In 1655, astronomer Christiaan Huygens became the first person to observe the beautiful ring system that surrounds Saturn. And while they are certainly the most spectacular, astronomers have since discovered that all the gas and ice giants of the Solar System (i.e. Jupiter, Saturn, Uranus and Neptune) have their own system of rings.
These systems have remained a source of fascination for astronomers, largely because their origins are still something of a mystery. But thanks to a recent study by researchers from Japan’s Tokyo Institute of Technology, Kobe University, the origins of these rings may be solved. According to the study, the rings are the result of chunks torn off of passing Dwarf Planets, and then ripped to pieces!
Quite the violent origin story, isn’t it? But this research does help to resolve many of the burning questions about the ring systems around our system’s giant planets. For the sake of their study – titled “Ring Formation around Giant Planets by Tidal Disruption of a Single Passing Large Kuiper Belt Object” – the Japanese team of researchers considered a number of factors.
The Kuiper Belt was named in honor of Dutch-American astronomer Gerard Kuiper, who postulated a reservoir of icy bodies beyond Neptune. Credit: JHUAPL
For starters, they considered the diversity of the various ring systems in our Solar System. For instance, Saturn’s rings are massive (about 100,000 trillion kg!) and composed overwhelmingly (90-95%) of water ice. In contrast, the much less massive rings of Uranus and Neptune are composed of darker material, and are believed to have higher percentage of rocky material in them.
To shed some light on this, the team looked to the Nice Model – a theory of Solar System formation that states that the gas giant migrated to their present location. According to this theory, the planets originated in the outer Solar System before migrated inward during the Late Heavy Bombardment – which took place between 4 and 3.8 billion years ago, and was characterized by objects were being kicked out of the Kuiper Belt.
They then considered recent models of Solar System formation, which postulate that the giant planets experienced close encounters in the past with Pluto-sized objects. From this, they developed the theory that the gas giants’ rings could be the result of these objects getting trapped and ripped apart by gravity. To test this theory, they performed a number of computer simulations to see what would happen in these instances.
As Ryuki Hyodo – a researcher at the Department of Planetology, Kobe University, and the lead author on the paper – told Universe Today via email:
“We performed two simulations. First, using SPH (Smoothed-particle hydrodynamics) simulations, we investigated tidal disruption of pluto-sized objects during the close encounters with giant planets and calculated the amount of fragments that are captured around giant planets. We found enough mass/fragments to explain current rings is captured. Then, we performed the longer-term evolution of the captured mass/fragments by using N-body simulations. We found that the captured fragments can collide each other with destructions and form thin equatorial circular rings around giant planets.”
A composite image of Uranus in two infrared bands, showing the planet and its ring system. Credit: W. M. Keck Observatory (Marcos van Dam)
What they found was that about 0.1 to 10% of the mass of a passing body would be captured by the gravity of these gas giants. They then performed simulations to see what would happen to these chunks under the influence of the giant planets’ gravity. These showed that the chunks would be tidally destroyed during the next several orbits, and that their remains would eventually be broken down into small particles that would form a low-velocity ring.
Their results of the simulation were also consistent with the mass of the ring systems observed around Saturn and Uranus. This included the inner regular satellites of both planets – which would have also been the product of the past encounters with KBOs. It also accounted for the differences in the rings’ composition, showing how the planet’s Roche limits can influence what kind of material can be effectively captured.
In short, their experimental results confirmed that the rings are likely to be the result of close encounters with KBOs that were the size of a dwarf planet. This study is especially significant because it offers verifiable evidence for one of the enduring mysteries of our Solar System, and could help us to understand others as well.
“Our theory suggested that, in the past, we had two possible epochs to form rings,” said Hyodo. “One is during the planet accretion phase and the other is during the Late heavy bombardment. Also, our model is naturally applicable to other planetary systems. So, our theory predicts that exoplanets also have massive rings around them.
Further Reading: arXiv
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