Cassini–Huygens is a robotic spacecraft mission currently studying the planet Saturn and its satellites, a system 10 times further away from Earth than the sun. A joint effort by NASA, the European Space Agency and the Agenzia Spaziale Italiana, the spacecraft consists of two main elements – the NASA-designed and constructed Cassini orbiter, and the ESA-developed Huygens probe.

Launched on 15 October 1997, it reached its destination seven years later, becoming the first probe to enter into Saturn’s orbit on 01 July 2004. Equipped with a high-resolution imaging system, including wide and narrow-angle cameras, the probe is packed with complex instrumentation, designed to measure dust particles, energy fields and the like, and map the planet’s surface, sending its information back to Earth for analysis.

The Cassini Imaging Central Laboratory for Operations – better known as CICLOPS – in Colorado handles the information from the imaging system, and is therefore often the first to detect phenomena that can be seen in visible or near-infra-red light.

The Cassini Imaging Science System (ISS) was specifically designed for exploring the Saturn system, including spectral filters and imaging capabilities for a multitude of scientific objectives.

These include capturing lightning, investigating the three-dimensional cloud structure and meteorology of the Saturn and Titan atmospheres, imaging the surfaces of Saturn’s many icy satellites, determining the composition and structure of its enormous ring system, and peering through the hazy Titan atmosphere down to its still unexplored surface.

The ISS consists of two framing cameras. The narrow-angle camera is a reflecting telescope with a focal length of 2000mm and a field of view of 0.35°, while the wide-angle camera is a refractor with a focal length of 200mm and a field of view of 3.5°.

Each is outfitted with a large number of spectral filters that, taken together, span the electromagnetic spectrum from 2000 Angstroms to 1.1 microns. At the heart of each camera is a CCD detector consisting of a 1024 square array of pixels.

Using this, the CICLOPS team has made a number of important discoveries, including seven previously unknown moons of Saturn, plus it found a plume of icy particles coming off the surface of Enceladus, from which they deduced that there might be pockets of liquid water beneath the surface.

This led to several excitable reports that there might be life on Enceladus, which the director of CICLOPS, Carolyn Porco, still hasn’t ruled out. “I consider the discovery of the jets of Enceladus and the possible habitable environment under its south pole to be our biggest discovery to date,” she says.

Investigating space from an imaging system in orbit around Saturn gives CICLOPS more information than it would be able to get from Earth-based telescopes, says Porco, but it does create a problem – how to get the information back.

The answer is that the imaging data is encoded on the spacecraft’s telemetry signals to Earth. The imaging data is then stripped off the telemetry stream, and is then arrayed into two dimensions to make an image. Those images are then sent to CICLOPS and the rest of the imaging team for analysis.

“Part of the process is taking the numerical value assigned to each pixel in the image and turning it into an absolute measure of the brightness of the target at that location, in a process called ‘calibration’,” says Porco.

Specially selected and processed images are made available to the public via the CICLOPS website, but all the images are used for scientific analysis by the mission’s imaging scientists.

In the future, Porco hopes to see how the Saturn system changes over time, such as how the atmosphere of Saturn differs over the seasons and how the cloud cover and distribution of lakes on the surface of Titan shift. As such, they’re building up our knowledge of the universe but, says Porco, they’re also building up our understanding of Earth.

“Through our imagery, we have now become intimately familiar with a distant planetary system and we are gaining precious insights into planetary processes that are, or have been, important on our planet,” she says. “This is critically important. We live on a planet, and we must fully understand the processes that make it work, so we can be proper custodians of it.”