A planetary ring system 200 times the size of Saturn's

An extrasolar planetary ring system discovered in 2012 has now been determined to be much more massive than the one orbiting Saturn.

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Michelle Starr is CNET's science editor, and she hopes to get you as enthralled with the wonders of the universe as she is. When she's not daydreaming about flying through space, she's daydreaming about bats.
Michelle Starr
3 min read

Artist's concept of the rings of J1407b. Ron Miller/University of Rochester

In 2012, researchers discovered, for the first time, a ring system outside the solar system. At 420 light years away, the system was spotted circling brown dwarf J1407b -- a planet orbiting star J1407 -- because of the unusual, unsteady light observed during a 52-day eclipse.

New analysis of the data by researchers at the Leiden Observatory in The Netherlands and the University of Rochester in the US has confirmed that it's not just a ring system -- it's a ring system of absolutely epic proportions.

"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," said Matthew Kenworthy of the Leiden Observatory in The Netherlands, who led the research.

"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. If we could replace Saturn's rings with the rings around J1407b, they would be easily visible at night and be many times larger than the full moon."

The system consists of over 30 rings, each tens of millions of kilometres in diameter, with gaps between that indicate that exomoons -- moons orbiting an extrasolar body -- may have formed; much like with Saturn. One clean gap in particular indicates a satellite that has carved a path in the rings.

In all, the ring system is much larger and heavier than Saturn's -- some 120 million kilometres in diameter, over 200 times the size of Saturn's, and containing roughly an Earth's worth of light-obscuring dust.

"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, multiday eclipse," said co-author Eric Mamajek of the University of Rochester.

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

Though it has been difficult to calculate the planet's mass, the team estimates that it is in the region of 30 to 40 Jupiters, with an orbital period around J1407 of roughly a decade. Over the next several million years, they also predict that the ring system will thin, eventually coalescing into exomoons -- ending up resembling Jupiter, with its 63 moons.

"The planetary science community has theorised 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 said. "However, until we discovered this object in 2012, no-one had seen such a ring system. This is the first snapshot of satellite formation on million-kilometre scales around a substellar object."

The team urged amateur astronomers to keep an eye on J1407 to help detect the next eclipse, since this is currently the only means of obtaining more data about J1407b's ring system.

The full study, "Modeling giant extrasolar ring systems in eclipse and the case of J1407b: sculpting by exomoons?", can be found online on arXiv.