The Cassini Mission to Saturn

What Has Cassini Found at Saturn?

Cassini mission to saturn
What Cassini will see as it makes its final orbits around Saturn in late 2017. NASA

The planet Saturn is the epitome of an alien-looking place, an alien-looking world with a set of glittering rings. It's also one of the first sky objects people want to see through a telescope. Through a small telescope, it looks rather like it has a pair of handles or "ears" on either side. Larger telescopes reveal more details, plus the existence of a number of moons.

Would you like to go to Saturn? It's an enticing thought, although human missions to the planet probably won't happen for decades. But, we have visited the planet via robotic explorers for many years and with telescopes ever since the first ones were built.

Since 2004, Saturn has been entertaining an earthly visitor — a spacecraft called Cassini. The mission was named after the 18th-century Italian mathematician Giovanni Domenico Cassini. He discovered four of Saturn's larger moons and was the first to notice a gap in the Saturnian rings, which is named the Cassini Division in his honor. 

Let's take an "executive summary" look at what the mission named for Cassini has found, so far.

The Cassini Mission

Missions to Saturn are few and far between. That's because the planet is so far away that it takes years for a spacecraft to get there. Also, the planet orbits in a very different "regime" of the solar system — a much colder one than near Earth. A spacecraft needs to be built for the long haul, with specially hardened electronics that are both lightweight and reliable for long-term studies. The Cassini craft carried cameras, specialized instruments to study surfaces and atmospheric chemistry of the Saturnian system, a power source, and communications facilities that relay data back to Earth. It was launched in 1997 and arrived at Saturn in 2004. For 13 years, it sent back a treasury of data about Saturn itself, its moons, and those gorgeous rings.

The Cassini mission is not the first spacecraft to visit Saturn. The Pioneer 11 spacecraft swept past the planet on September 1, 1979 (after a six-year journey out from Earth and a flyby of Jupiter), followed by Voyager 1 and Voyager  2 in 1980 and 1981, respectively. Cassini is the first multi-national mission to arrive at and study the ringed planet. Scientists and technicians from the USA and Europe worked together to build, launch, and do the science connected to the mission.

Cassini Science Highlights

So, what was Cassini sent to do at Saturn? As it turns out — a lot! Before any spacecraft arrived at Saturn, we knew the planet had moons and rings and an atmosphere. When the spacecraft arrived, it began an in-depth, up-close study of all the worlds plus the rings. The moons held the most promise of new finds, and they didn't disappoint. The spacecraft dropped a probe to the surface of Titan (the largest moon of Saturn). That Huygens probe studied the thick smoggy Titanian atmosphere on the way down and charted lakes, underground rivers, and many "landforms" on the icy surface. From the data Cassini returned, scientists now look at Titan as an example of what early Earth and its atmosphere may have been like. The big question: "Could Titan support life?" has not yet been answered. But, it's not so far-fetched as we might think. There's no reason that life forms that love cold, rainy, methane- and nitrogen-rich worlds couldn't be living happily somewhere on Titan. That being said, there's no evidence FOR such life...yet.

Enceladus: a Water World

The icy world Enceladus has also provided many surprises for planetary scientists. It is spraying water ice particles out from beneath its surface, which indicates the existence of an ocean beneath the craggy, icy surface. During one especially close flyby, the Cassini came within 25 kilometers (about 15 miles) from Enceladus's surface. 

As with Titan, the big question about life can also be asked: does this moon have any? Certainly, the conditions are right — there are water and warmth beneath the surface, and there is like something for the life to "eat", too. However, nothing leaped out at the mission's cameras, so that question will have to remain unanswered for now.

Peering at Saturn and Its Rings

The mission spent considerable time studying Saturn's clouds and stormy atmosphere. Saturn's a stormy place, with lightning in its clouds, auroral displays over its poles (although they're only visible in ultraviolet light), and a mysterious hexagonal-shaped vortex that swirls around over its north pole.

Of course, no spacecraft mission to Saturn would be complete without a look at those rings. While Saturn isn't the only place with rings, its system is the first and most massive that we've seen. Astronomers suspected that they were made mostly of water ice particles and dust, and Cassini instruments confirmed that. The particles range in size from tiny specks of sand and dust to worldlets the size of mountains here on Earth. The rings are divided into ring regions, with the A and B rings the largest. The larger gaps between rings are where moons orbit. The E-ring is made up of ice particles that spew out from Enceladus.

What Happens to Cassini Next?

The Cassini mission was originally slated to explore the system for four years. However, it was extended twice. Its final orbits took it over Saturn's north pole and then past Titan for a final gravity boost toward the planet. On September 15th, it plunged into the cloud decks of Saturn as it sent its last measurements of the upper atmosphere. Its final signals were received at 4:55 a.m. Pacific Daylight Time. This ending was planned by controllers as the spacecraft ran low on maneuvering fuel. Without an ability to correct its orbit, it was likely Cassini could collide with Enceladus or Titan, and possibly contaminate these worlds. Since Enceladus, in particular, is considered a possible abode for life, it was considered safer to have the spacecraft descend into the planet and avoid any future collisions.

The Cassini mission legacy will continue for years, as its teams of talented scientists study the data it returned. From its massive treasury of information they, and we, will eventually understand more about the most beautiful ringed planet in the solar system.