An amazing mission of discovery is scheduled to enter its final phase tomorrow. Cassini, which has been orbiting the giant planet Saturn since 2004, will change its flight path. The new course will take the craft between Saturn’s cloudtops and the inner edge of its beautiful rings.

Cassini has studied the rings in great detail during its journey. It’s found that the system consists of hundreds or thousands of individual rings. Most of the particles in the rings are made of ice, with a smattering of rock and dust.

Cassini has also discovered many small “moonlets” in the gaps between rings. These bodies are like shepherds tending their flocks; their gravity keeps the ring particles in their proper place.

The innermost ring is fairly thin and faint. Its inner edge reaches to within just a few thousand miles of Saturn itself. Bits of material from this ring probably drop into Saturn’s atmosphere, where they burn up as meteors.

To protect itself against possible impact, Cassini will use its large radio dish as a shield as it plunges through the plane of the rings. That should keep its instruments and electronics safe.

Tomorrow, Cassini will fly close to Titan, Saturn’s biggest moon. That’ll change Cassini’s path, setting up its first loop inside the rings next week. It’ll make 21 more passages over the next five months, leading up to its final act in September: a fatal dive into Saturn’s atmosphere, bringing its mission to an end.

Script by Damond Benningfield