(CNN) Prepare to say goodbye to Cassini. In the early morning hours of September 15, NASA's 13-year mission exploring Saturn and its moons will come to an end as the spacecraft deliberately dives into Saturn's atmosphere and plunges itself into the planet. Even then, Cassini will transmit new data about the planet's composition as long as its antenna remains pointed toward Earth, with the assist from small thrusters. No spacecraft has ever been so close to Saturn. "You can think of Cassini as the first Saturn probe," said Linda Spilker, Cassini project scientist. The Ion and Neutral Mass Spectrometer will act as the "nose" of the spacecraft, directly sampling the composition and structure of the atmosphere -- something that can't be done from orbit, said Hunter Waite, team lead for the spectrometer.The NASA Cassini mission ends Friday after 13 years observing the Saturn systemCassini data has revealed groundbreaking discoveries about Saturn and its moons
While many other options were considered -- such as "parking" the spacecraft in orbit around _ -- they didn't want to risk Cassini colliding with any of Saturn's moons.