on Strength in Numbers and the exo-moon-rings of J1407b

Artist’s conception of the extrasolar ring system circling the young giant planet or brown dwarf J1407b. The rings are shown eclipsing the young sun-like star J1407, as they would have appeared in early 2007. Credit: Ron Miller. Taken from the University of Rochester's page

Recent news from Dr. Eric Mamajek and Dr. Matthew Kenworthy is that a relatively nearby star has a massive, massive disk. It’s genuinely enormous, dwarfing the rings of Saturn. The disk around J1407b (full name 1SWASP J140747.93-394542.6, which is also its sky coordinates) something like 200 times larger, so it’s no fluke. You can read more about the particulars of the dust ring at that link above, where they go into some detail about just how huge this disk is – 200 times wider than Saturn’s, with at least 30 identifiable discrete ring segments – and where all of these results came from.

But what I find most interesting about all of this is the general concept: We have seen a ring system, but not a planet. In fact, we’ve seen gaps in the rings probably carved out by moons (which would make J1407b the first planet outside our Solar System with probable, if not definite, moons). That’s right, what we can see first and foremost is: the ring system around J1407. Not the planet, not even the moons it apparently has, but the tiny ring particles.

It’s strength in numbers!

Get enough dust, and spread it out over a large enough area, and you can blot out more light from the star than a planet can. There’s another famous case: The F-type supergiant epsilon Auriga, where a dark something obscures the star every 27 years – last time it happened was in 2009-2011, when the CHARA interferometric array imaged epsilon Auriga and confirmed that the dark object really was a disk, probably surrounding a B-type star that’s orbiting the supergiant.

Other good examples of dust being easier to see are, well, most of the nearby A-type stars. Dust glows in the infrared. Back in the early 1980s, the IRAS satellite was launched, and it scanned the entire sky. Vega, Fomalhaut, beta Pictoris, TW Hydra, and a whole host of others turned out to have infrared excesses, which were taken to be the signs of asteroid belts grinding themselves into powder via collisions. Fomalhaut’s dust disk is particularly famous because the released images of it look more than a little like the Eye of Sauron.

Fomalhaut, its dust ring, and the putative planet

All of that glow you see, the giant ring, are cold dust particles in orbit of the star. The fact that this disk is a narrow ring is because the asteroid belt is being shaped by a planet. And actually, the object marked off on the above image may be glowing dust in the ring system of the planet, rather than the planet itself. That much is still heavily debated, which makes J1407’s rings, and planet, and moons, all the more remarkable: it’s the first one! And maybe some day soon we’ll be able to see the planet directly.

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