A closer look at Saturn

The Cassini space probe's final plunge

Created date

July 28th, 2017
This artist’s concept shows an over-the-shoulder view of Cassini making one of its "Grand Finale" dives over Saturn.

This artist’s concept shows an over-the-shoulder view of Cassini making one of its "Grand Finale" dives over Saturn.

In the early-morning hours of October 15, 1997, a brilliant streak blazed across the sky above Florida’s Cape Canaveral Air Station. Aboard the Titan IVB/Centaur rocket was a historic payload: NASA’s Cassini orbiter and the Huygens atmospheric entry probe.

It was the start of an incredible journey. Making two swingbys of Venus and one of Earth to gain velocity, Cassini began its trip to the planet Saturn.

After seven years and some 840 million miles, the orbiter and its probe arrived at their destination. 

For nearly a decade and a half, it has given scientists at NASA’s Jet Propulsion Laboratory an unprecedented look at this ringed giant. But this year marks the end of Cassini’s mission. 

On September 15, 2017, it will make a final plunge into Saturn’s inhospitable atmosphere, breaking up and effectively becoming part of the planet itself. For those who want to follow the final stages of this “Grand Finale,” as NASA is calling it, here’s the background information you need to know.

Cassini’s mission and its journey

Cassini’s general objective is to explore Saturn, its rings, and its moons. The goal is to help scientists better understand the conditions in these various locations, the chemical composition of their environs, and to determine whether there’s a probability that life exists on any of them.

To accomplish this, Cassini had to cover an enormous distance. So the brains at NASA utilized the gravitational pull of Venus and Earth to essentially slingshot the Saturn-bound orbiter onto the proper course with enough speed to get there.

Between April 1998 and August 1999, Cassini made two orbital passes of Venus and one of Earth, collecting data in the process. From here, it was on to Saturn, but not before doing a flyby of Jupiter on December 30, 2000 (at this point, 478 million miles from Earth).

Exploration of Saturn’s moons

On July 1, 2004, Cassini inserted itself into Saturn’s orbit.

It has since provided NASA with an uncommonly close look at the planet and its moons. Even prior to this, the spacecraft made discoveries. 

On May 31, 2004, Cassini uncovered two previously unknown moons orbiting Saturn. Very small, Methone and Pallene are two and three miles in diameter respectively; their discovery brought Saturn’s total known moons to 60.

Then, there’s its biggest moon, Titan. In January 2005, Cassini’s passenger, the Huygens probe, landed there after a two-and-a-half-hour descent. 

To date, it is the first and only landing on a planetary body in the outer solar system. Here Cassini and its probe confirmed the existence of Titan’s several dozen lakes and seas of liquid methane and ethane ranging in size from three-quarters of a mile to 20 miles. 

Meanwhile, on another of Saturn’s moons, Enceladus, Cassini’s detection of ammonia strongly suggests the presence of liquid water—a necessary ingredient for life.

Cassini and Saturn

When it comes to Saturn, Cassini has its work cut out for it. It’s a violent place to go.

Saturn’s atmosphere is 75% hydrogen and 25% helium, along with minor quantities of methane and water ice. It has winds upwards of 1,118 mph, storms that extend as far as 9,000 miles longitudinally, and a visible orange-hued sulfuric cloud deck, beneath which temperatures can drop to -94 degrees Fahrenheit. 

Consequently, Cassini has been unable to actually enter Saturn’s inner environment, at least, for now.

The ‘Grand Finale’

In November 2016, Cassini started the first of 22 highly inclined orbits that will take the spacecraft above Saturn’s poles, gradually winding it into the planet’s interior. 

As it does so, it will pass through the famed rings, which are made of ice, rock, and debris from passing comets and the surrounding moons. During its 22 orbits, Cassini will collect data and return images.

The completion of its final pass, scheduled for September 15, will result in the spacecraft’s self-destruction.

As it plunges into the brutal conditions of Saturn’s interior, battling heavy winds, noxious gases, and crushing pressure, it will struggle to point its antennae toward Earth, sending its final communications and, hopefully, the best data yet on Saturn’s environs.

No one knows for sure what the spacecraft will tell us while it descends along its final glide path. But one thing is certain—Cassini will go down in history. 

To follow the countdown, please visit goo.gl/3Zwj37.