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In “Astronomers Make a Map of a Super Saturn's Rings,” from the January issue of Scientific American, the Leiden University astronomer Matthew Kenworthy tells the story of discovering a ring system some 200 times larger than Saturn’s around the distant star J1407. Despite its rather large size, across interstellar distances this ring system would normally be totally invisible to us—and in fact Kenworthy and his peers have yet to glimpse J1407b, the giant planet that must be its host. The only reason we know the ring system exists at all is that, by chance, Kenworthy and other researchers happened to see its shadow after it “transited” across the face of its star in 2007.
Kenworthy’s video animation below maps a model of J1407’s rings onto actual data (yellow-bordered dots) from that transit. Each ring blocks a small amount of starlight, casting a shadow that we can detect here on Earth. By stringing together the successive dips in starlight and studying how quickly each one occurred, Kenworthy and his colleagues were able to infer that the system contains at least a hundred rings, and that it is tilted at an angle respective to our perspective on Earth. Intriguingly, they also spied a large empty region in the system, a telltale sign of what might be a Mars-sized moon—an exomoon—sweeping out a gap as it moves through the rings.
No further transits have occurred since 2007—the unseen planet J1407b and its rings have yet to complete another orbit around their star. Kenworthy and several other astronomers are now monitoring J1407 almost every night, awaiting the first fateful dip in starlight from the onset of the next transit. If and when it occurs, a worldwide observation campaign will seek to confirm its architecture and its exomoon, while also mapping it in even more detail.