Hubble Space Telescope Cycle 11 General Observer ProposalEuropa: continuing the search for liquid waterPrincipal Investigator: Ms. Tiffany KatariaInstitution: State University of New York at Stony BrookUSA/NYElectronic mail: [email protected] category: SOLAR SYSTEMScientific keywords: IMAGING, SURFACES OF PLANETS/MOONS/OTHER,SPECTROSCOPYInstruments: NICMOS Proprietary period: 12Cycle 11 primary orbits: 14Cycle 11 parallel orbits: 0AbstractThis project aims to continue the search for liquid water on Europa. Using the grismson NICMOS, we will image and identify spectral features that signify the presence of waterin the near infrared. We will note in particular the absorption bands centered near 1.04,1.25, 1.5 and 2 microns, which are characteristic of salts.Ms. Tiffany KatariaEuropa: continuing the search for liquid waterInvestigator Institution CountryPI: Ms. Tiffany Kataria State University of New York at Stony Brook USA/NYCoI: Lord Bartholemew Ruff-ingtonIIIOxford EnglandTotal number of investigators: 2Observing Summary: Configuration,mode,aperture TotalTarget RA DEC V spectral elements orbits FlagsEUROPA 6 NICMOS/NIC1MULTIACCUMF110M,F140W5EUROPA 6 NICMOS/NIC3MULTIACCUMF200N,G096,G141,G2069Grand total orbit request 142Ms. Tiffany KatariaEuropa: continuing the search for liquid waterScientific JustificationEuropa is the sixth nearest and fourth largest satellite of Jupiter, slightly smaller than theEarth’s moon, with a mean density of 3.03 g/cm3. Europa is primarily composed of silicaterock, and has a thin outer layer of ice. Much has been learned about the surface of Europafrom images taken by the Galileo spacecraft, namely the existence of cryovolcanic geysersand ice volcanoes. These features suggest the existence of liquid water underneath the ice.Such a theory could be strengthened with the presence of sulfates, magnesium sulfates inparticular, which need oxidizing conditions to form.This proposed project aims to verify the existence of liquid water on Europa by analyzingits spectra, namely the spectral features in water ice. Water ice has a specific spectralsignature in the infrared, identified on Europa by the Near Infrared Mapping Spectrometer(1 ). This signature contains absorption bands centered near 1.04, 1.25, 1.5 and 2 microns,a weak temperature sensitive ice band at 1.65 microns on the edge of the 1.5 micron band,and fundamental O-H stretching transition near 3 microns (1 ).NICMOS is the ideal instrument to use because of its high sensitivity from 1.1 to 2microns. Because HST is located above Earth’s atmosphere, terrestrial effects on backgroundare removed.NICMOS utilizes three grisms for spectroscopy. A grism is a cross between a prismand a grating, designed to allow only a certain wavelength to pass undetected through thegrism (3 ). However, grisms are slitless, so images can overlap and spectra of spatiallyresolved targets can be confused. Therefore, it is necessary to image Europa using a filter, inaddition to the grism spectroscopy, to locate Europa and its spectral features more clearly.The three grisms present on NICMOS/NIC3 range from 0.8-1.2 microns, 1.1-1.9 microns,and 1.4-2.5 microns. Given the spectral features present in water ice, it is necessary to obtainspectra using all three grisms. For imaging Europa, the filters utilized on NICMOS/NIC1and NIC3 are F110M, with a wavelength range of 0.8-1.4 microns; F140W, with a range of1.0-1.8 microns, and F200N, with a range of 1.986-2.007 microns.NICMOS has a strong resolving power of about 200 per pixel in each grism over thefull field of view (3 ). According to the HST instrument manual for NICMOS, the mainsources of background above the atmosphere are zodiacal light at wavelengths shorter than1.6 microns and thermal background emission at wavelengths greater than 1.6 microns. Toaccount for this background, the filters are centered at 1.6 microns, where both sources areat a minimum. Dithering is necessary only for F200N, because its central wavelength islarger than 1.6 microns and therefore thermal background is a factor.Overall, HST is the ideal telescope to use for this project due to its lack of atmosphericseeing. The high sensitivity and correction for background of NICMOS in the infrared allowsfor deep photometry.References1. Dalton et al. Spectral comparison of heavily hydrated salts with disrupted terrains onEuropa. Icarus, 2005.3Ms. Tiffany KatariaEuropa: continuing the search for liquid water2. McCord et al. Salts on Europa’s Surface Detected by Galileo’s Near Infrared MappingSpectrometer. 2007.3. STScI. Near Infrared Camera and Multi-Object Spectrometer Instrument Handbook forCycle 16. 2006.Description of the ObservationsEach exposure will have an exposure time of 7000 seconds, based on the NICMOS exposuretime calculator, and exposure times in other documenation (1 ). In calculating orbits, Iaccount for 6 minutes to acquire the target, 19 seconds setup time, and 15 second overheardfor each filter change (NIC1 has 1 change, and NIC3 has 3). Futhermore, I account 4 secondsfor each MULTIACCUM, 580 seconds for changing cameras from NIC1 to NIC3 (as statedin Two-Gyro Mode Handbook), and dithering of about 13 seconds for the last grism, whichhas a wavelength longer than 1.7 microns, where thermal background is a factor. Lastly, Iaccount for the fact that only 52 minutes of the 96 minute orbit is available, because it is amoving target.In doing those calculations, I determine the number of orbits for NIC1 to be 5, whileNIC3 has 9 orbits, for a total of 14 orbits.References1. Hall, et al. The far-ultraviolet oxygen airglow of Europa and Ganymede.The AstrophysicalJournal,