UV spectra of the icy Saturnian satellites: Understanding exogenic processes and NH3 in the system

0 Assigned ID: 1115 ----- Attempting Submission 1 (Fri Apr 11 23:54:12 GMT 2014) ----- HST Phase I Proposal 1115 (cycle22_icysats.apt) successfully submitted. ----- Attempting Submission 2 (Fri Apr 11 23:58:27 GMT 2014) ----- HST Phase I Proposal 1115 (cycle22_icysats.apt) successfully submitted. 0 ----- Attempting Submission 1 (Thu Jul 24 21:18:46 GMT 2014) ----- HST Phase II Proposal 13694 (cycle22_phase2_icysats.apt) successfully submitted. ----- Attempting Submission 2 (Thu Jul 24 23:08:19 GMT 2014) ----- ----- Attempting Submission 3 (Wed Aug 06 13:06:53 GMT 2014) ----- UV spectra of the icy Saturnian satellites: Understanding exogenic processes and NH3 in the system Existing data from Cassini and HST inform us that the icy satellites of Saturn exhibit unidentified UV absorptions - an overall reddish slope in the ~200-400 nm range, with additional spectral features superimposed. We are unable to solve these mysteries surrounding the source(s) of these absorptions using Cassini datasets due to a gap in spectral coverage in the 190-350 nm range (broadband coverage is available to wavelengths as short as 260 nm). HST/STIS data are critical to understanding the spectra of these moons, and to resolving the sources and processes that cause the absorptions. We suspect that ammonia, with its distinctive and strong absorption near 200 nm, plays a role in the spectra of these moons, which has implications for geologic activity. These observations will provide the first-ever NUV observations of Mimas, improved coverage on Enceladus, and the first-ever STIS observations on Dione and Rhea. We base our observation strategy and estimated SNRs on existing high-quality STIS spectra of Tethys (from program 7316). Based on the existing spectra of the icy Saturnian satellites, we propose to measure the leading and trailing hemispheres of Mimas, Dione and Rhea, along with measuring Enceladus (either leading or trailing hemisphere) to understand UV-visible spectral shapes on these bodies and put together the story of compositional variations from one body to the next. Mimas has never been observed by STIS or FOS for UV spectral information, so this is sincerely needed. Enceladus has been measured with STIS using the 52x0.5 slit; however we can improve the quality of this spectrum by using the 52x0.2 slit to reduce background noise and improve SNR. Existing STIS datasets of Tethys are of good quality so we do not request time for that satellite. Dione and Rhea have never been measured by STIS, and the increased spectral coverage will be extremely valuable, to help refine what species are present at these moons that appear to be significantly different in spectral character from Tethys and the other moons. This suite of observations will result in observations of Enceladus, Mimas, Dione and Rhea of the quality of the existing Tethys observations, so that we have a good set of composite spectra to analyze as a set and investigate system-wide processes. We plan to optimize the observations to get the best-possible SNR toward the shorter wavelengths (near 180 nm), to aim for overlap with UVIS. The existing good-quality Tethys G230L spectra (program 7316) used the 52x0.2 slit with an exposure time of 2400 sec, and resulted in an SNR at 200 nm of ~10, increasing to ~895 at 300 nm, binning up 16 spectral elements. For these data, we do not require the highest spectral resolution, so could bin even more spectral pixels to increase SNR further. Thus, we estimate that we can achieve SNR values of this scale for the other satellites, using exposure times of ~2400 sec, keeping in mind that Mimas and Enceladus are smaller than Tethys (we can use the 52x0.1 slit for these objects) and we also expect that the scattered light will be more of an issue for these targets. Dione and Rhea have lower albedos but are larger bodies (we will use the 52x0.2 for Dione and the 52x0.5 slit for Rhea). For each satellite, we will supplement the G230L data with a single 60 sec G430L exposure, providing high SNR at longer wavelengths. We have used the STIS ETC to check exposure times and SNRs and we have determined that these exposure times and slit widths accommodate the MAMA count rate restrictions for bright objects, and do not saturate the CCD at the longer wavelengths in the passband, where the satellites are brighter. SOLAR SYSTEM Default false true false false false SUPPORTED SOLAR SYSTEM SATELLITE Mimas leading hemisphere STD=SATURN STD=MIMAS SEP OF MIMAS-LEADING SATURN FROM EARTH GT 19.0", SEP OF MIMAS-LEADING RHEA FROM EARTH GT 10", SEP OF MIMAS-LEADING TITAN FROM EARTH GT 10", CML OF MIMAS-LEADING FROM EARTH BETWEEN 70 110 EARTH SOLAR SYSTEM SATELLITE Mimas trailing hemisphere STD=SATURN STD=MIMAS SEP OF MIMAS-TRAILING SATURN FROM EARTH GT 18.0", SEP OF MIMAS-TRAILING RHEA FROM EARTH GT 10", SEP OF MIMAS-TRAILING TITAN FROM EARTH GT 10", CML OF MIMAS-TRAILING FROM EARTH BETWEEN 250 290 EARTH SOLAR SYSTEM SATELLITE Enceladus STD=SATURN STD=ENCELADUS SEP OF ENCELADUS SATURN FROM EARTH GT 26.5", SEP OF ENCELADUS RHEA FROM EARTH GT 10", SEP OF ENCELADUS TITAN FROM EARTH GT 10" EARTH SOLAR SYSTEM SATELLITE Dione leading hemisphere STD=SATURN STD=DIONE SEP OF DIONE-LEADING SATURN FROM EARTH GT 45", SEP OF DIONE-LEADING RHEA FROM EARTH GT 10", SEP OF DIONE-LEADING TITAN FROM EARTH GT 10", CML OF DIONE-LEADING FROM EARTH BETWEEN 70 110 EARTH SOLAR SYSTEM SATELLITE Dione trailing hemisphere STD=SATURN STD=DIONE SEP OF DIONE-TRAILING SATURN FROM EARTH GT 45", SEP OF DIONE-TRAILING RHEA FROM EARTH GT 10", SEP OF DIONE-TRAILING TITAN FROM EARTH GT 10", CML OF DIONE-TRAILING FROM EARTH BETWEEN 250 290 EARTH SOLAR SYSTEM SATELLITE Rhea leading hemisphere STD=SATURN STD=RHEA SEP OF RHEA-LEADING SATURN FROM EARTH GT 45", SEP OF RHEA-LEADING TITAN FROM EARTH GT 10", CML OF RHEA-LEADING FROM EARTH BETWEEN 70 110 EARTH SOLAR SYSTEM SATELLITE Rhea trailing hemisphere STD=SATURN STD=RHEA SEP OF RHEA-TRAILING SATURN FROM EARTH GT 45", SEP OF RHEA-TRAILING TITAN FROM EARTH GT 10", CML OF RHEA-TRAILING FROM EARTH BETWEEN 250 290 EARTH STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 1407293590379 Using ephemeris for target 13694-01-MIMAS-LEADING The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13694 :visit-id "01" :proposal-version -1 :trans-version "20140605" :date "05-Aug-2014 19:53:09.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 124256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13694 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13694 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2885 :al-overhead-at-end 0 :internal-dur-at-end 434 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) true 1 0 1407294103192 Using ephemeris for target 13694-02-MIMAS-TRAILING The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13694 :visit-id "02" :proposal-version -1 :trans-version "20140605" :date "05-Aug-2014 20:01:43.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 124256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13694 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13694 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2785 :al-overhead-at-end 0 :internal-dur-at-end 434 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) true 1 0 1407330277015 Using ephemeris for target 13694-03-ENCELADUS The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13694 :visit-id "03" :proposal-version -1 :trans-version "20140605" :date "06-Aug-2014 06:04:36.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 124256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13694 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13694 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2885 :al-overhead-at-end 0 :internal-dur-at-end 434 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) true 1 0 1407330278007 Using ephemeris for target 13694-04-DIONE-LEADING The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13694 :visit-id "04" :proposal-version -1 :trans-version "20140605" :date "06-Aug-2014 06:04:37.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 124240 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13694 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13694 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2889 :al-overhead-at-end 0 :internal-dur-at-end 434 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) true 1 0 1407330278868 Using ephemeris for target 13694-05-DIONE-TRAILING The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13694 :visit-id "05" :proposal-version -1 :trans-version "20140605" :date "06-Aug-2014 06:04:38.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 124240 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13694 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13694 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2889 :al-overhead-at-end 0 :internal-dur-at-end 434 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) true 1 0 1407330279761 Using ephemeris for target 13694-06-RHEA-LEADING The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13694 :visit-id "06" :proposal-version -1 :trans-version "20140605" :date "06-Aug-2014 06:04:39.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 124240 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13694 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13694 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2889 :al-overhead-at-end 0 :internal-dur-at-end 434 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) true 1 0 1407330280621 Using ephemeris for target 13694-07-RHEA-TRAILING The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13694 :visit-id "07" :proposal-version -1 :trans-version "20140605" :date "06-Aug-2014 06:04:40.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 124240 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13694 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13694 :visit-id "07" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2889 :al-overhead-at-end 0 :internal-dur-at-end 434 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) true 1 0