! File: 4268C.PROP ! Database: PEPDB ! Date: 20-FEB-1994:19:43:07 coverpage: title_1: HST IMAGING OF EUROPA: A TEST OF THE ION IMPLANTATION title_2: MODEL: CYCLE 3 SUPPLEMENTAL sci_cat: SOLAR SYSTEM sci_subcat: SATELLITES proposal_for: GO pi_fname: KEITH pi_mi: S. pi_lname: NOLL pi_inst: STSCI pi_country: USA hours_pri: 7.30 num_pri: 1 foc: Y funds_length: 12 off_fname: HERVEY off_mi: S. off_lname: STOCKMAN off_title: DEPUTY DIRECTOR off_inst: 3470 off_addr_1: 3700 SAN MARTIN DRIVE off_city: BALTIMORE off_state: MD off_zip: 21218 off_country: USA off_phone: 410-338-4700 ! end of coverpage abstract: line_1: Like most outer solar system satellites, the albedo of Europa drops in the UV line_2: below the albedo expected for an icy surface. Furthermore, the longitudinally line_3: averaged albedo near the antapex of Europa's orbital motion is more than a line_4: factor of two lower than the albedo near the apex. Because the surface of line_5: Europa resides in an environment filled with an energetic ion plasma line_6: consisting mainly of S and O ions, it is natural to expect that ion-surface line_7: interactions could play an important role in the darkening observed in the UV. line_8: This hypothesis seems to be further strengthened by the observation of a weak line_9: differential absorption seen in the ratio of the trailing hemisphere spectrum line_10: to the leading hemisphere spectrum that is consistent with S-O bands from line_11: isolated S ions in an ice matrix. However, the most direct test of this line_12: model, imaging at wavelengths most sensitive to sulfur impurities in ice, has line_13: never been done. We propose to obtain spatially resolved images of Europa line_14: using the Faint Object Camera with a spatial resolution of 200 km in order to line_15: directly address the question of plasma interactions with the surface and the line_16: balance of endogenic resurfacing and exogenic surface alteration on Europa. ! ! end of abstract general_form_proposers: lname: NOLL fname: KEITH title: DR. mi: S. inst: STSCI country: USA ! lname: SARTORETTI fname: PAOLA inst: STSCI country: USA ! ! end of general_form_proposers block general_form_text: question: 3 section: 1 line_1: We request images of Europa at 4 points in its orbit: 2 of them are line_2: within 40-140 degrees of orbital longitude and the other 2 within line_3: 220-320 degrees. At each point we will take 15 minute exposures with the line_4: FOC f/96 in the filter combinations: F220W+F231M+F1ND and line_5: F275W+F253M+F2ND. line_6: In the original proposal the orbital longitude ranges for each image line_7: were more tightly restricted. In order to simplify the proposal we line_8: have widened the orbital longitude ranges to cover the eastern and line_9: western halves of the orbit for two targets each. However, we would line_10: request that each SU be scheduled independently, increasing the line_11: chances of obtaining good longitudinal coverage in the four images line_12: that will be obtained. ! question: 4 section: 1 line_1: The HST is the only instrument capable of obtaining spatially resolved line_2: imaged of Europa for the forseeable future. The imaging experiments on line_3: the Galileo spacecraft which will arrive at Jupiter in 1995 extend only line_4: to 3800 A (Yeates et al. 1985). Ground based observations are limited line_5: to the spectral range longer than 3200A. The Voyager UV filter was line_6: similarly limited to wavelengths beyond 3500A. The possible S-O line_7: absorption is peaked at 2800A and therefore only the HST will be able to line_8: quantitatively assess the distribution of this absorber in Europa. There line_9: has been extensive observations of Europa with the IUE including line_10: 1-dimensional mapping in longitude by obtaining spectra at different line_11: orbital (and therefore satellite) longitudes. Nelson et al. (1987) line_12: describes the most complete set of these observations and we have line_13: discussed the results in detail in the scientific justification. line_14: However, we note again that the 1-dimensional mapping completed by the line_15: IUE is incapable of finding the albedo variegations that will either line_16: confirm or modify the current paradigm for UV darkening in Europa. The line_17: only unambiguous way to obtain this information is to directly image line_18: Europa. Only the HST has or will have that capability for the line_19: forseeable future. ! question: 4 section: 2 line_1: To obtain global coverage of Europa and thus characterize the global line_2: distribution of UV absorbers on the surface, it is necessary to observe line_3: at 4 longitudes to avoid eccessive foreshortening of some regions. The line_4: exposure times are based on our experience with previously acquired FOC line_5: images of Io as well as the standard formulae in the FOC handbook. In line_6: all cases we have chosen filter combinations and integration times to line_7: achieve a S/N $\sim$ 100. The detector response is linear for a count line_8: rate of up to 0.2 counts s$^{-1}$ pix$^{-1}$. We have calculated line_9: expected count rates for all the filters using a synthetic Europa line_10: spectrum and a convolution of the resolved disk with the HST line_11: point-spread- function. For example, for the F220W+F231M+F1ND line_12: combination we obtain a total count rate, after all corrections, of 0.09 line_13: counts s$^{-1}$ pix$^{-1}$, well below the maximum count rate required line_14: for a linear detector response. ! question: 5 section: 1 line_1: Real-time acquisition is required for the FOC images for bright object line_2: protection. ! question: 6 section: 1 line_1: None ! question: 7 section: 1 line_1: ! question: 7 section: 2 line_1: ! question: 8 section: 1 line_1: None ! question: 9 section: 1 line_1: ! question: 9 section: 2 line_1: ! question: 10 section: 1 line_1: ! !end of general form text general_form_address: lname: NOLL fname: KEITH mi: S. category: PI inst: STScI addr_1: 3700 SAN MARTIN DRIVE city: BALTIMORE state: MD zip: 21218 country: USA phone: 410-338-1828 ! ! end of general_form_address records ! No fixed target records found solar_system_targets: targnum: 1 name_1: EUROPA-EAST-OFFN descr_1: SATELLITE EUROPA lev1_1: STD = JUPITER lev2_1: STD = EUROPA lev3_1: TYPE = POS_ANGLE, lev3_2: RAD = 30, lev3_3: ANG = 0, lev3_4: REF = NORTH wind_1: OLG OF EUROPA BETWEEN 220 320, wind_2: SEP OF EUROPA CALLISTO wind_3: FROM EARTH GT 10", wind_4: SEP OF IO EUROPA FROM EARTH GT 10", wind_5: SEP OF EUROPA GANYMEDE wind_6: FROM EARTH GT 10" fluxnum_1: 1 fluxval_1: SURF(V)=5.07 ! targnum: 2 name_1: EUROPA-WEST-OFFN descr_1: SATELLITE EUROPA lev1_1: STD = JUPITER lev2_1: STD = EUROPA lev3_1: TYPE = POS_ANGLE, lev3_2: RAD = 30, lev3_3: ANG = 0, lev3_4: REF = NORTH wind_1: OLG OF EUROPA BETWEEN 40 140, wind_2: SEP OF EUROPA CALLISTO wind_3: FROM EARTH GT 10", wind_4: SEP OF IO EUROPA FROM EARTH GT 10", wind_5: SEP OF EUROPA GANYMEDE wind_6: FROM EARTH GT 10" fluxnum_1: 1 fluxval_1: SURF(V)=5.07 ! ! end of solar system targets ! No generic target records found exposure_logsheet: linenum: 1.000 targname: DARK config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F275W,F253M,F2ND num_exp: 1 time_per_exp: 17S s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: CYCLE 3 / 1-18; req_2: SEQ 1-2 NON-INT; req_3: SEQ 1-4 NO GAP; comment_1: PUT ELL 1-4 IN SEPARATE SU ! linenum: 2.000 targname: EUROPA-EAST-OFFN config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F275W,F253M,F2ND num_exp: 1 time_per_exp: 15M s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: REQ UPLINK; ! linenum: 3.000 targname: DARK config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F220W,F231M num_exp: 1 time_per_exp: 17S s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: SEQ 3-4 NON-INT; ! linenum: 4.000 targname: EUROPA-EAST-OFFN config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F220W,F231M num_exp: 1 time_per_exp: 15M s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: REQ UPLINK; ! linenum: 5.000 targname: DARK config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F275W,F253M,F2ND num_exp: 1 time_per_exp: 17S s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: CYCLE 3 / 1-16; req_2: SEQ 5-6 NON-INT; req_3: SEQ 5-8 NO GAP; comment_1: PUT ELL 5-8 IN SEPARATE SU ! linenum: 6.000 targname: EUROPA-EAST-OFFN config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F275W,F253M,F2ND num_exp: 1 time_per_exp: 15M s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: REQ UPLINK; ! linenum: 7.000 targname: DARK config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F220W,F231M num_exp: 1 time_per_exp: 17S s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: SEQ 7-8 NON-INT; ! linenum: 8.000 targname: EUROPA-EAST-OFFN config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F220W,F231M num_exp: 1 time_per_exp: 15M s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: REQ UPLINK; ! linenum: 11.000 targname: DARK config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F275W,F253M,F2ND num_exp: 1 time_per_exp: 17S s_to_n: 20 fluxnum_1: 1 priority: 1 req_2: SEQ 11-12 NON-INT; req_3: SEQ 11-14 NO GAP; comment_1: PUT ELL 11-14 IN A SEPARATE SU ! linenum: 12.000 targname: EUROPA-WEST-OFFN config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F275W,F253M,F2ND num_exp: 1 time_per_exp: 15M s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: REQ UPLINK; ! linenum: 13.000 targname: DARK config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F220W,F231M num_exp: 1 time_per_exp: 17S s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: SEQ 13-14 NON-INT; ! linenum: 14.000 targname: EUROPA-WEST-OFFN config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F220W,F231M num_exp: 1 time_per_exp: 15M s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: REQ UPLINK; ! linenum: 15.000 targname: DARK config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F275W,F253M,F2ND num_exp: 1 time_per_exp: 17S s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: SEQ 15-16 NON-INT; req_2: SEQ 15-18 NO GAP; comment_1: PUT ELL 15-18 IN A SEPARATE SU ! linenum: 16.000 targname: EUROPA-WEST-OFFN config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F275W,F253M,F2ND num_exp: 1 time_per_exp: 15M s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: REQ UPLINK; ! linenum: 17.000 targname: DARK config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F220W,F231M num_exp: 1 time_per_exp: 17S s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: SEQ 17-18 NON-INT; ! linenum: 18.000 targname: EUROPA-WEST-OFFN config: FOC/96 opmode: IMAGE aperture: 512X512 sp_element: F220W,F231M num_exp: 1 time_per_exp: 15M s_to_n: 20 fluxnum_1: 1 priority: 1 req_1: REQ UPLINK; ! ! end of exposure logsheet ! No scan data records found