8229( 3) - 07/27/99 13:22 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8229 Version: 3 Check-in Date: 18-Feb-1999 06:38:34 1.Proposal Title: Spatially Resolved Spectroscopy of Titan's Atmosphere and Surface ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Caitlin Griffith Northern Arizona University CoI: Dr. Keith Noll STsci N CoI: Dr. Eliot Young Southwest Research Institute N CoI: Dr. Chris McKay NASA Ames Research Center N CoI: Dr. Seran Gibbard Lawrence Livermore National Laboratory N CoI: Dr. Bruce Macintosh Lawrence Livermore National Laboratory N ------------------------------------------------------------------------------------ 5. Abstract Titan's atmosphere is likened to the Earth's atmosphere; it is nitrogen based, has a surface pressure of 1.5 bar, and has methane which plays the role that water plays on Earth. Because methane can exist in both gas and liquid phases, weather and methane clouds are hypothesized to exist on Titan. Yet Titan's greater column abundance of atmosphere and the cooler conditions may induce conditions more quiescent than found on Earth. Here we propose to investigate the clouds in Titan's atmosphere, first discovered this year (Griffith et al. 1998). Our goal is to study weather processes native to the Earth's lower atmosphere, yet in the exotic context offered by Titan. By scanning the 0.05'' STIS slit across of Titan's 0.8'' disk, we will build a 18x18 image of Titan. Each 0.05x0.05'' pixel will consist of a spectrum of resolution 500-1200 (grating G750L). With methane's varying absorption coefficient acting as a vertical discriminator, we will resolve the opacity structure of the atmosphere over a range of altitudes from 400 km down to the surface. This combination of spectroscopy and imaging will allow us to detect clouds in Titan's atmosphere, determine their coverage, thickness and altitude range. We will also measure the surface reflectivity of Titan at 0.9 microns, and map the distribution of haze in the northern and southern hemispheres at altitudes where the haze is formed. ------------------------------------------------------------------------------------ 8229( 3) - 07/27/99 13:22 - [ 2] Observations Description ------------------------ Each spectral image of Titan requires one orbit. An image is constructed by scanning the grating across Titan, and combining the observations taken from the series of slit positions. We request the 0.05'' slit, which we will step perpendicular to the slit by 0.05'' to cover Titan's 0.8'' disk in a series of 18 exposures. 70 seconds integration time is needed to achieve a signal to noise ratio of 50. Another 70 seconds will be needed for readout. An additional 10 seconds will be needed to offset the array 0.05''. Using the RPS2 package, we have verified that each image of Titan (18 70-sec integrations offset by 0.05'') and the guide star and target acquisitions fit into a single orbit. We request 4 orbits at 4-day intervals, with one night scheduled one to two days after Titan is at eastern elongation in its orbit around Saturn. At this time, Titan's bright surface terrain is in view. The other orbits provide maps of Titan's surface with surface features sampled at two differ ent Titan airmasses. The roll angle is not important, but care should be taken to avoid Saturn's disk. Summary of Cycle 8 orbits: Visit Orbits Date Exposures Grating 1 1 1st day 18/orbit G750L 2 1 1st day + 4 18/orbit G750L 3 1 1st day + 8 18 G750L 4 1 1st day + 12 18 G750L Real Time Justification ----------------------- None Calibration Justification ------------------------- None Additional Comments ------------------- None Titan's haze particles are smaller than 0.5 microns, which makes them poor scatterers at wavelengths longward of 1.5 microns, yet efficient scatterers at the visible wavelengths sampled by STIS. Therefore interpretation of STIS observations requires careful derivation of the haze characteristics, before understanding the clouds at deeper levels. Ground-based speckle observations from the Keck (Gibbard et al. 1998) have produced IR images of Titan at 1.7 and 2 microns with a spatial resolution of 0.04", superior to NICMOS images by over a factor of 9 in number of pixels on Titan's disk. These images are not sensitive to Titan's haze, yet quite sensitive to the larger sized cloud particles. On the other hand, the KECK observations lack the spectral information available to STIS. We are therefore proposing to obtain additional Keck images in concert with the STIS image cubes we propose here. The combination of Keck IR and STIS CCD images will enable us to image the stratos phere, the troposphere, and the surface of Titan. ------------------------------------------------------------------------------------ 8229( 3) - 07/27/99 13:22 - [ 3] Data Distribution Paper Products: YES Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8229( 3) - 07/27/99 13:22 - [ 4] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: TITAN-DAY0 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE First Titan image cube ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | STD=TITAN | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | CML OF TITAN FROM EARTH BETWEEN 110 130 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(V) = 7.5+/-1.0 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: TITAN-DAY4 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE Second Titan image cube ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | STD=TITAN | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(V) = 7.5+/-1.0 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 | TARGET NAME: TITAN-DAY8 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE Third Titan image cube ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | STD=TITAN | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(V) = 7.5+/-1.0 | | 8229( 3) - 07/27/99 13:22 - [ 5] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 4 | TARGET NAME: TITAN-DAY12 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE Fourth Titan image cube ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | STD=TITAN | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(V) = 7.5+/-1.0 | | ------------------------------------------------------------------------------------------------------------------------------------ 8229( 3) - 07/27/99 13:22 - [ 6] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: We prefer observations close to Saturn's opposition (near Nov. 1999) if possible, since Titan's disk is significantly bigger at that time. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 TITAN-DAY0 STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE,CHECKBOX=25, 1 0.1 S ONBOARD ACQ FOR 20 CD P DIFFUSE-CENTER=GEOMETRIC-CENTER ------------------------------------------------------------------------------------------------------------------------------------ 20 TITAN-DAY0 STIS/C ACCUM 52X0.05 G750L 7751 PATTERN=PERP-TO-SLIT,NUM-POS=18, 1 79 S POS TARG -0.45, 0 MAX DUR CD STEP-SIZE=0.05, 120 S PATTERN-DIRECTION=PLUS, SIZEAXIS2=256,CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 30 CCDFLAT STIS/C ACCUM 52X0.05 G750L 7751 2 DEF CD ------------------------------------------------------------------------------------------------------------------------------------ 8229( 3) - 07/27/99 13:22 - [ 7] Visit: 02 Visit Priority: Visit Requirements: AFTER 01 BY 3 D TO 5 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 TITAN-DAY4 STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE,CHECKBOX=25, 1 0.1 S ONBOARD ACQ FOR 20 CD P DIFFUSE-CENTER=GEOMETRIC-CENTER ------------------------------------------------------------------------------------------------------------------------------------ 20 TITAN-DAY4 STIS/C ACCUM 52X0.05 G750L 7751 PATTERN=PERP-TO-SLIT,NUM-POS=18, 1 79 S POS TARG -0.45, 0 MAX DUR CD STEP-SIZE=0.05, 120 S PATTERN-DIRECTION=PLUS, SIZEAXIS2=256,CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 30 CCDFLAT STIS/C ACCUM 52X0.05 G750L 7751 2 DEF CD ------------------------------------------------------------------------------------------------------------------------------------ 8229( 3) - 07/27/99 13:22 - [ 8] Visit: 03 Visit Priority: Visit Requirements: AFTER 01 BY 7 D TO 9 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 TITAN-DAY8 STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE,CHECKBOX=25, 1 0.1 S ONBOARD ACQ FOR 20 CD P DIFFUSE-CENTER=GEOMETRIC-CENTER ------------------------------------------------------------------------------------------------------------------------------------ 20 TITAN-DAY8 STIS/C ACCUM 52X0.05 G750L 7751 PATTERN=PERP-TO-SLIT,NUM-POS=18, 1 79 S POS TARG -0.45, 0 MAX DUR CD STEP-SIZE=0.05, 120 S PATTERN-DIRECTION=PLUS, SIZEAXIS2=256,CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 30 CCDFLAT STIS/C ACCUM 52X0.05 G750L 7751 2 DEF CD ------------------------------------------------------------------------------------------------------------------------------------ 8229( 3) - 07/27/99 13:22 - [ 9] Visit: 04 Visit Priority: Visit Requirements: AFTER 01 BY 11 D TO 13 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 TITAN-DAY12 STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE,CHECKBOX=25, 1 0.1 S ONBOARD ACQ FOR 20 CD P DIFFUSE-CENTER=GEOMETRIC-CENTER ------------------------------------------------------------------------------------------------------------------------------------ 20 TITAN-DAY12 STIS/C ACCUM 52X0.05 G750L 7751 PATTERN=PERP-TO-SLIT,NUM-POS=18, 1 79 S POS TARG -0.45, 0 MAX DUR CD STEP-SIZE=0.05, 120 S PATTERN-DIRECTION=PLUS, SIZEAXIS2=256,CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 30 CCDFLAT STIS/C ACCUM 52X0.05 G750L 7751 2 DEF CD ------------------------------------------------------------------------------------------------------------------------------------ 8229( 3) - 07/27/99 13:22 - [ 10] Summary Form for Proposal 8229 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.05 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=DIFFUSE CHECKBOX=25 DIFFUSE-CENTER=GEOMETRIC-CENTER CR-SPLIT=NO SIZEAXIS2=256 PATTERN-DIRECTION=PLUS STEP-SIZE=0.05 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 20 POS TARG -0.45, 0 MAX DUR 120 S AFTER 01 BY 3 D TO 5 D AFTER 01 BY 7 D TO 9 D AFTER 01 BY 11 D TO 13 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G750L ------------------------------------------------------------------------------------------------------------------------------------ Target Names TITAN-DAY0 CCDFLAT TITAN-DAY4 TITAN-DAY8 TITAN-DAY12 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 7751 ------------------------------------------------------------------------------------------------------------------------------------