Ground-based observations two weeks ago strongly suggest that the orbit of the small inner satellite of 2003 EL61, the 5th largest known dwarf planet, is possibly precisely edge-on and thus somewhere in the middle of a ~3 year long cycle of mutual eclipses, occultations, and transits. We anticipate that with another year of ground-based observation we may have sufficient data to accurately predict the times and durations of these events, but by then the events may well be over. If events are indeed occuring, measurement of the timing and depths of such events provides a wealth of precise geometric information for constraining sizes, shapes, orbits, and dynamics of the system. We propose to obtain 5 quick WFPC2 visits to 2003 EL61 over the ~19 day orbital period of the inner satellite to determine a precise orbit and predict mutual event times. We will instantly (within ~1 day of the end of the observations) make these predictions public to allow the maximum number of attempts to collect the data as possible.

A simple 2 color 4 image sequence with a dither in the middle of each orbit. SOLAR SYSTEM 0 false 0.0 0.0 false false false false false SUPPORTED SOLAR SYSTEM #136108 ASTEROID large Kuiper belt object TYPE=ASTEROID,A=43.18953285029598 ,E=.1935368665567537 ,I=28.22278478945061,O=122.090440581686,W=239.0521341253993,M=202.1241278203591,EQUINOX=J2000,EPOCH=14-MAY-2008:00:00:00 EARTH WFPC2 Imaging No F606W WFPC2 Imaging No F814W WFPC2 Imaging No F606W WFPC2 Imaging No F814W WFPC2 Imaging No F606W WFPC2 Imaging No F814W WFPC2 Imaging No F606W WFPC2 Imaging No F814W WFPC2 Imaging No F606W WFPC2 Imaging No F814W POS-TARG DITHER 0.3535 LINE false false 2 45.0 WFPC2-LINE 1 false 2003 EL61, 1st observation This visit should be scheduled as early as possible within the next scheduling period, which starts on May 12th. (Tic-Visit :proposal-id 11518 :visit-id "01" :proposal-version -1 :trans-version "20071214" :date "25-Apr-2008 16:08:04.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 179264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11518 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11518 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2709 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) false 1 0 2003 EL61,2nd observation (Tic-Visit :proposal-id 11518 :visit-id "02" :proposal-version -1 :trans-version "20071214" :date "25-Apr-2008 16:29:57.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 179264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11518 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11518 :visit-id "02" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2709 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) false 1 0 2003 EL61, 3rd observation (Tic-Visit :proposal-id 11518 :visit-id "03" :proposal-version -1 :trans-version "20071214" :date "25-Apr-2008 16:30:03.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 179264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11518 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11518 :visit-id "03" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2709 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) false 1 0 2003 EL61, 4th observation (Tic-Visit :proposal-id 11518 :visit-id "04" :proposal-version -1 :trans-version "20071214" :date "25-Apr-2008 16:30:07.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 179264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11518 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11518 :visit-id "04" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2709 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) false 1 0 2003 EL61,last observation This visit should be scheduled as late as possible within the 2003 EL61 visibility window. (Tic-Visit :proposal-id 11518 :visit-id "05" :proposal-version -1 :trans-version "20071214" :date "25-Apr-2008 16:28:35.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 179264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11518 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11518 :visit-id "05" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2709 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) false 1 0