8579( 2) - 03/17/00 16:07 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8579 Version: 2 Check-in Date: 02-Mar-2000 15:05:50 1.Proposal Title: A Search for the Martian Dust Belts ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Mark Showalter NASA Ames Research Center CoI: Douglas Hamilton University of Maryland N CoI: Philip Nicholson Cornell University N ------------------------------------------------------------------------------------ 5. Abstract It has been long believed that Mars should be encircled by two faint rings of dust, one originating from each of its moons Phobos and Deimos. Similar dust rings have recently been associated with all the inner small moons of Jupiter. On May 28, 2001, Earth will pass through Mars' equatorial plane within weeks of its opposition, providing a unique opportunity to detect these rings via direct imaging. Using WFPC2, we will be able to detect rings with normal optical depths of ~10^-8, which is well within the range of the Martian rings' predicted densities and 10-100 times fainter than the known Jovian rings. The rings have been predicted to show some interesting dynamical properties, including large asymmetries and inclinations. A positive detection will enable us to test these predictions, serving as an effective test of models developed to account for the faint rings of Jupiter and Saturn as well. It will also provide both photometric and dynamical constraints on the dust size distribution, enabling us to distinguish between several models of the rings' dynamics and evolution. ------------------------------------------------------------------------------------ 8579( 2) - 03/17/00 16:07 - [ 2] Observations Description ------------------------ We will observe the Martian dust belts using three HST orbits. Two orbits will image opposite ansae of the ring system with the WFC, to examine possible asymmetries in the system and to capture the full radial extent of the Deimos ring. A third orbit will be used to image one ansa of the Phobos ring in the PC, providing finer sensitivity and resolution. We plan to image the Martian rings by placing the planet inside one WFPC2 field while its ring system extends into an adjacent field. Our experience with imaging the faint E and G Rings of Saturn using HST (PI Philip Nicholson, GO-5836) in August 1995 confirms that this approach reduces the scattered light from the planet substantially. The images will be oriented such that the ring plane is vertical, so that the ring falls well outside Mars' diffraction spikes at 45 degrees. Our goal during each orbit will be to integrate for as long as possible on the ring system while ensuring that scattered light does not saturate in any individual ring image. Two aforementioned Saturn ring images, U2TF0104 and U2TF0105, are extremely useful for providing us with quantitative estimates of the scattered light. By an unusual coincidence, the size of Saturn on the sky in these images is nearly identical to the size of Mars on the sky in May 2001. Furthermore, the angular extent of Saturn's G Ring in the images is nearly identical to the anticipated extent of the Phobos ring. The edge-on G Ring was imaged successfully by placing Saturn in WF3 and allowing the rings to extend into WF2 (Nicholson et al. 1996, Fig. 8). The broad F555W (V) and F675W (R) filters were used to maximize the number of photons counted. AREA mode exposure times were 260 sec in filter F555W and 400 sec in F675W; the former was exposed perfectly and the latter had some saturation. Scaling the G Ring images for the different Sun-planet distances and the different albedos of Mars and Saturn, and abandoning AREA mode, we infer that scattered light will be acceptable if we expose a WFC image for 80 seconds in F555W and 50 seconds in F675W. Acceptable exposure times in the PC are approximately 5 times longer owing to the smaller pixel size. In addition, we will obtain one un-saturated exposure of Mars itself during each orbit, using the same pointing as for the other images. Exposure times of 0.5 seconds in narrow filter F502N should be acceptable. These will provide a pointing reference to our images, because Mars will be completely saturated in the ring exposures themselves. We will depend on the fact that HST pointing is extremely stable during a single orbit, so that Mars' position in this frame should match that in the much longer ring exposures. HST will be able to observe Mars for 53 minutes per orbit in May, 2001. Allowing for target acquisition and instrument readout times, and using CLOCKS=YES to reduce some instrument overheads, we find that we can obtain eight 50-second F675W images plus five 80-second F555W images during each orbit of WFC imaging. The total of integration time of 800 seconds in the WFC should make it possible to detect rings with optical depths as low as 10^-8, well within the range of predictions. For our PC images, we will use F555W exclusively and obtain five exposures of 350-400 seconds, for a total integration time of 1950 seconds. Thus, this orbit will provide significantly finer resolution and sensitivity on the Phobos ring. Real Time Justification ----------------------- Observations should take place as close as possible to May 28, 2001. Optimal viewing is within a few days of this date, and sensitivity begins to deteriorate rapidly before May 21 or after June 4. Mars will fall safely outside the Moon's 9-degree exclusion zone throughout this period. The images targeting each ansa need to be timed to exclude Phobos and Deimos from the field of view. Such opportunities occur frequently and should not severely interfere with observation planning. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8579( 2) - 03/17/00 16:07 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: MARS-RING-EAST ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: RING MARS ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=MARS | TYPE=TORUS,LONG=270,LAT=0,RAD=3398,POLE_ | LAT=90,POLE_LONG=0 | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | NOT OLG OF PHOBOS BETWEEN 21 159, NOT | OLG OF DEIMOS BETWEEN 8 172 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = -1.84 | East limb of Mars with both moons B-V = 1.41 | west of Mars | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: MARS-RING-WEST ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: RING MARS ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=MARS | TYPE=TORUS,LONG=90,LAT=0,RAD=3398,POLE_L | AT=90,POLE_LONG=0 | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | NOT OLG OF PHOBOS BETWEEN 201 339, NOT | OLG OF DEIMOS BETWEEN 188 352 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = -1.84 | West limb of Mars with both moons B-V = 1.41 | east of Mars | ------------------------------------------------------------------------------------------------------------------------------------ 8579( 2) - 03/17/00 16:07 - [ 4] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 25-MAY-2001 AND 31-MAY-2001 ORIENT 238D TO 268D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 MARS-RING-E WFPC2 IMAGE WF3-FIX F555W ATD-GAIN = 7,CR-SPLIT = 0.5, 2 160 S POS TARG 0, 48.18 AST CLOCKS = YES Comments: Mars deliberately positioned in WF2 ------------------------------------------------------------------------------------------------------------------------------------ 2 MARS-RING-E WFPC2 IMAGE WF3-FIX F555W ATD-GAIN = 7,CR-SPLIT = NO,CLOCKS 1 80 S SAME POS AS 1 AST = YES ------------------------------------------------------------------------------------------------------------------------------------ 3 MARS-RING-E WFPC2 IMAGE WF3-FIX F502N ATD-GAIN = 7,CR-SPLIT = NO,CLOCKS 1 0.23 S SAME POS AS 1 AST = NO ------------------------------------------------------------------------------------------------------------------------------------ 4 MARS-RING-E WFPC2 IMAGE WF3-FIX F675W ATD-GAIN = 7,CR-SPLIT = 0.5, 4 100 S SAME POS AS 1 AST CLOCKS = YES ------------------------------------------------------------------------------------------------------------------------------------ 8579( 2) - 03/17/00 16:07 - [ 5] Visit: 02 Visit Priority: Visit Requirements: BETWEEN 25-MAY-2001 AND 31-MAY-2001 ORIENT 238D to 268D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 MARS-RING-W WFPC2 IMAGE WF2-FIX F555W ATD-GAIN = 7,CR-SPLIT = 0.5, 2 160 S POS TARG 0,-48.09 EST CLOCKS = YES Comments: Mars deliberately positioned in WF3 ------------------------------------------------------------------------------------------------------------------------------------ 2 MARS-RING-W WFPC2 IMAGE WF2-FIX F555W ATD-GAIN = 7,CR-SPLIT = NO,CLOCKS 1 80 S SAME POS AS 1 EST = YES ------------------------------------------------------------------------------------------------------------------------------------ 3 MARS-RING-W WFPC2 IMAGE WF2-FIX F502N ATD-GAIN = 7,CR-SPLIT = NO,CLOCKS 1 0.23 S SAME POS AS 1 EST = NO ------------------------------------------------------------------------------------------------------------------------------------ 4 MARS-RING-W WFPC2 IMAGE WF2-FIX F675W ATD-GAIN = 7,CR-SPLIT = 0.5, 4 100 S SAME POS AS 1 EST CLOCKS = YES ------------------------------------------------------------------------------------------------------------------------------------ 8579( 2) - 03/17/00 16:07 - [ 6] Visit: 03 Visit Priority: Visit Requirements: BETWEEN 25-MAY-2001 AND 31-MAY-2001 ORIENT 238D to 268D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 MARS-RING-W WFPC2 IMAGE PC1-FIX F555W ATD-GAIN = 7,CR-SPLIT = 0.5, 2 800 S POS TARG 0,-25.29 EST CLOCKS = YES Comments: Mars deliberately positioned in WF4 ------------------------------------------------------------------------------------------------------------------------------------ 2 MARS-RING-W WFPC2 IMAGE PC1-FIX F555W ATD-GAIN = 7,CR-SPLIT = NO,CLOCKS 1 350 S SAME POS AS 1 EST = YES ------------------------------------------------------------------------------------------------------------------------------------ 3 MARS-RING-W WFPC2 IMAGE PC1-FIX F502N ATD-GAIN = 7,CR-SPLIT = NO,CLOCKS 1 0.23 S SAME POS AS 1 EST = NO ------------------------------------------------------------------------------------------------------------------------------------ 8579( 2) - 03/17/00 16:07 - [ 7] Summary Form for Proposal 8579 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WF3-FIX WF2-FIX PC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN = 7 CR-SPLIT = 0.5 CLOCKS = YES CR-SPLIT = NO CLOCKS = NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 25-MAY-2001 AND 31-MAY-2001 ORIENT 238D TO 268D POS TARG 0, 48.18 SAME POS AS 1 BETWEEN 25-MAY-2001 AND 31-MAY-2001 ORIENT 238D to 268D POS TARG 0,-48.09 POS TARG 0,-25.29 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F502N F675W ------------------------------------------------------------------------------------------------------------------------------------ Target Names MARS-RING-EAST MARS-RING-WEST ------------------------------------------------------------------------------------------------------------------------------------