Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 2393c Report Date: 09-May-96:17:05 Version: ********** Check-in Date: ********** 1.Proposal Title: D/H RATIO OF VENUS AND MARS FROM LYMAN ALPHA EMISSION ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID SOLAR SYSTEM GO Sub Category INNER PLANETS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Dr. Jean-loup Bertaux CNRS, DEPARTMENT OF AERONOMY FRANCE 311.64.47.42.5 CHEF DE DEPARTEMENT ------------------------------------------------------------------------------------ 7. Abstract It is proposed to measure with HRS the D/H ratio of Lyman alpha intensities from the visible disks of Venus and Mars in order to have a key clue on the evolution of water on these two planets. Whereas the D/H ratio for Earth is 1.6x10-4, indicating no substantial water escape since origin, one single measurement (through in situ mass spectrometry) for Venus indicated a ratio of 1.6 x 10-2 (enrichment 100). However, IUE La observations pushed to IUE ultimate capabilities failed to show the D La emission at 1.5 x 10^-2 of the H La emission, implying a D/H radio significantly smaller than previously reported (factor 8). This important finding needs to be confirmed with a positive detection at a lower level. On Mars, HDO has been detected, showing an enrichment of about 6 in the lower atmosphere. HST observation in the upper atmosphere would bring strong constraints on differentiation and escape of D probably valid for both planets. Even with the Earth's ratio of 1.6x 10^-4, D La can be detected both on Venus and Mars with HST/HRS. The two lines D and H are separated by 0.33 A and well resolved with HRS Echelle A. The D/H ratio in the bulk lower atmosphere transfers into a different D/H La emission ratio because of atmospheric processes, different solar excitation rates, and radiative transfer. All these effects require modellings which are well mastered by the proposers, with computer codes used in ------------------------------------------------------------------------------------ 8. Scientific Key Words: VENUS, MARS, ATMOSPHERE, EVOLUTION, UV SPECTROSCOPY ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 3.00 par: 0 10. Num targs pri: 2 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: HRS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 2393c PI: Dr. Jean-loup Bertaux Proposal Title: D/H RATIO OF VENUS AND MARS FROM LYMAN ALPHA EMISSION ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Dr. John T. Clarke MICHIGAN, UNIVERSITY OF USA Dr. Tobias Owen SUNY, STONY BROOK USA P.I. Jean-Loup Bertaux CNRS, DEPARTMENT OF AERONOMY FRANCE X Dr. Mike M. Mumma NASA, GODDARD USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. WE PROPOSE TO PERFORM TWO OBSERVATIONS USING THE HST/HRS COMBINATION WITH THE HRS ECHELLE A GRATING, WAVELENGTH CENTERED AT 1215.5 A, AND THE LARGE SCIENCE APERTURE (LSA) CENTERED ON THE VISIBLE DISKS OF MARS AND VENUS . IN THIS CASE WE WILL ACHIEVE A SPECTRAL RESOLUTION OF 0.10 ANGSTOM, A WAVELENGTH COVERAGE OF 6.2 ANGSTROM,AND A COUNT RATE ROUGHLY 1.1 COUNT PER SEC FOR 1 KILORAY- LEIGH SPREAD OVER 8 DIODES. THE LSA IS CHOSEN TO ACHIEVE THE HIGHEST SENSITIVITY FOR UNAMBIGUOUS MEASUREMENT OF THE DEUTERIUM LYMAN ALPHA LINE.THE INTRINSIC SPECTRAL RESOLUTION OF THE ECHELLE A IS ROUGHLY 0.013 ANGSTROM AND THE LSA SPREADS THE EMISSION OVER 8 DIODES (WITH SHARPLY DEFINED EDGES) SO THAT THE D LINE AT 1215.34 ANGSTROM IS WELL RESOLVED FROM H LYMAN ALPHA LINE AT 1215.67 ANGSTROM. THE SCATTERING OF ECHELLE A AT 0.33 ANGSTROM FROM LINE CENTER IS 0.0013 OF THE LINE CENTER INTENSITY, COMPARABLE TO THE EXPECTED D EMISSION FROM MARS AND FAR BELOW THAT FROM VENUS. THE RED WING OF THE H LINE CAN BE REFLECTED ABOUT LINE CENTER AND USED TO SUBTRACT THE LEVEL OF SCATTERED EMISSION. THE MEASURED BRIGHTNESSES OF THE H LYMAN ALPHA EMISSIONS FROM VENUS AND MARS ARE 20 KR AND 4 KR,RESPECTIVELY, FROM IUE OBSERVA- TIONS. ASSUMING D/H LYMAN-ALPHA RATIOS OF ROUGHLY 0.01 FOR VENUS AND MARS, WE WOULD ANTICIPATE D LY ALPHA EMISSIONS OF 200 R FROM VENUS AND 40 R FROM MARS, YIELDING SIGNAL-TO-NOISE RATIOS ( FOR 30 MINUTE EXPOSURES ) OF 15 AND 6 RESPECTIVELY FOR THE TWO D LINES. EVEN WITH THE EARTH'S RATIO OF 1.6E-4, D-LYMAN ALPHA CAN BE DETECTED BOTH ON VENUS AND MARS WITH HST/HRS. IN A SINGLE 30 MINUTE DARK ORBIT EXPOSURE A LIMITING SENSITIVITY OF ~8 CNTS WOULD BE ACHIEVED FOR AN EMISSION OF 4 R, THUS ALLOWING STRONG SCIENTIFIC CONCLUSIONS TO BE DRAWN. N.B. VENUS DEFINITELY CANNOT NOW WE OBSERVED IN CYCLE 1 SO HAS BEEN DROPPED FROM THE TARGET LIST. HOWEVER CONSIDERATIONS FOR OBSERVING VENUS ARE RETAINED IN SECTIONS 5 AND 6 FROM THE FIRST SUBMITTED PHASE 2 PROPOSAL. Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. Previous to HST, the only space instruments which had the necessary spectral resolution to resolve the D Lyman Alpha line at 1215.33 A technical drawback of IUE is that the short wavelength camera has some tail sensitivity at long wavelengths. Therfore, for exposures on the Venus bright disc, longer than 45 minutes, the stary light ( Rayleigh back-scattered solar UV radiation ) is a very serious problem precluding sensitive measurements. We have coadded all IUE archived good spectra taken on Venus with the large aperture and arrived at a useful upper limit of 300 R, since it translates into a D/H ratio lower than previously reported. It is now impossible to do better, because of low power conditions on IUE when observing at 45 degrees from the sun. The disc of Mars is smaller than the IUE large aperture, causing a loss of signal. From the ground, HDO has been succesfully measured in the IR on Mars, but not on Venus ( probably because of a much smaller H2O content ). Therefore a positive Venus measurement still needs to be done, independent of the in situ mass spectroscopy measurement which seems now in conflict withy the IUE result. Mars HST Lyman Alpha results when compared to the lower atmosphere D/H ratio, would put important constraints on the models of fractionation and differential escape of D versus H, of general relevance for planetary physics, including Earth and Venus. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. Two observations are foreseen with the LSA, one for Mars and one for Venus on the bright disc. For best resolution the GHRS Echelle-A will be selected. each of the D and H Lyman Alpha images will cover 8 diodes, seperated by 25 diodes ( centre-to-centre ). The number of detected counts per second, Nc, for an extended source of 1 kilo Rayleigh is 1.1 per second. In one single dark orbit exposure of 30 minutes, the Dark count is 8 counts for 8 diodes and the noise is ~3 counts. S/N ratio will be limited by counting statistics down to an intensity of ~ 5 Rayleigh. Counting in 30 min exposure Intens. Signal S/N(8 diodes) Venus H Ly-alpha 20 kR 39600 122.0 Venus D Ly-alpha 200 R 396 14.6 Mars D Ly-alpha 40 R 80 6.4 Geocorona H Ly-alpha 5 kR 9900 69.7 Lowest D Ly-alpha 4 R 8 1.6 ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. MARS The disc of Mars has a diameter of between 10 and 19 arcsec during the window of Cycle 1. We wish to observe the illuminated part of the disc, somewhere between the centre of the planet and the sub-solar point. Therefore the selected point will be defined by an offset from the centre of the planet in the direction of the sun. Provision has to be made for pointing errors in the case of blind pointing to avoid pointing outside the planetary disc. With the worst pointing error of 3 arcsec, an offset of 1 - 3 arcsec ( value of offset depends on actual date of observation ), ensures that the GHRS 2.0 aperture will be entirely on the illuminated disc. If the Doppler shift between Earth and Mars is smaller than 7 km/s , one exposure will be required completely offset from the disc ( 30 arcsec ) in order to record the pure Geocoronal emission. VENUS Venus must be observed at the greatest elongation, when HST is in Earth shadow. In this case there is a large enough Doppler shift between Earth and Venus so that no pure Geocoronal observation is required. The required offset from the centre of the planet towards the sun is 7.8 arcsec. A blind pointing error of upto 3 arcsec is acceptable. Page 4 ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. The planetary D Lyman-alpha is rather straightforward to obtain, by summing the signal over 8 diodes covering the 2.0 aperture field of view. Many adjacent diodes are void of signal and can be used to estimate the background and subtract from the signal. The planetary H Ly-alpha, thought much more intense, presents one difficulty: it will be partially contaminated by geocoronal Ly-alpha, which intensity depends on HST orbital position ( 1 - 5 kR for dark orbit ). For Venus observations, likely to be done near maximum elongation, there is a 16 km/s Doppler shift between geocoronal and Venus Ly-alpha, corresponding to a shift of 5 diodes. Therefore, 5 diodes will contain only geocoronal Ly-alpha, allowing to correct for contamination the three Venus diodes containing some geocoronal signal. For Mars, the same procedure will apply; in the case the observation is near opposition, with a low Doppler shift, the geocoronal Ly-alpha will be measured with a specific observation, slightly off the planet. There is no Earth D Ly-alpha ( Deuterium is confined below 150 km ) and no interplanetary Ly-alpha, because the line of sight to the planet is comnpletely inside the ionization cavity. The D and H Ly-alpha measurements will be compared with theoretical predictions produced in advance by computer codes ( equation of diffusion for the vertical profile of H and D, radiative transfer programs, and models of D escape ), ensuring prompt publication of the results. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Service d'Aeronomie personnel includes 5 computer science engineers. The Laboratory has its own VAX 8350 and is connected to three big computers. This ensures that all radiative transfer models will be ready in time for fast interpratation of the results. Travel money will come from CNRS, through the special HST programme. Service d'Aeronomie is associated to Universite Paris 6 where students are available if necessary. The Department of Atmosphere and Ocean Sciences at University of Michigan has also access to computers and students. ------------------------------------------------------------------------------------ 11. Address Information Name: JEAN L. BERTAUX Category: PI Institution: SERVICE D'AERONOMIE DU CNRS Address: BP 3 City: VERRIERES LE BUISSON State: Zip Code: 91371 Country: FRANCE Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 2393c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 MARS-1 PLANET MARS RA = 8H 6M 53.19S +/- 2000 1 SURF(V) = 3.3 +/- 0.6 0.01S, 2 W-LINE(1215) = 0.01 +/- 0.003 DEC = 21D 47' 22.0" +/- 3 SURF-LINE(1215) = 12 +/- 3 E-12 0.1" Comments: TIME ESTIMATE 1991 MAY 25 00:00:00 POINT AT MARS ------------------------------------------------------------------------------------------------------------------------------------ 2 MARS-2 PLANET MARS RA = 8H 7M 3.05S +/- 2000 1 SURF(V) = 3.3 +/- 0.6 0.01S, 2 W-LINE(1215) = 0.01 +/- 0.003 DEC = 21D 46' 50.7" +/- 3 SURF-LINE(1215) = 12 +/- 3 E-12 0.1" Comments: TIME ESTIMATE 1991 MAY 25 01:36:36 POINT AT MARS ------------------------------------------------------------------------------------------------------------------------------------ 3 MARS-3 PLANET MARS RA = 8H 7M 12.92S +/- 2000 1 SURF(V) = 3.3 +/- 0.6 0.01S, 2 W-LINE(1215) = 0.01 +/- 0.003 DEC = 21D 46' 19.3" +/- 3 SURF-LINE(1215) = 12 +/- 3 E-12 0.1" Comments: TIME ESTIMATE 1991 MAY 25 03:13:12 POINT AT MARS ------------------------------------------------------------------------------------------------------------------------------------ 4 MARS-4 PLANET MARS RA = 8H 7M 22.78S +/- 2000 1 SURF(V) = 3.3 +/- 0.6 0.01S, 2 W-LINE(1215) = 0.01 +/- 0.003 DEC = 21D 45' 47.9" +/- 3 SURF-LINE(1215) = 12 +/- 3 E-12 0.1" Comments: TIME ESTIMATE 1991 MAY 25 04:49:48 POINT AT MARS ------------------------------------------------------------------------------------------------------------------------------------ 5 MARS-5 PLANET MARS RA = 8H 7M 32.64S +/- 2000 1 SURF(V) = 3.3 +/- 0.6 0.01S, 2 W-LINE(1215) = 0.01 +/- 0.003 DEC = 21D 45' 16.4" +/- 3 SURF-LINE(1215) = 12 +/- 3 E-12 0.1" Comments: TIME ESTIMATE 1991 MAY 25 06:26:24 POINT AT MARS ------------------------------------------------------------------------------------------------------------------------------------ 6 MARS-6 PLANET MARS RA = 8H 7M 42.50S +/- 2000 1 SURF(V) = 3.3 +/- 0.6 0.01S, 2 W-LINE(1215) = 0.01 +/- 0.003 DEC = 21D 44' 44.9" +/- 3 SURF-LINE(1215) = 12 +/- 3 E-12 0.1" Comments: TIME ESTIMATE 1991 MAY 25 08:03:00 POINT AT MARS ------------------------------------------------------------------------------------------------------------------------------------ 7 MARS-OFFSET PLANET MARS RA = 8H 7M 52.36S +/- 2000 1 SURF(V) = 3.3 +/- 0.6 0.01S, 2 W-LINE(1215) = 0.01 +/- 0.003 DEC = 21D 44' 13.4" +/- 3 SURF-LINE(1215) = 12 +/- 3 E-12 0.1" Comments: TIME ESTIMATE 1991 MAY 25 09:39:36 POINT AT MARS +2 ARCMIN TOWARD SUN ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 2393c [ 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 MARS-1 HRS ACCUM 2.0 ECH-A 1215.50 STEP-PATT=6 1 20M 50 3 1 SPATIAL SCAN DOPPLER=ON 900S 2 SINGLE-EXP FP-SPLIT=STD REQ UPLINK CYCLE 1/1-7 Comments: ESTIMATED S/N IN 8 DIODES IN 900S FOR HYDROGEN LYMAN ALPHA. DEUTERIUM MUCH WEAKER BY ~100. SHORT EXPOSURES TO FOLLOW CHANGES IN GEOCORONAL LY-ALPHA ALONG HST ORBIT. ------------------------------------------------------------------------------------------------------------------------------------ 2 MARS-2 HRS ACCUM 2.0 ECH-A 1215.50 STEP-PATT=6 1 20M 50 3 1 SPATIAL SCAN DOPPLER=ON 900S 2 SINGLE-EXP FP-SPLIT=STD REQ UPLINK ------------------------------------------------------------------------------------------------------------------------------------ 3 MARS-3 HRS ACCUM 2.0 ECH-A 1215.50 STEP-PATT=6 1 20M 50 3 1 SPATIAL SCAN DOPPLER=ON 900S 2 SINGLE-EXP FP-SPLIT=STD REQ UPLINK ------------------------------------------------------------------------------------------------------------------------------------ 4 MARS-4 HRS ACCUM 2.0 ECH-A 1215.50 STEP-PATT=6 1 20M 50 3 1 SPATIAL SCAN DOPPLER=ON 900S 2 SINGLE-EXP FP-SPLIT=STD REQ UPLINK ------------------------------------------------------------------------------------------------------------------------------------ 5 MARS-5 HRS ACCUM 2.0 ECH-A 1215.50 STEP-PATT=6 1 20M 50 3 1 SPATIAL SCAN DOPPLER=ON 900S 2 SINGLE-EXP FP-SPLIT=STD REQ UPLINK ------------------------------------------------------------------------------------------------------------------------------------ 6 MARS-6 HRS ACCUM 2.0 ECH-A 1215.50 STEP-PATT=6 1 20M 50 3 1 SPATIAL SCAN DOPPLER=ON 900S 2 SINGLE-EXP FP-SPLIT=STD REQ UPLINK ------------------------------------------------------------------------------------------------------------------------------------ 7 MARS-OFFSET HRS ACCUM 2.0 ECH-A 1215.50 STEP-PATT=6 1 20M 50 3 1 SPATIAL SCAN DOPPLER=ON 900S 2 SINGLE-EXP FP-SPLIT=STD REQ UPLINK ------------------------------------------------------------------------------------------------------------------------------------ Scan Paramters Form Proposal ID: 2393c [ 7] ------------------------------------------------------------------------------------------------------------------------------------ Data ID: 1 Exposure Logsheet lines: 1-7 FGS Scan: N CONTINUOUS Dwell Only: dwell points/line: 0 Seconds per dwell: 0.00 Scan width (arc-secs): 0.0000 Scan length (arc-secs): 30.3540 Angle between sides (degrees) 0.00 Number of lines: 1 Scan rate (arc-sec/sec): 0.0228 PA of first scan line (degrees) 101.988 Scan frame (CEL or S/C): CEL Length Offset (arc-sec): 0.0 Width Offset (arc-sec): 0.0 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 2393c [ 8] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters STEP-PATT DOPPLER FP-SPLIT=STD ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 3.00 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category INNER PLANETS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SPATIAL SCAN SINGLE-EXP; REQ UPLINK; CYCLE 1/1-7 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements ECH-A ------------------------------------------------------------------------------------------------------------------------------------ Target Names MARS-1 MARS-2 MARS-3 MARS-4 MARS-5 MARS-6 MARS-OFFSET ------------------------------------------------------------------------------------------------------------------------------------