And its final plunge will reveal even more about the make-up of Saturn's atmosphere before Cassini disintegrates like a meteor. The probe discovered seasonal changes on Saturn, a hexagon-shaped pattern on the north pole and the moon Titan's resemblance to a primordial Earth.
"Our spacecraft has entered Saturn's atmosphere, and we have received its final transmission", Nasa said in a tweet.
No other spacecraft has ever explored this unique region.
Since April 2017, NASA's Cassini spacecraft has been writing the final, thrilling chapter of its remarkable 20-year-long story of exploration, its Grand Finale.
Carolyn Porco's favorite image of Saturn and its moon Enceladus was taken with the Cassini spacecraft wide-angle camera on March 16, 2006, at a distance of approximately 1.3 million miles from Saturn.
The spacecraft's dive to the planet is the final step of the mission, which was to take pictures and collect key information about its environment.
"Through the Eyes of Cassini" is a free e-book released by NASA, which highlights the scientific key discoveries and intriguing images, sourced from its Cassini mission to the Saturn.
The Grand Finale, as NASA calls it, came about as Cassini's fuel tank started getting low after 13 years exploring the planet.
While telescopes will be pointed at Saturn to try and capture Cassini's last moments, it likely will be moving too fast (and is too small) for any images.
Including Titan, Cassini explored a total of 19 Saturnian moons in detail.
Huygens landed successfully on one of Saturn's moons, Titan in 2005.
For the curious, here's how Cassini's last few minutes are going to go down. Once they are firing at full capacity, the thrusters can do no more to keep Cassini stably pointed, and the spacecraft will begin to tumble. Check out all the final images at NASA's Cassini Grand Finale website, but first take a look at some of the work from fans of the mission, who processed those raw pictures to produce these incredible results.
"It will be sad to see Cassini go on Friday, especially as the instrument we built is still working perfectly", said Stanley Cowley, professor of solar planetary physics at the University of Leicester.