The rings of Uranus turn edge-on to Earth in May and August 2007. In between, we will have a rare opportunity to see the unlit face of the rings. With the nine optically thick rings essentialy invisible, we will observe features and phenomena that are normally lost in their glare. We will use this opportunity to search thoroughly for the embedded "shepherd" moons long believed to confine the edges of the rings, setting a mass limit roughly 10 times smaller than that of the smallest shepherd currently known, Cordelia. We will measure the vertical thicknesses of the rings and study the faint dust belts only known to exist from a single Voyager image. We will also study the colors of the newly-discovered faint, outer rings; recent evidence suggests that one ring is red and the other blue, implying that each ring is dominated by a different set of physical processes. We will employ near-edge-on photometry from 2006 and 2007 to derive the particle filling factor within the rings, to observe how ring epsilon responds to the "traffic jam" as particles pass through its narrowest point, and to test the latest models for preserving eccentricities and apse alignment within the rings. Moreover, this data set will allow us to continue monitoring the motions of the inner moons, which have been found to show possibly chaotic orbital variations; by nearly doubling the time span of the existing ACS astrometry, the details of the variations will become much clearer.

We will center on Uranus and orient the rings along the x-axis. With this orientation, we can saturate the planet and still obtain good detections of the rings and moons, because saturated pixels bloom along the HRC and PC y-axes. Visits must be timed to exclude the brightest moons---Ariel, Umbriel, Titania and Oberon. Miranda moves too quickly to be completely excluded, but we avoid times when it overlaps the main ring system. Some visits are specifically timed so that Mab is visible, so that we can study its orbital libration. During August-September 2006 we will obtain photometry of the rings and moons approaching opposition, while the rings are open to Earth by only 4 degrees. Five single-orbit visits will sample phase angles of approximately 1, 0.5, 0.2, 0.1 and 0.05 degrees. Filters F330W, F475W, F606W and F814W will be used to obtain color information. These visits will employ a 2.5-pixel dither shift along the x-axis to improve radial resolution on the rings. Each visit will include 3 long, CLEAR exposures to continue imaging faint outer rings and small moons including Mab and Cupid. In spring 2007 we will observe the rings with the PC during the brief window when Earth is on the north side of the ring plane but the Sun is still shining on the south side; the main rings will be especially dark during this period, potentially making fainter rings and smaller moons detectable. We will carry out four visits of four orbits each. Each orbit will begin and end with long, F606W exposures for moon tracking. One or two exposures in the middle of each orbit will obtain ring color using F450W and F814W. We will also obtain a small number of unsaturated images of the planet. We will position Uranus at slightly different locations at each visit so that any optical flaws tied to the PC pixel grid do not always overlap the rings. SOLAR SYSTEM 12 false 0.0 false false false false false false AVAILABLE SOLAR SYSTEM Uranus with Ariel, Umbriel, Titania and Oberon more than 100,000 km away in projected distance along the ring ansa; this guarantees that any bright, vertical diffraction spike falls beyond the orbit of Mab. Also, Miranda's diffraction spike must stay outside the ring system. PLANET Uranus STD=URANUS NOT OLG OF ARIEL BETWEEN 0.0 31.5, NOT OLG OF ARIEL BETWEEN 148.5 211.5, NOT OLG OF ARIEL BETWEEN 328.5 360.0, NOT OLG OF UMBRIEL BETWEEN 0.0 22.1, NOT OLG OF UMBRIEL BETWEEN 157.9 202.1, NOT OLG OF UMBRIEL BETWEEN 337.9 360.0, NOT OLG OF TITANIA BETWEEN 0.0 13.3, NOT OLG OF TITANIA BETWEEN 166.7 193.3, NOT OLG OF TITANIA BETWEEN 346.7 360.0, NOT OLG OF OBERON BETWEEN 0.0 9.9, NOT OLG OF OBERON BETWEEN 170.1 189.9, NOT OLG OF OBERON BETWEEN 350.1 360.0, NOT OLG OF MIRANDA BETWEEN 0.0 25.0, NOT OLG OF MIRANDA BETWEEN 155.0 205.0, NOT OLG OF MIRANDA BETWEEN 335.0 360.0 SOLAR SYSTEM Uranus with Mab within 40 degrees of maximum elongation. Ariel, Umbriel, Titania and Oberon are required to be more than 100,000 km from the center of Uranus in projected distance along the ring ansa; this guarantees that any bright, vertical diffraction spike falls beyond the orbit of Mab. Also, Miranda's diffraction spike must stay outside the ring system and at least 1 arcsec from Mab. PLANET Uranus STD=URANUS NOT OLG OF ARIEL BETWEEN 0.0 31.5, NOT OLG OF ARIEL BETWEEN 148.5 211.5, NOT OLG OF ARIEL BETWEEN 328.5 360.0, NOT OLG OF UMBRIEL BETWEEN 0.0 22.1, NOT OLG OF UMBRIEL BETWEEN 157.9 202.1, NOT OLG OF UMBRIEL BETWEEN 337.9 360.0, NOT OLG OF TITANIA BETWEEN 0.0 13.3, NOT OLG OF TITANIA BETWEEN 166.7 193.3, NOT OLG OF TITANIA BETWEEN 346.7 360.0, NOT OLG OF OBERON BETWEEN 0.0 9.9, NOT OLG OF OBERON BETWEEN 170.1 189.9, NOT OLG OF OBERON BETWEEN 350.1 360.0, NOT OLG OF MAB BETWEEN 0.0 50.0, NOT OLG OF MAB BETWEEN 130.0 230.0, NOT OLG OF MAB BETWEEN 310.0 360.0, NOT OLG OF MIRANDA BETWEEN 0.0 25.0, NOT OLG OF MIRANDA BETWEEN 155.0 205.0, NOT OLG OF MIRANDA BETWEEN 335.0 360.0, SEP OF MIRANDA MAB FROM EARTH GT 1.0" SOLAR SYSTEM Uranus with Mab crossing maximum elongation during a 4-orbit visit. Ariel, Umbriel, Titania and Oberon are required to be more than 100,000 km from the center of Uranus in projected distance along the ring ansa; this guarantees that any bright, vertical diffraction spike falls beyond the orbit of Mab. Also, Miranda's diffraction spike must stay outside the ring system and at least 1 arcsec from Mab. PLANET Uranus STD=URANUS NOT OLG OF ARIEL BETWEEN 0.0 31.5, NOT OLG OF ARIEL BETWEEN 148.5 211.5, NOT OLG OF ARIEL BETWEEN 328.5 360.0, NOT OLG OF UMBRIEL BETWEEN 0.0 22.1, NOT OLG OF UMBRIEL BETWEEN 157.9 202.1, NOT OLG OF UMBRIEL BETWEEN 337.9 360.0, NOT OLG OF TITANIA BETWEEN 0.0 13.3, NOT OLG OF TITANIA BETWEEN 166.7 193.3, NOT OLG OF TITANIA BETWEEN 346.7 360.0, NOT OLG OF OBERON BETWEEN 0.0 9.9, NOT OLG OF OBERON BETWEEN 170.1 189.9, NOT OLG OF OBERON BETWEEN 350.1 360.0, NOT OLG OF MAB BETWEEN 0.0 10.0, NOT OLG OF MAB BETWEEN 170.0 190.0, NOT OLG OF MAB BETWEEN 350.0 360.0, NOT OLG OF MIRANDA BETWEEN 0.0 25.0, NOT OLG OF MIRANDA BETWEEN 155.0 205.0, NOT OLG OF MIRANDA BETWEEN 335.0 360.0, SEP OF MIRANDA MAB FROM EARTH GT 1.0" SOLAR SYSTEM Uranus with Mab crossing maximum elongation during a 4-orbit visit. Ariel, Umbriel, Titania and Oberon are required to be more than 100,000 km from the center of Uranus in projected distance along the ring ansa; this guarantees that any bright, vertical diffraction spike falls beyond the orbit of Mab. Also, Miranda's diffraction spike must stay outside the ring system and at least 1 arcsec from Mab. PLANET Uranus STD=URANUS NOT OLG OF ARIEL BETWEEN 0.0 31.5, NOT OLG OF ARIEL BETWEEN 148.5 211.5, NOT OLG OF ARIEL BETWEEN 328.5 360.0, NOT OLG OF UMBRIEL BETWEEN 0.0 22.1, NOT OLG OF UMBRIEL BETWEEN 157.9 202.1, NOT OLG OF UMBRIEL BETWEEN 337.9 360.0, NOT OLG OF TITANIA BETWEEN 0.0 13.3, NOT OLG OF TITANIA BETWEEN 166.7 193.3, NOT OLG OF TITANIA BETWEEN 346.7 360.0, NOT OLG OF OBERON BETWEEN 0.0 9.9, NOT OLG OF OBERON BETWEEN 170.1 189.9, NOT OLG OF OBERON BETWEEN 350.1 360.0, NOT OLG OF MAB BETWEEN 170.0 190.0, NOT OLG OF MIRANDA BETWEEN 0.0 25.0, NOT OLG OF MIRANDA BETWEEN 155.0 205.0, NOT OLG OF MIRANDA BETWEEN 335.0 360.0, SEP OF MIRANDA MAB FROM EARTH GT 1.0" ACS/HRC Imaging No No F330W CLEAR1S ACS/HRC Imaging No No F475W CLEAR2S ACS/HRC Imaging No No F606W CLEAR2S ACS/HRC Imaging No No F814W CLEAR2S POS-TARG DITHER 0.07105 This is a single horizontal shift along the HRC pixel grid of 2.5 pixels. It should enable finer radial resolution along the ring ansa, which is also aligned with the pixel grid. LINE false false 2 5.8 LINE 1 false Uranus near phase angle 1 degree. Rings open by only 4 degrees. (Tic-Visit :proposal-id 10870 :visit-id "41" :proposal-version -1 :trans-version "20070325" :date "15-Apr-2007 13:32:24.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 220816 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10870 :visit-id "41" :obset-id "41" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10870 :visit-id "41" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2669 :al-overhead-at-end 0 :internal-dur-at-end 280 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) false 1 0 Uranus near phase angle 0.5 degree. Rings open by only 4 degrees. (Tic-Visit :proposal-id 10870 :visit-id "42" :proposal-version -1 :trans-version "20070325" :date "15-Apr-2007 13:32:26.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 220816 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10870 :visit-id "42" :obset-id "42" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10870 :visit-id "42" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2669 :al-overhead-at-end 0 :internal-dur-at-end 280 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) false 1 0 Uranus near phase angle 0.2 degree. Rings open by only 4 degrees. (Tic-Visit :proposal-id 10870 :visit-id "43" :proposal-version -1 :trans-version "20070325" :date "15-Apr-2007 13:32:28.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 220816 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10870 :visit-id "43" :obset-id "43" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10870 :visit-id "43" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2669 :al-overhead-at-end 0 :internal-dur-at-end 280 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) false 1 0 Uranus near phase angle 0.1 degree. Rings open by only 4 degrees. (Tic-Visit :proposal-id 10870 :visit-id "44" :proposal-version -1 :trans-version "20070325" :date "15-Apr-2007 13:32:31.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 220816 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10870 :visit-id "44" :obset-id "44" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10870 :visit-id "44" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2669 :al-overhead-at-end 0 :internal-dur-at-end 280 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) false 1 0 Uranus near opposition. Rings open by only 4 degrees. (Tic-Visit :proposal-id 10870 :visit-id "45" :proposal-version -1 :trans-version "20070325" :date "15-Apr-2007 13:32:33.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 220816 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10870 :visit-id "45" :obset-id "45" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10870 :visit-id "45" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2669 :al-overhead-at-end 0 :internal-dur-at-end 280 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) false 1 0 Extended search to study moons and rings. Uranus positioned 2'' above and right of the PC center point. Ring plane oriented 33 degrees clockwise from the x-axis, which is as close to the x-axis as ORIENT constraints allow. We prefer that this visit be scheduled as early in the window as possible. (Tic-Visit :proposal-id 10870 :visit-id "51" :proposal-version -1 :trans-version "20070325" :date "04-May-2007 16:31:36.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 2330432 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10870 :visit-id "51" :obset-id "51" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10870 :visit-id "51" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :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 10870 :visit-id "51" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :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 10870 :visit-id "51" :orbit-number 3 :pcs-time 355 :si-vis-utilization 2409 :al-overhead-at-end 120 :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 10870 :visit-id "51" :orbit-number 4 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) true 4 0 Extended search to study moons and rings. Uranus positioned 2'' above and left of the PC center point. Ring plane oriented 23 degrees clockwise from the x-axis, which is as close to the x-axis as ORIENT constraints allow. (Tic-Visit :proposal-id 10870 :visit-id "52" :proposal-version -1 :trans-version "20070325" :date "15-Apr-2007 13:32:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 2285616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10870 :visit-id "52" :obset-id "52" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10870 :visit-id "52" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :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 10870 :visit-id "52" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :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 10870 :visit-id "52" :orbit-number 3 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :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 10870 :visit-id "52" :orbit-number 4 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) false 4 0 Extended search to study moons and rings. Uranus positioned 2'' below and right of the PC center point. Ring plane oriented 23 degrees clockwise from the x-axis, which is as close to the x-axis as ORIENT constraints allow. (Tic-Visit :proposal-id 10870 :visit-id "53" :proposal-version -1 :trans-version "20070325" :date "15-Apr-2007 13:32:48.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 2285616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10870 :visit-id "53" :obset-id "53" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10870 :visit-id "53" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :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 10870 :visit-id "53" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :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 10870 :visit-id "53" :orbit-number 3 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :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 10870 :visit-id "53" :orbit-number 4 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) false 4 0 Extended search to study moons and rings. Uranus positioned 2'' above and right of the PC center point. Ring plane oriented 33 degrees clockwise from the x-axis, which is as close to the x-axis as ORIENT constraints allow. We prefer that this visit be scheduled as early in the window as possible. (Tic-Visit :proposal-id 10870 :visit-id "61" :proposal-version -1 :trans-version "20070325" :date "04-May-2007 16:38:07.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 1165216 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10870 :visit-id "61" :obset-id "61" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10870 :visit-id "61" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2409 :al-overhead-at-end 120 :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 10870 :visit-id "61" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2649 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) false 2 0