What’s new at saturn?
Cassini is the gift that keeps on giving when it comes to discoveries
It’s been over a year since the demise of NASA’s Cassini spacecraft, yet astronomers are still carefully analysing the data it transmitted back to Earth in an attempt to answer the many questions that surround the ringed gas giant. In the space of less than a week scientists made two separate discoveries about fundamental aspects of the planet: how long is a day on Saturn, and how old are its rings?
Determining a day on Saturn is harder than it appears. On Earth it is simply how long it takes for the whole body to complete one rotation, whereas Saturn’s gaseous exterior makes it difficult to track any type of consistent rotation. The answer wasn’t hidden in the planet, however; it was hidden in its rings. Christopher Mankovich, a graduate student in astronomy and astrophysics at UC Santa Cruz, studied the vibrations of the rings corresponding to the vibrations within the planet itself, and this analysis revealed the length of a day on Saturn to be 10 hours, 33 minutes and 38 seconds.
"The researchers used waves in the rings to peer into Saturn's interior, and out popped this long-sought, fundamental characteristic of the planet. And it's a really solid result," says Cassini project scientist Linda Spilker. "The rings held the answer."
The rings also hold their own mysteries, such as their origin. Towards the end of Cassini’s lifetime the spacecraft underwent dives through the rings, which consist of dust, rocks and ice. This passage let Cassini feel the effects of Saturn’s gravity on the rings, and the radio signals of the gravity science data were sent back to Earth to reveal the age of the famous cosmic halo. The results from this study indicate that the rings were formed between 10 million and 100 million years ago. To put that into perspective, Saturn’s rings were forming around the same time dinosaurs were roaming around planet Earth.
"Only by getting so close to Saturn in Cassini's final orbits were we able to gather the measurements to make the new discoveries," says Cassini radio science team member Luciano Iess of Sapienza University of Rome, Italy. "And with this work Cassini fulfils a fundamental goal of its mission: not only to determine the mass of the rings, but to use the information to refine models and determine the age of the rings.”
Although these results may seem to go under the radar, they are fundamental for future research. The only way to answer the more complicated questions about Saturn and its evolution is by understanding its simplest aspects and building from there. For instance, now the age of the rings can be well constrained, astronomers can try and figure out how the rings formed. This rules out any ideas that the rings formed early on in the planet’s life after its formation 4.5 billion years ago. Instead it’s more likely that a comet wandered too close to Saturn and its gravity dismantled it or there was an event that destroyed one of Saturn’s ancient icy moons.