Cassini’s Close-Up of Saturn

The name Cassini has come to be associated with the sixth planet in our solar system, Saturn. The Cassini spacecraft—named for Jean-Domenique Cassini, who discovered some of Saturn’s many moons as well as a notable gap in the rings that also bears his name—took 7 years to journey from the Earth to Saturn and traveled 4.9 billion miles over the course of its 20 year mission. By the time it purposely crashed into the gaseous planet in 2017, Cassini had orbited the planet 294 times in the pursuit of knowledge about the giant planet and its wondrous rings.

Saturn is a gas giant comprised mostly of hydrogen. It is the second largest planet in the solar system after Jupiter, has 62 moons, and is famously adorned with the most visually spectacular ring system in our celestial neighborhood. Saturn orbits the sun at about 10 times the distance from the Sun to the Earth, and it is the farthest planet from Earth that can be seen with the naked eye.

Cassini, in its 13 years orbiting the planet, taught humanity more about Saturn than we’d learned in the previous 400 years since its first telescopic observation in 1610. Its Huygens probe was the first to land in the outer solar system (on Saturn’s moon Titan), and the first to sample an extraterrestrial ocean. Titan—one of the largest moons in the solar system—was revealed to be one of the most Earth-like bodies we have encountered; it has its own substantial atmosphere, and even has lakes, rivers, and oceans of liquid methane.

In addition, Cassini’s observations of the moon Enceladus helped to pave the way for future missions to the outer solar system—Enceladus’ icy surface hides an ocean of liquid water which, thanks to data from Cassini, suggest it may hold the necessary ingredients for sustaining life. Future missions, particularly  Europa Clipper (a mission planned for the 2020s which will explore Jupiter’s similarly icy moon Europa), will further investigate the possibility of extraterrestrial life using what we learned from Cassini as a starting point.

Seemingly insignificant in the grand scheme of things, but meaningful all the same: Saturn also gave us perspective. Astronauts have spoken about the indescribable sensation of looking down at our planet from space, unable to see country borders, lines of conflict, anything beyond the home of the human race. Some of the thousands of pictures taken by Cassini contain a bright speck in the background. That speck is our world. Our Earth. From the depths of space, humanity is united simply by living on the same planet. This view, and the perspective it provides, is irreplaceable.

Artist’s conception of Cassini traveling between Saturn and its rings. Image courtesy of NASA.

The conclusion of Cassini’s mission was well documented—the final plunge into the depths of the gaseous planet on September 15, 2017. As it ran out of fuel, at the end of a mission that had been extended more than once past its intended duration, the final remaining goal was to preserve. If Enceladus or any of Saturn’s other moons did contain the ingredients for life, it was essential to keep it that way. Had Cassini simply been allowed to remain in orbit, the chances of the spacecraft contaminating one of these moons were too great. So it took the plunge—Cassini’s Grand Finale—sending back data until the last possible moment, a dramatic end to one of the most productive planetary missions in history.

–Claire Douglas