Cassini Enters the Final Plunge

The time is coming when we will all say goodbye to Cassini, the spacecraft exploring Saturn since it first turned its cameras to stare at the planet in 2002. It began its Grand Finale activities some months ago with final orbits, final images, and other “last” looks at the Saturn system. The last pass around the moon Titan is done. The spacecraft got a gravitational kick from that loop that sends it right into Saturn’s northern hemisphere clouds on Friday. The last command sequences are sent. All controllers can do now is wait, monitor transmissions coming back from Cassini, and make any last-minute changes as necessary.

Cassini Opened New Windows on Saturn

As I look over the many, many images and other data reports from the mission, it’s hard to select a “favorite” result. It continues to show us way more than simply a ringed planet with a bunch of moons and some gorgeous rings. Granted, we are used to seeing great images of the system from the Voyager spacecraft in the 1980s. But, Cassini did it in high-res for years.

One of the great truisms about planetary science tells us that while it’s good to take snapshots of a target, it’s even better to study how that target changes over time. It’s the difference between taking a baby picture of someone and having a series of pictures taken during their lifetimes. You get to see how they grow and change.  Cassini opened windows of opportunity to watch the Saturn system change over time — from its storms and cloud belts and zones to activities on some of its moons and within its rings.

Encountering Enceladus

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A 14-hour image sequence of Enceladus made by Cassini shows plumes spewing ice crystals out to space. Courtesy NASA/Cassini Mission.

Still, if I had to select just one result that’s really important, I’d go with the discovery and long-term study of the moon Enceladus and its jets. Those geysers spew out to space and create the E ring. Their ice particles told scientists about the ocean hidden beneath the icy crust of that little moon. The fact that there’s an ocean there at all is a major surprise. The finding that it’s salty and “warm” (i.e. not frozen) indicates conditions could be hospitable to life.

Now, to be clear, life hasn’t been discovered there. But, the conditions exist. For a world that far from the Sun’s heat, that’s a tantalizing finding. It rewrites what we know about frozen worlds in the outer solar system.

After Cassini, What Happens?

Saturn propellor
A “propeller” of ring material swirling around a tiny moonlet near the Encke Gap in Saturn’s rings. This one is named “Earhart” after Amelia Earhart, a famous aviator in the early 20th century. Courtesy Cassini mission.

The Enceladus discoveries are enough to start people looking at future missions to Saturn. Those will follow up on Cassini’s accomplishments. While we’re thinking about sending more spacecraft to Saturn, it wouldn’t be a bad idea to check out Titan again. That world was another surprise, with its frigidly weird landscapes and lakes. The rings could use some more study, too. Those tiny little ‘propellers’ that interact with ring particles in an intricate dance are intriguing.

Both worlds merit closer looks and in-depth surveys, if not landers. It may be many years before those missions happen. NASA might not be leading those missions. Perhaps other countries will see what the international Cassini team has achieved and will launch probes to these worlds. However we get back to this system (and who ever does it next), Cassini made it possible.

Follow the final few days of Cassini’s historic mission as it sails into the clouds. NASA’s Cassini link is your best source of info.

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