Cassini Sheds Light On Saturn's Rings, Say SwRI Scientists
For decades, scientists studying Saturn have been saying a small amount of water vapor and granules were falling from its closest ring — the D-ring — and into the planet’s atmosphere. These findings were based on observations from the spacecrafts Pioneer, and Voyagers 1 and 2.
But newly released studies Friday contradicted these decades-old theories with a paper in the journal Science written by scientists on the Cassini mission.
NASA’s Cassini space probe finished its 19-year mission Sept.15, when it plummeted beneath the clouds of Saturn.
Dubbed the “grand finale,” the final 22 orbits of Saturn included unprecedented dives between the planet and its rings. The data from those dives are now being published and it is challenging what was known about Saturn’s rings, their composition, and how they interact with the planet and their age.
First, the makeup of what was falling into the planet.
"It was this huge complex spectrum,” said Hunter Waite, Southwest Research Institute scientist and principal investigator on Cassini’s Ion Neutral Mass Spectrometer, which takes in particles and analyzes them in the same way a nose does.
But while INMS was smelling water, it was also smelling something that baffled Waite’s team: carbon monoxide, methane, ammonia, and complex organics.
“The first time that (scientist) Rebecca Perryman and I looked at it, we went … 'Is something wrong?' Seriously, we looked at it like: ‘What did we do with our instrument?' “ he said.
Expecting water, which scientists say make up more than 90 percent of the rings, the presence of this organic cocktail was a jolt, he said. They theorized Cassini’s speed was allowing granules to hit the instrument and possibly shake off particles from years earlier, when the probe was discovering methane lakes and other organics on carbon-rich Titan.
They verified the data from other instruments, he said, and the initial readings were correct.
Waite and his co-investigators had a similar shock when they calculated the total amount of the compounds falling into the planet.
"We didn't know how much material was falling in, and when we did that, we had our second 'Whoa, this is 10,000 kg (22,000 lbs) of material falling in per second, can that be right?'
“The D-ring grinds right up against the planet,” said Waite, adding that the material is losing speed and 22,000 pounds per second is falling in. “It has significant implications for the rings.”
The current makeup of the D-ring could fall into the planet in the next 100,000 years, but that doesn’t mean the ring will be gone. Cassini scientists also observed material from other rings being transferred to the D-ring,
“You can sort of imagine it’s this kind of conveyor belt, a process where stuff is drifting in,” said Paul Estrada, senior scientist in charge of astrophysics at the SETI Institute, a nonprofit research organization.
The surface area of the rings is so big that it makes it susceptible to being struck by micrometeorites, allowing things to drift into the D-ring, he said.
Because of the measurement of the mass of the rings, its composition and how much has been added from outside the system, Estrada said there is more evidence the rings are much younger than previously thought.
“Those three little pieces of evidence together tell you that the rings are only 100 million years old,” he said.
Historically, there have been two camps debating the age of Saturn’s rings, Waite said. One group argues the rings formed at the same time as the solar system, a popular theory until the Voyager missions. And since the data from the Voyager missions in the 70s, the other group argues the rings are a few hundred million years old.
Waite declined to weigh in on that debate, saying a paper from Cassini mission scientists would be coming out soon.
Other papers presented in the special edition of Science include the discovery of a radiation belt, an in-depth look at the composition of the material falling into the planet’s atmosphere, and new details about the planet’s magnetic fields.