Saturn’s rings may be far older than we thought

Saturn’s rings could be much older than previously thought and may have formed at the same time as the planet, according to a modeling study. But not all astronomers are convinced, and a researcher who was part of a team that estimated Saturn’s rings were relatively young says the new work doesn’t change their findings.

For most of the 20th century, scientists believed that Saturn’s rings formed along with the planet, 4.5 billion years ago. But when NASA’s Cassini spacecraft visited Saturn in 2004, it found that the rings were not contaminated by tiny space rocks, known as cosmic dust. This clean appearance indicated that they were much younger Estimates in 2023 range from 100 to 400 million years.

now, Ryuki Hyodo in the year Japan Institute of Space and Astronautical Sciences and his colleagues have calculated that Saturn’s rings should be much more resistant to cosmic dust contamination than previously thought, so they could keep their pristine appearance for a long time. Hyodo and his team haven’t calculated a new age for the rings, but suggest they could be as old as the planets, as astronomers thought.

Hyodo and his colleagues simulated for the first time how high-velocity cosmic dust, accelerated by Saturn’s gravity, would break up the rings. They found that the collision would produce such extreme temperatures that the dust it would cause would have to evaporate. This vapor, after expanding into a cloud, would condense into charged nanoparticles, similar to the particles observed by Cassini.

The researchers then modeled how these particles would move through Saturn’s magnetic field, and found that only a small proportion would settle in the rings, with the majority being swept into Saturn’s atmosphere or returned to space. “The accretion efficiency of Saturn’s rings is only a few percent, which is much, much lower than previously thought,” says Hyodo. That could stretch previous estimates of the ring’s age to hundreds of billions of billions of years, he says.

Sascha Kempf At the University of Colorado Boulder, a member of the team that came up with an earlier, much younger estimate of the age of Saturn’s rings says he and his colleagues used a more complex method than the effectiveness of ring contamination, given how long it takes. so that the material reaches the rings and disappears. Kempf says that the value calculated by Hyodo and his colleagues should not change the general findings for age. “We’re sure that doesn’t mean we have to go back to the drawing board.”

But according to Hyodo, the less effective pollution should change the age dramatically. “They assumed an efficiency of 10 percent, we reported 1 percent. You can see from the equation that it becomes 1000 million years or a billion years.”

Kempf also says that the new simulations assume that Saturn’s rings are made of solid ice particles, while the rings are actually made of soft particles of a much larger size than modeled in the study. “If you shoot particles at these more complex and softer structures, the outcome of those collisions will be very different,” he says.

Hyodo says this assumption is standard in many similar studies. “No one knows what the effect of the different ices is,” says Hyodo. “It may or may not reduce efficiency further.”

Lotfi Ben-Jaffel At France’s Institute of Astrophysics in Paris, which was not involved in the age estimation efforts, says the new work suggests the rings are not as young as has been claimed in recent years. “This is a positive step in the modeling effort that is lacking to properly address the fundamental problem of the formation and evolution of a planetary ring system,” he says.

However, Hyodo and his team still need to improve their modeling to better estimate the contamination of the rings so they can work out their age more precisely, he says.