6650( 7) - 07/12/96 14:57 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6650 Version: 7 Check-in Date: 12-Jul-1996 14:51:55 1.Proposal Title: Atmospheric Dynamics and Cloud Structure on Neptune ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle SOLAR SYSTEM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: LAWRENCE SROMOVSKY UNIVERSITY OF WISCONSIN CoI: Sanjay Limaye University of Wisconsin N CoI: Andrew Ingersoll California Institute of Technology N CoI: Kevin Baines Jet Propulsion Laboratory N ------------------------------------------------------------------------------------ 6. Abstract Neptune's atmospheric circulation and cloud structure will be investigated using two successive multispectral maps of Neptune's cloud top surface, constructed to support detection of both bright and dark cloud features, the tracking of motions and rapid dynamical changes of isolated features, the identification of zonal band structures, and the inference of vertical structure from observed wavelength and center-to-limb variations. These observations will also extend the time base of HST Neptune observations gathered in 1991, 1994, and 1995, so that longer term variations in Neptune's atmosphere can be tracked. This program of observations provides observations relatively closely spaced in time to provide maximum longitudinal coverage at high northern latitudes where a new dark spot was discovered (at 30 degrees N), and to provide at lower latitudes multiple views of features on the same rotation to track short-term variations and minimize uncertainties in feature identification between images. ------------------------------------------------------------------------------------ 6650( 7) - 07/12/96 14:57 - [ 2] Observations Description ------------------------ From Voyager and ground-based observations we know that dynamical time scales on Neptune range from hours to years. Some bright cloud features develop and dissipate in a small fraction of one rotation of Neptune (Limaye and Sromovsky, 1991; JGR 96, 18941-18960). On the other hand, major cloud features can persist for many months, move significant distances in latitude and, in some cases, exhibit periodic variations in position, shape, and brightness (Sromovsky et al., 1993; Icarus 105, 110-141). In 1989 the Great Dark Spot (GDS) was drifting towards a November 1990 equator crossing, and apparently did not survive. A new dark spot discovered at 30 degrees N (Hammel et al., 1995; Science 268, 1740- 1742) may now also be heading for a similar catastrophe, possibly during cycle 6 if it moves equatorward at the GDS rate. Ground-based observations of bright cloud features at latitudes where none were seen by Voyager and large changes in light curve amplitudes from year to year also suggest major developments or large latitudinal excursions over a several year period. The observations described here will provide a relatively detailed view of dynamical activity and vertical cloud structure over a relatively short period, i.e. two rotations of Neptune, but also provide a tie point for coordinated earth-based observations made near the same time, and extend the time base for studying the longer term phenomena that occur on scales of months to years. The time intervals chosen for the observations are governed by two main objectives: (1) complete longitudinal coverage for feature detection, and (2) multiple views of the same feature to allow measurement of wind speed and dynamical changes without ambiguities about feature identification. During August 1996 the earth subpoint latitude on Neptune is 27.45 S (planetographic), making it hard to observe high northern latitudes. If a cloud feature must be 21 degrees of great circle arc away from the limb, then at 35 degrees N only about 66 degrees of longitude can be seen in a single image, and about 2 orbits of HST (about 3.234 hrs) are required for that region to rotate out of view and be replaced by the adjacent region. We thus need to make images every other orbit to cover the entire rotation in six 66 degree steps. At lower latitudes and especially at northern latitudes this sampling results in multiple views of the same feature on the same rotation: at the equator every feature will be seen twice on the first rotation, while at 66 degrees S every feature will be seen three times. After the first rotation is used to establish identity with clear views over short intervals, a sparser sampling (half as frequent) is used to pick up the features on the next rotation of Neptune, providing enhanced wind speed accuracy for those features that last over the longer time interval. Filters were selected to maximize contrast of each feature, to characterize changes in the vertical structure of the features, and to provide good correlation with ground observations and Voyager imaging data. Three filters carry the main burden for tracking dynamical changes. The F467M filter is chosen to provide greatest contrast for dark features (the Voyager blue filter covering the range from 0.43-0.53 microns gave the greatest contrast for the dark core of the Great Dark Spot, and the new dark spot at 30 N was also seen in an F467M HST image). The F673N filter is in a window region relatively free of CH4 absorption and less affected by Rayleigh scattering than the blue region of the spectrum (it provides views similar to the Voyager orange filter spanning the 0.54-0.64 micron range, showing mid level (such as the Scooter) and higher bright cloud features as well as showing subtle banded structure quite well, including showing a dark ring around the equator that appears bright in the 6190 methane band image). The FQCH4P15 filter covering the 0.89 micron methane band provides very high contrast for bright cloud features and good views of the limb (better than at 0.619 microns which shows significant limb brightening; although this filter blots out some of the lower cloud features and subtle zonal bands, these are covered well by the F673N filter. The F850LP filter provides a continuum reference for the 0.89 micron band. To better define the vertical structure of the isolated cloud features and zonal banded features we also include the methane band filter at 0.619 microns (FQCH4N15) and a corresponding continuum reference at 0.631 microns (F631N). Short wave bands that can descriminate vertical structure by varying amounts of Rayleigh scattering are provided by F255W, F336W, F410M, and F588N. The the UV filter F255W is only used during the last three visits, while the latter three are alternated with FQCH4N15 during the first six visits. The observation sequence is summarized in the following table. rel. time group 1 group 2 number of visit orbit (hrs) filters filters images -------------------------------------------- ------------- 1 1 0 F467M,F673N, FQCH4N15, 6 FQCH4P15,F850LP F631N 2 3 3.234 F467M,F673N, F336W,F588N, 7 FQCH4P15,F850LP F410M 3 5 6.468 F467M,F673N, FQCH4N15, 6 FQCH4P15,F850LP F631N 4 7 9.702 F467M,F673N, F336W,F588N, 7 FQCH4P15,F850LP F410M 5 9 12.936 F467M,F673N, FQCH4N15, 6 FQCH4P15,F850LP F631N 6 11 16.170 F467M,F673N, F336W,F588N, 7 FQCH4P15,F850LP F410M 7 15 22.638 F467M,F673N, FQCH4P15, 6 FQCH4P15,F850LP F255W 8 19 29.106 F467M,F673N, FQCH4P15, 6 FQCH4P15,F850LP F255W 9 23 35.574 F467M,F673N, FQCH4P15, 6 FQCH4P15,F850LP F255W -------------------------------------------------------- Total Images 57 Exposure calculation: The number of electrons/second generated in one detector pixel from an extended source of photon radiance N(wl) (phot/cm^2 sec sr Angstrom) can be approximated as I_e = QE(wl) x tau(wl) x A x Omega x N(wl) x spectral bandpass where tau(wl) is the telescope and filter transmission, Omega is the solid angle of the FOV, A is the area of mirror (neglecting central obscuration), wl is the effective mean wavelength, and QE is the quantum efficiency of the detector and telescope. Using A x Omega =2.20E -9 cm^2sr, a field of view of 0.0455 arc seconds square, geometric albedos and solar fluxes from Neff et al. (1984), and quantum efficiencies and filter characteristics from the WFPC2 Instrument Handbook Vers. 3, we calculated reference full-scale exposures for average disk and unit albedo features. The planned exposures are typically set for below full scale (27,000 electrons, gain 7) for the brightest anticipated features (about midway between unit albedo and average planetary albedo). The very underexposed F255W image will be mainly used to interpret large-scale patterns for which spatial averaging can be used to enhance signal to noise ratios. bandpass x [ bandpass radiance>] Full Sc. Full Sc. Planned Filter (Angst) (Angst) (ph/cm2s sr) QE*Tau Exp,sec Exp,sec Exp,sec ----------------------------------- -------------------------------- F255W 2586 393 1.24E11 0.0051 19305 8180 200 F336W 3342 381 1.17E12 0.0353 297 131 100 F410M 4094 147 1.01E12 0.0457 266 118 100 F467M 4669 167 1.61E12 0.0605 126 56 40 F588N 5894 49 4.79E11 0.1600 160 59 70 F631N 6306 31 2.50E11 0.1597 307 91 70 F673N 6732 47 2.37E11 0.1483 370 153 160 F850LP 9072 986 7.21E11 0.0364 467 21 20 FQCH4N15 6214 41 1.10E11 0.1245 1700 197 300 FQCH4P15 8915 139 3.69E10 0.0166 5200 296 400,500 ---------------- --------------------------------------------------- Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- The optimum sampling interval needed to complete the first rotational map is every other orbit, until 6 orbits of data have been accumulated. This timing is needed to avoid longitude sampling gaps at high latitudes. The last three visits are optimally spaced relative to each other and should not be delayed substantially from the proposed program to avoid problems in cloud feature identification resulting from the greater possibility of cloud evolution over longer time intervals. However, a small delay (of a few orbits to a day) in the start of the last group of three visits would not seriously compromise the science return. We will propose IRTF NSFCAM observations to provide better spectral leverage on resolving vertical structure because of the much stronger methane bands that can be used. Additional observing time will be proposed to support HST observations with coordinated simultaneous ground based observations as far as possible. We will also be proposing observations on the newly commissioned WIYN telescope at Kitt Peak. These coordinated observations should clarify the relationship between features seen at visual wavelengths and those seen at K and L bands. It may be desirable to adjust the start date for the HST observations to coordinate with ground-based observations. ------------------------------------------------------------------------------------ 6650( 7) - 07/12/96 14:57 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6650( 7) - 07/12/96 14:57 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: NEPTUNE ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET NEPTUNE ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=NEPTUNE | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 7.85 | B-V = +0.43 | | ------------------------------------------------------------------------------------------------------------------------------------ 6650( 7) - 07/12/96 14:57 - [ 5] Visit: 01 Visit Requirements: PCS MODE Fine BETWEEN 31-JUL-96 AND 31-AUG-96 On Hold Comments: Additional Comments: Neptune should be positioned on the PC chip at a location that avoids chip defects and filter vignetting or any other position dependent performance problem; in selecting among regions of comparable filter/chip performance use the region that places Neptune nearest the center of the chip so that Triton can be imaged for use as an orientation reference. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NEPTUNE WFPC2 IMAGE PC1 F467M ATD-GAIN=7 1 40 S SEQ 1-6 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 NEPTUNE WFPC2 IMAGE PC1 F673N ATD-GAIN=7 1 160 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 500 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 4 NEPTUNE WFPC2 IMAGE PC1 F850LP ATD-GAIN=7 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 5 NEPTUNE WFPC2 IMAGE FQCH4N1 FQCH4N15 6193 ATD-GAIN=7 1 300 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 NEPTUNE WFPC2 IMAGE PC1 F631N ATD-GAIN=7 1 70 S ------------------------------------------------------------------------------------------------------------------------------------ 7 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 400 S SEQ 7-12 NON-INT 5 ------------------------------------------------------------------------------------------------------------------------------------ 8 NEPTUNE WFPC2 IMAGE PC1 F850LP ATD-GAIN=7 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 9 NEPTUNE WFPC2 IMAGE PC1 F467M ATD-GAIN=7 1 40 S ------------------------------------------------------------------------------------------------------------------------------------ 10 NEPTUNE WFPC2 IMAGE PC1 F673N ATD-GAIN=7 1 160 S ------------------------------------------------------------------------------------------------------------------------------------ 11 NEPTUNE WFPC2 IMAGE PC1 F255W ATD-GAIN=7 1 200 S ------------------------------------------------------------------------------------------------------------------------------------ 12 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 400 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 13 NEPTUNE WFPC2 IMAGE PC1 F467M ATD-GAIN=7 1 40 S SEQ 13-19 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 14 NEPTUNE WFPC2 IMAGE PC1 F673N ATD-GAIN=7 1 160 S ------------------------------------------------------------------------------------------------------------------------------------ 15 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 500 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 16 NEPTUNE WFPC2 IMAGE PC1 F850LP ATD-GAIN=7 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 17 NEPTUNE WFPC2 IMAGE PC1 F336W ATD-GAIN=7 1 100 S ------------------------------------------------------------------------------------------------------------------------------------ 18 NEPTUNE WFPC2 IMAGE PC1 F588N ATD-GAIN=7 1 70 S ------------------------------------------------------------------------------------------------------------------------------------ 19 NEPTUNE WFPC2 IMAGE PC1 F410M ATD-GAIN=7 1 100 S ------------------------------------------------------------------------------------------------------------------------------------ 6650( 7) - 07/12/96 14:57 - [ 6] Visit: 02 Visit Requirements: PCS MODE Fine AFTER 1 by 3.9 ORBITS TO 4.1 ORBITS On Hold Comments: Additional Comments: Neptune should be positioned on the PC chip at a location that avoids chip defects and filter vignetting or any other position dependent performance problem; in selecting among regions of comparable filter/chip performance use the region that places Neptune nearest the center of the chip so that Triton can be imaged for use as an orientation reference. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NEPTUNE WFPC2 IMAGE PC1 F467M ATD-GAIN=7 1 40 S SEQ 1-6 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 NEPTUNE WFPC2 IMAGE PC1 F673N ATD-GAIN=7 1 160 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 500 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 4 NEPTUNE WFPC2 IMAGE PC1 F850LP ATD-GAIN=7 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 5 NEPTUNE WFPC2 IMAGE FQCH4N1 FQCH4N15 6193 ATD-GAIN=7 1 300 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 NEPTUNE WFPC2 IMAGE PC1 F631N ATD-GAIN=7 1 70 S ------------------------------------------------------------------------------------------------------------------------------------ 7 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 400 S SEQ 7-12 NON-INT 5 ------------------------------------------------------------------------------------------------------------------------------------ 8 NEPTUNE WFPC2 IMAGE PC1 F850LP ATD-GAIN=7 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 9 NEPTUNE WFPC2 IMAGE PC1 F467M ATD-GAIN=7 1 40 S ------------------------------------------------------------------------------------------------------------------------------------ 10 NEPTUNE WFPC2 IMAGE PC1 F673N ATD-GAIN=7 1 160 S ------------------------------------------------------------------------------------------------------------------------------------ 11 NEPTUNE WFPC2 IMAGE PC1 F255W ATD-GAIN=7 1 200 S ------------------------------------------------------------------------------------------------------------------------------------ 12 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 400 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 13 NEPTUNE WFPC2 IMAGE PC1 F467M ATD-GAIN=7 1 40 S SEQ 13-19 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 14 NEPTUNE WFPC2 IMAGE PC1 F673N ATD-GAIN=7 1 160 S ------------------------------------------------------------------------------------------------------------------------------------ 15 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 500 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 16 NEPTUNE WFPC2 IMAGE PC1 F850LP ATD-GAIN=7 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 17 NEPTUNE WFPC2 IMAGE PC1 F336W ATD-GAIN=7 1 100 S ------------------------------------------------------------------------------------------------------------------------------------ 18 NEPTUNE WFPC2 IMAGE PC1 F588N ATD-GAIN=7 1 70 S ------------------------------------------------------------------------------------------------------------------------------------ 19 NEPTUNE WFPC2 IMAGE PC1 F410M ATD-GAIN=7 1 100 S ------------------------------------------------------------------------------------------------------------------------------------ 6650( 7) - 07/12/96 14:57 - [ 7] Visit: 03 Visit Requirements: PCS MODE Fine AFTER 1 BY 7.9 ORBITS TO 8.1 ORBITS On Hold Comments: Additional Comments: Neptune should be positioned on the PC chip at a location that avoids chip defects and filter vignetting or any other position dependent performance problem; in selecting among regions of comparable filter/chip performance use the region that places Neptune nearest the center of the chip so that Triton can be imaged for use as an orientation reference. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NEPTUNE WFPC2 IMAGE PC1 F467M ATD-GAIN=7 1 40 S SEQ 1-6 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 NEPTUNE WFPC2 IMAGE PC1 F673N ATD-GAIN=7 1 160 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 500 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 4 NEPTUNE WFPC2 IMAGE PC1 F850LP ATD-GAIN=7 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 5 NEPTUNE WFPC2 IMAGE FQCH4N1 FQCH4N15 6193 ATD-GAIN=7 1 300 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 NEPTUNE WFPC2 IMAGE PC1 F631N ATD-GAIN=7 1 70 S ------------------------------------------------------------------------------------------------------------------------------------ 7 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 400 S SEQ 7-12 NON-INT 5 ------------------------------------------------------------------------------------------------------------------------------------ 8 NEPTUNE WFPC2 IMAGE PC1 F850LP ATD-GAIN=7 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 9 NEPTUNE WFPC2 IMAGE PC1 F467M ATD-GAIN=7 1 40 S ------------------------------------------------------------------------------------------------------------------------------------ 10 NEPTUNE WFPC2 IMAGE PC1 F673N ATD-GAIN=7 1 160 S ------------------------------------------------------------------------------------------------------------------------------------ 11 NEPTUNE WFPC2 IMAGE PC1 F255W ATD-GAIN=7 1 200 S ------------------------------------------------------------------------------------------------------------------------------------ 12 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 400 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 13 NEPTUNE WFPC2 IMAGE PC1 F467M ATD-GAIN=7 1 40 S SEQ 13-19 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 14 NEPTUNE WFPC2 IMAGE PC1 F673N ATD-GAIN=7 1 160 S ------------------------------------------------------------------------------------------------------------------------------------ 15 NEPTUNE WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=7 1 500 S 5 ------------------------------------------------------------------------------------------------------------------------------------ 16 NEPTUNE WFPC2 IMAGE PC1 F850LP ATD-GAIN=7 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 17 NEPTUNE WFPC2 IMAGE PC1 F336W ATD-GAIN=7 1 100 S ------------------------------------------------------------------------------------------------------------------------------------ 18 NEPTUNE WFPC2 IMAGE PC1 F588N ATD-GAIN=7 1 70 S ------------------------------------------------------------------------------------------------------------------------------------ 19 NEPTUNE WFPC2 IMAGE PC1 F410M ATD-GAIN=7 1 100 S ------------------------------------------------------------------------------------------------------------------------------------ 6650( 7) - 07/12/96 14:57 - [ 8] Summary Form for Proposal 6650 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=7 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE Fine BETWEEN 31-JUL-96 AND 31-AUG-96 SEQ 1-6 NON-INT SEQ 7-12 NON-INT SEQ 13-19 NON-INT PCS MODE Fine AFTER 1 by 3.9 ORBITS TO 4.1 ORBITS PCS MODE Fine AFTER 1 BY 7.9 ORBITS TO 8.1 ORBITS ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F467M F673N FQCH4P15 F850LP FQCH4N15 F631N F255W F336W F588N F410M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NEPTUNE ------------------------------------------------------------------------------------------------------------------------------------