Proposal_Information Title: Clouds and Aerosols on Saturn and Uranus Proposal_Category: GO Scientific_Category: Solar System Cycle: 5 Investigators PI_name: Dr. Martin Tomasko PI_Institution: Lunar and Planetary Lab CoI_Name: Dr. Erich Karkoschka CoI_Institution: Lunar and Planetary Lab Contact: N Abstract: Our goal is to determine the vertical and horizontal distributions, and the optical and microphysical properties, of aerosols and clouds in the atmospheres of the outer planets. This information is needed to understand the roles of aerosols in forcing atmospheric circulation and particle microphysics. To achieve these goals we propose to acquire WFPC2 images of Saturn and Uranus in the UV, visible, and near -IR methane and continuum regions. UV and blue images provide vertical sounding of the absorptive part of the aerosol opacity, critical for heat-balance studies, while the methane bands give information on the scattering part. The combination of the two provides an estimate of particle size from the wavelength dependence of the opacity. HST observations are critical because (1) UV images can only be obtained by HST, (2) the high resolution provided by HST is required for center-to-limb coverage, and (3) of existing space observations, only HST provides a suitable wide range of filters. Observations taken during Saturn's ring-plane crossing in 1995 permit superior imaging of both hemispheres, especially in methane bands. New observations of Uranus can take advantage of the improved geometry for center-to-limb observations. This proposal is similar to one originally selected for Cycle 1 (program number 2564) for the outer planets that had to be limited to Jupiter and Saturn due to the degraded performance of the original HST optics. Questions Observing_Description: Our analyses requires a series of images in continuum and methane band filters. We need three methane band filters: FQCH4N15 (619 nm), FQCH4N (727 nm), and FQCH4P15 (892 nm). For Uranus, we use four continuum filters: F336W, F467M, F673N, and F850LP (which gets most of its light from the 940 nm continuum region). For Saturn we also use the continuum filters F255W, F410M, and F588N, and we replace the F850LP by the F953N filter. The most important filters are repeated for Saturn, since Saturn shows some changes with time and longitude. For most of the filters we achieve 70 per cent of the saturation level with relatively short exposure times. For those exposures, the maximum exposure time is set equal to the desired exposure time, so they will not be lengthened in case more time is available as described in the Phase II Proposal Instructions. A few exposures are not close to saturation as indicated by a longer maximum duration. Saturn's rings fit into the PC1 aperture only for some orientations. The optimal orientation is described in the visit requirements. Because of the asymmetric field of view of the 892 nm methane filter, we specify an offset from the centered position (POS TARG). The offset for both of the orbits of visit #3 is slightly different so that CCD blemishes will not fall on the same area. Real_Time_Justification: Our long exposures on Saturn in the strongest methane bands require the rings to be dark in order not to saturate the image. The earth-facing side of the rings is not illuminated from 22 May 1995 to 11 August 1995 and from 19 November 1995 to 12 February 1996. Additionally, starting near 10 November 1995, the solar illumination will be so shallow that the rings will be faint enough. We want to observe two interesting phases of the ring-plane crossings of this season. In visit #2, the sun will shine through the transparant rings yielding scattering information about the rings at higher spatial resolution than possible from the ground. In visit #3, the sun will illuminate the rings at an angle of 0.03 degrees, giving a very sensitive probe of non-planar ring features. Voyager observed some bending waves when the sun was illuminating the rings at an angle of a few degrees. The extremly shallow illumination on 18/19 November 1995 has prospects for discoveries of ring features. If we miss this opportunity, the next one will be on 24 January 2039. In October, 1994, HST observations yielded the first map of Titan's surface. With proper scheduling, our Saturn observations could be made when Titan is in the field. Our filter set is more complete than the filter used on Titan so far. Our F953N filter may probe the surface better than the F850LP filter which showed surface features of highest contrast so far. On the other hand, we have a poor orbital coverage with only two positions if the observation can be scheduled according to our visit requests. Thus, our data set would be complementary to the existing one. We will conduct spectrophotometry of Saturn and Uranus at the 1.5 m spectroscopic telescope at the European Southern Observatory on 6-10 July 1995. These observations will provide spectroscopic information at 1 nm resolution with relatively low spatial resolution, while the HST images will provide high spatial resolution at a few wavelengths sampling the spectrum. Such supplemental data sets have been proven to be very valuable in the past. For example, HST filter transmission curves can be convolved with the planetary spectrum for an accurate interpretation of the HST images. We prefer if one or two of our visits can be scheduled in July, 1995. Solar_System_Targets Target_Number: 1 Target_Name: URANUS Description: PLANET URANUS Level_1: STD = URANUS Window: OLG OF URANUS BETWEEN 300 60 Flux: V = 5.6 B-V = 0.6 U-B = 0.3 Comments: Window requirement means within 2 months of opposition. Target_Number: 2 Target_Name: SATURN-NO-RING Description: PLANET SATURN Level_1: STD = SATURN Window: WND FROM 22-MAY-95 TO 11-AUG-95 WND FROM 10-NOV-95 TO 11-FEB-96 OLG OF TITAN BETWEEN 174 183 SEP OF TITAN SATURN FROM EARTH GT .5" Flux: V = 1.1 B-V = 1.1 U-B = 0.6 Comments: The WND requirement is the time period when Saturn's rings are so dark that they will not saturate in methane filter exposures. This is essential as described in the proposal. We request Titan in the field of view (orbital longitude 174-183 degrees). This is not a requirement. Target_Number: 3 Target_Name: SATURN-DIM-RING Description: PLANET SATURN Level_1: STD = SATURN Window: WND FROM 22-MAY-95 TO 11-AUG-95 WND FROM 10-NOV-95 TO 11-FEB-96 Flux: V = 1.1 B-V = 1.1 U-B = 0.6 Comments: The WND requirement is the time period when Saturn's rings are so dark that they will not saturate in methane filter exposures. This is essential as described in the proposal. Visits Visit_Number: 1 Visit_Requirements: BEFORE 25-JUL-95 Visit_Comments: We request that this visit occurs within a few weeks of our observing run at the European Southern Observatory 6-10 July 1995 where we will aquire spectroscopic data of Uranus. In case of scheduling difficulties, the BEFORE request can be deleted. Exposure_Number: 11 Target_Name: URANUS Config: WFPC2 Opmode: IMAGE Aperture: FQCH4W4 Sp_Element: F467M Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 8S Special_Requirements: MAX DUR 8S Exposure_Number: 12 Target_Name: URANUS Config: WFPC2 Opmode: IMAGE Aperture: FQCH4W4 Sp_Element: FQCH4N Wavelength: 7274 Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 160S Special_Requirements: MAX DUR 180S Exposure_Number: 13 Target_Name: URANUS Config: WFPC2 Opmode: IMAGE Aperture: FQCH4P15 Sp_Element: F336W Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: MAX DUR 120S Exposure_Number: 14 Target_Name: URANUS Config: WFPC2 Opmode: IMAGE Aperture: FQCH4P15 Sp_Element: FQCH4N15 Wavelength: 6211 Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 160S Special_Requirements: MAX DUR 230S Exposure_Number: 15 Target_Name: URANUS Config: WFPC2 Opmode: IMAGE Aperture: FQCH4P15 Sp_Element: F673N Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: MAX DUR 100S Exposure_Number: 16 Target_Name: URANUS Config: WFPC2 Opmode: IMAGE Aperture: FQCH4P15 Sp_Element: F850LP Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: MAX DUR 120S Exposure_Number: 17 Target_Name: URANUS Config: WFPC2 Opmode: IMAGE Aperture: FQCH4P15 Sp_Element: FQCH4P15 Wavelength: 8922 Optional_Parameters: ATD-GAIN=7 CLOCKS=YES Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: MAX DUR 1500S Visit_Number: 2 Visit_Requirements: ORIENT 272D TO 276D BEFORE 12-AUG-95 Visit_Comments: We request a position angle of the X-axis of the WFPC2 of 229 degrees within a few degrees. This orientation optimizes the location of Saturn's rings on the CCD. We request that this visit occurs within the first dark-ring period since we obtain spectroscopic data of Saturn at the European Southern Observatory during this period (6-10 July 1995). This is not a requirement. Exposure_Number: 21 Target_Name: SATURN-NO-RING Config: WFPC2 Opmode: IMAGE Aperture: WF4-FIX Sp_Element: F255W Optional_Parameters: ATD-GAIN=7 Number_of_Iterations: 1 Time_Per_Exposure: 160S Special_Requirements: MAX DUR 300S POS TARG 13,-17 Exposure_Number: 22 Target_Name: SATURN-NO-RING Config: WFPC2 Opmode: IMAGE Aperture: WF4-FIX Sp_Element: FQCH4N Wavelength: 7274 Optional_Parameters: ATD-GAIN=15 CLOCKS=YES Number_of_Iterations: 1 Time_Per_Exposure: 12S Special_Requirements: MAX DUR 12S POS TARG 13,-17 Exposure_Number: 23 Target_Name: SATURN-NO-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F336W Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 70S Special_Requirements: MAX DUR 70S POS TARG -2,-1 Exposure_Number: 24 Target_Name: SATURN-NO-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F467M Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 16S Special_Requirements: MAX DUR 16S POS TARG -2,-1 Exposure_Number: 25 Target_Name: SATURN-NO-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: FQCH4N15 Wavelength: 6211 Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 30S Special_Requirements: MAX DUR 30S POS TARG -2,-1 Exposure_Number: 26 Target_Name: SATURN-NO-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F673N Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 18S Special_Requirements: MAX DUR 18S POS TARG -2,-1 Exposure_Number: 27 Target_Name: SATURN-NO-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F953N Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: MAX DUR 120S POS TARG -2,-1 Exposure_Number: 28 Target_Name: SATURN-NO-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: FQCH4P15 Wavelength: 8922 Optional_Parameters: ATD-GAIN=15 CLOCKS=YES Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: MAX DUR 700S POS TARG -2,-1 Visit_Number: 3 Visit_Requirements: ORIENT 92D TO 96D BETWEEN 16-NOV-95:20:00 AND 17-NOV-95:13:00 Visit_Comments: We request a position angle of the X-axis of the WFPC2 of 49 degrees within a few degrees. This orientation optimizes the location of Saturn's rings on the CCD. We request that this visit occurs at the beginning of the crossing of the solar disk through the ring plane of Saturn, yielding an extremely shallow illumination which makes non-planar ring features visible. The next day such a geometry is observable to HST is on 24 January 2039. In case of scheduling difficulties the start time of the requested period could be shifted half a day or one day later, which still would yield a quite shallow illumination. Exposure_Number: 31 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F673N Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 18S Special_Requirements: MAX DUR 18S POS TARG -2,-2 Exposure_Number: 32 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F953N Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: MAX DUR 120S POS TARG -2,-2 Exposure_Number: 33 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: FQCH4P15 Wavelength: 8922 Optional_Parameters: ATD-GAIN=15 CLOCKS=YES Number_of_Iterations: 1 Time_Per_Exposure: 400S Special_Requirements: MAX DUR 1200S POS TARG -2,-2 Exposure_Number: 34 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: FQCH4P15 Wavelength: 8922 Optional_Parameters: ATD-GAIN=15 CLOCKS=YES Number_of_Iterations: 1 Time_Per_Exposure: 300S Special_Requirements: MAX DUR 400S POS TARG -2,-2 Exposure_Number: 35 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: WF4-FIX Sp_Element: FQCH4N Wavelength: 7274 Optional_Parameters: ATD-GAIN=15 CLOCKS=YES Number_of_Iterations: 1 Time_Per_Exposure: 23S Special_Requirements: MAX DUR 23S POS TARG 13,-17 Exposure_Number: 36 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: WF4-FIX Sp_Element: FQCH4N Wavelength: 7274 Optional_Parameters: ATD-GAIN=15 CLOCKS=YES Number_of_Iterations: 1 Time_Per_Exposure: 10S Special_Requirements: MAX DUR 10S POS TARG 13,-17 Exposure_Number: 37 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: WF4-FIX Sp_Element: F255W Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 350S Special_Requirements: MAX DUR 350S POS TARG 13,-17 Exposure_Number: 41 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F336W Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 80S Special_Requirements: MAX DUR 80S POS TARG -2,-1 Exposure_Number: 42 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F410M Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 40S Special_Requirements: MAX DUR 60S POS TARG -2,-1 Exposure_Number: 43 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F467M Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 18S Special_Requirements: MAX DUR 18S POS TARG -2,-1 Exposure_Number: 44 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F588N Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 14S Special_Requirements: MAX DUR 14S POS TARG -2,-1 Exposure_Number: 45 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: FQCH4N15 Wavelength: 6211 Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 30S Special_Requirements: MAX DUR 30S POS TARG -2,-1 Exposure_Number: 46 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F673N Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 18S Special_Requirements: MAX DUR 18S POS TARG -2,-1 Exposure_Number: 47 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F953N Optional_Parameters: ATD-GAIN=15 Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: MAX DUR 120S POS TARG -2,-1 Exposure_Number: 48 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: FQCH4P15 Wavelength: 8922 Optional_Parameters: ATD-GAIN=15 CR-SPLIT=NO CLOCKS=YES Number_of_Iterations: 1 Time_Per_Exposure: 700S Special_Requirements: MAX DUR 1200S POS TARG -2,-1 Exposure_Number: 49 Target_Name: SATURN-DIM-RING Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: FQCH4P15 Wavelength: 8922 Optional_Parameters: ATD-GAIN=15 CLOCKS=YES Number_of_Iterations: 1 Time_Per_Exposure: 160S Special_Requirements: MAX DUR 300S POS TARG -2,-1 Data_Distribution Medium: 8MM ! 8MM or 6250BPI or 1600BPI Blocking_Factor: 10 ! 10 or 1 Ship_To: PI_Address ! STSCI or PI_Address or Ship_Via: UPS ! UPS (2-day) or OVERNIGHT