Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5219 Report Date: 18-Jul-95:17:04 Version: ********** Check-in Date: ********** 1.Proposal Title: SATURN'S AURORA, AIRGLOW, AND EXTENDED ATMOSPHERE ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID SOLAR SYSTEM GTO/WF2 Sub Category GIANT PLANETS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Dr. John Trauger 2370 USA 818-354-9594 PROJECT SCIENTIST ------------------------------------------------------------------------------------ 7. Abstract This proposal is for far-UV imaging of Saturn's aurora and airglow emissions, primarily from H Ly alpha (1216 A) and the H2 Lyman and Werner bands (900-1650 A). We will determine the extent and spatial distribution of the UV auroral oval emissions in the northern polar region, believed to be at high magnetic latitudes. With the north pole tilted toward the Earth, we can image the entire northern auroral oval. The airglow emissions will appear brightest near the limb, where we can obtain an altitude resolution of 760 km/WF pixel. The changes in the airglow near the ring shadow region will be particularly interesting in determining the source of the known enhanced electron-excited emissions from the outer planets. These observations constitute the first phase on this WFPC2 GTO program on Saturn's upper atmosphere and rings. ------------------------------------------------------------------------------------ 8. Scientific Key Words: SATURN ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 2.35 par: 0 10. Num targs pri: 2 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: WF/PC ------------------------------------------------------------------------------------ 12. Special sched req: Time Critical obs. ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5219 PI: Dr. John Trauger Proposal Title: SATURN'S AURORA, AIRGLOW, AND EXTENDED ATMOSPHERE ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Dr. John T. Trauger 2370 USA Prof. John T. Clarke 2660 USA Chris Burrows STSCI USA David Crisp JPL USA John Hoessel UNIV. OF WISCONSIN USA Jay Gallagher UNIV. OF WISCONSIN USA Richard Griffiths JOHNS HOPKINS UNIV USA Jeff Hester ARIZONA STATE UNIV. USA John Holtzman LOWELL OBSERVATORY USA Jeremy Mould CALTECH USA James Westphal CALTECH USA ------------------------------------------------------------------------------------ 2. Scientific Justification. ------------------------------------------------------------------------------------ 3. Description of proposed observations. During cycle 4 the north pole of Saturn will be tilted toward the Earth, and we can image most of the high latitude northern auroral zone at all times with F160BW to detect the H Ly a and H2 emissions. Three exposures will be made during the noon meridian crossing of System III longitude 115, a sector seen by Voyager to show enhanced H2 auroral emission in this geometry. (WF in 2X2 mode may be used to improve the S/N.) An exposure with F160BW and F165LP will measure solar scattered light longward of 1650 A for subtraction from the auroral images: this FUV region is affected by haze absorption which may be stronger in the auroral atmosphere as observed on Jupiter. A short F673N image will be made for limb positioning. With the UV images, addition of pixels along the radial direction will be made near the limb (1 WF pixel ~ 760 km resolution) to determine the scale heights of the Ly a and H2 band emissions which are limb brightened. These images will include the region of the ring shadow on the atmosphere and show the extent to which the airglow brightness decreases in regions shadowed by the rings but magnetically conjugate to regions with high (sunlit) electron densities: the purpose is to study the relative importance of sunlight and ionospheric particles on the airglow. These images will also show temporal behavior of aurora. The extended Ly a cloud around Saturn may possibly be detected by co-adding images and subregions. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The far-UV emissions of Saturn's aurora and airglow can only be recorded from a space-based platform due to atmospheric absorption. The UV emissions are important because they are directly excited by precipitating energetic particles. The HST is the only instrument capable of providing 0.1 arc sec resolution to image the UV emissions with high spatial resolution, and this has application to the ring shadow and limb airglow emissions as well as the aurora. The extended H corona emissions can only be detected in the UV in Ly a. The exposure strategy is outlined above. The UV images are timed for maximum sensitivity with a longitude-averaged view of the auroral zone in the north and the ring shadow and limb emissions. The F673N images are to register the limb position. In cycle 5, the auroral emission sequences will be made due to the known variability in Saturn's Ly a auroral intensity to determine the emission variability with Saturnian rotation. Page 3 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. We request the scheduling of all the Saturn exposures to be made near opposition, to obtain the best possible angular resolution, and we further request the observations to be made when the tilt of Saturn is still appreciabble, which falls around opposition or within about two months afterwards. In this window, most of the northern auroral oval can be imaged from Earth, and the ring shadow is the largest possible to detect the effect of sunlight on the airglow emissions. No ground-based observations of Saturn are planned in connection with the FUV images: H3+ emission near 2 or 4 microns has been found to be very weak and difficult to detect, and no CnHn aurora has yet been detected. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. Scheduling during dark time is required. We are imaging FUV emissions from H (Lyman alpha) and H2 (Lyman and Werner bands), some are very weak emissions which therefore require minimum contamination from geocoronal Ly a emission to obtain the best possible S/N. The exposures cannot be interrupted due to Saturn's rotation (10 hours) and known temporal variability in the emissions. The exposures series have been planned accordingly. ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. The images will be reduced and analyzed on Unix workstations using IDL and the WFPC2 system SPICA. We have complete software packages for the reduction of WFPC images, and this software is being developed further in working on the data from the JPL TV test. We are or will be devolping soon algorithms to analyze the data, such as for determining the center of Saturn and limb position from a visible image of the planet, addition of pixels for example in the radial direction or at a given height to improve the S/N. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. NONE ------------------------------------------------------------------------------------ 9. Description of previous HST work. No images of Saturn in the UV have been obtained with HST or any other instrument. We estimate that WFPC2 with the Na metal filter will have 4-5 times higher efficiency and a much larger dynamic range than would be possible with the FOC. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Unix workstations are available with IDL and the WFPC2 system SPICA software packages. Page 4 ------------------------------------------------------------------------------------ 13. Although Saturn is similar to Jupiter in size and composition, aeronomically it is very different. This proposal is the first part of our program to image the upper atmosphere in its auroral and airglow emissions. The north aurora Ly a emission observed with IUE shows sporadic variability that does not seem to correlate with the sector near longitude 115 found by Voyager to be active in H2 emissions when near the noon meridian (as seen in the kilometric radio emissions thought to be associated the aurora). Saturn's tilt in cycle 4 allows to resolve the spatial structure of most of the north auroral oval with HST, and in H vs H2 emissions and vs time. The airglow emissions will be best observed near the limb, where they brighten by a factor of 5-10 and the background is negligible. Like Jupiter, Saturn has levels of upper atmospheric heating and airglow emission in excess of those resulting from absorption of solar UV, although Saturn is much darker and cooler in the UV than Jupiter. The importance of sunlight relative to ionospheric charged particles in airglow processes can be studied on Saturn by imaging the airglow emissions in regions shadowed by the rings and magnetically conjugate to high electron density regions. In cycle 5 Saturn's tilt reverses and we will see the south aurora for the first time since Voyager. In addition, the tenuous ring atmosphere will be imaged during the ring crossings for higher S/N. ------------------------------------------------------------------------------------ 11. Address Information Name: JOHN T. TRAUGER Category: PI Institution: 2370 Address: MS 179-225 4800 Oak Grove Drive City: Pasadena State: CA Zip Code: 91109 Country: USA Telephone: 818-354-9594 Telex (or e-mail): ------------------------------------------------------------------------------------ Name: JOHN T. CLARKE Category: Institution: 2660 Address: City: State: Zip Code: Country: Telephone: 313-747-3540 Telex (or e-mail): ------------------------------------------------------------------------------------ Name: GILDA E. BALLESTER Category: Institution: 2660 Address: City: State: Zip Code: Country: Telephone: 313-747-3670 Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 5219 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: SAT-N-AUR1 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET SATURN ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = SATURN | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | CML OF SATURN FROM EARTH BETWEEN | 40 250, | OLG OF SATURN BETWEEN 330 60, | SEP OF TITAN SATURN FROM EARTH GT 15" | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | 1 |V = -0.6 +/- 0.5 | SATURN NORTH AURORA EXPOSURES WITH 2 |F-LINE(1400)=1+/-3E-14,W-LINE(1400)=420 | THE WFC WITH 3 FILTER COMBINATIONS 3 |F-CONT(1800) = 4 +/- 5 E-13 | TO BE MADE IN SEQUENTIAL ORBITS. THE 4 |SIZE = 16 +/- 13 | F160BN15 EXPOSURES SHOULD COVER BE 5 |F-CONT(5500) = 7.8 +/- 3 E-12 | MADE WHEN SYSTEM III CML IS 115 6 |SIZE = 1.1 | DEGREE S.OLG WINDOWS CAN BE EXPANDED | | SOMEWHAT IF NEEDED FOR SCHEDULING. | | SCHEDULE DURING DARK TIME. | ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5219 [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 1.1 SAT-N-AUR1 WFPC2 IMAGE WF3-FIX F673N ATD-GAIN=15 1 2.0S 120 5 1 CYCLE 4 CR-SPLIT=NO 6 SEQ 1.1 - 1.4 NO GAP PCS MODE F Comments: RED IMAGE OF SATURN WITH SAME GUIDE STARS AS IN LINENUM 1.2- 1.4 TO IDENTIFY LIMB OF PLANET. ------------------------------------------------------------------------------------------------------------------------------------ 1.2 SAT-N-AUR1 WFPC2 IMAGE WF3-FIX F160BN15, ATD-GAIN=7 1 1500.0 5 3 1 CYCLE 4 F165LP CR-SPLIT=NO 4 PCS MODE F CR- TOLERANCE=0.1 Comments: IMAGE OF SATURN'S BACKGROUND UV SCATTERED LIGHT TO SUBTRACT FROM FUV IMAGES OF AURORA. CR- SPLIT TO BE MADE AGAINST IMAGES OBTAINED IN LINENUM 1.3. ------------------------------------------------------------------------------------------------------------------------------------ 1.3 SAT-N-AUR1 WFPC2 IMAGE WF3-FIX F160BN15 ATD-GAIN=7 3 1000.0 9 2 1 CYCLE 4 CR-SPLIT=NO 3 PCS MODE F 4 Comments: FUV IMAGE OF SATURN'S NORTH AURORAL H AND H2 EMISSIONS. TAKE 4 IMAGES IN DARK CONSECUTIVE HST ORBITS TO AVOID SMEAR BY PLANET ROTATION. IMAGES SHOULD COVER SYSTEM III CML 115. MAKE EXPOS. AS LONG AS POSSIBLE ------------------------------------------------------------------------------------------------------------------------------------ 1.31 SAT-N-AUR1 WFPC2 IMAGE WF3-FIX F160BN15 ATD-GAIN=7 1 820.0 S 9 2 1 CYCLE 4 CR-SPLIT=NO 3 PCS MODE F 4 Comments: FUV IMAGE OF SATURN'S NORTH AURORAL H AND H2 EMISSIONS. TAKE 4 IMAGES IN DARK CONSECUTIVE HST ORBITS TO AVOID SMEAR BY PLANET ROTATION. IMAGES SHOULD COVER SYSTEM III CML 115. MAKE EXPOS. AS LONG AS POSSIBLE ------------------------------------------------------------------------------------------------------------------------------------ 1.4 SAT-N-AUR1 WFPC2 IMAGE WF3-FIX F673N ATD-GAIN=15 1 2.0 S 120 5 1 CYCLE 4 CR-SPLIT=NO 6 PCS MODE F Comments: RED IMAGE OF SATURN WITH SAME GUIDE STARS AS IN LINENUM 1.1- 1.3 TO IDENTIFY LIMB OF PLANET. ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5219 [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN CR-SPLIT=NO CR-TOLERANCE=0.1 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GTO/WF2 ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 2.35 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category GIANT PLANETS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4; SEQ 1.1 - 1.4 NO GAP; PCS MODE F ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F673N F160BN15, F165LP F160BN15 ------------------------------------------------------------------------------------------------------------------------------------ Target Names SAT-N-AUR1 ------------------------------------------------------------------------------------------------------------------------------------