Resolving Changes on Triton's Surface: Imaging over Triton's full longitudinal range. We have found, from ground-based photometry, evidence of possible seasonal surface changes on Triton which may be brought about by geophysical activity and which have transpired since as recently as 1995. We propose to confirm and characterize these changes using the HST ACS instrument to image Triton at UV, B, V, I and Methane-band wavelengths over as much of its surface as visible from near Earth. By so doing, we will determine the resurfacing rates and set model constraints on activity and surface temperature as well as composition. Such constraints have profound implications for our understanding of Triton's evolution as well as the history of other outer solar system bodies, including outer solar system satellites which may undergo similar geophysical processes or have similar composition.
With Triton's angular diameter of nearly 0.13 arcsec in size, ACS's HRC mode affords an approximately 5X5 pixel image of Triton's surface. With HST's resolution, four regions can be resolved at a time, and particular surface features may be restricted to a certain quadrant of Triton's surface. These observations will allow us to distinguish southern polar cap features from those at equatorial latitudes. Our request for 6 observing longitudes will allow us to resolve the longitude of surface features to within 60 degrees. Our requested exposure times are (in units of seconds): 600 for the UV250W filter, 140 for the JonB filter, 75 in JonV, 60 for sdssI, and 500 in the Mth890 filter. These times are designed to yield reasonably high SN values (several hundred) in each filter. We request two consecutive exposures in the JonB, JonV, and sdssI filters per HST orbit in order to further minimize cosmic-ray contamination during any one longitude sampling. We estimate a total overhead of 24 minutes and a total integration time of 28 minutes per orbit observation set, allowing a 2.5 minute unocculted margin in a 2 hour long orbit. We desire to maximize the exposures and signal-to-noise within the reasonable constraints and safety margins of the ACS. In order to avoid saturation by Neptune's disk we will place the planet off of the imaging array an angular distance of approximately 5 arcsec during each exposure. We have request 6 observations, regularly spaced at one every 23.5(+/- 0.5) hours. In order to avoid large variations in brightness from Triton's opposition surge, we request that the observations not be at solar phase angles < 0.02, (i.e. not during Aug 8-9, 2005). Note that we have not constrained the orientation or offsets for removing Neptune off the image in the original PhaseII submission in order to allow flexibility in planning. The offsets are dependent on the time of viewing of each observation and the orientation of the ACS-HRS aperture. However, it is extremely important that Neptune be offset out of the ACS-HRS field of view (FOV) while Triton remains within it. The minimum separation between the two bodies is 12 arcsec, and Neptune's angular radius is approximately 1.2 arcsec. Hence, if Neptune's center is removed 5 arcsec out of the FOV in the proper direction, Triton should be at least 7 arcsec on-chip from the FOV edge, which should suffice even with a 1 arcsec pointing error. 12 false 0.0 false false false false false SUPPORTED SOLAR SYSTEM I = 12.6 +/- 0.2, B = 14.1 +/- 0.4 SATELLITE Neptune's largest satellite STD=NEPTUNE STD=TRITON TYPE=POS_ANGLE,RAD=9.7,ANG=309.96,REF=NORTH SOLAR SYSTEM I = 12.6 +/- 0.2, B = 14.1 +/- 0.4 SATELLITE Neptune's largest satellite STD=NEPTUNE STD=TRITON TYPE=POS_ANGLE,RAD=9.0,ANG=22.78,REF=NORTH SOLAR SYSTEM I = 12.6 +/- 0.2, B = 14.1 +/- 0.4 SATELLITE Neptune's largest satellite STD=NEPTUNE STD=TRITON TYPE=POS_ANGLE,RAD=6.0,ANG=71.32,REF=NORTH SOLAR SYSTEM I = 12.6 +/- 0.2, B = 14.1 +/- 0.4 SATELLITE Neptune's largest satellite STD=NEPTUNE STD=TRITON TYPE=POS_ANGLE,RAD=9.6,ANG=129.91,REF=NORTH SOLAR SYSTEM I = 12.6 +/- 0.2, B = 14.1 +/- 0.4 SATELLITE Neptune's largest satellite STD=NEPTUNE STD=TRITON TYPE=POS_ANGLE,RAD=9.0,ANG=202.74,REF=NORTH SOLAR SYSTEM I = 12.6 +/- 0.2, B = 14.1 +/- 0.4 SATELLITE Neptune's largest satellite STD=NEPTUNE STD=TRITON TYPE=POS_ANGLE,RAD=6.0,ANG=251.3,REF=NORTH /hera/data1/royle/work/OP-cache/10422-v01.xml We desire to maximize the exposures and signal-to-noise within the reasonable constraints and safety margins of the ACS. In order to avoid saturation by Neptune's disk we will place the planet off of the imaging array an angular distance of approximately 5 arcsec during each exposure. We have request 6 observations, regularly spaced at one every 23.5(+/- 0.5) hours. In order to avoid large variations in brightness from Triton's opposition surge, we request that the observations not be at solar phase angles < 0.02, (i.e. not during Aug 8-9, 2005) (Tic-Visit :proposal-id 10422 :visit-id "01" :proposal-version -1 :trans-version "20050323" :date "20-May-2005 12:37:31.0" :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 294416 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10422 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10422 :visit-id "01" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2706 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 /var/tmp/OPVisit52615.xml /hera/data1/royle/work/OP-cache/10422-v02.xml We desire to maximize the exposures and signal-to-noise within the reasonable constraints and safety margins of the ACS. In order to avoid saturation by Neptune's disk we will place the planet off of the imaging array an angular distance of approximately 5 arcsec during each exposure. We have request 6 observations, regularly spaced at one every 23.5(+/- 0.5) hours. In order to avoid large variations in brightness from Triton's opposition surge, we request that the observations not be at solar phase angles < 0.02, (i.e. not during Aug 8-9, 2005) (Tic-Visit :proposal-id 10422 :visit-id "02" :proposal-version -1 :trans-version "20050323" :date "20-May-2005 12:37:39.0" :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 294416 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10422 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10422 :visit-id "02" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2706 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 /var/tmp/OPVisit52616.xml /var/tmp/OPVisit44551.xml We desire to maximize the exposures and signal-to-noise within the reasonable constraints and safety margins of the ACS. In order to avoid saturation by Neptune's disk we will place the planet off of the imaging array an angular distance of approximately 5 arcsec during each exposure. We have request 6 observations, regularly spaced at one every 23.5(+/- 0.5) hours. In order to avoid large variations in brightness from Triton's opposition surge, we request that the observations not be at solar phase angles < 0.02, (i.e. not during Aug 8-9, 2005) (Tic-Visit :proposal-id 10422 :visit-id "03" :proposal-version -1 :trans-version "20050323" :date "31-May-2005 14:50:15.0" :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 294416 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10422 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10422 :visit-id "03" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2706 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 /var/tmp/OPVisit52617.xml /hera/data1/royle/work/OP-cache/10422-v04.xml We desire to maximize the exposures and signal-to-noise within the reasonable constraints and safety margins of the ACS. In order to avoid saturation by Neptune's disk we will place the planet off of the imaging array an angular distance of approximately 5 arcsec during each exposure. We have request 6 observations, regularly spaced at one every 23.5(+/- 0.5) hours. In order to avoid large variations in brightness from Triton's opposition surge, we request that the observations not be at solar phase angles < 0.02, (i.e. not during Aug 8-9, 2005) (Tic-Visit :proposal-id 10422 :visit-id "04" :proposal-version -1 :trans-version "20050323" :date "20-May-2005 12:38:03.0" :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 294416 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10422 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10422 :visit-id "04" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2706 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 /var/tmp/OPVisit52618.xml /hera/data1/royle/work/OP-cache/10422-v05.xml We desire to maximize the exposures and signal-to-noise within the reasonable constraints and safety margins of the ACS. In order to avoid saturation by Neptune's disk we will place the planet off of the imaging array an angular distance of approximately 5 arcsec during each exposure. We have request 6 observations, regularly spaced at one every 23.5(+/- 0.5) hours. In order to avoid large variations in brightness from Triton's opposition surge, we request that the observations not be at solar phase angles < 0.02, (i.e. not during Aug 8-9, 2005) (Tic-Visit :proposal-id 10422 :visit-id "05" :proposal-version -1 :trans-version "20050323" :date "20-May-2005 12:38:11.0" :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 294416 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10422 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10422 :visit-id "05" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2706 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 /var/tmp/OPVisit52619.xml /var/tmp/OPVisit44552.xml We desire to maximize the exposures and signal-to-noise within the reasonable constraints and safety margins of the ACS. In order to avoid saturation by Neptune's disk we will place the planet off of the imaging array an angular distance of approximately 5 arcsec during each exposure. We have request 6 observations, regularly spaced at one every 23.5(+/- 0.5) hours. In order to avoid large variations in brightness from Triton's opposition surge, we request that the observations not be at solar phase angles < 0.02, (i.e. not during Aug 8-9, 2005) (Tic-Visit :proposal-id 10422 :visit-id "06" :proposal-version -1 :trans-version "20050323" :date "31-May-2005 14:50:20.0" :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 294416 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10422 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10422 :visit-id "06" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2706 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3236 :pcs-gap 0 ) true 1 0 /var/tmp/OPVisit52620.xml