We propose to explore the spatial structure and temporal variability of Europa's O2 atmosphere with ACS/SBC. Previous HST images display non-uniform UV emission from Europa's atmosphere, which maximizes within the disk of Europa on its anti-Jovian northern quadrant. These images were taken at western elongation and are not conclusive, but bring up the exciting question whether the non-uniform emission is due to a locally enhanced neutral atmosphere. A locally inhomogeneous atmosphere would imply locally modified surface properties. This might provide clues on inhomogeneities of the underlying ice structure and thus properties of a potential subsurface ocean. Since the inhomogeneous emission comes from within the disk of Europa, we propose to study Europa at eastern and western elongation to decide if the locally enhanced emission is truly an atmospheric effect. We propose to take for each elongation five contiguous observations within one rotation period of Jupiter to discriminate between a competing effect that produces inhomogeneous emission patterns, i.e., the electrodynamic interaction with Jupiter's magnetosphere. We will use ACS/SBC with PR130L prism to completely separate the two prominent FUV oxygen lines OI 1304 A and OI 1356 A emitted from Europa's atmosphere.

We propose to use ACS/SBC with prism PR130L to investigate the spatial structure of Europa's atmosphere. With this prism we will eliminate contributions from the long wavelength end of the SBC bandpass due to reflected sun light on Europa's surface by spectrally dispersing the image. We will be able to separate the two prominent FUV oxygen lines OI 1304 A and OI 1356 A emitted from Europa's atmosphere. We propose to center the disk of Europa (maximum diameter ~ 1.2") to obtain a symmetric field of view around the disk of Europa. We are requesting five contiguous orbits at eastern elongation, i.e., for the leading/downstream (longitude 90 degrees) hemisphere of Europa. The western elongation has been previously observed by STIS in cycle 8. Five orbits span more than one half of a Jovian rotation, so that a significant change of the orientation of Jupiter's magnetic field relative to Europa occurs over the course of the observations. This will allow us to test the dependence of the observed emission morphology on the magnetic field orientation. SOLAR SYSTEM 12 false 0.0 0.0 false false false false false SUPPORTED SOLAR SYSTEM SATELLITE Jovian satellite STD=JUPITER STD=EUROPA OLG OF JUPITER BETWEEN 330.0 30.0, OLG OF EUROPA-EAST BETWEEN 70.0 110.0, SEP OF GANYMEDE EUROPA FROM EARTH GT 5" EARTH ACS/SBC Spectroscopic No No PR130L (Tic-Visit :proposal-id 11186 :visit-id "01" :proposal-version -1 :trans-version "20070325" :date "25-Apr-2007 14:18:24.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 370272 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11186 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11186 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2774 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11186 :visit-id "01" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2777 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11186 :visit-id "01" :orbit-number 3 :pcs-time 355 :si-vis-utilization 2777 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11186 :visit-id "01" :orbit-number 4 :pcs-time 355 :si-vis-utilization 2777 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11186 :visit-id "01" :orbit-number 5 :pcs-time 355 :si-vis-utilization 2777 :al-overhead-at-end 0 :internal-dur-at-end 140 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) true 5 0