[LINK] More than an exo-Saturn

[rfmcdonald]

Via Bad Astronomy news comes about an another astonishing exoplanet discovery. Calling this an "exo-Saturn" is misleading--the rings are much larger than Saturn's, while the planet itself may be so massive that it isn't a planet but a brown dwarf instead. What's remarkable to me is the fine detail that's produced.

The planet was discovered with the SuperWASP (Wide Angle Search for Planets) telescopes — a UK project that employs low-magnification but very sensitive cameras which can observe large areas of the sky at the same time. It orbits a young star called 1SWASP J140747.93-394542.6, which is 420 light years away. The star’s youth — 16 million years — indicates that the rings are probably the leftover remnants from when the planet formed.

The planet and its rings were discovered using the transit method: looking for small dips in starlight as a planet passes directly between us and the star. This is how the vast majority of exoplanets are found. Usually, when you graph the brightness of the star over time, the dip in the plot as the planet transits the star starts suddenly, drops to some minimum, then jumps back up (see here for example). The whole thing is usually over in a matter of hours at most.

But this planet took nearly two months to transit the star! And the dip was weird: there were multiple times the star dimmed then got brighter again, at one point having 95% of its light blocked. Even though the planet wasn’t seen directly, the most obvious explanation is a ring system similar to Saturn’s (though much larger), blocking the light. It must have gaps in the rings, like Saturn’s do, to explain the starlight jumping up again over time. Overall, four rings were detected, and they stretch tens of millions kilometers in diameter!

And, of course, there are the moons that may yet be sighted.

Perhaps most intriguing about all this are those gaps in the rings. The easiest way to explain them is that there are objects there, moons, sweeping out the material in the rings. Saturn’s rings have gaps for this reason. In fact, there are hundreds of gaps in Saturn’s rings! These are caused by resonances: if a ring particle orbits twice for every one time a moon orbits, for example, the moon’s gravity tugs on it every time it swings by, pulling it into a different orbit. Over time, all the particles in that orbit are gone, leaving behind a gap.

If the planet itself is big, how big are those moons? Could one be Earth-sized? It’s an idea that’s been around awhile, but none has ever been seen… yet. All these super-Jupiters being found have a lot of gravity, and it’s possible they have big moons. We’re also getting better at detecting smaller objects, so it wouldn’t surprise me if that announcement is made sometime relatively soon, too!