Titan's atmosphere is mainly nitrogen gas with several trace constituents, including methane at the few percent level. The presence of methane has been a puzzle for decades, since the CH4 in Titan's atmosphere is expected to be destroyed by UV photolysis in ten million years or so. The source of Titan's atmospheric methane continues to be a major question. We propose a set of three STIS image cubes with the G750M grating at 0.62, 0.72 and 0.89 |*|m methane bands. These bands probe altitudes from the surface to 70 km; unlike CH4 bands at 1.6 or 2.3 |*|m, these cubes will provide a 3-D picture of Titan's troposphere (below 40 km). The Cassini/VIMS visible channel has not been useful for this purpose for two reasons: its spectral resolution (about R=100) is coarse and its inconsistent background subtraction scheme that can lead to "stripes." HST/STIS resolves Titan's 1" disk into over 80 spatially resolved spectra, each with a spectral resolution greater than R=5000. STIS is a unique tool for mapping the 3-D distributions of CH4 and aerosols in Titan's troposphere. We request observations within a day of the Cassini flyby of Titan on April 5, 2013 around 21:40 UT in order to combine Cassini/VIMS and STIS mage cubes. Together, the visible (STIS) and IR (VIMS) image cubes will probe altitudes from the surface to the stratosphere (several hundred km). The proposed STIS image cubes will provide the best tropospheric map of CH4 to date, relevant to surface/atmospheric coupling of CH4, latitudinal inhomogeneity of CH4 or aerosols, or the presence of condensates at low altitudes. This proposal consists of three orbits to observe Titan with the G750M grating, each identical except for the wavelength setting. The schedule for each orbit consists of an initial acquisition followed by 20 spectra using the 52x0.05 arcsec slit, which we will step across Titan in 0.05 arcsec increments to produce image cubes. The three wavelength settings are centered at 6252, 7283 and 8825 Angstroms, respectively. This proposal needs to be concident with Cassini/VIMS spacecraft observations, specifically, the Cassini T90 flyby of Titan. The window for these three orbits is between 1:00 to 6:00 UT on April 6, 2013. We are concerned about wavelength-dependent scattered light in the 8825 spectra. This was a huge issue for us in previous G750L spectra, and although the PSF is slightly smaller in the G750M spectra, we still think it will be a problem. In GO-8580 we had WFPC2 images of Titan at selected wavelengths that we could use to correct the red "anti-leak", but we do not have time to make similar calibration observations in this program. SOLAR SYSTEM 12 false false 0.0 0.5 false false false AVAILABLE SOLAR SYSTEM SATELLITE Titan STD=SATURN STD=TITAN SEP OF TITAN SATURN FROM EARTH GT 45", SEP OF TITAN RHEA FROM EARTH GT 10" EARTH STIS/CCD Spectroscopic No No G750M 6252 STIS/CCD Spectroscopic No No G750M 7283 STIS/CCD Spectroscopic No No G750M 8825 POS-TARG MOSAIC DITHER 0.05 STIS-ALONG-SLIT false true 20 0.0 POS-TARG STIS-PERP-TO-SLIT 90.0 1 false Using ephemeris for target 12900-01-TITAN ephemeris data for target 12900-01-TITAN does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 12.212 to 14.092. ephemeris interval: 12.213 to 14.213 The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. First image cube of Titan, consisting of 20 spectra obtained by stepping the 52x0.05 slit across Titan at 0.05 increments. This FIRST orbit includes the initial acquisition of Titan, and thus allocates less time to the spectra. The second and third orbits (at longer wavelengths) will avoid the main acquisition overhead. (Tic-Visit :proposal-id 12900 :visit-id "01" :proposal-version -1 :trans-version "20120712" :date "20-Aug-2012 10:56:08.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 466144 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12900 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12900 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2816 :al-overhead-at-end 0 :internal-dur-at-end 80 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3229 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12900 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2918 :al-overhead-at-end 0 :internal-dur-at-end 1224 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3229 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12900 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2918 :al-overhead-at-end 0 :internal-dur-at-end 1484 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3229 :pcs-gap 0 ) true 3 0