Saturn’s distinctive appearance may be rooted in the death of an ancient moon

Saturn may owe its sweeping ring system and characteristic inclination to the death of an ancient moon called Chrysalis, according to the results of a new study.

The gas giant Saturn is one of the most amazing sights in our solar system. However, although it has been the target of many ambitious missions in the past, important questions remain about how the iconic planet acquired its impressive ring system, and why exactly it rotates at an inclination of 26.7 degrees relative to its orbital plane.

For a while, astronomers believed that Saturn’s bubbling angle was the result of a gravitational interaction between the gas giant, its 83 moons and its locomotive moons that Neptune exerted on it. The relationship with the latter was drawn when astronomers realized that Saturn’s spin-like motion corresponded very well to Neptune’s orbital rhythm.

In other words, the two massive planets were thought to share a strong gravitational relationship – also known as resonance.

Data collected by the Cassini spacecraft, which explored the Saturn system between June 2004 – September 2017, further informed the relationship, by revealing that the massive moon Titan was moving away from Saturn at a surprising speed of 11 cm per year.

This led some scientists to suggest that the gravitational influence and external motion of this natural satellite—which is much larger than Earth’s—were likely responsible for maintaining the orbital resonance between Saturn and Neptune.

However, this theory was based on one major and largely non-specific feature of Saturn – the “moment of inertia”. This is the term used to describe the distribution of mass within a celestial body.

The moment of inertia is an important factor for astronomers looking to understand the orbital characteristics of the world, as the distribution and density of mass in a planet’s interior can have a significant impact on its tilt. So if scientists don’t have a good understanding of the moment of inertia, it becomes increasingly difficult to know the exact history of that planet when using computer modeling, for example.

Cassini Legacy

Now, a team of researchers get it now Cassini data is used From the final part of its mission – known as the “Great Conclusion” – to improve Saturn’s idle moment, it was discovered that it lies outside the range required to maintain an orbital resonance with Neptune.

During the “Great Conclusion,” Cassini was directed to make a series of daring dives between the surface of Saturn’s cloud and its deepest rings. A total of 22 dives were made, during which the spacecraft collected data about the internal structure of Saturn, the distribution of mass in it.

The team used computer modeling to create a map of Saturn’s mass distribution that fits Cassini’s real-world gravity measurements. While it was close, the team’s results revealed that Titan’s drag isn’t enough to maintain the gravitational resonance between Saturn and Neptune. However, based on Saturn’s present-day tilt, the team believes there was an echo that lasted billions of years in the past, which was later broken.

To unravel this mystery, the team began running computer simulations that essentially turned back the clock on Saturn’s evolution in an effort to discover the gravitational instability that could explain the separation from Neptune.

After running several simulations, the team came to the conclusion that Saturn at least once hosted at least another major satellite about the size of Iapetus, which has a current diameter of 457 miles (736 km).

death of the moon

According to the study results, Published in Science, the gravitational influence of this long dead moon would have maintained the fragile resonance between Saturn and Neptune. Over the course of several billion years, this gravitational dance between gas giants and moons could have slowly pushed Saturn’s axis to an extreme inclination.

However, the relationship did not last. The team estimates that approximately 160 million years ago, the Moon was subjected to the gravitational influence of its siblings Titan and Iapetus, and was forced to move closer to Saturn’s surface.

In the end, the cocoon could have been torn apart by the colossal forces exerted on it. The greater part of the Moon’s mass may disappear beneath the surface of Saturn’s cloud. However, a small amount would escape this fate, eventually settling around the equator.

With the destruction of the Moon, the finely balanced resonance broke, leaving Saturn with its characteristic orbital inclination, creating the remarkable system of rings we see today.

Anthony Wood is a freelance science writer at IGN

Image Credit: NASA / JPL / Space Science Institute