NASA photo
Cassini's plunge
Cassini’s last moments were meticulously planned out. NASA/JPL-Caltech

After almost 20 years of exploration, discoveries and gorgeous pictures, it’s time to say goodbye to Cassini.

Launched in 1997, it took the Cassini spacecraft seven years to reach it’s ultimate destination—Saturn. For thirteen years, it has sent us back glorious images and incredible new data about newly-discovered moons, geysers of water shooting into space, and lakes of hydrocarbons with electrically-charged sand. But Cassini is almost out of the rocket fuel that helped propel it into the distant reaches of our solar system.

Though the robot’s electrical systems and instruments could have continued to run on the radioisotope thermoelectric generator (RTG)—or a nuclear battery, without fuel for maneuvering there was a small chance that Cassini would have crashed into Titan or Enceladus.

Both of those moons are intriguing possibilities in the ongoing search extraterrestrial life. And Cassini never went through the rigorous clean-room procedures that would be required to make such a landing without fear of introducing Earth-based life.

To avoid even the slightest chance of imperiling future missions to those moons, NASA researchers decided to play it safe and vaporize Cassini in Saturn’s outer atmosphere.

This Friday, it will make its final plunge into the surface, the last step of a months-long Grand Finale that sent Cassini diving between Saturn and its rings on a path to destruction. But it won’t die in vain. In its last moments, Cassini will collect and stream back unprecedented data about Saturn’s atmosphere.

Here’s how NASA says Cassini’s last few days will unfold (all times EDT—exact timing may vary due to atmospheric conditions):

  • September 11, 3:04 P.M., Cassini gives Titan a ‘goodbye kiss’, approaching it for a final, distant flyby and using the moon’s pull to force itself into the final descent.

  • September 12, 9:19 P.M., Earth starts receiving Cassini’s last data on Titan.

  • September 14, 3:58 P.M., Cassini’s cameras take their last pictures. The clouds of Saturn will serve as the subject of this bittersweet photoshoot.

  • September 14, 4:22 P.M., Cassini’s last batch of data—including those last pictures—begin streaming back to Earth. NASA plans to post raw images online as they are received. Earth will start receiving those signals at 5:45 P.M.

  • September 15, 3:14 A.M., The spacecraft rolls into position to collect atmospheric data during the descent, and re-configures its systems to transmit data in real-time. Because of the sheer distance between Earth and Saturn, these signals will be received on Earth at about 4:37 A.M.

  • September 15, 6:31 A.M., Cassini enters Saturn’s atmosphere.

  • September 15, 6:32 A.M., Cassini’s antenna points away from Earth, leading to a loss of signal. Shortly afterwards, the spacecraft is vaporized in the high pressure and temperature of Saturn’s atmosphere.

  • September 15, 7:00 A.M.-8:30 A.M., NASA livestreams the scene at mission control at NASA JPL, with live commentary about the end of the mission.

  • September 15, 7:55 A.M., Earth registers the loss of signal, indicating the end of Cassini.