News science column

A fiery end for Cassini, Saturn’s space orbiter

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One of Cassini's last looks at Saturn and its main rings from a distance.
Courtesy of NASA

This Friday, the Cassini space orbiter will finish its 20-year-long mission by making a “death dive” into Saturn’s atmosphere, where heat and pressure will cause it to disintegrate. During its final minutes, the spacecraft will send data back to Earth in real-time eking out as much precious data from the mission as it possibly can — for who knows when humanity will have an opportunity like this again?

The Cassini spacecraft was launched from Cape Canaveral in October 1997 and then spent seven years in transit to Saturn. On the way, it flew by Venus twice, studied the composition of the asteroid belt, and worked with the Galileo spacecraft to observe Jupiter and its system. Cassini also carried the Huygens probe, which landed on Titan, Saturn’s largest moon, in 2005 and sent data about the moon’s surface and atmosphere to Cassini for 72 minutes before the signal was interrupted by the horizon.

From orbit, Cassini has provided researchers with such a wealth of data that its mission was extended twice, first for the northern hemisphere’s spring equinox in 2010 and then for the summer solstice in 2017. During its time in orbit, Cassini has discovered numerous moons, made over a hundred fly-bys of Titan, taken hundreds of thousands of photographs of Saturn and its 62 moons, and provided the data to identify 101 saltwater geysers erupting on the 6th largest moon, Enceladus. During the spring equinox, Cassini could capture the way the sunlight hit Saturn’s rings edge-on, allowing researchers to measure the summits of mountains they saw rising from the rings. And seven years later, the summer solstice provided astonishing views of Saturn’s north pole, which changes from blue to yellow over the course of the planet’s year, ostensibly due to reactions between organic compounds in the atmosphere.

After all of its contributions to our understanding of Saturn and the outer solar system, Cassini has been on a doomed trajectory since April. That’s when NASA guided Cassini into an orbital path that took it, for the first time ever, between Saturn and its rings. Cassini has made 20 of these sub-ring orbits, using the last five to dip so close to Saturn that it could directly measure the planet’s atmosphere. And it’s this path that set Cassini on an inevitable course for vaporization.

The last hours of Cassini’s mission could provide valuable data to answer some of researchers’ most persistent questions: How was Saturn formed, does it have a solid core, and how long is a Saturnian day?

One might also wonder why NASA is throwing its $2 billion spacecraft into a “death dive” instead of trying to land it or recover it. The answer lies in planetary protection — or, in this case, moon protection. If it’s possible that moons like Titan and Enceladus might currently, or could one day, harbor life, then humanity has a responsibility to leave such landscapes uncontaminated.