6013( 9) - 11/21/95 10:54 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6013 Version: 9 Check-in Date: ********** 1.Proposal Title: Mapping the UV Surface Albedo Distribution of Triton ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Solar System GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Brian C. Flynn Southwest Research Institute CoI: S. Alan Stern Southwest Research Institute N CoI: Laurence Trafton University of Texas at Austin N CoI: John Stansberry NASA Ames Research Center N CoI: Keith Noll Space Telescope Science Institute N ------------------------------------------------------------------------------------ 6. Abstract We propose to measure the albedo distribution of Triton at three rotational epochs in two key ultraviolet and visible bandpasses using the FOC. The unique, high- resolution and UV capabilities of HST will allow us to resolve Triton's disk and to map a new spectral region never before imaged on Triton. Our scientific objectives are to: (1) Place further compositional constraints on Triton's surface by imaging farther into the UV than did Voyager 2; (2) obtain a baseline HST measurement for comparison with future HST albedo maps as seasonal change brings about volatile transport; (3) provide context for FOS spectroscopy of Triton; and (4) enhance confidence in albedo maps obtained from similar FOC imaging of Pluto and other small bodies in the solar system through a comparison of HST and Voyager imaging of Triton. ------------------------------------------------------------------------------------ 6013( 9) - 11/21/95 10:54 - [ 2] Observations Description ------------------------ We are proposing to obtain FOC images of Triton using the f/96 chain with two filter combinations: F278M+F275W, and F410M+F4ND. These filters were chosen to bracket a well-known UV absorption edge between ~eq3000-3500 Angstrom\ for non- icy materials. The F410M filter overlaps the 4100 Angstrom\ imaging of Voyager 2. Triton has never been mapped at wavelengths below 3500 Angstrom. The FOC obtains its maximum spatial resolution near 3000 Angstrom; this resolution of 0.020-0.034'' (Paresce, pers. comm.) is higher than is possible with WFPC2 and is the best obtainable on HST. It corresponds to ~eq400-700 km per resolution element on Triton's 2700 km diameter disk. To isolate UV light with the F278M bandpass, we will simultaneously employ F275W to supress red leaks. For the blue F410M image configuration, a neutral density filter is required to supress N_max and thus operate the FOC detector in the linear regime. Each image will be exposed to obtain a S/N of ~eq30-40 per resolution element. This will permit the detection of relative albedo contrasts of ~eq8-10 percent pixel-to-pixel, or ~eq5-7 percent between resolution elements, at the two-sigma level. We estimate that this can be accomplished in three orbits per pair of F278M+F275W and F410M+F4ND images. However, because we were granted 8 orbits, one visit will consist of two orbits and will therefore have a shortened UV image. Three pairs of images are requested in three visits on Triton. Each set will consist of a UV and a blue image. These image pairs will be spaced about Triton in rotational phase (Triton rotates in 5.88 days). It is not necessary to obtain all 3 image sets in a single rotation. We request 3 evenly-spaced rotational epochs in order to obtain good overlap, i.e., 60 degrees of longitudinal overlap for two adjacent rotational epochs. For all of the observations, the 512*512 aperture will be combined with an FOC IMAGE mode with 0.014'' pixels, to give a field of view (FOV) of 7.2'' across. This FOV is large compared to Triton's diameter (0.12''). The FOV will also allow us keep Neptune well off the detector, because the Triton-Neptune separation ranges from ~eq12-17'' at mean opposition. We will acquire Triton in the FOC FOV using blind pointing, which the Cycle 5 FOC Handbook describes as the standard acquisition mode for all imaging observations with a FOV>3''. During exposures, HST will be held in Fine Lock mode. Fine Lock provides a pointing stability of 0.005'', which is several times smaller than the optical resolution. Real Time Justification ----------------------- There no special dark time, time-critical, CVZ, or TOO observations required for this program. No special calibrations are needed. However, to achieve the desired goals, each of the 3 requested rotational epochs must be timed to within +/-30 degrees of the specified Triton central meridian longitude, corresponding to an ~eq24 hour window centered on each rotational phase. However, these observations may be obtained out of sequence and at any apparition of the specified rotational phases while the illumination phase angle of Triton (or, equivalently, Neptune) is between 1.70-2.00 degrees (quadrature), when it is changing most slowly. Each desired rotational phase window recurs every 5.88 days. The three requested visits must occur within two Triton rotations (12 days), so that the illumination phase angle varies by only a few percent between visits. None. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6013( 9) - 11/21/95 10:54 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6013( 9) - 11/21/95 10:54 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: TRITON-000 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE TRITON ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = NEPTUNE | STD = TRITON | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | CML OF TRITON FROM EARTH BETWEEN -30 30 | PHASE OF NEPTUNE FROM EARTH BETWEEN 1.70 | 2.00 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V=13.47 B-V=0.72 U-B=0.29 SIZE=0.128 | IMAGE TRITON AT CML OF 0 DEG. FLUX | PARAMETERS ARE FOR MEAN OPPOSITION. | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: TRITON-120 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE TRITON ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = NEPTUNE | STD = TRITON | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | CML OF TRITON FROM EARTH BETWEEN 90 150 | PHASE OF NEPTUNE FROM EARTH BETWEEN 1.70 | 2.00 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V=13.47 B-V=0.72 U-B=0.29 SIZE=0.128 | IMAGE TRITON AT CML OF 120 DEG. FLUX | PARAMETERS ARE FOR MEAN OPPOSITION. | ------------------------------------------------------------------------------------------------------------------------------------ 6013( 9) - 11/21/95 10:54 - [ 5] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 | TARGET NAME: TRITON-240 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE TRITON ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = NEPTUNE | STD = TRITON | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | CML OF TRITON FROM EARTH BETWEEN 210 270 | PHASE OF NEPTUNE FROM EARTH BETWEEN 1.70 | 2.00 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V=13.47 B-V=0.72 U-B=0.29 SIZE=0.128 | IMAGE TRITON AT CML OF 240 DEG. FLUX | PARAMETERS ARE FOR MEAN OPPOSITION. | ------------------------------------------------------------------------------------------------------------------------------------ 6013( 9) - 11/21/95 10:54 - [ 6] Visit: 01 Visit Requirements: GROUP 1-3 WITHIN 12D BETWEEN 20-SEP-95 AND 11-NOV-95 On Hold Comments: Additional Comments: ALL 3 VISITS MUST BE DONE WITHIN 2 TRITON ROTATIONS BETWEEN 22-MAR-96 AND 16-MAY-96 is also OK. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 TRITON-000 FOC/96 IMAGE 512X512 F410M,F4N CHECK- 1 1539S SEQ 1-2 NON-INT D FILTER=YES Comments: BLUE IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 2 TRITON-000 FOC/96 IMAGE 512X512 F410M,F4N 1 373S END ORBIT EXPAND D Comments: BLUE IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 3 TRITON-000 FOC/96 IMAGE 512X512 F410M,F4N 1 1350S SEQ 3-4 NON-INT D Comments: BLUE IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 4 TRITON-000 FOC/96 IMAGE 512X512 F278M,F27 CHECK- 1 959S EXPAND END ORBIT 5W FILTER=YES Comments: UV IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 5 TRITON-000 FOC/96 IMAGE 512X512 F278M,F27 1 1601S SEQ 5-6 NON-INT 5W Comments: UV IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 6 TRITON-000 FOC/96 IMAGE 512X512 F278M,F27 1 826S EXPAND END ORBIT 5W Comments: UV IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 6013( 9) - 11/21/95 10:54 - [ 7] Visit: 02 Visit Requirements: BETWEEN 20-SEP-95 AND 11-NOV-95 On Hold Comments: Additional Comments: ALL 3 VISITS MUST BE DONE WITHIN 2 TRITON ROTATIONS BETWEEN 22-MAR-96 AND 16-MAY-96 is also OK. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 TRITON-120 FOC/96 IMAGE 512X512 F410M,F4N CHECK- 1 1539S SEQ 1-2 NON-INT D FILTER=YES Comments: BLUE IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 2 TRITON-120 FOC/96 IMAGE 512X512 F410M,F4N 1 373S END ORBIT EXPAND D Comments: BLUE IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 3 TRITON-120 FOC/96 IMAGE 512X512 F410M,F4N 1 1350S SEQ 3-4 NON-INT D Comments: BLUE IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 4 TRITON-120 FOC/96 IMAGE 512X512 F278M,F27 CHECK- 1 959S END ORBIT EXPAND 5W FILTER=YES Comments: UV IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 5 TRITON-120 FOC/96 IMAGE 512X512 F278M,F27 1 1601S SEQ 5-6 NON-INT 5W Comments: UV IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 6 TRITON-120 FOC/96 IMAGE 512X512 F278M,F27 1 826S END ORBIT EXPAND 5W Comments: UV IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 6013( 9) - 11/21/95 10:54 - [ 8] Visit: 03 Visit Requirements: BETWEEN 20-SEP-95 AND 11-NOV-95 On Hold Comments: Additional Comments: ALL 3 VISITS MUST BE DONE WITHIN 2 TRITON ROTATIONS BETWEEN 22-MAR-96 AND 16-MAY-96 is also OK. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 TRITON-240 FOC/96 IMAGE 512X512 F410M,F4N CHECK- 1 1539S SEQ 1-2 NON-INT D FILTER=YES Comments: BLUE IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 2 TRITON-240 FOC/96 IMAGE 512X512 F410M,F4N 1 373S END ORBIT EXPAND D Comments: BLUE IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 3 TRITON-240 FOC/96 IMAGE 512X512 F410M,F1N CHECK- 1 631S SEQ 3-4 NON-INT D,F2ND FILTER=YES Comments: BLUE IMAGE. NEUTRAL DENSITY CHANGED FROM F4ND TO F1ND+F2ND TO INCREASE COUNT RATE AND SHORTEN EXPOSURE TIME FOR THIS BLUE EXPOSURE. COUNT RATE WILL BE IN NON-LINEAR RANGE, BUT ALBEDO CONTRASTS WILL BE PRESERVED. ------------------------------------------------------------------------------------------------------------------------------------ 4 TRITON-240 FOC/96 IMAGE 512X512 F278M,F27 CHECK- 1 1580S END ORBIT EXPAND 5W FILTER=YES Comments: UV IMAGE ------------------------------------------------------------------------------------------------------------------------------------ 6013( 9) - 11/21/95 10:54 - [ 9] Summary Form for Proposal 6013 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOC/96 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CHECK-FILTER=YES ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Solar System ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GROUP 1-3 WITHIN 12D BETWEEN 20-SEP-95 AND 11-NOV-95 SEQ 1-2 NON-INT END ORBIT EXPAND SEQ 3-4 NON-INT EXPAND END ORBIT SEQ 5-6 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F410M,F4ND F278M,F275W F410M,F1ND,F2ND ------------------------------------------------------------------------------------------------------------------------------------ Target Names TRITON-000 TRITON-120 TRITON-240 ------------------------------------------------------------------------------------------------------------------------------------