There May Be an Exoplanet Ring System 200 Times the Size of Saturn's
Could there be a giant ring system that's 200 times the size of Saturn's famous rings? University of Rochester's Eric Mamajek thinks so, although many astronomers remain unconvinced, partially as a result of the sheer incomprehensibility of the proposed object.
Mamajek's incredible paper came out of an analysis of old data from the WASP planet search project. Usually, when a planet passes in front of a star, the star is blocked and its brightness is dimmed for a matter of hours. But in the case of this particular exoplanet, the dimness lasted for two whole months.
(An artist's impression of the planet's giant ring system by Ron Miller)
This may have led to the conclusion that the exoplanet itself is impossibly large, but for the fact that the dimness was not constant. The starlight would become bright and then dim again on a cyclical basis, which stumped the researchers for a time. When Mamajek made this discovery, he claimed that he "took a printout of the light curve, put it on the wall, and stared at it for a week."
Ultimately, the only conclusion that made sense was a gigantic ring system, much like Saturn's, but 200 times larger. According to Mamajek's analysis, the exoplanet itself would be 10 to 40 times the size of our "gas giant" Jupiter, and if the rings surrounded Earth, they would stretch all the way to the Sun. If Mamajek's conclusion is correct, then the WASP data caught the rings during a relatively short window of existence, before the outer bands condense into moons.
"It took us a year even to convince ourselves of what we were seeing," said Mamajek. They were unable to directly observe the planet itself in their analysis, but that would be consistent with their conclusions as long as the planet was off-center when it passed the star. This theory is explained in Mamajek's animation below:
And there's precedent for discovering ring systems by observing starlight brightness; as Mamajek puts it, "It's the same indirect way the rings of Uranus were discovered in 1977." But the fact that the size of the rings is unheard of thus far, and the fact that the data must have caught the rings in a transient, short-lived state, gives other astronomers pause.
"I agree with the authors that it's appropriate to consider an interpretation based on rings," said Penn State astronomer Eric Ford. "[But] whenever your explanation involves catching something during a phase that won't last very long," Ford says, "it's a little concerning."
But experts in the field have failed to come up with another plausible explanation thus far, so the scientific community aims to confirm this phenomenon by replicating Mamajek's results when the planet (presumably) passes by the star again.