Past HST observations of Saturn’s aurora have concentrated on the morphology and the relationship between the solar wind and the brightness of the aurora. With STIS back to work, time has come to move into a more quantitative era where FUV spectroscopy is used as a powerful tool to remotely sense the characteristics of the precipitated electrons and their effect on the H2 gas. In the proposed program, we focus on images and spectroscopy linking precipitated particles with the morphology observed quasi simultaneously. We have a unique opportunity to address key questions concerning the characteristic energy of the auroral electrons and their effects on the temperature of the upper atmosphere. In particular, we propose to combine HST FUV imaging with STIS long slit low and medium resolution spectroscopy to determine the spatial variations of the FUV color ratio, the altitude of the aurora and to map the temperature in the high-latitude region. A combined HST-Cassini campaign has been planned at the time of Saturn’s opposition in 2011 to complement HST spatial spectroscopy with observations from UVIS covering both hemispheres from a different vantage point. This compact and timely program is designed to provide key observations toward a better understanding of the physical interactions taking place in Saturn’s aurora.

This program is based on coordinated STIS spectral observations of Saturn's FUV north aurora with simultaneous Cassini-UVIS measurements distributed over 3 visits. A time-tag image will be obtained at the beginning of each visit to view the global context of the spectra. STIS FUV images of Saturn previously obtained by the PI and other team members have demonstrated that the STIS count rate limit is far from being reached during such observations. Time-tagged spectral observations with the 52x0.5" long slit aperture will use the G140L and G140M gratings. The slit will scan the north auroral oval from the equatorward boundary of the oval up to several 1000s km above the north limb. The slit will be oriented with the minimum possible inclination angle on the planetary equatorial plane compatible with the spacecraft orientation constraints, with a maximum value of +/- 30°. These roll angles will be requested on an as-available basis for the orientation of HST at the time of observations. We wish to minimize the geocoronal Ly-alpha emission by observing in Earth shadow whenever possible. The sequence of the observations will be: VISITS #11 and #12 (consecutive orbits 1 and 2) : orbit 1: one 25MAMA STIS CLEAR image of the planetary disk, followed by one S-N scan of the north auroral region with the 52x0.5" slit and G140L grating. Both exposures will be time tagged. orbit 2: one 25MAMA STIS CLEAR image of the planetary disk, followed by one S-N scan of the north auroral region with the 52x0.5" slit and G140M grating in the time-tag mode, with lambcentral = 1567 Å. VISITS #21 and #22 (consecutive orbits 3 and 4) and VISITS #31 and #32 (consecutive orbits 5 and 6): will repeat the same sequences. These observations will be scheduled in coordination with the auroral observing campaigns planned for Cassini during Cycle 18. Although the detailed observation sequences of Cassini are not full defined yet, 3 periods have already been defined in the Cassini planning in support of this HST program. The dates are: 23-DEC-2010 17-APR-2011, with Cassini located near orbital periapsis 8-9-JUL-2011 The HST visits have been defined based on these observation plans, which may still be revised. Not yet knowing the orbital HST ephemeris during this cycle, the detailed scheduling will be decided in coordination with STScI. SOLAR SYSTEM 12 false 0.0 0.0 false false false false SUPPORTED SOLAR SYSTEM Image center (STIS FOV center) should be ~on Saturn center PLANET Saturn center for image STD=SATURN TYPE=POS_ANGLE,RAD=0.0,ANG=0,REF=NORTH EARTH SOLAR SYSTEM Apply S-N slew to STIS long slit, from ~55° centric latitude to ~7000 km above limb (~above NP). SLEW=3.5" in 1500 s (201.6"/day). The slew is towards the north of Saturn RAD and ANG are for slit center Auroral zone is well covered (slew+2*slit half width =3.5"+2*0.5"/2=4"), even with +/- 1" offset from nominal pointing. RAD and R_RAD assume that planet tilt is small (~0°) so that slew is perpendicular to ecliptic plane (for simplicity) EPOCH is indicative and depends on final schedule. STIS slit should be as // as possible to Saturn equatorial plane (within 30°) PLANET Auroral zone in Saturn's northern hemisphere STD=SATURN TYPE=POS_ANGLE,RAD=7.0,ANG=0,REF=NORTH,R_RAD=144,EPOCH=10-MAY-2011:13:10:25 EARTH SOLAR SYSTEM Image center (STIS FOV center) should be ~on Saturn center PLANET Saturn center for image STD=SATURN TYPE=POS_ANGLE,RAD=0.0,ANG=0,REF=NORTH EARTH SOLAR SYSTEM Apply S-N slew to STIS long slit. The slew is towards the north of Saturn RAD and ANG are for slit center. Auroral zone is well covered (slew+2*slit half width =3.5"+2*0.5"/2=4"), even with +/- 1" offset from nominal pointing. RAD and R_RAD assume that planet tilt is small (~0°) so that slew is perpendicular to ecliptic plane (for simplicity) EPOCH is indicative and depends on final schedule. STIS slit should be as // as possible to Saturn equatorial plane (within 30°) PLANET Auroral zone in Saturn's northern hemisphere STD=SATURN TYPE=POS_ANGLE,RAD=6,ANG=0,REF=NORTH,R_RAD=239.55,EPOCH=17-APR-2011:22:03:05 EARTH SOLAR SYSTEM Image center (STIS FOV center) should be ~on Saturn center PLANET Saturn center for image STD=SATURN TYPE=POS_ANGLE,RAD=0.0,ANG=0,REF=NORTH EARTH SOLAR SYSTEM Apply S-N slew to STIS long slit, from ~55° centric latitude to ~7000 km above limb (~above NP). SLEW=3.5" in 1500 s (201.6"/day). The slew is towards the north of Saturn RAD and ANG are for slit center Auroral zone is well covered (slew+2*slit half width =3.5"+2*0.5"/2=4"), even with +/- 1" offset from nominal pointing. RAD and R_RAD assume that planet tilt is small (~0°) so that slew is perpendicular to ecliptic plane (for simplicity) EPOCH is indicative and depends on final schedule. STIS slit should be as // as possible to Saturn equatorial plane (within 30°) PLANET Auroral zone in Saturn's northern hemisphere STD=SATURN TYPE=POS_ANGLE,RAD=6.8,ANG=0,REF=NORTH,R_RAD=201.6,EPOCH=28-JAN-2011:12:11:13 EARTH SOLAR SYSTEM Apply S-N slew to STIS long slit, from ~55° centric latitude to ~7000 km above limb (~above NP). SLEW=3.5" in 1500 s (316.8"/day). The slew is towards the north of Saturn RAD and ANG are for slit center Auroral zone is well covered (slew+2*slit half width =3.5"+2*0.5"/2=4"), even with +/- 1" offset from nominal pointing. RAD and R_RAD assume that planet tilt is small (~0°) so that slew is perpendicular to ecliptic plane (for simplicity) EPOCH is indicative and depends on final schedule. STIS slit should be as // as possible to Saturn equatorial plane (within 30°) EPOCH set for visit 32 exposure 2 to start at 2011.076:18:25:10 (minus Saturn->Earth light travel time). PLANET Auroral zone in Saturn's northern hemisphere STD=SATURN TYPE=POS_ANGLE,RAD=5.5,ANG=0,REF=NORTH,R_RAD=316.8,EPOCH=17-MAR-2011:17:13:09 EARTH SOLAR SYSTEM Apply S-N slew to STIS long slit, from ~55° centric latitude to ~7000 km above limb (~above NP). SLEW=3.5" in 1500 s (316.8"/day). The slew is towards the north of Saturn RAD and ANG are for slit center Auroral zone is well covered (slew+2*slit half width =3.5"+2*0.5"/2=4"), even with +/- 1" offset from nominal pointing. RAD and R_RAD assume that planet tilt is small (~0°) so that slew is perpendicular to ecliptic plane (for simplicity) EPOCH is indicative and depends on final schedule. STIS slit should be as // as possible to Saturn equatorial plane (within 30°) EPOCH set for visit 32 exposure 4 to start at 2011.076:20:00:49 (minus Saturn->Earth light travel time). PLANET Auroral zone in Saturn's northern hemisphere STD=SATURN TYPE=POS_ANGLE,RAD=5.5,ANG=0,REF=NORTH,R_RAD=316.8,EPOCH=17-MAR-2011:18:48:48 EARTH SOLAR SYSTEM Apply S-N slew to STIS long slit. The slew is towards the north of Saturn RAD and ANG are for slit center. Auroral zone is well covered (slew+2*slit half width =3.5"+2*0.5"/2=4"), even with +/- 1" offset from nominal pointing. RAD and R_RAD assume that planet tilt is small (~0°) so that slew is perpendicular to ecliptic plane (for simplicity) EPOCH is indicative and depends on final schedule. STIS slit should be as // as possible to Saturn equatorial plane (within 30°) PLANET Auroral zone in Saturn's northern hemisphere STD=SATURN TYPE=POS_ANGLE,RAD=7,ANG=0,REF=NORTH,R_RAD=133.87,EPOCH=17-APR-2011:23:38:12 EARTH SOLAR SYSTEM Apply S-N slew to STIS long slit, from ~55° centric latitude to ~7000 km above limb (~above NP). SLEW=3.5" in 1500 s (201.6"/day). The slew is towards the north of Saturn RAD and ANG are for slit center Auroral zone is well covered (slew+2*slit half width =3.5"+2*0.5"/2=4"), even with +/- 1" offset from nominal pointing. RAD and R_RAD assume that planet tilt is small (~0°) so that slew is perpendicular to ecliptic plane (for simplicity) EPOCH is indicative and depends on final schedule. STIS slit should be as // as possible to Saturn equatorial plane (within 30°) PLANET Auroral zone in Saturn's northern hemisphere STD=SATURN TYPE=POS_ANGLE,RAD=7.0,ANG=0,REF=NORTH,R_RAD=144,EPOCH=10-MAY-2011:14:44:18 EARTH STIS/FUV-MAMA Imaging No No 25MAMA STIS/FUV-MAMA Spectroscopic No No G140M 1567 STIS/FUV-MAMA Spectroscopic No No G140M 1222 STIS/FUV-MAMA Imaging No No 25MAMA STIS/FUV-MAMA Spectroscopic No No G140L 1425 STIS/FUV-MAMA Spectroscopic No No G140M 1567 Using ephemeris for target 12235-11-SATURN-A-FIX Using ephemeris for target 12235-11-SATURN-A-SLEW-S-N The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. Orbit 1/2 of visit 1x STIS slit should be as parallel as possible to Saturn's rings plane **IMPORTANT** Epoch on target SATURN-A-SLEW-S-N must be updated if BETWEEN changes. (Tic-Visit :proposal-id 12235 :visit-id "11" :proposal-version -1 :trans-version "20100902" :date "28-Apr-2011 10:48:06.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 1008832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12235 :visit-id "11" :obset-id "11" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12235 :visit-id "11" :obset-id "A1" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12235 :visit-id "11" :obset-id "B1" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12235 :visit-id "11" :obset-id "C1" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12235 :visit-id "11" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2901 :al-overhead-at-end 0 :internal-dur-at-end 442 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12235 :visit-id "11" :orbit-number 2 :pcs-time 333 :si-vis-utilization 2872 :al-overhead-at-end 0 :internal-dur-at-end 442 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) true 2 0 assumes pointing and radial slew assumes pointing and radial slew Using ephemeris for target 12235-21-SATURN-B-FIX Using ephemeris for target 12235-21-SATURN-B-SLEW-S-N The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. Orbit 1/2 of visit 2x Cassini Rev 147 STIS slit should be as parallel as possible to Saturn's rings plane **IMPORTANT** Epoch on target SATURN-B-SLEW-S-N must be updated if BETWEEN changes. 1303076048000 111.61073297365567 (Tic-Visit :proposal-id 12235 :visit-id "21" :proposal-version -1 :trans-version "20100505" :date "05-Jul-2010 17:24:46.0" :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 504416 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12235 :visit-id "21" :obset-id "21" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12235 :visit-id "21" :obset-id "B1" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12235 :visit-id "21" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2851 :al-overhead-at-end 0 :internal-dur-at-end 442 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) false 1 0 assumes pointing and radial slew for 17APR2011 assumes pointing and radial slew for 17APR2011 Using ephemeris for target 12235-31-SATURN-C-FIX Using ephemeris for target 12235-31-SATURN-C-SLEW-S-N The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. Orbit 1/2 of visit 3x STIS slit should be as parallel as possible to Saturn's rings plane ***IMPORTANT*** Epoch on target SATURN-C-SLEW-S-N must be updated if BETWEEN changes. NOTE: Other scheduling times are possible on January 28, 2011 with appropriate changes to EPOCH and BETWEEN. 1296220666000 283.50322759886853 (Tic-Visit :proposal-id 12235 :visit-id "31" :proposal-version -1 :trans-version "20100505" :date "29-Sep-2010 13:45:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 939248 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12235 :visit-id "31" :obset-id "31" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12235 :visit-id "31" :obset-id "A1" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12235 :visit-id "31" :obset-id "B1" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12235 :visit-id "31" :obset-id "C1" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12235 :visit-id "31" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2901 :al-overhead-at-end 0 :internal-dur-at-end 442 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12235 :visit-id "31" :orbit-number 2 :pcs-time 333 :si-vis-utilization 2901 :al-overhead-at-end 0 :internal-dur-at-end 442 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) false 2 0 assumes pointing and radial slew for 08JUL2011 assumes pointing and radial slew for 08JUL2011 Repeat of failed visit 31. STIS slit should be as parallel as possible to Saturn's rings plane ***IMPORTANT*** Epoch on target SATURN-D-SLEW-S-N must be updated if BETWEEN changes. NOTE: Other scheduling times are possible with appropriate changes to EPOCH and BETWEEN. 1300384540000 312.0 (Tic-Visit :proposal-id 12235 :visit-id "31" :proposal-version -1 :trans-version "20100505" :date "29-Sep-2010 13:45:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 939248 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12235 :visit-id "31" :obset-id "31" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12235 :visit-id "31" :obset-id "A1" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12235 :visit-id "31" :obset-id "B1" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12235 :visit-id "31" :obset-id "C1" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12235 :visit-id "31" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2901 :al-overhead-at-end 0 :internal-dur-at-end 442 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12235 :visit-id "31" :orbit-number 2 :pcs-time 333 :si-vis-utilization 2901 :al-overhead-at-end 0 :internal-dur-at-end 442 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) false 2 0 assumes pointing and radial slew for 08JUL2011 assumes pointing and radial slew for 08JUL2011