Saturn’s rings may be much older than we thought

Modeling studies suggest that Saturn’s rings are much older than previously thought and may have formed around the same time as Saturn. But not all astronomers are convinced, and the researchers who were part of the team that calculated that Saturn’s rings are relatively young insist that the new findings do not change their findings. are.

For most of the 20th century, scientists believed that Saturn’s rings formed with the planet about 4.5 billion years ago. But when NASA’s Cassini spacecraft visited Saturn in 2004, it found its rings to be noticeably free of contamination from tiny space rocks known as cosmic dust. This primitive appearance indicates that they are much younger, with 2023 estimates pegging their age between 100 million and 400 million years.

Now, Tatsuki Hyodo of Japan’s Institute of Space and Astronautical Science and colleagues have calculated that Saturn’s rings are far more resistant to contamination from space dust than previously thought, and can maintain their pristine appearance for long periods of time. Hyodo and his team have not calculated a new age for the rings, but they suggest they could be as old as Earth, as astronomers once believed.

Hyodo and his colleagues first simulated how high-speed space dust accelerated by Saturn’s gravity would collide with the rings. They found that the collisions produced extreme temperatures that evaporated the impacting dust. After spreading into the cloud, this vapor should condense into charged nanoparticles, similar to the particles observed by Cassini.

The researchers then modeled how these particles moved through Saturn’s magnetic field, and found that only a small fraction settled on the rings, while the majority were drawn into Saturn’s atmosphere. It turned out that the object was either destroyed or bounced back into space. “The accretion efficiency of Saturn’s rings is only a few percent, which is much smaller than previously assumed,” says Professor Hyodo. This could extend previous ring age estimates by hundreds of millions to billions of years, he said.

Sasha Kemp of the University of Colorado Boulder is a member of the team that calculated an earlier, much younger estimate of the age of Saturn’s rings, but he and his colleagues believe that the rings’ contamination efficiency alone is not sufficient. Instead, they said they used a more complex method. It takes time for the substance to reach the ring and disappear. The values ​​calculated by Hyodo and his colleagues do not change the overall results for that age, Kemp said. “I’m sure this doesn’t mean we really have to go back to square one.”

However, Hyodo argues that times should change dramatically as pollution efficiency declines. “They assumed an efficiency of 10%, but we reported 1%. The equation tells us that it’s a billion years, or a billion years.”

Kemp also said that while the new simulation assumes that Saturn’s rings are made of solid ice particles, the actual rings are made of soft particles of much larger size than those modeled in the study. He said there was. “If you fire particles into these fairly complex, soft structures, the outcomes of such collisions are very different,” Kemp says.

Hyodo argues that this assumption is standard for many similar studies. “No one knows what kind of effect the difference in ice will have,” says Hyodo. “It may or may not be more efficient.”

Lotfi Ben Jaffel of France’s Paris Institute of Astrophysics, who was not involved in either age-estimation study, said the study suggests the rings are not as young as recently claimed. He said there was. “This is a positive step toward a lack of modeling efforts needed to adequately address the fundamental question of planetary ring system formation and evolution,” he says.

But Hyodo and his team need to improve their modeling to more accurately estimate the ring’s contamination, he says, so they can more accurately determine its age.