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Gigantic ring system discovered around exoplanet J1407b

Astronomers from the Leiden Observatory and from the University of Rochester (in the US) have discovered that the planetary ring system that covered the very young sun-like star J1407 is actually of enormous proportions. In fact, it’s much larger and heavier than the ring system surrounding Saturn. The ring system – the first found outside our solar system – was only discovered in 2012.

More than thirty rings

A new study of the data has revealed that the ring system consists of more than thirty rings, of which the largest is almost as big as the earth’s orbit around the sun. The astronomers also discovered a number of holes in the rings, suggesting that exomoons have been formed as well. The results have just been accepted for publication in Astrophysical Journal.

Structure of the ring system

Clues about the structure of the ring system were discovered by systematically measuring the amount of starlight emanating from the J1407 throughout the year 2007. “The details that can be seen in the light curve are just incredible. The eclipse lasted for several weeks, but you see rapid changes on time scales of tens of minutes, caused by the fine structures in the rings,” the Leiden astronomer and first author Matthew Kenworthy says. “The star is simply too far away for us to observe the rings directly, but we were able to make a detailed model by using the data from the rapid brightness variations in the starlight. If we could place these rings from the J1407b around Saturn, we would easily be able to see them at night. They would be many times larger than the full moon.”

Dimmed light

The astronomers analysed the data from the SuperWASP project, a survey originally made to discover gas giants moving past their parent star. In 2012, Mamajek and colleagues (University of Rochester) reported their discovery of the young star J1407 and its unusual eclipses, originally proposing that these were caused by a moon-forming disk around a young giant planet or a brown dwarf. But in their recent study, led by Kenworthy, direct observations were made using adaptive optics and Doppler spectroscopy, enabling them to estimate the mass of the ringed object. Their conclusion, based on these and previous studies of the intriguing system J1407, is that a giant planet – which hasn’t yet been seen – has a gigantic ring system. This system is responsible for the repeated dimming of the star’s light over a period of two months in early 2007.

A diameter of 123 million kilometres

After a detailed analysis of the light curve, the astronomers reached the surprising conclusion that the ring system’s diameter is actually about 123 million kilometres, or more than one hundred times as large as the rings of Saturn. As co-author Mamajek added: “The ring system probably contains at least an Earth’s worth of mass in light-obscuring dust particles as well. And even more material can probably be found in the satellites that determine the ring’s substructure. Their interpretation of the data also led the astronomers to conclude that there was at least one hole in the ring structure. “One of the most obvious explanations for this phenomenon is that a satellite moon is formed at this location,” says Kenworthy. “The exact same process can be seen in the ring system of Saturn, where gaps are also formed by its moons.” The mass of the moon surrounding the J1407b could be between that of Earth and Mars, and it could take the moon approximately two years to completely orbit around the star.”

Observe the next eclipse

The astronomers expect that the rings will continue to become thinner and thinner over the course of the coming millions of years, and will even eventually disappear after multiple satellites are formed. They estimate that the undiscovered planet with the ring system takes 10 years to completely orbit around the J1407, and has a mass that is at least ten to forty times that of Jupiter. (Amateur) astronomers are now keeping a close eye on J1407 to observe the next eclipse once it happens, while this team is currently going through other databases to find comparable ring systems. “Now that we know what we’re looking for, finding these kinds of exotic exoplanets has become a lot easier”, Kenworthy says.


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