Cassini will plunge into Saturn and pull our heartstrings with it

Requiem for a machine.

Cassini
An artist's impression of Cassini during one of its final dives between Saturn and its rings.NASA/JPL-Caltech

In the early hours of Friday, September 15, our planet will lose the Cassini spacecraft's signal just before it disintegrates in Saturn's atmosphere. That radio silence will mark the end of 13 years of exploration—and nearly 30 years of work. Though the moment Cassini will perish is still days away, tears are already flowing, as emotional tributes to our window to another world fill timelines on social media.

Yes, there are some people who watch the smashing of a spacecraft into another planet from a detached distance, but many people who love space are truly greiving the loss of this hunk of human inginuity, metal, and plutonium.

The mourners knew this moment was coming. Unlike other ends, which might come in sudden explosions or by way of other unexpected failures, this conclusion was announced, planned for, and anticipated. Cassini received its death sentence months ago. All that's left for observers to do is to wait for the last signals of a vaporized spacecraft to arrive back to Earth.

We’ve had time to prepare for this. Why does it still hurt so much?

"This mission is special, and it's making it more difficult to say goodbye because it's lasted so long," says Jonathan Lunine, Director of the Cornell Center for Astrophysics and Planetary Science. Lunine worked on Cassini as an interdisciplinary scientist. He points out that the mission, which launched nearly 20 years ago, was only supposed to last for four years—but kept getting extensions. "We ended up with a 13 year tour around Saturn," he says.

And the souvenirs Cassini sent home provided a constant source of wonderment for Earth's planetary scientists.

“Cassini has made observations that weren’t even thought of when the mission was designed. It's certainly produced science far and away greater than anyone anticipated,” Lunine says.

Like many people on the project, Lunine’s emotions are mixed. “My feelings are, on the one hand, that it’s such a spectacular job and we should celebrate. But it's also hard to be in the moment right now where it's still operating, still collecting data, knowing in three days that won’t be the case.”

Cassini touched the lives of many in the planetary science community, even beyond the many scientists who devoted decades to pouring over its data and making minute course corrections from millions of miles away.

"All of my research for the past 13 years has basically been inspired by Cassini in some part," says Sarah Hörst. "In that sense I owe a huge chunk of my career to Cassini."

Hörst, a planetary scientists who studies Saturn's moon Titan, has worked with the spacecraft's data since she was in graduate school.

“There's something really beautiful about Cassini,” she says. “I think that one reason that people feel a connection to it, both within the planetary science community and outside of it, is that it’s a powerful spacecraft. You don’t have to love Saturn, you don’t have to think the rings are the greatest things, you don’t have to be a Titan person—though I don’t personally understand that—there’s something for everyone.”

That even includes people who don't make their living studying distant worlds. Through Cassini, the general public dipped their toes into methane seas on Titan, drifted through plumes of something a lot like seltzer water shooting out of Enceladus, and gazed in wonder at some of the most stunning images of Saturn and its rings ever taken.

While the mass-spectrometry data Cassini collected wasn't necessarily thrilling to people outside the fields of chemistry or planetary science, the pictures it snapped were stunning to all. Hörst's favorite features sunlight glinting off Jingpo Lacus, a lake on Titan.

“That image of sun reflecting off an extraterrestrial body of liquid for the first time...I’ve seen it a hundred thousand times at this point, and every time I see it, I still get chills down my back,” Hörst says.

Sadly, NASA has no plans to return to the Saturn system any time soon.The next large-scale mission to the outer solar system will be the Europa Clipper, which will study a moon of Jupiter, bypassing Saturn. While there are proposals to revisit the tantalizing mysteries that Cassini uncovered, including projects that would further explore the potentially life-harboring moons Titan and Enceladus, there are no missions currently in the works.

“I think that part of what is contributing to the feeling of loss is not knowing what’s next. And for some people there is no next. This is their last mission, they’re retiring, and that also contributes to the sense of loss,” Hörst says.

Lunine and Hörst both point out that the planetary science community has found themselves in this position before, and both hope that history repeats itself. After the Voyager spacecrafts gave researchers a tantalizing glimpse of Saturn in the early 1980's, they wanted more data—but had no missions pending. Into the void, Cassini was born, pieced together by a burning, collaborative effort to know more about this unexplored area of the Solar System.

“It was paid for by taxpayers from a number of countries, not just the United States. It was an international mission, an intergenerational mission,” Hörst says. “We’ve never had a mission like it, and It will likely be a while before we have another mission similar to it again.”