Cassini Imaging Science: Instrument Characteristics And Anticipated Scientific Investigations At Saturn

Abstract

The Cassini Imaging Science Subsystem (ISS) is the highest-resolution two-dimensional imaging device on the Cassini Orbiter and has been designed for investigations of the bodies and phenomena found within the Saturnian planetary system. It consists of two framing cameras: a narrow angle, reflecting telescope with a 2-m focal length and a square field of view (FOV) 0.35 • across, and a wide-angle refractor with a 0.2-m focal length and a FOV 3.5 • across. At the heart of each camera is a charged coupled device (CCD) detector consisting of a 1024 square array of pixels, each 12 µ on a side. The data system allows many options for data collection, including choices for on-chip summing, rapid imaging and data compression. Each camera is outfitted with a large number of spectral filters which, taken together, span the electromagnetic spectrum from 200 to 1100 nm. These were chosen to address a multitude of Saturn-system scientific objectives: sounding the three-dimensional cloud structure and meteorology of the Saturn and Titan atmospheres, capturing lightning on both bodies, imaging the surfaces of Saturn's many icy satellites, determining the structure of its enormous ring system, searching for previously undiscovered Saturnian moons (within and exterior to the rings), peering through the hazy Titan atmosphere to its yet-unexplored surface, and in general searching for temporal variability throughout the system on a variety of time scales. The ISS is also the optical navigation instrument for the Cassini mission. We describe here the capabilities and characteristics of the Cassini ISS, determined from both ground calibration data and in-flight data taken during cruise, and the Saturn-system investigations that will be conducted with it. At the time of writing, Cassini is approaching Saturn and the images returned to Earth thus far are both breathtaking and promising. r forty-five (45) close 'targeted' flybys of Titan (40 of which approach within 2500 km of the surface, and 24 of these within 1000 km of the surface); r very close 'targeted' flybys of Enceladus (4) (Figure 3), Dione, Rhea, Iapetus, and Hyperion, all approaching within ∼1500 km of the surface; r thirty-one (31) non-targeted but still close (within 100,000 km of the surface) flybys of Iapetus and the five major icy satellites Mimas, Enceladus, Tethys, Dione and Rhea;

Saturn’s G and D Rings Provide Nearly Complete Measured Scattering Phase Functions of Nearby Debris Disks

“…Both of these cameras have multiple filters, but for the purposes of this analysis we only considered images obtained through the clear filters or the RED filter on the WAC. Note that the effective wavelength of the RED filter (647 nm) is close to the effective wavelengths of the NAC and WAC clear filters (651 nm and 634 nm, respectively, Porco et al 2004). Thus the measured brightness through these different filters should be insensitive to the rings' spectral slopes.…”

Reflected Light Curves, Spherical and Bond Albedos of Jupiter- And Saturn-Like Exoplanets*

“…The ultraviolet channel is sensitive to the upper haze layer and Rayleigh scattering. The filter details can be found in Figure 2(g) and in Porco et al (2004), Zhang et al (2013). The data points are available in digital form as supplementary online material.…”

Dynamics of Saturn's South Polar Vortex

“…The peak zonal velocityū was (5). An image at 889 nm, where methane gas is a strong absorber, is projected onto the blue plane.…”