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If you’re a kid interested in astronomy, as I was, there are few thrills to compare with your first view of the rings of Saturn. So you can imagine how excited astronomers (and ex-kids like myself) are with the imminent arrival of the International Cassini-Huygens Mission at Saturn.

The $3 billion space probe, launched October 15, 1997, is scheduled to enter orbit around Saturn on June 30. The maneuver place it there promises to be nailbitingly tense. Cassini will fire its main engine for 96 minutes to reduce its speed enough for it to be captured by Saturn’s gravity. As it enters orbit, it will pass right through one of the gaps in Saturn’s rings. It will then begin the first of 76 planned orbits (over four years) which will take it close to the planet and to 52 encounters with seven of Saturn’s 31 known moons (13 of which have been discovered since Cassini launched!).

Cassini has a backup engine in case the main engine fails, and the best Earth-based and space-based telescopes have scoured its route for hazards. However, since even particles too small to be seen from Earth could be fatal, Cassini will be turned so that its large high-gain antenna acts as a meteor shield.

Cassini is 6.7 meters long, four meters wide, and masses around one metric tonne. Its 12 scientific instruments include a variety of spectrometers for determining the chemical makeup of Saturn’s atmosphere, rings and moons; devices for measuring the planet’s magnetic field; a cosmic dust analyzer and an imaging radar.

Riding piggyback is the 2.7-metre-diameter, 320-kilogram wok-shaped Huygens probe. On Christmas Eve (our time), it will be released. For 20 days it will fall toward Titan, Saturn’s largest moon. On January 14, 2005, it will enter the moon’s dense atmosphere (1.5 times as dense as Earth’s), deploy parachutes, and begin 2.5 hours of intensive scientific observations as it drifts down toward the surface. Among other things, it will analyze the chemical makeup of the atmosphere at various altitudes, take pictures of cloud formations and the surface, and possibly even send a few minutes of data after it lands (or splashes) on the surface. The data will be relayed to Earth via Cassini.

Cassini was built by the Jet Propulsion Laboratory in the U.S.; Huygens is a project of the European Space Agency. In all, 260 scientists from 18 different nations worked on the project. Cassini is named after the Italian-French astronomer Jean Dominique Cassini, who in 1675 discovered that Saturn’s rings are split largely into two parts by a narrow gap–now known as the “Cassini Division.” He also discovered several of Saturn’s major moons. Hugyens is named after Dutch scientist Christiaan Huygens, who discovered Titan and, in 1659, determined that what Galileo had perceived as mysterious waxing-and-waning “arms” around Saturn was, in fact, a thin, flat ring.

Why study the Saturn system? There are many reasons, starting with those famous rings. Although Jupiter, Uranus and Neptune also have rings, Saturn’s are unique in their extent and brightness. They’ve served as a physical model for the disc of gas and dust that scientists believed surrounded the early Sun and from which the planets formed. By learning more about Saturn’s system of rings and moons, we can therefore learn more about the earliest history of our solar system and others.

As well, represented among Saturn’s moons are a remarkable variety of chemical, geologic and atmospheric processes; learning more about them may shed valuable light on the evolution planets everywhere.

Of all of Saturn’s moons, the most intriguing is Titan. It’s the only moon in the solar system with a dense atmosphere. Not only that, its atmosphere is rich in the carbon-based compounds–especially methane–on which living organisms are based. Its atmosphere may, in fact, be very similar to the early Earth’s atmosphere, the so-called “primeval soup” in which scientists believe life first appeared through the combining of complex carbon compounds. By studying its atmosphere, then, we may learn not only about Titan’s present, but Earth’s past.

Cassini will execute 45 flybys of Titan, coming as close as 950 kilometres, using its imaging radar to conduct high-resolution mapping of the surface through the methane haze.

Over the next few months we’ll learn more about Saturn and its moons than the original Cassini and Huygens could ever possibly have dreamed of.

And I’m just as excited about it as I was to see that tiny ringed disk in my little telescope 30-plus years ago.

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