The Cassini Ultraviolet Imaging Spectrograph Investigation

Abstract

The Cassini Ultraviolet Imaging Spectrograph (UVIS) is part of the remote sensing payload of the Cassini orbiter spacecraft. UVIS has two spectrographic channels that provide images and spectra covering the ranges from 56 to 118 nm and 110 to 190 nm. A third optical path with a solar blind CsI photocathode is used for high signal-to-noise-ratio stellar occultations by rings and atmospheres. A separate Hydrogen Deuterium Absorption Cell measures the relative abundance of deuterium and hydrogen from their Lyman-α emission. The UVIS science objectives include investigation of the chemistry, aerosols, clouds, and energy balance of the Titan and Saturn atmospheres; neutrals in the Saturn magnetosphere; the deuterium-to-hydrogen (D/H) ratio for Titan and Saturn; icy satellite surface properties; and the structure and evolution of Saturn's rings.

ABSORPTION CROSS SECTION OF GASEOUS ACETYLENE AT 85 K IN THE WAVELENGTH RANGE 110-155 nm

“…Spectral observation in the VUV range is effective for the identification and determination of abundances of hydrocarbon species in space; VUV spectra thus provide a powerful means that has been applied during spacecraft missions (Broadfoot et al 1977;Esposito et al 2004;Ajello et al 2005;Yoshioka et al 2010). As part of the NASA Cassini-Huygens Mission, for example, the Cassini Ultraviolet Imaging Spectrograph (UVIS) included channels for extreme-ultraviolet (EUV) and far-ultraviolet (FUV) spectral imaging (Esposito et al 2004) to record VUV spectra of targets in the exploration of the Saturn system Shemansky et al 2005).…”

“…As part of the NASA Cassini-Huygens Mission, for example, the Cassini Ultraviolet Imaging Spectrograph (UVIS) included channels for extreme-ultraviolet (EUV) and far-ultraviolet (FUV) spectral imaging (Esposito et al 2004) to record VUV spectra of targets in the exploration of the Saturn system Shemansky et al 2005). During the Titan flyby on 2004 December 13, the UVIS detected six compounds-CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , HCN, and C 4 H 2 -in the atmosphere of Titan (Shemansky et al 2005) through their absorption of light from two stars; these observations covered an unprecedented range from 450 to 1600 km of altitude above the surface.…”

Remote sensing of the Io torus plasma ribbon using natural radio occultation of the Jovian radio emissions

“…The origins of these variations were attributed to changes in Io's volcanic activity. A detailed analysis of such short-term variations associated with the Io torus was performed by the Ultraviolet Imaging Spectrograph, UVIS (Esposito et al, 2004), onboard the Cassini spacecraft, from October 2000 to March 2001. The broad spectral range, high spectral resolution (compared to Voyager), and temporal coverage of the UVIS experiment resulted in the creation of a unique and rich data set of the Io plasma torus in the ultraviolet.…”

The surface composition of Enceladus: clues from the Ultraviolet

“…Toward shorter UV wavelengths, the spectrum of Enceladus has not been previously studied. Here we investigate the reflectance spectrum of Enceladus as measured by the Cassini Ultraviolet Imaging Spectrograph (UVIS) (Esposito et al 2004 of the Enceladus disk during this observation was 0.8 mrad; the size of a UVIS pixel during this observation was 1.0 × 1.5 mrad, so Enceladus was sub-pixel in size and UVIS measured a disk-average spectrum. We calculate the disk-average reflectance by taking into account the size of the body in the UVIS slit and dividing by the solar spectrum as measured by SORCE SOLSTICE (McClintock et al 2000), scaled to 9.2 AU, Enceladus' heliocentric distance on the day of the observation.…”