Methane is highly abundant in Pluto's atmosphere, and methane photolysis is the starting point for a series of chemical processes that should result in the production of hydrocarbons and nitriles. Photochemical modeling of Pluto's atmosphere has suggested that detectable abundances of various hydrocarbons and nitriles should occur on Pluto. However, past analysis of 40 orbits of archival HST/FOS data in the mid-UV has only produced upper limits on abundances of C4H2, C6H2, HC3N, and C4N2. We will use COS to obtain spectra from 2060-2460A, including absorption bands of the hydrocarbon diacetylene (C4H2) and the nitrile cyanoacetylene (HC3N). Previously-measured 2-sigma upper limits for these compounds are somewhat below the values computed in the poorly-constrained models; the measurement uncertainties themselves are of the same order as the modeled values. By reducing the uncertainties by a factor of a few to several, we aim to detect the presence of these compounds, or to provide more restrictive abundance limits. These measurements will provide valuable new data on the nature and chemistry of the Plutonian atmosphere.

COS NUV spectra of Pluto from 2060 to 2460A using G230L at 3360A central wavelength, for a total of 5 orbits. Only one grating position (central wavelength) is required to cover the specified wavelength band. Observations will be divided into two visits: 2 orbits at one central meridional longitude, and 3 orbits at another; in this way, the spectra can be coadded for the greatest signal-to-noise, and compared to look for longitude-specific differences in absorption spectrum. The chosen longitudes (90 and 270 degrees) correspond to greatest angular separation of Charon from Pluto, reaching 0.85"; the position angle (CCW from north) of Charon from Pluto is about 153 and 333 degrees for these cases. ORIENT is specified in order to minimize spectral confusion, by aligning Charon in the cross-dispersion direction. ORIENT calculation: U3 axis is at 135 degrees from COS +Y (spatial) direction, and at 135+180 = 315 degrees from -Y With Pluto viewed at CML = 90, Charon is near position angle 153 degrees; Pluto-Charon vector can extend along either +Y or -Y. So we have ORIENT near 135+153 = 288 degrees or near 315 + 153 = 468 ==> 108 degrees. With Pluto viewed at CML = 270, Charon is near position angle 333 degrees (180 degrees from above). Same calculation as above -- 135 + 333 ==> 108 degrees orient, 315 + 333 ==> 288 degrees. We've specified the desired CML +/- 15 degrees, which provides ~12 hr obs windows; ORIENT window of +/- 5 degrees keeps 4+ months available. SOLAR SYSTEM 12 false 0.0 0.0 false false false false false false SUPPORTED SOLAR SYSTEM about 1 magnitude dimmer in mid-UV relative to visible, based on albedo measurements -- 0.2 - 0.25 in mid UV, instead of 0.5 - 0.66 in visible (used mV = 15 solar-type spectrum for ETC) Specified window -- CML of 90+/-10 degrees -- puts Charon near largest separation from Pluto, and at position angle near 150 degrees. F(2400)=1E-16 PLANET PLANET PLUTO STD=PLUTO CML OF PLUTO FROM EARTH BETWEEN 80 100 EARTH SOLAR SYSTEM Specified window -- CML of 270+/-10 degrees -- puts Charon near largest separation from Pluto, and at position angle near 330 degrees. F(2400)=1E-16 PLANET PLANET PLUTO STD=PLUTO CML OF PLUTO FROM EARTH BETWEEN 260 280 EARTH COS/NUV Spectroscopic No No G230L Using ephemeris for target 11540-01-PLUTO-90LONG ephemeris data for target 11540-01-PLUTO-90LONG does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 08.245 to 11.032. ephemeris interval: 10.031 to 12.032 The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. 1283264194000 105.0 (Tic-Visit :proposal-id 11540 :visit-id "01" :proposal-version -1 :trans-version "20091209" :date "24-Feb-2010 09:34:46.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "32" :si-bright-earth-limb-angle 20.0 :data-volume 252304 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11540 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11540 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2901 :al-overhead-at-end 0 :internal-dur-at-end 116 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11540 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3012 :al-overhead-at-end 0 :internal-dur-at-end 116 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11540 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3012 :al-overhead-at-end 0 :internal-dur-at-end 428 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) false 3 0 COS ETC: COS75940 for estimation of acquisition time. Assumed solar-type Kurucz spectrum with effective m_V=15.0, normal airglow. ETC: COS75942 gives buffer-time of 2/3 * 10327s Using ephemeris for target 11540-02-PLUTO-270LONG ephemeris data for target 11540-02-PLUTO-270LONG does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 08.245 to 11.032. ephemeris interval: 10.031 to 12.032 The scheduling data was generated by CASM 18.1. 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