Proposal_Information Title: Observation of OH and CI in the Mars/Phobos neutral cloud with FOS Proposal_Category: GO Scientific_Category: Solar System Cycle: 5 Investigators PI_name: Dr. Philip Matheson PI_Institution: University of Southern California CoI_Name: Donald Shemanksy CoI_Institution: University of Southern California Contact: N Abstract: ! Free format text (please update) We will use the FOS/BL instrument to search for neutral emissions from the planetary/magneto environment of Mars. Neutral OH is observable in the A-X (0,0) band at 3085 Angstroms. The program consists of 4 orbits, using the the FOS/BL G270H with C-3 aperture. Interest in the neutral environment of Mars is spurred by inferences gathered from PHOBOS-2 that Phobos produces prodigious amounts of dust and OH along its orbit, forming a neutral cloud or torus similar to that associated with the icy moons of Saturn. It is estimated that Phobos, primarily an icy body itself, sources 10^23 H_2O molecules s^-1. Water quickly dissociates to OH and atomic oxygen. The behavior of Phobos may be somewhat comet-like in this respect. Three orbits will be used to target the FOS along a line of sight through the ansa of Phobos' orbit to maximize path length, but will exlude Phobos from the field of view. The fourth orbit will include Phobos in the field of view to possibly observe source processes. The source process for Phobos neutrals may be similar to those which produce the recently discovered O2 atmosphere at Europa and possible OH cloud about that satellite such as the neutral OH cloud discovered by us in the Saturn magnetosphere near Tethys and Dione. Phobos' composition is germane to comet/asteroid studies, particularly at present, because of unresolved issues over the composition of comet P/Shoemaker- Levy-9. Questions ! Free format text (please update) Observing_Description: The program consists of two targets: PHOBOS and MARS-PHOBOS-TORUS. Target MARS-PHOBOS-TORUS defines the orbital ansa of the moon Phobos, 9378 km from Mars' center. We nominally plan for an observation date of July 14. On that date, Mars will be at a solar elongation of 64.6 degrees East. The Phobos ansa will be 7.42 arc seconds from the center of Mars. The observation is to be made through the dawn ansa. Pointing should be determined by acquiring Phobos. Phobos will then be observed and then HST should slew to MARS-PHOBOS-TORUS. The observing configuration for MARS-PHOBOS-TORUS is FOS/BL G270H grating with the 2.0-PAIR-A aperture. Exposure time is 3 orbits. Aperture should be centered on ansa, with Phobos excluded from the field of view.The observational setup for target PHOBOS is identical except that Phobos should physically be within the aperture. Exposure time 1 orbit minus time needed for target acquisition. Desired signal derives from OH A-X(0,0) band about 3085 A. However, the OH signal will be severely diluted by off-axis scattering by sunlight reflected from Mars. Full integration time will be required to obtain adequate signal-to-background. Estimated flux: Emission probability in the A-X(0,0) band is g_Lambda=1E-04 photon/sec/molecule. Taking a path length of 10^9cm and density of 2500 OH cm-3 gives an extended source brightness of 250 rayleighs over the whole band. The equivalent flux with the C-3 aperture is approximately 2.E-16 ergs cm-2 s-1 ang-1, giving a count rate of ~ .17 counts s-1 diode-1. However, the signal rate from off-axis scattering of the solar continuum at 7."42 from Mars is estimated to be 5.9E-15 ergs cm-2 s-1 ang-1 for a background count rate of 5 c s-1 diode-1. FOS/BL is selected to minimize grating scatter in this region of the spectrum. Four orbits should give detection. Observation must be made within the first 8 weeks of cycle 5. Mars comes within 50 degrees solar elongation on August 25, 1995. Solar_System_Targets Target_Number: 1 Target_Name: MARS-PHOBOS-TORUS Description: TORUS MARS Level_1: STD = MARS Level_2: TYPE = TORUS, LONG = 270, LAT = 0, RAD = 9400, POLE_LAT = 90 Window: OLG OF PHOBOS BETWEEN 120 360 Flux: SURF-LINE(3085) = 2.00 +/- 0.5E-16, SURF-CONT-BKG(3085) = 5.9 +/- 0.5 E-15, W-LINE(3085) = 11.4 +/- 1 Comments: OFF-AXIS solar scattering gives large BKG. Phobos should be excluded from FOV Note that information on large off-axis scattering not available at Phase1 deadline. Scattering determined by recent observations of Europa and Saturn magnetosphere. Solar_System_Targets Target_Number: 2 Target_Name: PHOBOS Description: SATELLITE PHOBOS Level_1: STD = MARS Level_2: STD = PHOBOS Window: OLG OF PHOBOS BETWEEN 66 113 Flux: SURF-LINE(3085) = 2.00 +/- 0.5E-16, SURF-CONT-BKG(3085) = 5.9 +/- 0.5 E-15, W-LINE(3085) = 11.4 +/- 1 Comments: OFF-AXIS solar scattering give rise to Large SURF-CONT-BKG. Exposure should be made on Dawn side of planet with Phobos included inside FOV. Visits Visit_Number: 01 Visit_Requirements: BETWEEN 01-JUL-95 AND 25-AUG-95 Exposure_Number: 1 Target_Name: PHOBOS Config: FOS/BL Opmode: ACQ/PEAK Aperture: 4.3 Sp_Element: G270H Number_of_Iterations: 1 Time_Per_Exposure: 15S Optional_Parameters: SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SCAN-STEP-Y=1.23 Special_Requirements: ONBOARD ACQ FOR 2 Exposure_Number: 2 Target_Name: PHOBOS Config: FOS/BL Opmode: ACQ/PEAK Aperture: 1.0 Sp_Element: G270H Number_of_Iterations: 1 Time_Per_Exposure: 15S Optional_Parameters: SEARCH-SIZE-X=6 SEARCH-SIZE-Y=2 SCAN-STEP-X=.61 SCAN-STEP-Y=.61 Special_Requirements: ONBOARD ACQ FOR 3-8 Exposure_Number: 3 Target_Name: PHOBOS Config: FOS/BL Opmode: ACCUM Aperture: 1.0-PAIR-A Sp_Element: G270H Wavelength: 3085 Number_of_Iterations: 1 Time_Per_Exposure: 10.5M Optional_Parameters: STEP-PATT=SINGLE Exposure_Number: 4 Target_Name: MARS-PHOBOS-TORUS Config: FOS/BL Opmode: ACCUM Aperture: 1.0-PAIR-A Sp_Element: G270H Wavelength: 3085 Number_of_Iterations: 1 Time_Per_Exposure: 30.5M Optional_Parameters: STEP-PATT=SINGLE Special_Requirements: EXPAND Comments: In the event that suitable guide stars are not available, exposures 4-9 may be performed with single star guiding or even gyro guiding. Exposure_Number: 5 Target_Name: MARS-PHOBOS-TORUS Config: FOS/BL Opmode: ACCUM Aperture: 1.0-PAIR-A Sp_Element: G270H Wavelength: 3085 Number_of_Iterations: 1 Time_Per_Exposure: 22.5M Optional_Parameters: STEP-PATT=SINGLE Special_Requirements: EXPAND Exposure_Number: 6 Target_Name: MARS-PHOBOS-TORUS Config: FOS/BL Opmode: ACCUM Aperture: 1.0-PAIR-A Sp_Element: G270H Wavelength: 3085 Number_of_Iterations: 1 Time_Per_Exposure: 10M Optional_Parameters: STEP-PATT=SINGLE Special_Requirements: EXPAND Exposure_Number: 7 Target_Name: MARS-PHOBOS-TORUS Config: FOS/BL Opmode: ACCUM Aperture: 1.0-PAIR-A Sp_Element: G270H Wavelength: 3085 Number_of_Iterations: 1 Time_Per_Exposure: 22.5M Optional_Parameters: STEP-PATT=SINGLE Special_Requirements: EXPAND Exposure_Number: 8 Target_Name: MARS-PHOBOS-TORUS Config: FOS/BL Opmode: ACCUM Aperture: 1.0-PAIR-A Sp_Element: G270H Wavelength: 3085 Number_of_Iterations: 1 Time_Per_Exposure: 10M Optional_Parameters: STEP-PATT=SINGLE Special_Requirements: EXPAND Data_Distribution Medium: 8MM ! 8MM or 6250BPI or 1600BPI Blocking_Factor: 10 ! 10 or 1 Ship_To: PI_Address ! STSCI or PI_Address or Ship_Via: UPS ! UPS (2-day) or OVERNIGHT