Saying Goodbye to the Saturn-Exploring Cassini

Posted on Thu, September 14, 2017

I think it surprises a lot of people that a mission as successful as the Cassini-Huygens Mission would be terminated on purpose. Not just shutting the spacecraft off, but terminated with such style by sending it on a destructive dive into Saturn’s atmosphere. Cassini will burn up and be destroyed in a similar way that a meteorite is broken up in Earth’s atmosphere.

But here’s the thing: Cassini has done an incredible job of revealing Saturn, its rings; its weird dumpling moons; its icy, dynamic worlds with methane lakes, jets of water spewing into space, and some that might be habitable. The Cassini spacecraft has aged over its 13 year mission (not including its seven year, 2.2 billion mile cruise to Saturn) and there isn’t enough fuel to maintain control of the spacecraft. There is a very real danger that Cassini could crash into Saturn’s moons Enceladus or Titan, and Cassini just wasn’t cleaned well enough before its launch to make contact with any of these moons. We didn’t know that there would be worlds of such high astrobiological interest!

When we plan to land a mission on a planetary surface, whether it roves around, sits in one place, or could crash into a surface, there are strict guidelines that require the spacecraft to be clean. Not just squeaky clean, but all the way clean: no dust, no dander, no germs of any kind. We want to protect all those places in our solar system that might harbor life, so that if we go back looking for it, we will know for certain that we didn’t put it there! And as Cassini has found us all kinds of new worlds to study, we want to be sure that if we get to go back to any of these places, we won’t be studying something that we accidentally put there.

Illustration of Cassini crossing the rings of Saturn

In this illustration, Cassini is shown diving between Saturn and the planet's innermost ring. Image: NASA/JPL

Cassini’s finale began in April, as it started a series of 22 daring dives between Saturn and its rings. This is not the kind of maneuver that anyone would have considered planning with a spacecraft mid-mission because it’s way too risky to the spacecraft. There was no telling if the gap between the rings and the planet was clear or if it was full of dust and/or debris. But the risk paid off. Cassini was able to collect data to refine measurements of Saturn’s gravity, magnetic field, internal structure, and rotation rate.

I’m sad that the Cassini mission is coming to a close, but here’s what I think is really cool: Cassini is going to keep taking data as it dives through Saturn’s atmosphere and will send it back to us until it just can’t anymore. All of the amazing data Cassini and the Huygens probe have returned to Earth will continue to carry the memory of Cassini through the coming years and decades and will continue to lead to new and exciting discoveries, and I’m pretty darn excited about that.