Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5330 Report Date: 18-Jul-95:17:09 Version: ********** Check-in Date: ********** 1.Proposal Title: HIGH RESOLUTION MAPPING OF PLUTO'S ALBEDO DISTRIBUTION ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID SOLAR SYSTEM GO Sub Category SATELLITES ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Alan Stern SOUTHWEST RESEARCH INSTITUTE USA [210]-522-5127 ------------------------------------------------------------------------------------ 7. Abstract This proposal requests time to map Pluto's albedo distribution, using the highest possible resolution of the CYCLE 4 HST. Maps will be made in several key UV and visible bandpasses. Our scientific objectives are to (a) study the distribution of light and dark areas, (b) make the first disk-resolved estimates of Pluto's limb darkening, and (c) compositional discriminate pure from contaminated frost regions. These objectives have not been previously achievable, but are essential to understanding the surface morphology, volatile transport, and the root cause of Pluto's secular lightcurve variations. It may also be possible to detect evidence of the reported limb haze layer(s) in Pluto's atmosphere. These maps will also provide the first direct check on Pluto maps made through indirect techniques. Owing to Pluto's elliptic orbit, we expect the distribution of albedo to change (on a years- to-decade timescale) as Pluto draws away from perihelion and volatile transport proceeds. The proposed observations will document the albedo state at three rotational epochs near the time of perihelion. These maps will be obtained in two colors, by the FOC. No other astronomical instrument has sufficient resolution to accomplish these important scientific objectives. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 5.87 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOC ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5330 PI: Alan Stern Proposal Title: HIGH RESOLUTION MAPPING OF PLUTO'S ALBEDO DISTRIBUTION ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Alan Stern 3440 USA Larry M. Trafton 3550 USA Marc Buie 2540 USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. We are proposing to obtain FOC images of Pluto using the f/96 chain with two filter combinations: F278M+F275W, and F410M. The FOC obtains its maximum spatial resolution near 3000 \AA; this resolution of 0.020-0.034 arcsec (Paresce, personal communication) is the best obtainable on HST. To isolate UV light with the F278M bandpass, we will simultaneously employ F275W to supress red leaks. For both the UV F278M+F275W and blue F410M image configurations, neutral density filters are required to supress $N_{max}$ and thus operate the FOC detectors in the linear regime. Each image will be exposed to obtain a S/N of 20-25 per resolution element. This will permit the detection of 10\% pixel-to-pixel relative albedo contrasts with confidence. Four sets of images are requested. Each set will consist of a UV and a BLUE image. These image sets will be spaced about eqaully in rotational phase (Pluto rotates in 6.4 days). For all of the observations, the 512x512 aperture will be combined with an FOC IMAGE mode with 0.014 arcsec pixels, to give a field of view (FOV) of 7x7 arcsec across. This FOV is large compared to both Pluto's diameter and the Pluto-Charon separation, which never exceeds 0.9 arcsec. We will acquire Pluto in the FOC FOV using blind pointing, which the Cycle 4 FOC Handbook describes as the standard acquisition mode for all imaging observations with a FOV >3 arcsec. During exposures, HST will be held in Fine Lock mode. Fine Lock provides a pointing stability of 0.005 arcsec, which is several times smaller than the optical resolution. The F410M filter will map Pluto at a wavelength where a considerable amount of photometric lighcurves have been made. We calculated our exposure times assuming Pluto's radius is 1180 km, Pluto is 30 AU from both the Earth and the Sun, its visible geometric albedo is 0.55 (Binzel 1988), and its UV geometric albedo is 0.38 (derived from IUE low-resolution UV reflectance spectra; Stern et al. 1991). Assuming a background level of $1x10^{-4}$ counts/sec/pixel, and a resolution element size of 0.025 arcsec, FOC f/96 images with S/N of 20 or greater should be obtainable in 44 min at a count rate of 0.14 Hz. This is far below the FOC $N_{max}$ constraint of 0.6 Hz set by the selected IMAGE observing mode. Using a target count rate of 0.15 Hz, and the FOC prescription for count rate estimates given on page 78 of the Cycle 4 FOC Handbook, we reach the following conclusions: 1) for F410M images, the F4ND filter is required; for the F278M+F275W images, the F2ND filter is required. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The studies we are proposing rely on UV techniques and spatial resolutions which only HST can accomplish. Pluto's 0.1 arc-sec diameter is simply too small to be directly imaged from beneath the terrestrial atmosphere. No other spacecraft can obtain the resolution or UV performance required by the scientific objectives of this program. Although a NASA mission may well be sent to reconnoiter Pluto, the earliest feasible arrival date is over 11 years hence. Page 3 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. No real-time observations or special calibrations are required. To achieve the desired goals, each of the 4 requested rotational epochs must be achieved to within 2% rotational phase (+/- 7 deg). This corresponds to a 17 hour window centered on each rotational phase. These observations may be obtained on any apparition of the specified rotational phases in the Cycle. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. None. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. None. ------------------------------------------------------------------------------------ 9. Description of previous HST work. PI Stern: P4024 High Resolution UV Spectroscopy of Triton (as PI); P2560 UV Rotational Light Curves of Pluto, and Charon's UV Spectrum (as CoI); P3803 CO Abundance and FUV Survey (as CoI); P4005 Observations of Jovian Aurora in Support of Ulysses (as PI); P4462 Deep UV Spectroscopy of Triton (as CoI). CoI Trafto8: P1202 Lyman-alpha and H2 Survey; P1203 Jovian Auroral Ly-alpha Profile (as PI); P1204 Io Proton Aurora (as PI); 1206 Sulfur Near Io (as PI); P1290 Uranus and Neptune below 3000 A (as PI); 2569 UV Rotational Light Curves for Pluto, & Charon's UV Spectrum (as PI); P2957 High Resolution UV Spectroscopy of Triton (as CoI); P2560 Integrated Dynamical and Spectroscopic Observations of Jupiter and Saturn (as CoI); P3803 Pluto's FUV Spectrum: CO Abundance and FUV Survey (as PI); P4001 H2 Survey of Jupiter's Northern Aurora During Ulysses Flyby (as PI); P4005 HST UV Imaging of Jupiter to Support the Interpretation of Ulysses X-ray Measurements (as CoI). Buie: Separate Lightcurves of Pluto and Charon; P3848 (as PI). The Structure of the Inner Coma of Comet Chiron; P3769 (as CoI). ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Our proposal team has experience with IUE and HST ultraviolet spectroscopy (Stern & Trafton) and HST visible photometry (Buie) of Pluto. All three investigators are well-recognized experts on Pluto. CoI Buie has led one of the two primary groundbased mapping groups. PI Stern and CoI Trafton have been involved in atmospheric and volatile transport work for over a decade. Southwest Research Institute will support this project by providing all required computing facilities for the PI, and by foregoing overhead on PI travel and the salary of any postdoc involved in data analysis. The individual CoI institutions (U.~Texas and Lowell Observatory) will provide existing workstations for each CoI. A pool of astronomy graduate students is available at The University of Texas to draw research assistants. ------------------------------------------------------------------------------------ 11. Address Information Name: ALAN STERN Category: PI Institution: 3440 Address: SPACE SCIENCE DEPARTMENT SOUTHWEST RESEARCH INSTITUTE 6220 CULEBRA ROAD City: SAN ANTONIO State: TX Zip Code: 78238 Country: USA Telephone: [210]522-5127 Telex (or e-mail): ALAN@SWRI.SPACE.SWRI.EDU ------------------------------------------------------------------------------------ Page 4 Name: Category: CON Institution: Address: City: State: Zip Code: Country: Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 5330 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: PLUTO ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET PLUTO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=PLUTO, ACQ = 0.01 | STD=PLUTO | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | STD=PLUTO | | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | 1 |V=13.7 | OUR TARGET IS PLUTO. ITS SATELLITE 2 |B-V=0.72 | CHARON WILL BE IN THE FIELD. | | ACQ=0.01 TO ENSURE FINE LOCK, PER | | ALEX STORRES SUGGESTION. | ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5330 [ 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 PLUTO FOC/96 IMAGE 512X512 F278M, 001 37M 55 1 01 CYCLE 4 F275W, 34M PCS MODE F F1ND SAME ORIENT FOR 1 AS 2 GROUP 1-2 NO GAP REPEAT 1-2 EVERY Comments: 1) BLIND ACQ; FINE LOCK. 2) 38H +/- 3H EXPOSE 2) EXPOSE FOR 3 MORE TIMES F275W+F278M+F1ND; 3) THEN AT 15-MAY-94 +/- F410M+F4ND WITH SAME ORIENT. 85D REPEAT 3 TIMES AS PLUTO ROTATES SAME POS FOR 1 AS (EVERY 38+/-3H). GUIDE=FINE 2 MODE. EXPOSE <65D FROM OPPOSITION TO MINIMIZE PLUTO DIST ------------------------------------------------------------------------------------------------------------------------------------ 2 PLUTO FOC/96 IMAGE 512X512 F410M, 001 44M 20 1 01 CYCLE 4 F4ND 44M PCS MODE F Comments: 1) BLIND ACQ; FINE LOCK. 2) EXPOSE F275W+F278M+F1ND; 3) THEN F410M+F4ND WITH SAME ORIENT. REPEAT 3 TIMES AS PLUTO ROTATES (EVERY 38+/-3H). GUIDE=FINE MODE. EXPOSE <65D FROM OPPOSITION TO MINIMIZE PLUTO DIST ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5330 [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOC/96 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 5.87 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category SATELLITES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4; PCS MODE F; SAME ORIENT FOR 1 AS 2; GROUP 1-2 NO GAP; REPEAT 1-2 EVERY 38H +/- 3H FOR 3 MORE TIMES; AT 15-MAY-94 +/- 85D; SAME POS FOR 1 AS 2; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F278M,F275W,F1ND F410M,F4ND ------------------------------------------------------------------------------------------------------------------------------------ Target Names PLUTO ------------------------------------------------------------------------------------------------------------------------------------