The Grand Finale

Cassini's closest approach to Titan technically occurs Saturday, April 22 at 2:08 a.m. EDT (6:08 UTC). At that time, the probe's altitude will be about 1,000 kilometers—a little more than double the height of the International Space Station.

Cassini will spend its final close flyby scanning Titan's methane lakes, focusing in particular on the "magic island" feature that has changed shape over the course of multiple observations. The spacecraft will also make some new lake depth measurements.

The first ring crossing will occur three days later, on April 26. NASA is dubbing this phase of the mission the Grand Finale—with good reason.

"I wouldn't be a bit surprised if some of the discoveries we make with Cassini might be the very best of the mission," said Linda Spilker, the mission's project scientist.

The ring crossings will provide wild, closeup imagery of Saturn's clouds and rings from never-before-seen angles. Cassini may be able to see ring pieces as small as a kilometer across. Instruments on board the spacecraft will reveal new insights about the planetary system, including the mass of the rings.

An accurate mass reading could help scientists solve a long-standing puzzle: How old are the rings, and where did they come from?

"If the rings are a lot more massive than we expect, perhaps the rings are old—maybe as old as Saturn itself," Spilker said. "On the other hand," she said, "If the rings are less massive, perhaps they're very young—maybe forming as little as a hundred million years ago. Maybe a moon or a comet got too close, and got torn apart by Saturn's gravity."