Icy Satellites of the Saturnian System, University College London, 29-30 June 2009
by Anne Verbiscer
Geraint Jones, UCL
Fun with Saturn Images
Following the Cassini Project Science Group meeting in London last month, several icy satellite scientists met for two days to discuss their recent results and plan for future observations. Carly Howett presented Cassini Composite Infrared Spectrometer (CIRS) measurements of the thermal emission from Enceladus obtained during close flybys in March and October of 2008 when the spacecraft flew within 300 and 450 km respectively of the moon's south polar terrain. She has examined data obtained at the highest spatial resolution ever recorded from CIRS' Focal Plane 1 (FP1) instrument, which detects radiation at wavelengths between 17 microns and 1 millimeter, in the far-infrared region of the electromagnetic spectrum. FP1 has a circular field of view, or footprint, and in the figure below, numerous FP1 footprints are shown with colors corresponding to the relative emission detected, with purple representing the temperature of a surface heated only by incident sunlight and yellow indicating higher temperatures. Her results, summarized in the figure below, show that endogenic emission, or warmth emerging from beneath the surface of Enceladus, is not restricted to the tiger stripes themselves, but is also observed in the regions between them. The region between Damascus and Baghdad sucli is much warmer (light blue/green) than the region to the left of Damascus (darker blue). Similarly, the region between Baghdad and Cairo is also warm. Jet source locations (black squares) identified by Cassini's Imaging Science Subsystem (ISS) do not necessarily correspond to the warmest regions; however, only a few jets lie within the areas observed by CIRS' FP1.
CIRS Detects Warm Emissions
ndogenic emissions across Enceladus' tiger stripe region determined from Cassini's Composite Infrared Spectrometer (CIRS). Purple indicates regions with temperatures no higher than that found on a surface heated only by incident sunlight, while light blue to yellow indicates regions of higher temperatures, presumably due to geologic activity. Black squares show the locations of jets identified by Cassini's Imaging Science Subsystem (ISS).
t will be interesting to compare these measurements with those obtained later this year in November when Cassini will make its next close flybys of Enceladus. CIRS, along with the rest of Cassini's optical remote sensing instruments, will be aimed at the south pole during closest approach in one of these. (The other flyby includes a deep plume passage at closest approach when the in-situ instruments will be aimed at the plumes.) With equinox approaching next month on August 11, by November, the south polar region will be slipping into darkness.
How will the diminishing sunlight affect the observed endogenic emission? Fortunately, we have less than six months to wait for the next close-up views of this geologically active corner of the Solar System.
Anne Verbiscer is a Research Associate Professor at the University of Virginia. She studies the surfaces of icy bodies in the outer Solar System and has been involved with the Cassini mission to Saturn since 2007. Currently a visitor at Southwest Research Institute, she has been enjoying the past year living in the mountains above Boulder, Colorado.