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29th January 2015

Astronomers find exoplanet with gigantic ring system

Astronomers have discovered an exoplanet with a gigantic ring system, 200 times larger than that around Saturn.


giant ring system of exoplanet


An international team of astronomers has produced a new analysis of exoplanet data, showing how a ring system eclipses a star about 420 light years from Earth. Known as J1407, the star's age is estimated to be 16 million years, making it very young in stellar terms, with a mass 90% that of our Sun's. The accompanying planet is very large, at between 10 and 40 Jupiter masses, so it may in fact be a brown dwarf.

The planet's ring system – the first of its kind to be found outside our Solar System – is of gigantic size, much larger and heavier than Saturn's and described as "Saturn on steroids" by one astronomer. It is divided into at least 30 sections with a total diameter of 120 million km (75 million miles), equivalent to 80% of the distance between Earth and our Sun. Furthermore, gaps in the rings indicate that large satellites (“exomoons”) are present and may be up to 0.8 Earth masses.

“The details that we see in the light curve are incredible,” says Professor Matthew Kenworthy from the Leiden Observatory in the Netherlands, who led the study. “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. 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.”


ring system in earth sky
Credit: Matthew Kenworthy, Leiden Observatory


“This planet is much larger than Jupiter or Saturn, and its ring system is roughly 200 times larger than Saturn’s rings are today,” said Eric Mamajek, professor of physics and astronomy at the University of Rochester, who co-authored the paper. “You could think of it as kind of a super Saturn.”

“We see the rings blocking as much as 95 percent of the light of this young Sun-like star for days,” he adds. “So there is a lot of material there that could then form satellites.”

In their data, the astronomers found at least one clean gap within the ring structure: “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.”

The researchers believe that the rings will become thinner in the next several million years and eventually disappear altogether as satellites coalesce from the material in the disks. They are encouraging amateur astronomers to help monitor this remarkable star system, to help detect the next eclipse of the rings and narrow down the possible range of values for the planet's orbital characteristics and mass.

“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 explains. “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 study has been accepted for publication in the Astrophysical Journal.



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