So fall Saturn’s falls

An artist's interpretation of the Cassini spacecraft maneuvering close enough to graze Saturn's rings.
An artist's interpretation of the Cassini spacecraft maneuvering close enough to graze Saturn's rings.
An artist’s interpretation of the Cassini spacecraft maneuvering close enough to graze Saturn’s rings.

By Graham Richard —

Twenty years ago a team of Earthlings launched the spacecraft Cassini to explore interplanetary space and learn more about our celestial cousins. The elephant-sized craft used home planet Earth and harbinger Venus as slingshots, plunging into their gravity and exiting again to fling itself on a seven-year voyage past Jupiter to Saturn.

The probe is equipped with a complex of robotic eyes and antennae, including a ‘plasma spectrometer’, and a ‘synthetic aperture radar mapper’. A long, yellow magnetometer sniffs out magnetic mysteries and a high-gain radio antenna dish acts as a giant ear to hear Cassini’s earth-bound pilots.

During its 12-year tenure circling Saturn the little, drifting elephant spied out some 20 targets at close-quarters. It has witnessed occult wonders like the hundred geysers that cast ammonium-laden water into space from the icy moon Enceladus, creating a massive and diffuse plume that hangs in a ring 238,000 km above the gas giant. Below this, the hydrogen planet’s more brilliant rings of water-ice fall eternally starting at a height of 139,500 km. These ‘falls’ are suspended between Saturn’s gravity and the resonant alignment of its 62 known moons.

In November 2016, Cassini began a series of plunges, grazing the outermost of Saturn’s rings. This thin strand of icebergs formed when Saturn’s moons Prometheus and Pandora collided. As Prometheus travels, it shepherds the peripheral ring of scattered ice into a delicate halo that encompasses the massive planet below. With each revolution the crater-strewn moon reclaims pieces as debris falls out of the ring and into its gravity.

In April 2017, Cassini will skip inward, swooping through the 2,400-kilometer gap between Saturn’s highest clouds and its innermost ring. Throughout 22 consecutive orbits it will uncover the first secrets of its mission, closely studying the silent rings above and the endless tempests below. On its twenty-third lap, having finally spent its fuel supply, the dutiful explorer will plunge into the Jovian giant’s frozen equator in September 2017. Winds reaching 1,800 kilometres per hour will tear the 20-year space craft to shreds. After tumbling 50,000 kilometres the celestial servant’s mangled appendages will fall into the storm-ridden glaciers of Saturn’s earth-sized core, never to rise again.

The spacecraft was named after French astronomer Giovanni Domenico Cassini (1652-1712) who discovered the gap in Saturn’s rings known as Cassini’s division.

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