Why NASA Is Crashing Its Cassini Spacecraft into Saturn

NASA's Cassini spacecraft has been studying Saturn for two decades and is finally running out of rocket fuel, ending its mission in a blaze of glory by crashing into Saturn on September 15, 2017.

Sabrina Stierwalt, PhD
5-minute read
Episode #253

Image from nasa.gov

On September 15th, NASA will send the Cassini spacecraft hurtling toward Saturn at more than 70,000 miles per hour relative to the Earth. Cassini will continue its descent into the giant gas world until the spacecraft disintegrates in Saturn’s atmosphere and is thus destroyed, taking measurements and sending data back to Earth until the very end.

The 20-year mission is going out in a blaze of glory because the spacecraft does not have enough rocket fuel left to continue exploring Saturn, its rings, and its moons, as it has been doing for the past 13 years. Rather than take the risk of the probe crashing into one of Saturn’s moons in the future, moons that could possibly hold the potential for hosting life, scientists have decided to purposely send Cassini on a crash route into the planet’s atmosphere.  

Did You Know? 6 Cassini Spacecraft Facts

  1. Cassini has been preparing for its final descent since April 2017.
  2. Cassini will do its science until the very end.
  3. Cassini has provided the highest resolution images ever of Saturn's rings.
  4. Cassini got an up-close look at Saturn's weather. 
  5. Cassini, together with the Huygens probe, revealed the surprisingly Earth-like nature of Saturn’s largest moon, Titan.
  6. Cassini revealed that Saturn’s moon Enceladus is one of the most promising places in the solar system to host life.

Learn more about why you should celebrate this extraordinary mission and Cassini’s final days.

1. Cassini has been preparing for its final descent since April 2017.

In what NASA is calling the Grand Finale, Cassini has made a series of 22 death-defying dives through the ~1200-mile wide gap between the planet Saturn and its giant ring system. Cassini is the first spacecraft to enter this region, a move that was too risky to consider while the spacecraft still had enough fuel to continue its regular mission.

Once NASA scientists decided Cassini would have to meet its demise – and thus had nothing to lose – they directed the probe to receive a gravitational assist from Saturn’s largest moon, Titan, so that the spacecraft could change course toward the gap.

2. Cassini will do its science until the very end.

As the spacecraft dives toward Saturn, it will continue taking measurements for as long as it can keep its transmitting antenna pointed back at Earth, so that scientists can gather every last bit of data possible. An instrument on the probe called a mass spectrometer, for example, will take measurements on the composition of the atmosphere as it plunges closer and closer toward the planetary surface.

Other measurements in the probe’s final days will map Saturn’s gravity and magnetic fields, both of which can help scientists understand the structure of the planet. Such detailed information could help solve one particular mystery: the mismatch between Saturn’s rotation speed (aka how long a day is on Saturn) as measured by the Voyager probes versus Cassini itself when it first arrived at the planet.   

3. Cassini has provided the highest resolution images ever of Saturn’s rings.

Throughout its mission, Cassini was the first probe to study the size, temperature, and composition of Saturn’s rings from an orbit around Saturn. The probe has caught interactions between the rings and Saturn’s moons, including the discovery that jets of water from Saturn’s moon Enceladus are predominantly responsible for the material in one of Saturn’s major rings known as the E ring.

The particles in Saturn’s rings have sizes that range from a grain of sand to a large mountain. Throughout its Grand Finale, Cassini’s repeated close approaches have provided the highest resolution images ever taken of Saturn’s rings. These images will allow scientists to make a more complete census of how much material is in the rings and thus better piece together their origin story.


About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.

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