And, of course, I forgot to add, a brown dwarf would be even less suitable than a red star. 
I’ve wondered about that, due to recent scientific results. In recent years astronomers have discovered that unlike our own system, many solar systems have gas giant planets that orbit very close to their star. A moon orbiting such a planet might very well end up tide locked to the much closer gas giant, which would keep it from being tide locked by the star. And we already know such moons can be large enough to have atmospheres, from our own system.
Just a quick note that Mercury is tidally locked at a 3:2 ratio rather than 1:1, so all sides get some sun.
Brian
That looks quite plausible and is very similar to the star/large planet/large satellite arrangement used by Allen Steele in his Coyote trilogy where he used 47 Ursae Majoris (LINK) as the setting for his rebel colony. That’s the only example I’ve encountered where this concept was used in science fiction. However, 47Uma is brighter than our sun and I doubt that the concept would be very feasible with a red star and certainly not with a brown dwarf.
What about a Red Dwarf?
It’s easy to pick apart a detail of the plot from the larger picture, which I intend on keeping to myself. However, I’d like to get the science right at this juncture. If it doesn’t fit, I’ll come up with another motive. It’s not at all pivotal to the rest of the story. I was only intrigued by a planet that is full of heavy water, rather than regular. What that would mean for human explorers that tried to set up shop there, as well as the clash between the humans and whatever has evolved within it’s oceans.
Deuterium IS useful to us. And granted a civilization that has the ability for interstellar travel might not be interested in such a chemical that can reasonably be made here on earth. But I’m still trying to set up the mythology, and it’d be nice if the heavy water could come in to play somehow without appearing too contrived.
On a random note, this gave me a fun idea for a story I should write one day:
Human explorers find a planet that has “oceans” full of twinkies, evidently left behind by an advanced civilization millions of years before (and still well within their shelf life! :D)
I come up with random stuff like this all the time.
Which, of course, the planet is a giant Ding Dong, with a creme filled core… good luck getting past the aluminum-foil atmosphere.
It’s not clear how common this is – current information is heavily biased by selection effects (i.e. a gas giant in a close-in rapid orbit is easier to detect at interstellar distances than a gas giant in a more distant slow orbit).
I know, but keep in mind that astronomy is not really that huge of an endeavor. The fact that we’ve found so many of them with what limited resources we are using implies that there are likely quite a few such systems.
Um, no. According to the article, the oceans would be mildly toxic to humans. It says:
In other words, you’re going to have to drink a lot of heavy water to get poisoned by it.
Why? Let me guess . . . life there uses nuclear fusion at a subcellular level? Nah, couldn’t be that . . .
I first encountered the concept in Asimov’s Nemesis, and in his end notes, he seemed to imply that he came up with the idea himself, independently (which does not necessarily mean first).
Also, given heavy water’s low toxicity, the colonists could fairly easily cut their expensive imported water with the local stuff. And even if all the hydrogen on the planet is heavy, there are probably other hydrogen sources available in the same solar system, which the aliens didn’t bother to enrich. A single comet would provide enough water for a colony for a very long time, even without recycling, and if that’s not an option for some reason, you could probably scoop hydrogen out of the local gas giant to replace the D in the heavy water for a lot cheaper than you could ship Earth-water there.
Unless, of course, it suits your storytelling purposes for light water to be scarce, in which case you could say that the aliens converted everything, or even say that your colony world is the only thing orbitting its star. I don’t think our current knowledge of solar-system formation can actually rule out that possibility.
I would assume that all the hydrogen on the planet (at least the crust) would have to be deuterium, or else ordinary water would form from the non-heavy hydrogen and dilute the heavy water oceans.
Another interesting possibility is that light water could poison the local lifeforms, and possibly at lower concentrations than heavy water poisons Earth critters.