Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5437 Report Date: 18-Jul-95:17:23 Version: ********** Check-in Date: ********** 1.Proposal Title: UV SPECTROIMAGING OF SATURN AND SEARCH FOR EXOGENOUS WATER IN THE ATMOSPHERE: A CRITICAL TEST FOR RING EROSION THEORIES ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID SOLAR SYSTEM GO Sub Category GIANT PLANETS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Renee M Prange INSTITUT D'ASTROPHYSIQUE SPA FRANCE 331 69858582 ------------------------------------------------------------------------------------ 7. Abstract After about three years of exciting new results with HST, especially in the UV wavelength range, none, but one, concerns UV diagnostic of Saturn's atmosphere. The atmospheric dynamics at the cloud level is well documented from ground based observations in the visible and IR. UV wavelengths are diagnostic of regions higher in the atmosphere and our knowledge is primarily due to IUE and Voyager, plus some IR observations. This program addresses several outstanding issues concerning the stratosphere of Saturn above ~100 mbar by means of UV single bandpass imaging with the FOC, and spectroscopy of particular regions with the FOS. The wavelength range of interest is 1400 A - 2200 A, a range already studied with IUE, and the issues cover thermochemical equilibrium and dynamics of the atmosphere through the abundance and latitudinal distribution of the species (hydrocarbons, phosphine). We will particularly focus on the detection of water absorption features. The presence of exogenous water in the atmosphere of Saturn is suggested by a large body of independent observations, ranging from the presence of CO and of large H abundance, to decreases in the ionospheric density and latitudinally organized 'anomalous' features. Its direct detection (or non detection) would be an essential test of electro- magnetic theories of ring erosion and of the age of the rings. In anycase, the proposed observations will provide the first UV image at any level of detail of the disc of Saturn, and the first spatially resolved UV spectra. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 9.33 par: 0. 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOS FOC ------------------------------------------------------------------------------------ 12. Special sched req: Time Critical obs. Real Time obs. ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5437 PI: Renee M Prange Proposal Title: UV SPECTROIMAGING OF SATURN AND SEARCH FOR EXOGENOUS WATER IN THE ATMOSPHERE: A CRITICAL TEST FOR RING EROSION THEORIES ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Jack Ep Connerney 2856 USA Regis Courtin 5468 FRANCE X Keith Noll 3470 USA Jack Mcconnell 4678 CANADA Page 3 ------------------------------------------------------------------------------------ 3. Description of proposed observations. We propose to associate mapping of Saturn's disc in two wavelength ranges (one including significant water absorption bands) and spectroscopy in two selected regions where water abundance is expected to be maximum and minimum respectively . The spectra will provide detailed information on the composition of the atmosphere locally (including water,hydrocarbons and phosphine). They will complement images which provide high spatial resolution albedo distributions, and which can be interpreted in terms of spatial distribution of water,phosphine and hydrocarbon absorption, but not uniquely. In particular, the theory predicts increased abundance of water in narrow arcs at constant latitude (~.1" to 1"wide as seen from Earth), conjugate from specific distances in the rings. For the UV imaging of the disc of Saturn, we use the FOC f/96 with the 14"X14" format,the zoomed pixels and the 8-bit words (low count-rate per pixel). Since the FOV is smaller than the planet disc after COSTAR, we take separate images for the north and south hemispheres WITH THE SAME POINTING within 0.1 to 0.2" because the limb retrieved from the mosaic must be very accurate (see binning). We use two UV filters in series to avoid contamination by the visible disc emissions: F175W+F170M [1] to map the H2O absorption, and F220W+F190M [2] used as 'non H2O' reference (H2O is not an absorber above 1860 A).In both maps, we will also find the signature of other species, i.e. C2H2 (absorption in [1]+[2]) and PH3 (signature in [2] alone). In addition to wavelength criteria, these signatures will be recognised from H2O by their latitudinal dependence (smooth equator/pole variations for C2H2, large 'belt-like' structures for PH3). To compensate for the very low count-rate, we will use a special pixel binning along constant latitude arcs, adapted to the expected H20 arc geometry, and derive a 1-D latitudinal curve of reflected flux. The result of this binning is very sensitive to any uncertainty in the pointing. A 180 M exposure in [1] will provide an excellent contrast between the south H2O absorbing feature and the planet disc (five contiguous points with S/N~30 each). The narrower arcs in the north are expected to be defined by four points S/N~15 each. The transmission of [2] is such that an exposure time of 30 M, provides the same S/N for hydrocarbon or phosphine absorption. Saturation in [2] will be avoided by splitting the exposure. The sequences will then be 6x30M with [1] and 2x12.5M with [2]. The spectra are taken in the 1400-2400A range of the IUE data. We use the FOS and two gratings (G130H,G190H) to cover the main spectral signatures. We observe the south latitudes conjugate of the inner B ring where the H2O influx is predic ted to be stronger and more extended. A compromise between sensitivity and spatial resolution is the .86" square aperture. Information on the size of the south arc will come from a four spectra scan with a step of ~.45". In order to relate the location of the absorbing region scanned to models, the pointing accuracy must be similar to the resolution of the 1-D profiles. This will be best accomplished by an onboard acquisition of a satellite of Saturn. Each G130H and G190H spectrum will last 23M and 7M respectively, for a S/N>10. A reference spectrum will be taken in a region not connected to the ring system, in the north equatorial region. Page 4 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. Ground-based observations have given evidence of absorption in the IR methane bands, whereas the Voyager visible images have identified a narrow dark banded structure. In both cases they have been attributed to variations in the aerosol layer thickness, or pressure and altitude. Even though the primary effect could be water influx, no direct evidence has ever be obtained,and cannot be obtained from ground based telescopes in the visible or the IR, since H2O absorption cannot be observed through the earth atmosphere. As for presently operating spacecrafts, IUE has identified a planetwide absorption in the 1500-1850 angstroms range which can be attributed to H2O (Wilkenstein et al., 1983). However IUE is not an imaging instrument, and its spatial resolution is too limited to resolve the narrow spatial features where water abundance is expected to be significantly increased, and it can only detect the average water density. This average value is too small to provide an unambiguous identification of absorbtion signature in the spectra. Since these absorbing features can only be detected detected at high spatial resolution, and preferably with an imaging instrument to avoid the problem of insufficient pointing accuracy, the Hubble Space Telescope is the only opportunity for imaging the absorption pattern of H2O, and on the HST, the FOC. Several UV images have been taken at UV wavelengths with HST. None with in the range studied in this program. In addition, the two WF/PC images suffered from red leak contamination, and the one FOC image (GTO 1269) is saturated on the disc at mid and low latitude, and is only usable at high latitude (polar structures). ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. The spectral observations are not time critical. On the contrary, the images are constrained.The retrieval of the latitudinal structure of the surface brightness is extremely dependent on the accuracy of the limb fitting. We need to reconstruct very precisely the planet disc from the north and the south images. This imposes two conditions (1) the offset between the north and south images must be known very precisely (0.1-0.2") in order to make a mosaic. They must consequently be performed with tracking on the same guide star. The two shortwavelength exposures extend over more than 18 hours. This imposes the observations to be done not too far from the stationary point. (2) Even though, the limb will be corrrectly defined only if enough of each hemisphere is in the FOV, i.e. far enough from opposition. This imposes the orbital longitude to be between ~45 deg. and ~100 deg. both sides of opposition. Since the size of the planet disc decreases with increasing distance to opposition, the most convenient period is between ~70 and ~100 both sides. This would even allow for the images at the two wavelengths to be performed with the same set of guide star. This would be helpful because the reference maps at longer wavemength will have a larger count/pix, and therefore its limb, better defined than the limb of the "water" image could be used for both. If the condition on the 2' of apparent motion of the target were relaxed somewhat, the limit of 100 deg would be relaxed similarly. Page 5 ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. The Institut d'Astrophysique Spatiale, the Goddard Space Flight Center's Laboratory for Extraterrestrial Physics VAX, the Space Telescope Institute, the Observatoire de Meudon, and York University all possess computational facilities consisting in VAX computers and VAX, SUN and HP UNIX workstation, available for the data analysis. All are connected to local and international networks. Besides the usual reduction techniques: calibration, deconvolution of the instrumental transmission function, background reduction,filtering, curve fitting), we plan to use for the analysis of the FOC images an adapted pixel- binning since the features to be detected are expected to map constant magnetic latitude arcs. We will thus consider as an "element resolution" such constant width arcs (a spatial resolution of .25 deg. at 40-50 deg. corresponds to almost a thousand pixels) the geometry of which is obtained through the Z3 magnetic field model (Connerney et al., 1982). The 1-D latitudinal profile will directly derive from this data processing. Depending on the column density of H2O above 20mbars, there will appear a more or less contrasted absorption feature at specific latitudes in the F175W+F170M data. If these features are due to water they will not appear in the F220W+F190M data, whereas acetylene, ethane and/ or phosphine are expected to exhibit a correlated signature in both sets of data Then the latitude of the absorbing features will be mapped along field lines to their radial location on the rings using the magnetic field model developed by J.E.P. Connerney. The success of the analysis depends on an accurate determination of the arcs' geometry and location on the image. The first point is relevant to analysis procedures (mapping of equatorial features down along model magnetic field lines to predict the location of non equatorial observable features) which have already been developed by J.E.P. Connerney at the Goddard Space Flight Center's Laboratory for Extraterrestrial Physics and successfully applied to the identification of the signature of satellite orbits in the magnetospheric energetic plasma of the outer planets visited by Voyager. The second point requires an accurate knowledge of the planet limb. The PI R. Prange has already been associated in the successful analysis of FOC images of the Jovian aurorae on program GTO 1269 where planet limb determination are also needed. In this case, the images of the north and south hemisphere will have to be merge with the technique used for the mosaics. On the other hand, the spectra will be analyzed in the same way as the Wilkenstein et al, 1983 ones. They will be fittted by various atmospheric models such as those developed by R. Courtin, and the resulting composition of the atmosphere, together with the latitudinal variations derived from the images will be interpreted in terms of photochemical atmospheric models with main contribution from J. McConnell and K. Noll, and dynamical models (in particular the vertical circulation of phosphine) by R. Courtin who has already developed theoretical models. The effect of significant H2O precipitation on the upper atmosphere (H abundance, production of CO etc, ) will be investigated by R. Prange, J. McConnell, and K. Noll. Page 6 ------------------------------------------------------------------------------------ 9. Description of previous HST work. 1. GTO 1269 - "Far UV imaging of the giant planets" 2 .GO 4472 - "Abundance and distribution of the atomic deuterium in the jovian upper atmosphere through the D -Lyman alpha line profile analysis at the planet limb" 3. GO 4601 - "Jupiter's H Ly alpha Auroral and Airglow Emission Line Profiles" 4. GO 4716 - "Search for Exogenous Water in Saturn's Atmosphere: A Critical Test for Ring Erosion Theories" 5. GO 4806 - "Multispectral multitimescale observation of Jupiter" 6. GO/AR 4910 - "Search for CO and NH3 in Neptune's atmosphere" 1,5. Good data of the Lyman alpha and H2 aurorae, although low S/N. Found 1st of Jovian aurora corotating with the planet, and of separate auroral features at various latitudes. Evidence of correlation of part of the aurora with field aligned currents measured simultaneously with Ulysses. Several sets of H2 images with evidence of time variability. Partly analyzed. 2. Observations performed in july 1993. The D line has been identified. 3,4 Cycle 3, no observations yet. 6. Cycle 3 archival program - database search to commence in summer 1993. - Dols, V., J.C. Gerard, F. Paresce, R. Prange, and A. Vidal-Madjar, Far ultraviolet imaging of the Jovian aurora with the Hubble Space Telescope, Geophys. Res. Lett., 19, 1806,1992 - Gerard, J.C., V. Dols, F. Paresce, R. Prange, Morphology and time variation of the far UV Jovian aurora : HST observations,J. Geophysic. Res., in press, 1993. - Gerard, J.C., V. Dols, F. Paresce, R. Prange, and A. Vidal-Madjar, Far ultraviolet imaging of JupiterUs northern polar regions with the FOC, Proceedings of the HST workshop (Sardinia, July 1992), 1993 - Dols, V., J.C. Gerard, F. Paresce, R. Prange, High resolution observation of the morphology of the Jovian far UV aurora with the Hubble Space Telescope, Abstract, Ann. Geophys. Suppl., 11, C492, 1993. - Dougherty, M., R. Prange, M. Dunlop, D. Southwood, A. Bishop, V. Dols and J.C. Gerard, Field aligned currents and auroral emissions in the Jovian magnetosphere, Abstract, Ann. Geophys. Suppl., 11, C492, 1993. - Gerard, J.C., V. Dols, F. Paresce, R. Prange, and A. Vidal-Madjar, First Ly-alpha images of the Jovian aurora with the HST, Abstract, Ann. Geophys. Suppl., 10, 1992 - Gerard, J.C., V. Dols, F. Paresce, R. Prange, Observations of H and H2 ultraviolet aurora with the HST Faint Object Camera, Abstract DPS, BAAS, 1992. - Gerard, J.C., V. Dols, F. Paresce, R. Prange, Abst.,Ann. Geophys. Suppl., 1993 - Prange, R., V. Dols, J. C. Gerard, and F. Paresce, Analysis of the first image of the Jovian aurora at Lyman alpha obtained with the HST, Poster and invited talk in "Variable Phenomena in Jovian Systems", Annapolis, 23-26, July, 1992. _ Prange. R., M.K. Dougherty, M.W. Dunlop, and A. Balogh, Field aligned current driven aurora in the Jovian magnetosphere: A possible identification with correlated HST and Ulysses observations, DPS, Boulder, oct. 1993, BAAS, in press ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). The GSFC's Laboratory for Extraterrestrial Physics VAX computational facilities and staff, as well as the Observatoire de Meudon and IAS facilities, which also consist in VAX computers and VAX and SUN workstations, are available for the data analysis. As for any further development of the analysis, J.E.P. Connerney has access to a wealth of correlative data archived at the GSFC's National Space Science Data Center. Many Voyager coinvestigators and experiment participants reside at the GSFC and are available for consultation. ------------------------------------------------------------------------------------ 11. Address Information Name: RENEE M PRANGE Category: PI Institution: INSTITUT D'ASTROPHYSIQUE SPATIALE Address: BATIMENT 121 UNIVERSITE PARIS XI City: ORSAY State: Zip Code: 91405 Country: FRANCE Telephone: 331 69858582 Telex (or e-mail): IASLAB::PRANGE, PRANGE@FRIAS51, PRANGE@IA ------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 5437 [ 7] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 6 | TARGET NAME: SATURN-SOUTH-I ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: OFFSET SATURN SOUTH HEMISPHERE ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = SATURN, ACQ = 1 | TYPE=TORUS,LONG=347,LAT=-17, | RAD = 59690, POLE_LAT = +90, | POLE_LONG = 0 | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG OF SATURN BETWEEN -100 +100 | SIZE SATURN LT 18.3 | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | 1 |SURF(V) = 7.0 +/- 0.1 | NEEDS 1" POINTING TO HAVE WHOLE LIMB 2 |SURF(1750) = 1.5 +/- 0.7 E-15 | IN FOV FOR LIMB FITTING. LONG AND 3 |SURF(2150) = 2.0 +/- 0.5 E-14 | LAT DEPEND ON DATE OF OBS. VALUES | | ABOVE ARE FOR JUNE 1994 MUST BE | | UPDATED FOR FINAL SCHEDULE. SIZE | | 18.3" IS REACHED FOR OLG +/-40 AND | | PUTS ALSO A LIMIT ON SATURN'S | | APPARENT MOTION OF SATURN. IN THIS | | OLG RANGE, OLG CLOSEST TO -110 OR | | +100 ARE PREFERRED BECAUSE DISK IS | ------------------------------------------------------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 5437 [ 8] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 7 | TARGET NAME: SATURN-NORTH-I ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: OFFSET SATURN SOUTH HEMISPHERE ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = SATURN, ACQ = 1 | TYPE = TORUS, LONG = 14, LAT = +31, | RAD = 58415, POLE_LAT = +90, | POLE_LONG = 0 | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG OF SATURN BETWEEN -100 +100 | SIZE SATURN LT 18.3 | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | 1 |SURF(V) = 7.0 +/- 0.1 | NEEDS 1" ABS. POINTING,WITH REL. 2 |SURF(1750) = 1.5 +/- 0.7 E-15 | POINTING TO TARGET 8 OF 0.1" LONG 3 |SURF(2150) = 2.0 +/- 0.5 E-14 | AND LAT DEPEND ON DATE OF OBS. | | VALUES ABOVE ARE FOR JUNE 1994 MUST | | BE UPDATED FOR FINAL SCHEDULE. SIZE | | 18.3" IS REACHED FOR OLG +/-40 AND | | PUTS ALSO A LIMIT ON SATURN'S | | APPARENT MOTION OF SATURN. IN THIS | | OLG RANGE, OLG CLOSEST TO -110 OR | | +100 ARE PREFERRED BECAUSE DISK IS | ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5437 [ 9] ------------------------------------------------------------------------------------------------------------------------------------ 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 SATURN- FOC/96 IMAGE 512x102 F175W, PIXEL=50x25 1 28M 30 2 1 SEQ 11-12 NO GAP NORTH-I 4 F170M CHECK- 200M CYCLE 4 / 11-15 FILTER=YES Comments: S/N IS FOR A RESOLUTION ELE- MENT OF 3000 Z-PIXS AND AVE. ABSORPTION OF 0.2 OF SURFACE FLUX IN THE FILTER BANDPASS LINENUM 11-15 ARE INDEPEN- DANT OF LINENUM 1-12 ------------------------------------------------------------------------------------------------------------------------------------ 11.1 SATURN- FOC/96 IMAGE 512x102 F175W, PIXEL=50x25 1 102M 30 2 1 NORTH-I 4 F170M 200M ------------------------------------------------------------------------------------------------------------------------------------ 12 SATURN- FOC/96 IMAGE 512x102 F175W, PIXEL=50x25 1 102M 30 2 1 SOUTH-I 4 F170M 200M ------------------------------------------------------------------------------------------------------------------------------------ 13 SATURN- FOC/96 IMAGE 512x102 F175W, PIXEL=50x25 1 68M 30 2 1 SEQ 13-15 NO GAP SOUTH-I 4 F170M CHECK- 200M FILTER=YES ------------------------------------------------------------------------------------------------------------------------------------ 13.1 SATURN- FOC/96 IMAGE 512x102 F175W, PIXEL=50x25 1 34M 30 2 1 NORTH-I 4 F170M 200M ------------------------------------------------------------------------------------------------------------------------------------ 14 SATURN- FOC/96 IMAGE 512x102 F220W, PIXEL=50x25 2 16M 15 3 1 NORTH-I 4 F190M CHECK- 25M FILTER=YES Comments: S/N IS FOR A RESOLUTION ELEMENT OF 3000 ZOOMED PIXELS AND AVE. ABSOR- PTION OF 0.2 OF THE SURFACE FLUX IN THE FILTER SET BANDPASS. ------------------------------------------------------------------------------------------------------------------------------------ 15 SATURN- FOC/96 IMAGE 512x102 F220W, PIXEL=50x25 2 16M 15 3 1 SOUTH-I 4 F190M 25M Comments: 11-13 ON THE SAME PAIR OF GUIDE STAR IF POSSIBLE AND HANDOFF FROM 13 TO 15. IF NOT POSSIBLE SPLIT 11-15 INTO TWO GROUPS, EACH ON THE SAME PAIR OF GUIDE STARS WITH EQUAL NUMBER OF NORTH & SOUTH ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5437 [ 10] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOC/96 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters PIXEL=50x25 CHECK-FILTER=YES ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 9.33 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category GIANT PLANETS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SEQ 11-12 NO GAP; CYCLE 4 / 11-15; SEQ 13-15 NO GAP ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F175W, F170M F220W, F190M ------------------------------------------------------------------------------------------------------------------------------------ Target Names SATURN-SOUTH-I SATURN-NORTH-I ------------------------------------------------------------------------------------------------------------------------------------