These rings are 200 times bigger than Saturn’s

An illustration of the ring system with Saturn and its ring system to scale in the upper right. (Credit: Ron Miller)

Scientists have discovered what appears to be a young giant exoplanet with an enormous ring system—much larger and heavier than the system around Saturn.

ring comparison
The rings around J1407b are so large that if they were put around Saturn, we could see the rings at dusk with our own eyes. (Credit: M. Kenworthy/Leiden)

The 30 or more rings around J1407b are each tens of millions of kilometers in diameter. If these rings were around Saturn, they would be visible at night from Earth.

“You could think of it as kind of a super Saturn,” says Eric Mamajek, professor of physics and astronomy at the University of Rochester.

He led the team that reported the discovery of the young star J1407 in 2012—and unusual eclipses, which they proposed were caused by a moon-forming disk around a young giant planet or brown dwarf.

A new analysis of the data, led by Matthew Kenworthy of the Leiden Observatory in the Netherlands, revealed the enormous size of the ring system.

“The details that we see in the light curve are incredible. The eclipse lasted for several weeks, but you see rapid changes on time scales of tens of minutes as a result of fine structures in the rings,” says Kenworthy.

“The star is much too far away to observe the rings directly, but we could make a detailed model based on the rapid brightness variations in the star light passing through the ring system.”

Rings filled with dust

The astronomers analyzed data from the SuperWASP project—a survey that is designed to detect gas giants that move in front of their parent star.

In a recent study also led by Kenworthy, astronomers used adaptive optics and Doppler spectroscopy to estimate the mass of the ringed object.

The light curve tells astronomers that the diameter of the ring system is nearly 120 million kilometers, more than two hundred times as large as the rings of Saturn. The ring system likely contains roughly an Earth’s worth of mass in light-obscuring dust particles.

Mamajek puts into context how much material is contained in these disks and rings.

“If you were to grind up the four large Galilean moons of Jupiter into dust and ice and spread out the material over their orbits in a ring around Jupiter, the ring would be so opaque to light that a distant observer that saw the ring pass in front of the sun would see a very deep, multi-day eclipse,” Mamajek says.

“In the case of J1407, we see the rings blocking as much as 95 percent of the light of this young Sun-like star for days, so there is a lot of material there that could then form satellites.”

What’s in the gap?

In the data the astronomers found at least one clean gap in the ring structure, which is more clearly defined in the new model.


“One obvious explanation is that a satellite formed and carved out this gap,” says Kenworthy. “The mass of the satellite could be between that of Earth and Mars. The satellite would have an orbital period of approximately two years around J1407b.”

Astronomers expect that the rings will become thinner in the next several million years and eventually disappear as satellites form from the material in the disks.

“The planetary science community has theorized for decades that planets like Jupiter and Saturn would have had, at an early stage, disks around them that then led to the formation of satellites,” Mamajek explains. “However, until we discovered this object in 2012, no-one had seen such a ring system.

Astronomers estimate that the planet has an orbital period roughly a decade in length. The mass of J1407b has been difficult to constrain, but it is most likely in the range of about 10 to 40 Jupiter masses.

Source: University of Rochester