10:44:51 1.Proposal Title: The Atmosphere of Uranus: Vertical Aerosol Structure and Horizontal Inhomogeneity ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle SOLAR SYSTEM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Heidi Hammel Massachusetts Institute of Technology CoI: Kathy Rages Space Physics Research Institute N CoI: Wes Lockwood Lowell Observatory N ------------------------------------------------------------------------------------ 6. Abstract In the past few years, evidence is emerging that the atmosphere of the distant gas giant Uranus may be beginning to undergo interesting changes as the planet moves away from southern summer solstice in 1986 toward equinox in 2007. The planet's equatorial region is now moving into sunlight after being in darkness for many years, and historical data along with recent HST images suggest that discrete cloud structure may become more common over the next decade. In Cycle 6, we propose to image Uranus to document these changes. The goal is to model the present distribution of vertical aerosols. Uranus is getting darker, but current vertical aerosol models cannot reproduce this secular change without invoking very large and unlikely variations in color and/or distribution of vertical aerosols. It is not clear whether seasonal or latitudinal effects (or both) are creating this discrepancy. We will separate these possibilities by modeling the yearly observed aerosol distribution using both the center-to-limb reflectivity as a function of latitude and the wavelength-dependent reflectivity of the atmosphere (and of individual features if any are detected). Observations will be coordinated with groundbased imaging and photometry, linking the HST data to a 22-year record of photometry. ------------------------------------------------------------------------------------ 6818( 3) - 03/04/96 11:03 - [ 2] Observations Description ------------------------ To fully map Uranus in longitude, three "samples" are required. Two samples (one of each hemisphere) are insufficient, because limb effects (e.g., foreshortening of features, limb-brightening, limb-darkening) render identification and interpretation of any putative discrete features near the limb ambiguous, if not impossible. The first two "samples" are separated in time by about 9 hours, which is roughly 1/2 of the planet's atmospheric rotation period (about 17 hours on average). The third "sample" is about 16 hours after the second "sample," to reacquire any discrete features and hence determine rotation periods, and to characterize limb effects. To cover all wavelengths, 2 orbits per "sample" are be required. For S/N better than 1000, the exposure times for F336W, F467M, F547M, F673N, F953N, FQCH4N15 (619 nm), and FQCH4P15 (890 nm) are 120, 8, 10, 120, 60, 240, and 600 seconds, respectively. These exposures (plus overhead) fit into one orbit (about 23 m integration + 21 m overhead + 8 m GS acquisition = 52 m). We propose to add the F255W filter, and calculate a required exposure time of 1500 seconds (note: Uranus is darker in the UV than Neptune). Because this will necessarily be in a second orbit, we will also measure the color of the aerosols in the remainder of the orbit: integrate at F467 (8 s) and take slightly shorter integrations at 619 nm (180 s) and 890 nm (480 s) (i.e., 36 m integration + 11 m overhead + 6 m reacq = 53 m). Therefore, one complete map (three "samples" with two orbits per "sample") requires 6 orbits. Real Time Justification ----------------------- None. We will attempt to coordinate the HST observations with groundbased observing (imaging, photometry, and spectroscopy) at several sites. In the past, we have used the UH 2.2-m telescope and the NASA Infrared Telescope Facility (both on Mauna Kea, HI), and facilities at Lowell Observatory (Flagstaff, AZ). Use of supporting groundbased data minimizes the amount of HST time needed to characterize the atmosphere, and provides more detailed understanding of Uranus by adding wavelengths which are not accessible to HST's Planetary Camera (e.g. the intermediate methane band at 727 nm, and IR wavelengths longward of 2 microns). Through this coordination, the HST data can be tied into the longterm ground-based data taken over the past 22 years by the Co-I Lockwood. Hammel has also obtained Uranus imaging periodically during the past 9 years, most recently in August 1995 at the IRTF. These data will be included in the analysis where appropriate. Some funds will be requested for the PI to make supporting observations, and for minimal support of the data analysis. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6818( 3) - 03/04/96 11:03 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: 54-416*77 Massachusetts Avenue*Cambridge, MA*02139 Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6818( 3) - 03/04/96 11:03 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: URANUS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET URANUS ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=URANUS | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG OF URANUS BETWEEN 320 40 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 5.52 | THE WINDOW AROUND OPPOSITION (OLG B-V = 0.56 | NEAR 0) IS REQUESTED TO COORDINATE U-B = 0.28 | WITH GROUNDBASED OBSERVATIONS. IF | THIS WINDOW IS UNAVAILABLE, THEN WE | CAN RELAX THE CONSTRAINT SOMEWHAT. | CONTACT PI H. B. HAMMEL (MIT) FOR | INFO. | ------------------------------------------------------------------------------------------------------------------------------------ 6818( 3) - 03/04/96 11:03 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Uranus Visit 1 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 URANUS WFPC2 IMAGE PC1 F336W 1 26S SEQ 01-08 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 URANUS WFPC2 IMAGE PC1 F467M 1 10S ------------------------------------------------------------------------------------------------------------------------------------ 3 URANUS WFPC2 IMAGE PC1 F547M 1 2.6S ------------------------------------------------------------------------------------------------------------------------------------ 4 URANUS WFPC2 IMAGE PC1 F673N 1 100S ------------------------------------------------------------------------------------------------------------------------------------ 5 URANUS WFPC2 IMAGE PC1 F953N 1 50S ------------------------------------------------------------------------------------------------------------------------------------ 6 URANUS WFPC2 IMAGE FQCH4N1 FQCH4N15 6211.0 1 100S 5 ------------------------------------------------------------------------------------------------------------------------------------ 7 URANUS WFPC2 IMAGE FQCH4P1 FQCH4P15 8922.0 1 350S 5 ------------------------------------------------------------------------------------------------------------------------------------ 8 URANUS WFPC2 IMAGE FQCH4P1 FQCH4P15 8922.0 1 350S 5 ------------------------------------------------------------------------------------------------------------------------------------ 9 URANUS WFPC2 IMAGE PC1 F255W 1 1300S SEQ 09-10 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 10 URANUS WFPC2 IMAGE PC1 F953N 1 50S ------------------------------------------------------------------------------------------------------------------------------------ 11 URANUS WFPC2 IMAGE FQCH4P1 FQCH4P15 8922.0 1 350S 5 ------------------------------------------------------------------------------------------------------------------------------------ 6818( 3) - 03/04/96 11:03 - [ 6] Visit: 02 Visit Requirements: AFTER 01 BY 7.5H TO 8.5H On Hold Comments: Additional Comments: Uranus Visit 2 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 URANUS WFPC2 IMAGE PC1 F336W 1 26S SEQ 01-08 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 URANUS WFPC2 IMAGE PC1 F467M 1 10S ------------------------------------------------------------------------------------------------------------------------------------ 3 URANUS WFPC2 IMAGE PC1 F547M 1 2.6S ------------------------------------------------------------------------------------------------------------------------------------ 4 URANUS WFPC2 IMAGE PC1 F673N 1 100S ------------------------------------------------------------------------------------------------------------------------------------ 5 URANUS WFPC2 IMAGE PC1 F953N 1 50S ------------------------------------------------------------------------------------------------------------------------------------ 6 URANUS WFPC2 IMAGE FQCH4N1 FQCH4N15 6211.0 1 100S 5 ------------------------------------------------------------------------------------------------------------------------------------ 7 URANUS WFPC2 IMAGE FQCH4P1 FQCH4P15 8922.0 1 350S 5 ------------------------------------------------------------------------------------------------------------------------------------ 8 URANUS WFPC2 IMAGE FQCH4P1 FQCH4P15 8922.0 1 350S 5 ------------------------------------------------------------------------------------------------------------------------------------ 9 URANUS WFPC2 IMAGE PC1 F255W 1 1300S SEQ 09-10 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 10 URANUS WFPC2 IMAGE PC1 F953N 1 50S ------------------------------------------------------------------------------------------------------------------------------------ 11 URANUS WFPC2 IMAGE FQCH4P1 FQCH4P15 8922.0 1 350S 5 ------------------------------------------------------------------------------------------------------------------------------------ 6818( 3) - 03/04/96 11:03 - [ 7] Visit: 03 Visit Requirements: AFTER 01 BY 23.5H TO 24.5H On Hold Comments: Additional Comments: Uranus Visit 3 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 URANUS WFPC2 IMAGE PC1 F336W 1 26S SEQ 01-08 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 URANUS WFPC2 IMAGE PC1 F467M 1 10S ------------------------------------------------------------------------------------------------------------------------------------ 3 URANUS WFPC2 IMAGE PC1 F547M 1 2.6S ------------------------------------------------------------------------------------------------------------------------------------ 4 URANUS WFPC2 IMAGE PC1 F673N 1 100S ------------------------------------------------------------------------------------------------------------------------------------ 5 URANUS WFPC2 IMAGE PC1 F953N 1 50S ------------------------------------------------------------------------------------------------------------------------------------ 6 URANUS WFPC2 IMAGE FQCH4N1 FQCH4N15 6211.0 1 100S 5 ------------------------------------------------------------------------------------------------------------------------------------ 7 URANUS WFPC2 IMAGE FQCH4P1 FQCH4P15 8922.0 1 350S 5 ------------------------------------------------------------------------------------------------------------------------------------ 8 URANUS WFPC2 IMAGE FQCH4P1 FQCH4P15 8922.0 1 350S 5 ------------------------------------------------------------------------------------------------------------------------------------ 9 URANUS WFPC2 IMAGE PC1 F255W 1 1300S SEQ 09-10 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 10 URANUS WFPC2 IMAGE PC1 F953N 1 50S ------------------------------------------------------------------------------------------------------------------------------------ 11 URANUS WFPC2 IMAGE FQCH4P1 FQCH4P15 8922.0 1 350S 5 ------------------------------------------------------------------------------------------------------------------------------------ 6818( 3) - 03/04/96 11:03 - [ 8] Summary Form for Proposal 6818 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SEQ 01-08 NON-INT SEQ 09-10 NON-INT AFTER 01 BY 7.5H TO 8.5H AFTER 01 BY 23.5H TO 24.5H ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F336W F467M F547M F673N F953N FQCH4N15 FQCH4P15 F255W ------------------------------------------------------------------------------------------------------------------------------------ Target Names URANUS ------------------------------------------------------------------------------------------------------------------------------------