Currently, there is an unprecedented opportunity to observe the atmosphere of Venus. The Japanese Venus Climate Orbiter (VCO) mission, successfully launched on May 21, 2010, will be observing Venus simultaneously with Venus Express (VEx) Mission from December 2010 onward. A campaign for Earth-based observations coincident with the arrival of VCO at Venus is currently under-way. Fortuitously, the window for observing Venus with HST at a solar elongation greater than 45 degrees is December 25, 2010, thru January 28, 2011. Thus, we are applying to use HST/STIS during that time to observe Venus upper cloud deck (65-75 km) in the ultraviolet (200-600 nm) at high spectral (0.3-0.6 nm) and spatial (40-60 km/pixel) resolution using the G230LB (0.17-0.31 microns) and G430L (0.30-0.57 microns) gratings, with the 52x0.1 slit and the CCD detector. By observing Venus with the slit in its nominal 45 degree orientation, we will map, as a function of latitude, longitude, and time of day, variations in the spatial distribution of the SO2, SO and S2 gases, which absorb strongly between 200 and 320 nm, and an un-identified ultraviolet (UV) absorber known to absorb strongly above 320 nm. Because the spatial distribution of all of the UV absorbers (named and un-named) is tied to the motion of the upper cloud, VCO plans to image the spatial distribution of the UV absorbers and their relationship with the cloud structure and the wind field, in order to derive the wind vectors at the cloud top (Rossow et al., 1990). However, neither VEx nor VCO has the capability to obtain high spectral and spatial resolution spectroscopy of Venus upper clouds at 200-600 nm. The proposed HST observations will characterize and quantify the absorbers responsible for the cloud features recorded in the UV (200-600 nm) images to be obtained by the VCO/UVI and VEx/VIRTIS instruments, mapping the spatial distribution of these UV absorbers as function of the zonal cloud motion. Additionally, photodissociation of each of the identified UV absorbers is a key component of the system of reactions that leads to the formation of sulfur-oxides, the loss of atomic oxygen, and the subsequent formation of Venus H2SO4 clouds via the reaction of the sulfur-oxides with H2O. The density of H2O and OCS, the remaining atmospheric species that directly impact the rate of sulfur-oxide production and H2SO4 cloud formation within Venus atmosphere, will be obtained via ground-based and VEx/SOIR measurements. Thus, the proposed HST observations, when combined with VCO, VEx, and ground-based observations, will provide a complete picture of the latitudinal, longitudinal, time of day, and wind-driven variation of each of the key species involved in the sulfur-oxidation cycle. These results will be used to inform and develop models designed to i) investigate outstanding questions regarding the formation of Venus global sulfuric acid clouds and the abundance of oxygen in the atmosphere and ii) investigate the climatic evolution of Venus atmosphere.

The main objective of our observing proposal is to support and enhance the science return of the VEx and VCO missions; thus, investigators from both these teams are eager to coordinate with any observations granted by HST (see appended letters). Our goals are to obtain HST observations that can be directly compared to VEx/VIRTIS and VCO/UVI images of Venus upper cloud deck, the low spectral resolution VEx/SPICAV observations, and the high-spectral resolution NIR VEx/SOIR occultation observations, so that the spatial distribution of the Venus dominant UV absorbers can be quantified and mapped as a function of altitude, latitude, time of day, and the zonal cloud motion. While VCO plans to make continuous measurements of Venus low latitude regions, coordination of the observations with the VEx observations requires more precise planning. For example, the VEx/SOIR team has already committed to obtaining solar occultation observations of the lowlatitude regions of Venus during the HST observing window; but, the VEx/SOIR observations can only be obtained during the time period extending from December 25-December 30, 2010, when Venus is at a solar elongation angle of 45.8-46.3 degrees. The VEx/SPICAV and VEx/VIRTIS observations of Venus Earth-facing sunlit hemisphere can be made throughout the HST observing window. However, in late December VEx observations of Venus Earth-facing sunlit atmosphere can only be made at a high emission angle, while VEx observations made later in January (e.g. between January 25-28, when Venus is at a solar elongation angle of 45.9-45.6 degrees) can be obtained near nadir viewing, which will result in a significantly broader spatial coverage. To achieve the highest level of science return from our proposed observations we request 6 orbits of observations of Venus over 3 days (i.e. 2 orbits per day). This would allow us to track changes in the atmospheric density within Venus upper cloud deck along with the zonal (or E-W) motion of the clouds during Venus 5-day cloud rotation period. VCO/UVI plans to track the spatial distribution of the Venus characteristic ultraviolet absorption features and their relationships with the cloud structure and the wind field. The proposed HST observations would provide distinct measurement of the density of each of the UV absorbers that produce the UV albedo pattern of Venus clouds as a function of the zonal motion of the clouds that could be compared directly with the VCO/UVI images. Implementation of this program would allow us to achieve all of our primary science goals. However, if 3 consecutive days of observation are not possible then 2 days of observation in late December sometime within the VEx/SOIR observing window, using 2 orbits per day, plus 2 orbits of observation acquired on a single visit in late January to coincide with the VEx/SPICAV nadir observing window would be of great value. SOLAR SYSTEM 12 false 0.0 0.0 false false false false false false AVAILABLE SOLAR SYSTEM Venus 15 degrees south latitude on central meridian. The longitude value specified here is the CML for visit 01 observing time (28-Dec-2010 0:00-2:00UT). The longitude value must be updated if a new observing time is selected. PLANET Planet Venus STD=VENUS TYPE=PGRAPHIC,LONG=61,LAT=-15 SEP OF VENUS SUN FROM EARTH GT 45.5D EARTH SOLAR SYSTEM Venus 32 degrees south latitude on central meridian. The longitude value specified here is the CML for visit 01 observing time (28-Dec-2010 0:00-2:00UT). The longitude value must be updated if a new observing time is selected. PLANET Planet Venus STD=VENUS TYPE=PGRAPHIC,LONG=61,LAT=-32 SEP OF VENUS SUN FROM EARTH GT 45.5D EARTH SOLAR SYSTEM Venus 45 degrees south latitude on central meridian. The longitude value specified here is the CML for visit 02 observing time (22-Jan-2011 15:00-17:00UT). The longitude value must be updated if a new observing time is selected. PLANET Planet Venus STD=VENUS TYPE=PGRAPHIC,LONG=136.5,LAT=-45 SEP OF VENUS SUN FROM EARTH GT 45.5D EARTH SOLAR SYSTEM Venus 65 degrees south latitude on central meridian. The longitude value specified here is the CML for visit 02 observing time (22-Jan-2011 15:00-17:00UT). The longitude value must be updated if a new observing time is selected. PLANET Planet Venus STD=VENUS TYPE=PGRAPHIC,LONG=136.5,LAT=-65 SEP OF VENUS SUN FROM EARTH GT 45.5D EARTH SOLAR SYSTEM Venus 45 degrees south latitude on central meridian. The longitude value specified here is the CML for visit 03 observing time (27-Jan-2011 14:30-15:30UT). The longitude value must be updated if a new observing time is selected. PLANET Planet Venus STD=VENUS TYPE=PGRAPHIC,LONG=160,LAT=-45 SEP OF VENUS SUN FROM EARTH GT 45.5D EARTH SOLAR SYSTEM Venus 65 degrees south latitude on central meridian. The longitude value specified here is the CML for visit 03 observing time (27-Jan-2011 14:30-15:30UT). The longitude value must be updated if a new observing time is selected. PLANET Planet Venus STD=VENUS TYPE=PGRAPHIC,LONG=160,LAT=-65 SEP OF VENUS SUN FROM EARTH GT 45.5D EARTH SOLAR SYSTEM 5.5 degree offset from Venus in the anti-sunward direction. OFFSET Offset Venus STD=VENUS TYPE=POS_ANGLE,RAD=19800,ANG=180,REF=SUN EARTH SOLAR SYSTEM 5.4 degree offset from Venus in the anti-sunward direction. OFFSET Offset Venus STD=VENUS TYPE=POS_ANGLE,RAD=19440,ANG=180,REF=SUN EARTH STIS/CCD Spectroscopic No No G230LB 2375 STIS/CCD Spectroscopic No No G430L 4300 STIS/CCD Spectroscopic No No G230LB 2375 STIS/CCD Spectroscopic No No G430L 4300 STIS/CCD Spectroscopic No No G230LB 2375 STIS/CCD Spectroscopic No No G430L 4300 BETWEEN for simultaneous observing with Venus Express. 1293490875000 289.93613659975017 (Tic-Visit :proposal-id 12433 :visit-id "01" :proposal-version -1 :trans-version "20100902" :date "23-Nov-2010 12:47:25.0" :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 110464 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12433 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "01" :obset-id "A1" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "01" :obset-id "B1" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "01" :obset-id "C1" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "01" :obset-id "D1" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12433 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 1329 :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 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12433 :visit-id "01" :orbit-number 2 :pcs-time 333 :si-vis-utilization 1464 :al-overhead-at-end 0 :internal-dur-at-end 322 :dark-offset 9 :dark-utilization 320 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12433 :visit-id "01" :orbit-number 3 :pcs-time 333 :si-vis-utilization 1464 :al-overhead-at-end 0 :internal-dur-at-end 322 :dark-offset 9 :dark-utilization 320 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) false 3 0 This exposure establishes a pointing near Venus but outside of HST's solar avoidance zone. Doing this minimizes the slew distance when slewing to Venus. This is a precautionary measure to protect against an unusually large pointing error after the slew to Venus. While such an error is unlikely in general, it is even more unlikely for a small slew. The 22 minute exposure time ensures a gyro bias update will take place. Observe Venus while HST is within the Earth's shadow. Exposure time for Venus will be severly constrained, and this observation is designed to maximize the time available for the Venus science exposure. No wavecal requested (WAVECAL=NO). Use single star guiding. These are both specified to increase the limited time available for this science exposure. Special commanding to ignore STIS "take data" flag and still proceed with science observation in the case of a guide star acquisition failure. Return to safe pointing that is more than 50 degrees from the Sun. Observe Venus while HST is within the Earth's shadow. Exposure time for Venus will be severly constrained, and this observation is designed to maximize the time available for the Venus science exposure. No wavecal requested (WAVECAL=NO). Use single star guiding. These are both specified to increase the limited time available for this science exposure. Special commanding to ignore STIS "take data" flag and still proceed with science observation in the case of a guide star acquisition failure. Return to safe pointing that is more than 50 degrees from the Sun. BETWEEN for simultaneous observing with Akatsuki. (Tic-Visit :proposal-id 12433 :visit-id "02" :proposal-version -1 :trans-version "20100902" :date "23-Nov-2010 12:47:28.0" :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 110464 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12433 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "02" :obset-id "A2" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "02" :obset-id "B2" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "02" :obset-id "C2" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "02" :obset-id "D2" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12433 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 1329 :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 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12433 :visit-id "02" :orbit-number 2 :pcs-time 333 :si-vis-utilization 1381 :al-overhead-at-end 0 :internal-dur-at-end 322 :dark-offset 9 :dark-utilization 237 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12433 :visit-id "02" :orbit-number 3 :pcs-time 333 :si-vis-utilization 1381 :al-overhead-at-end 0 :internal-dur-at-end 322 :dark-offset 9 :dark-utilization 237 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) false 3 0 This exposure establishes a pointing near Venus but outside of HST's solar avoidance zone. Doing this minimizes the slew distance when slewing to Venus. This is a precautionary measure to protect against an unusually large pointing error after the slew to Venus. While such an error is unlikely in general, it is even more unlikely for a small slew. The 22 minute exposure time ensures a gyro bias update will take place. Observe Venus while HST is within the Earth's shadow. Exposure time for Venus will be severly constrained, and this observation is designed to maximize the time available for the Venus science exposure. No wavecal requested (WAVECAL=NO). Use single star guiding. These are both specified to increase the limited time available for this science exposure. Special commanding to ignore STIS "take data" flag and still proceed with science observation in the case of a guide star acquisition failure. Return to safe pointing that is more than 50 degrees from the Sun. Observe Venus while HST is within the Earth's shadow. Exposure time for Venus will be severly constrained, and this observation is designed to maximize the time available for the Venus science exposure. No wavecal requested (WAVECAL=NO). Use single star guiding. These are both specified to increase the limited time available for this science exposure. Special commanding to ignore STIS "take data" flag and still proceed with science observation in the case of a guide star acquisition failure. Return to safe pointing that is more than 50 degrees from the Sun. BETWEEN for simultaneous observing with both Akatsuki and Venus Express. (Tic-Visit :proposal-id 12433 :visit-id "03" :proposal-version -1 :trans-version "20100902" :date "06-Jan-2011 13:58:03.0" :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 147232 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12433 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "03" :obset-id "A3" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "03" :obset-id "B3" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "03" :obset-id "C3" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12433 :visit-id "03" :obset-id "D3" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12433 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 1329 :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 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12433 :visit-id "03" :orbit-number 2 :pcs-time 333 :si-vis-utilization 1515 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset 9 :dark-utilization 502 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12433 :visit-id "03" :orbit-number 3 :pcs-time 333 :si-vis-utilization 1556 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset 9 :dark-utilization 543 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) false 3 0 This exposure establishes a pointing near Venus but outside of HST's solar avoidance zone. Doing this minimizes the slew distance when slewing to Venus. This is a precautionary measure to protect against an unusually large pointing error after the slew to Venus. While such an error is unlikely in general, it is even more unlikely for a small slew. The 22 minute exposure time ensures a gyro bias update will take place. Observe Venus while HST is within the Earth's shadow. Exposure time for Venus will be severly constrained, and this observation is designed to maximize the time available for the Venus science exposure. No wavecal requested (WAVECAL=NO). Use single star guiding. These are both specified to increase the limited time available for this science exposure. Special commanding to ignore STIS "take data" flag and still proceed with science observation in the case of a guide star acquisition failure. Observe Venus while HST is within the Earth's shadow. Exposure time for Venus will be severly constrained, and this observation is designed to maximize the time available for the Venus science exposure. No wavecal requested (WAVECAL=NO). Use single star guiding. These are both specified to increase the limited time available for this science exposure. Special commanding to ignore STIS "take data" flag and still proceed with science observation in the case of a guide star acquisition failure. Return to safe pointing that is more than 50 degrees from the Sun. Observe Venus while HST is within the Earth's shadow. Exposure time for Venus will be severly constrained, and this observation is designed to maximize the time available for the Venus science exposure. No wavecal requested (WAVECAL=NO). Use single star guiding. These are both specified to increase the limited time available for this science exposure. Special commanding to ignore STIS "take data" flag and still proceed with science observation in the case of a guide star acquisition failure. Observe Venus while HST is within the Earth's shadow. Exposure time for Venus will be severly constrained, and this observation is designed to maximize the time available for the Venus science exposure. No wavecal requested (WAVECAL=NO). Use single star guiding. These are both specified to increase the limited time available for this science exposure. Special commanding to ignore STIS "take data" flag and still proceed with science observation in the case of a guide star acquisition failure. Return to safe pointing that is more than 50 degrees from the Sun.