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
- Cassini has been preparing for its final descent since April 2017.
- Cassini will do its science until the very end.
- Cassini has provided the highest resolution images ever of Saturn's rings.
- Cassini got an up-close look at Saturn's weather.
- Cassini, together with the Huygens probe, revealed the surprisingly Earth-like nature of Saturn’s largest moon, Titan.
- 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.
4. Cassini got an up-close look at Saturn’s intense weather.
Before Cassini was launched in October of 1997 and later entered Saturn’s orbit in June of 2004, Saturn had only been viewed from a few spacecraft flybys. Cassini has now spent 13 Earth years exploring the planet and its surroundings which is nearly half of a Saturn year (1 Saturn year is equivalent to roughly 29 Earth years).
While Saturn is more than 700 times the volume of our planet Earth, its core is believed to be only a bit larger than Earth’s core, meaning that most of the planet is composed of turbulent layers of gas. Cassini was able to gather detailed information on some of these intense storms and the jets they inspired.
Protecting Saturn's moons from contamination is the main reason behind sending Cassini plummeting into Saturn in just a few days.
5. Cassini, together with the Huygens probe, revealed the surprisingly Earth-like nature of Saturn’s largest moon, Titan.
The Cassini spacecraft was part of the Cassini-Huygens mission, a joint effort between NASA, the European Space Agency, and the Italian Space Agency. In 2005, shortly after reaching Saturn, the Cassini spacecraft delivered the 700-pound, shellfish-shaped Huygens probe to Saturn’s largest moon, Titan. Huygens became the first probe to land on a world in the outer solar system.
Cassini and ESA’s Huygens probe found evidence of an ocean of water beneath the entirety of Titan’s thick icy surface and an atmosphere around the moon full of prebiotic chemicals, both necessary ingredients for life. A third ingredient, an energy source, may also be present according to models of the moon’s ocean.
The evidence for the underground ocean was based on tides – Saturn’s gravity pulls and deforms Titan’s shape as the moon orbits the giant planet in a way that would not be possible if the moon was made only of more inflexible rock.
Cassini and Huygens further revealed that Titan hosts liquid methane seas above ground. So despite being 10 times farther from the Sun than the Earth is, Titan was revealed to be the only other place in the solar system known to host a stable liquid on its surface.
6. Cassini revealed that Saturn’s moon Enceladus is one of the most promising places in the solar system to host life.
Before Cassini, Enceladus, another one of Saturn’s more than 60 moons, was thought to be too small to hold onto enough heat to also maintain an underground liquid ocean. However, Cassini’s incredible discovery of hydrothermal activity near the moon’s south pole led to the understanding that not only does the moon host a global liquid water ocean, but that ocean is home to salts and simple organic molecules and possibly hydrothermal vents.
Protecting Titan, Enceladus, and their potentially life-hosting conditions from contamination is the main reason behind sending Cassini plummeting into Saturn in just a few days.
NASA has posted a detailed timeline for the entirety of the Cassini mission, including flybys of Titan, Enceladus, and other moons. They have also provided a countdown to Cassini’s end of mission and a (quickly decreasing) measure of the probe’s distance from Saturn on NASA’s Grand Finale page. For Cassini’s current speed relative to the Earth and to Saturn, you can also check out NASA’s Where is Cassini Now? feature. And of course, be sure to check out the stunning images of the distant solar system worlds that Cassini has provided throughout its lifetime.
Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.
Image courtesy of nasa.gov
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