After 12 years of touring the Saturn system, NASA’s Cassini spacecraft is about to enter a new orbit — one that will take the probe up close to the planet’s famous rings. These Ring-Grazing Orbits, as NASA is calling them, will bring Cassini within nearly 5,000 miles of Saturn’s F ring, which marks the border of the main ring system. These orbits will allow Cassini to study the particles and gas molecules that linger near the rings, as well as observe the small moons that orbit along the rings’ edges.

It marks the beginning of the end for Cassini

As exciting as this move is, it also marks the beginning of the end for Cassini, which has been traveling through space for 20 years now. NASA says the Ring-Grazing Orbits will serve as the prelude to Cassini’s “Grand Finale” — when the spacecraft will get closer to the planet’s surface, repeatedly diving through the gap between Saturn’s cloud tops and its inner rings. After that, Cassini will perform a death plunge into Saturn’s atmosphere on September 15th, 2017, bringing its long mission to a close.

Things get underway tomorrow, when Cassini performs its second to last flyby of Saturn’s moon Titan. During the maneuver, Cassini will take visible and infrared images of the cloudy moon, as well as map out Titan’s north pole to see if anything has changed since the spacecraft’s last Titan flybys. Cassini will also use its onboard infrared spectrometer to create a temperature map of Titan, allowing scientists to understand the composition of the moon’s atmosphere.

As Cassini gathers data from Titan, the spacecraft will also get a gravity assist from the moon, putting the spacecraft into its Ring-Grazing Orbits. Cassini officially enters this new orbit on November 30th, and will remain on this highly elliptical path until April 2017. During that time, the probe will dive near Saturn’s F ring once a week, 20 times in total.

While Saturn has much fainter rings beyond its main ring system, the F ring serves as the boundary of the primary A, B, and C rings. The F ring is relatively thin compared to its partners — just 500 miles across. It’s also constantly morphing, sprouting “bright streamers, wispy filaments, and dark channels,” according to NASA. Cassini will be able to study the F ring closer than ever before with its Ring-Grazing Orbits, and even get unprecedented views of the A and B rings. The close proximity will allow Cassini to make detailed observations of Saturn’s smaller, lesser known moons — such as Pandora, Pan, Daphnis, and Atlas. And the spacecraft will help investigate never-before-seen moonlets that are thought to orbit inside Saturn’s main rings. Propeller-shaped features inside the rings are believed to indicate the presence of these tiny space rocks.

Cassini’s first graze of the F ring is scheduled for December 4th

Cassini’s first graze of the F ring is scheduled to occur on December 4th. During that pass, Cassini will also briefly ignite its main engine to help fine-tune its orbit. It will be the 183rd time the spacecraft turns on its engine, as well as its last time, if all goes according to plan. NASA plans to use the spacecraft’s smaller thrusters to maneuver Cassini into its Grand Finale orbit — a path that will bring the vehicle a little over 1,000 miles within Saturn’s cloud-top surface every six days. Cassini will perform this type of orbit a total of 22 times, mapping out Saturn’s gravity and magnetic fields and measuring icy particles from the rings that are being funneled into the planet’s atmosphere. Oh, and it will be snapping some of the closest images of Saturn we’ve ever seen.

Then in mid-September, Cassini will perform its death dive into the planet. The reason Cassini’s mission has to end is because it’s running low on fuel, and NASA would eventually lose control of the probe if its fuel supplies are depleted. Plus, the space agency wants to ensure that Cassini doesn’t accidentally contaminate Enceladus or Titan, two of Saturn’s moons that may be able to support life, with stowaway microbes from Earth. So the spacecraft is headed into Saturn’s atmosphere, where it will meet its (timely) end.

It’s nearly a year before that happens though, so there’s no need to be sad just yet. However, if you want a daily reminder that Cassini’s mission is almost over, this Twitter bot is happy to oblige.

NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO Cassini can't be ending — Cassini Noooo (@CassiniNooo) November 28, 2016

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