D-17: The Great Eye

The following was first published on the Stellaris forums.


Today we’re going to talk about a star which has fascinated humanity for ages: Fomalhaut, in the constellation Pisces. Fomalhaut’s name comes from Arabic because it was extensively studied by Arab astronomers of the Golden Age, which tells you just how long we’ve liked it. Many astrologers and other mystics have come up with complex meanings for this brilliant pure-white star. The astronomy-obsessed H P Lovecraft mentioned Fomalhaut as the haunt of a Great Old One. To modern astronomers, however, the planet resembles another fictional franchise entirely.

Meet the Eye of Sauron.

(Image courtesy NASA)

Fomalhaut is surrounded by a huge spinning ring of assorted space debris, mostly dust, which appears red in this false-colour image. This is puzzling because she’s a very hot white star, hot enough for her solar wind to blast the dust away. We believe that new dust is continually being formed by larger lumps of rock and ice slamming into one another, which replaces the dust that she blasts away. It’s certainly beautiful.

(The ring is actually perfectly round; the elliptical effect on this image comes from us seeing it at an angle. The central sphere of black comes from the fact that there’s not much dust close in because Fomalhaut is blasting it away with deadly solar winds.)

There’s a term for this sort of collision between lumps of stuff in orbit: planet formation. And indeed, there are three candidates for protoplanets orbiting Fomaulhaut. Two of them are in the outer reaches and were detected using conventional methods. The first and best, however, was seen in 2008.

Yes, seen. We’ve actually seen it, not just measured its effects. Here’s a photo of Fomalhaut b. This was the first exoplanet we ever saw directly.

(Image courtesy National Geographic)

This planet was named Dagon as a nod to Lovecraft, which irritates those of us who are obsessive enough about our Lovecraft lore to remember that it was Cthugha which was located here. It is also sometimes known as the Mote in Sauron’s Eye as a nod to a classic Larry Niven novel.

This is probably a useful way to tell you how big the Eye of Sauron is. Dagon orbits at a distance of 109 to 245 AU. (For reference, Neptune is 30 AU from the Sun.) A-class white stars like Fomalhaut have a large and distant habitable zone, but even so Dagon is a very long way outside of it.

The normal method of detecting planets tells us their mass but not their volume. Here we have the other problem: we know Dagon’s volume (because we can see the light that it reflects and therefore its surface area) but not its mass. However, the fact that we can’t detect it using normal methods means that Dagon isn’t more than twice the mass of Jupiter. That said, it’s a lot bigger than Jupiter, which means that Dagon is not so much a gas giant as a loose cloud of stuff which is in the process of becoming a gas giant. That loose cloud is reflecting enough of Fomalhaut’s light that we can see it in the above picture.

There may, however, be other planets. As the Eye of Sauron settles down to become a normal planetary ring, it’s easy to imagine other planets forming. The European Southern Observatory didn’t find Dagon but did find signs which suggest that there may be another two planets here.

The difficulty is time: Fomalhaut is a hot A-class star and while it might be young, stars like this only live a few hundred million years. Earth is already 4.5 billion years old. Life may have emerged on earth as early as 3.9 billion years ago, but that means it took 600 million years from the formation of the planet to the formation of single-celled life. On this scale, Fomalhaut will never even have bacteria before she dies.

However, this might be an excellent place for an already space-dwelling species to settle. Fomalhaut has some iron and may have other metals too, which means the Eye of Sauron and its larger bodies may be worth mining. Anyone living here would have to construct sturdy shelters to protect themselves from high-velocity dust and also from the radiation of the white sun.


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