We will use a subarray of the WFC3/UVIS to study the inner rings, arcs and moons of Neptune with a sensitivity that exceeds that achieved by any previous observations, including Voyager 2 during its 1989 flyby. Our study will reveal any inner moons down to V magnitude 25, corresponding to a radius ~ 20 km (assuming 9% albedo), to address a peculiar, apparent truncation in the size distribution of inner moons and to look for the "shepherds" and source bodies for Neptune's dusty rings. (For comparison, the radius of Neptune's smallest known regular moon, Naiad, is ~ 33 km.) Monitoring of the arcs at fine resolution and sensitivity will reveal their ongoing evolution more clearly and will enable us to assess the role of Galatea, whose resonant perturbations are widely believed to confine the arcs. Our study will also reveal any broad, faint rings with optical depth ~ 10^-6, comparable to those now known to encircle all of the other giant planets.

Each of our five orbits contains eight exposures of 275 seconds duration through the F606W filter. The long exposures will provide the finest possible sensitivity to small moons and faint rings, and the sequence will yield "movies" that can be animated to search effectively for small moving targets. The planet will be vastly over-exposed in these frames, but its saturated pixels will bloom along the y-axis and so will not interfere with features oriented close to the x-axis. However, our orientation constraint is only available for a few days around Neptune's opposition. Additional, brief exposures through filters F475W, F625W and F775W will be used for color measurements of the moons and for cross-calibration of the F606W filter. We will use five consecutive orbits targeted at Neptune to obtain the most complete possible coverage in time, because moons and arcs are most detectable if imaged near their maximum elongation from the planet. These five orbits are organized in a set of two consecutive visits, with slightly different ORIENT constraints. By positioning the rings and moons 15-20 degrees off the x-axis, but in opposite directions, we will obtain a better model for the scattered light from the planet and will be able to separate it from any faint, outer rings that might be present. Dithering is accomplished shifting Neptune up and down along the y-axis between (not during) orbits. The rotational change between visits will also allow for a clearer identification of hot pixels and any other reproducible imperfections in the CCD. SOLAR SYSTEM 12 false 0.0 0.0 false false false false false AVAILABLE SOLAR SYSTEM PLANET Planet Neptune STD=NEPTUNE EARTH ACS/HRC Imaging No No CLEAR1S ACS/HRC Imaging No No F475W ACS/HRC Imaging No No F606W ACS/HRC Imaging No No F814W Using ephemeris for target 11656-01-NEPTUNE ephemeris data for target 11656-01-NEPTUNE does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 08.306 to 11.001. ephemeris interval: 09.151 to 11.152 Timing link suitability includes constraints ([02 After 01 by 0.2 to 0.2 days]) The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. Neptune's pole is aligned with the columns of the CCD for ORIENT = 114 or 294. For this visit, we rotate the rings 15-20 degrees clockwise. We shift the target upward by 0.2 arcsec (5 pixels) for the second of the three orbits to get the benefits of dithering while retaining stable pointing during each orbit. (Tic-Visit :proposal-id 11656 :visit-id "01" :proposal-version -1 :trans-version "20090130" :date "03-Jun-2009 23:22:20.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 122320 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11656 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11656 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2673 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11656 :visit-id "01" :orbit-number 2 :pcs-time 195 :si-vis-utilization 2816 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11656 :visit-id "01" :orbit-number 3 :pcs-time 195 :si-vis-utilization 2824 :al-overhead-at-end 0 :internal-dur-at-end 172 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) false 3 0 Using ephemeris for target 11656-02-NEPTUNE ephemeris data for target 11656-02-NEPTUNE does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 08.306 to 11.001. ephemeris interval: 09.151 to 11.152 Timing link suitability includes constraints ([02 After 01 by 0.2 to 0.2 days]) The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. Neptune's pole is aligned with the columns of the CCD for ORIENT = 114 or 294. For this visit, we rotate the rings 15-20 degrees counter-clockwise. We shift the target upward by 0.2 arcsec (5 pixels) for the first of the two orbits to get the benefits of dithering while retaining stable pointing during each orbit. This visit is timed to begin on the orbit immediately after Visit 01 finishes. (Tic-Visit :proposal-id 11656 :visit-id "02" :proposal-version -1 :trans-version "20090130" :date "03-Jun-2009 23:22:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 78640 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11656 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11656 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2673 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11656 :visit-id "02" :orbit-number 2 :pcs-time 195 :si-vis-utilization 2801 :al-overhead-at-end 0 :internal-dur-at-end 124 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) false 2 0