Cassini Meets The Lord of the Rings

SCIENCE

NASA is deliberately crashing its $3.9-billion spacecraft in a fiery “Grand Finale” on Saturn. Why? (NASA)

Revisit Cassini’s legacy with our study guides on two of its discoveries.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

Illustration by NASA/Jet Propulsion Laboratory-Caltech

The world is watching as NASA prepares to crash its Cassini spacecraft into the gas giant Saturn. What is Cassini?
- Cassini is a sophisticated robotic spacecraft orbiting Saturn and studying the Saturnian system in detail.
  - Cassini is a joint endeavor of NASA, the European Space Agency (ESA) and Agenzia Spaziale Italiana (ASI), the Italian space agency. Cassini originally carried a probe called Huygens, which parachuted to the surface of Saturn’s largest moon, Titan, in January 2005.
  - Cassini has 12 science instruments grouped to study three aspects of the Saturnian system.
    - Optical Remote Sensing: The Composite Infrared Spectrometer (CIRS), Imaging Science Subsystem (ISS), Ultraviolet Imaging Spectrograph (UVIS) and Visible and Infrared Mapping Spectrometer (VIMS) study the Saturnian system using the electromagnetic spectrum.
    - Fields, Particles, and Waves: The Cassini Plasma Spectrometer (CAPS), Cosmic Dust Analyzer (CDA), Ion and Neutral Mass Spectrometer (INMS), Magnetometer (MAG), Magnetospheric Imaging Instrument (MIMI), and Radio and Plasma Wave Science (RPWS) study the dust, plasma, and magnetic fields around Saturn.
    - Microwave Remote Sensing: Radar and the Radio Science Subsystem (RSS) map atmospheres, determine the mass of moons, collect data on ring particle size, and unveil the surface of Titan.
  - Make a model of Cassini with a 3D printer, paper-and-scissors … or dessert!

Cassini was launched in 1997. What has it helped scientists achieve, discover, and learn in its 20-year mission?
- Huygens transmitted data for about 90 minutes after landing on Titan, and remains the most distant landing of any human-made object. Learn more about Huygens’ discoveries here.
- Cassini discovered active, icy plumes spraying from the moon Enceladus. Learn more about Enceladus’ extraterrestrial ocean here.
- Cassini-Huygens helped scientists interpret Saturn’s famous ring system as a (relatively) tiny laboratory of how planets and rings formed in the early solar system. Learn more about that process here.
- Cassini-Huygens found that Titan is an active celestial body, with rain, rivers, lakes and seas … made of methane. Learn more about Titan here.
- Cassini imaging helped scientists track the life and death of a massive, planet-spinning storm. Learn how that storm “choked on its own tail” here.
- Cassini’s “Fields, Particles, and Waves” instruments help reveal fluctuations in its radio waves. Learn more about Saturn’s radio waves and the solar wind here.
- Cassini revealed vertical “splash” structures in Saturn’s rings up to 3 kilometers (2 miles) high. Learn more about those weird structures here.
- Cassini-Huygens helped scientists identify both Titan and Enceladus as having “prebiotic” chemistry—a natural environment that has the chemical ingredients for life. Learn more about the search for microbial life on Enceladus and Europa here.
- Cassini helped solve the puzzle of the “two-faced” surface of the moon Iapetus—the dark spots indicate where dark dust in Iapetus’ path has crashed onto the planet. Learn more about Iapetus here.
- Cassini discovered and took a good look at giant hurricanes at both of Saturn’s poles. Learn more about Saturn’s strange storm here.

Why is NASA crashing Cassini?
- Vox sums it up nicely: “The space agency really has no other choice. Cassini is nearly out of fuel, and has already been stretched years beyond its intended mission duration. What’s more, keeping it going risks potentially contaminating one of Saturn’s moons … with microbes from Earth.”
  - We don’t want to pollute the solar system!

Could terrestrial microbes really pollute moons in the outer solar system?
- Yes. “Based upon exposure experiments on the Space Station, it is known that some microbes and microbial spores from Earth are able to survive many years in the space environment– even with no air or water, and minimal protection from radiation. Therefore, NASA has chosen to dispose of the spacecraft in Saturn’s atmosphere in order to avoid the possibility that viable microbes from Cassini could potentially contaminate Saturn’s moons at some time in the future.”

OK, we have to save the Saturnian system from earthly pollution. What is the “Grand Finale”?
- It’s awesome, is what it is. We love objects discovering the escape velocity of gas giants.
- “In April 2017, Cassini was placed on an impact course that unfolded over five months of daring dives—a series of 22 orbits that each pass between the planet and its rings. Called the Grand Finale, this final phase of the mission has brought unparalleled observations of the planet and its rings from closer than ever before. On September 15 [Friday], the spacecraft will make its final approach to the giant planet Saturn. But this encounter will be like no other. This time, Cassini will dive into the planet’s atmosphere, sending science data for as long as its small thrusters can keep the spacecraft’s antenna pointed at Earth. Soon after, Cassini will burn up and disintegrate like a meteor.”
  - Some astronomers nickname the Grand Finale the “death plunge.” We much prefer this sort of taking the plunge.)

Why a plunge instead of another method of disposal, such as sending Cassini somewhere else in the solar system, attempting a landing on one of the moons, or crashing into the rings?
- For science! “The Grand Finale of close dives past the outer and inner edges of the rings, and ultra-close brushes with the planet and its small, inner moons, offered such enormous scientific value that this scenario was chosen for the mission’s conclusion.”

If Cassini’s death plunge takes it into Saturn, won’t it pollute the Saturnian atmosphere the way it might pollute the moons?
- Nope. Saturn’s atmosphere is in no way prebiotic; it does not have chemicals or conditions favorable to life as we know it. In addition, “Disposing of Cassini in Saturn’s atmosphere is safe. The spacecraft will enter Saturn’s atmosphere at high speed and will burn up like a meteor. Any spacecraft material that survives atmospheric entry, potentially including its radioisotope fuel, will sink deep into the planet where it will melt and become completely diluted as it mixes with the hot, high-pressure atmosphere of the giant planet.”
  - This is probably our favorite example of what happens when an object meets a gas giant.

What are the final data scientists are hoping to glean from Cassini as it makes its fiery plunge?
- The spacecraft will make detailed maps of Saturn’s gravity and magnetic fields, revealing how the planet is arranged internally, and possibly helping to solve the irksome mystery of just how fast Saturn is rotating.
- The final dives will vastly improve our knowledge of how much material is in the rings, bringing us closer to understanding their origins.
- Cassini’s particle detectors will sample icy ring particles being funneled into the atmosphere by Saturn’s magnetic field.
- Its cameras will take amazing, ultra-close images of Saturn’s rings and clouds.
- Stay tuned!